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1 | \input texinfo |
2 | @setfilename ld.info | |
56dd11f0 | 3 | @c Copyright 1991-2013 Free Software Foundation, Inc. |
252b5132 | 4 | @syncodeindex ky cp |
dff70155 | 5 | @c man begin INCLUDE |
252b5132 RH |
6 | @include configdoc.texi |
7 | @c (configdoc.texi is generated by the Makefile) | |
c428fa83 | 8 | @include bfdver.texi |
dff70155 | 9 | @c man end |
252b5132 RH |
10 | |
11 | @c @smallbook | |
12 | ||
ff5dcc92 SC |
13 | @macro gcctabopt{body} |
14 | @code{\body\} | |
15 | @end macro | |
16 | ||
0285c67d NC |
17 | @c man begin NAME |
18 | @ifset man | |
19 | @c Configure for the generation of man pages | |
20 | @set UsesEnvVars | |
21 | @set GENERIC | |
0285c67d | 22 | @set ARM |
ac145307 | 23 | @set C6X |
49fa1e15 | 24 | @set H8300 |
0285c67d | 25 | @set HPPA |
0285c67d | 26 | @set I960 |
0285c67d | 27 | @set M68HC11 |
7fb9f789 | 28 | @set M68K |
833794fc | 29 | @set MIPS |
3c3bdf30 | 30 | @set MMIX |
2469cfa2 | 31 | @set MSP430 |
2a60a7a8 AM |
32 | @set POWERPC |
33 | @set POWERPC64 | |
49fa1e15 AM |
34 | @set Renesas |
35 | @set SPU | |
36 | @set TICOFF | |
2ca22b03 | 37 | @set WIN32 |
e0001a05 | 38 | @set XTENSA |
0285c67d NC |
39 | @end ifset |
40 | @c man end | |
41 | ||
9160ea82 AM |
42 | @ifnottex |
43 | @dircategory Software development | |
44 | @direntry | |
252b5132 | 45 | * Ld: (ld). The GNU linker. |
9160ea82 AM |
46 | @end direntry |
47 | @end ifnottex | |
252b5132 | 48 | |
0e9517a9 | 49 | @copying |
e49e529d JM |
50 | This file documents the @sc{gnu} linker LD |
51 | @ifset VERSION_PACKAGE | |
52 | @value{VERSION_PACKAGE} | |
53 | @end ifset | |
54 | version @value{VERSION}. | |
252b5132 | 55 | |
56dd11f0 | 56 | Copyright @copyright{} 1991-2013 Free Software Foundation, Inc. |
252b5132 | 57 | |
cf055d54 | 58 | Permission is granted to copy, distribute and/or modify this document |
793c5807 | 59 | under the terms of the GNU Free Documentation License, Version 1.3 |
cf055d54 NC |
60 | or any later version published by the Free Software Foundation; |
61 | with no Invariant Sections, with no Front-Cover Texts, and with no | |
62 | Back-Cover Texts. A copy of the license is included in the | |
36f63dca | 63 | section entitled ``GNU Free Documentation License''. |
0e9517a9 | 64 | @end copying |
252b5132 RH |
65 | @iftex |
66 | @finalout | |
67 | @setchapternewpage odd | |
71ba23f6 | 68 | @settitle The GNU linker |
252b5132 | 69 | @titlepage |
71ba23f6 | 70 | @title The GNU linker |
252b5132 | 71 | @sp 1 |
e49e529d JM |
72 | @subtitle @code{ld} |
73 | @ifset VERSION_PACKAGE | |
74 | @subtitle @value{VERSION_PACKAGE} | |
75 | @end ifset | |
252b5132 RH |
76 | @subtitle Version @value{VERSION} |
77 | @author Steve Chamberlain | |
78 | @author Ian Lance Taylor | |
252b5132 RH |
79 | @page |
80 | ||
81 | @tex | |
82 | {\parskip=0pt | |
704c465c NC |
83 | \hfill Red Hat Inc\par |
84 | \hfill nickc\@credhat.com, doc\@redhat.com\par | |
71ba23f6 | 85 | \hfill {\it The GNU linker}\par |
252b5132 RH |
86 | \hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par |
87 | } | |
88 | \global\parindent=0pt % Steve likes it this way. | |
89 | @end tex | |
90 | ||
91 | @vskip 0pt plus 1filll | |
0285c67d | 92 | @c man begin COPYRIGHT |
56dd11f0 | 93 | Copyright @copyright{} 1991-2013 Free Software Foundation, Inc. |
252b5132 | 94 | |
0285c67d | 95 | Permission is granted to copy, distribute and/or modify this document |
793c5807 | 96 | under the terms of the GNU Free Documentation License, Version 1.3 |
0285c67d NC |
97 | or any later version published by the Free Software Foundation; |
98 | with no Invariant Sections, with no Front-Cover Texts, and with no | |
99 | Back-Cover Texts. A copy of the license is included in the | |
36f63dca | 100 | section entitled ``GNU Free Documentation License''. |
0285c67d | 101 | @c man end |
252b5132 | 102 | |
252b5132 RH |
103 | @end titlepage |
104 | @end iftex | |
4ecceb71 | 105 | @contents |
252b5132 RH |
106 | @c FIXME: Talk about importance of *order* of args, cmds to linker! |
107 | ||
84ec0e6d | 108 | @ifnottex |
252b5132 | 109 | @node Top |
71ba23f6 | 110 | @top LD |
e49e529d JM |
111 | This file documents the @sc{gnu} linker ld |
112 | @ifset VERSION_PACKAGE | |
113 | @value{VERSION_PACKAGE} | |
114 | @end ifset | |
115 | version @value{VERSION}. | |
252b5132 | 116 | |
cf055d54 | 117 | This document is distributed under the terms of the GNU Free |
793c5807 NC |
118 | Documentation License version 1.3. A copy of the license is included |
119 | in the section entitled ``GNU Free Documentation License''. | |
cf055d54 | 120 | |
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121 | @menu |
122 | * Overview:: Overview | |
123 | * Invocation:: Invocation | |
124 | * Scripts:: Linker Scripts | |
125 | @ifset GENERIC | |
126 | * Machine Dependent:: Machine Dependent Features | |
127 | @end ifset | |
128 | @ifclear GENERIC | |
129 | @ifset H8300 | |
130 | * H8/300:: ld and the H8/300 | |
131 | @end ifset | |
c2dcd04e NC |
132 | @ifset Renesas |
133 | * Renesas:: ld and other Renesas micros | |
252b5132 RH |
134 | @end ifset |
135 | @ifset I960 | |
136 | * i960:: ld and the Intel 960 family | |
137 | @end ifset | |
36f63dca NC |
138 | @ifset ARM |
139 | * ARM:: ld and the ARM family | |
140 | @end ifset | |
93fd0973 SC |
141 | @ifset M68HC11 |
142 | * M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families | |
143 | @end ifset | |
7ca01ed9 NC |
144 | @ifset HPPA |
145 | * HPPA ELF32:: ld and HPPA 32-bit ELF | |
146 | @end ifset | |
7fb9f789 NC |
147 | @ifset M68K |
148 | * M68K:: ld and Motorola 68K family | |
149 | @end ifset | |
833794fc MR |
150 | @ifset MIPS |
151 | * MIPS:: ld and MIPS family | |
152 | @end ifset | |
2a60a7a8 AM |
153 | @ifset POWERPC |
154 | * PowerPC ELF32:: ld and PowerPC 32-bit ELF Support | |
155 | @end ifset | |
156 | @ifset POWERPC64 | |
157 | * PowerPC64 ELF64:: ld and PowerPC64 64-bit ELF Support | |
158 | @end ifset | |
49fa1e15 AM |
159 | @ifset SPU |
160 | * SPU ELF:: ld and SPU ELF Support | |
161 | @end ifset | |
74459f0e TW |
162 | @ifset TICOFF |
163 | * TI COFF:: ld and the TI COFF | |
164 | @end ifset | |
2ca22b03 NC |
165 | @ifset WIN32 |
166 | * Win32:: ld and WIN32 (cygwin/mingw) | |
167 | @end ifset | |
e0001a05 NC |
168 | @ifset XTENSA |
169 | * Xtensa:: ld and Xtensa Processors | |
170 | @end ifset | |
252b5132 RH |
171 | @end ifclear |
172 | @ifclear SingleFormat | |
173 | * BFD:: BFD | |
174 | @end ifclear | |
175 | @c Following blank line required for remaining bug in makeinfo conds/menus | |
176 | ||
177 | * Reporting Bugs:: Reporting Bugs | |
178 | * MRI:: MRI Compatible Script Files | |
704c465c | 179 | * GNU Free Documentation License:: GNU Free Documentation License |
370b66a1 | 180 | * LD Index:: LD Index |
252b5132 | 181 | @end menu |
84ec0e6d | 182 | @end ifnottex |
252b5132 RH |
183 | |
184 | @node Overview | |
185 | @chapter Overview | |
186 | ||
187 | @cindex @sc{gnu} linker | |
188 | @cindex what is this? | |
0285c67d | 189 | |
0879a67a | 190 | @ifset man |
0285c67d | 191 | @c man begin SYNOPSIS |
ff5dcc92 | 192 | ld [@b{options}] @var{objfile} @dots{} |
0285c67d NC |
193 | @c man end |
194 | ||
195 | @c man begin SEEALSO | |
196 | ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and | |
197 | the Info entries for @file{binutils} and | |
198 | @file{ld}. | |
199 | @c man end | |
200 | @end ifset | |
201 | ||
202 | @c man begin DESCRIPTION | |
203 | ||
ff5dcc92 | 204 | @command{ld} combines a number of object and archive files, relocates |
252b5132 | 205 | their data and ties up symbol references. Usually the last step in |
ff5dcc92 | 206 | compiling a program is to run @command{ld}. |
252b5132 | 207 | |
ff5dcc92 | 208 | @command{ld} accepts Linker Command Language files written in |
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209 | a superset of AT&T's Link Editor Command Language syntax, |
210 | to provide explicit and total control over the linking process. | |
211 | ||
0285c67d NC |
212 | @ifset man |
213 | @c For the man only | |
ece2d90e | 214 | This man page does not describe the command language; see the |
71ba23f6 NC |
215 | @command{ld} entry in @code{info} for full details on the command |
216 | language and on other aspects of the GNU linker. | |
0285c67d NC |
217 | @end ifset |
218 | ||
252b5132 | 219 | @ifclear SingleFormat |
ff5dcc92 SC |
220 | This version of @command{ld} uses the general purpose BFD libraries |
221 | to operate on object files. This allows @command{ld} to read, combine, and | |
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222 | write object files in many different formats---for example, COFF or |
223 | @code{a.out}. Different formats may be linked together to produce any | |
224 | available kind of object file. @xref{BFD}, for more information. | |
225 | @end ifclear | |
226 | ||
227 | Aside from its flexibility, the @sc{gnu} linker is more helpful than other | |
228 | linkers in providing diagnostic information. Many linkers abandon | |
229 | execution immediately upon encountering an error; whenever possible, | |
ff5dcc92 | 230 | @command{ld} continues executing, allowing you to identify other errors |
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231 | (or, in some cases, to get an output file in spite of the error). |
232 | ||
0285c67d NC |
233 | @c man end |
234 | ||
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235 | @node Invocation |
236 | @chapter Invocation | |
237 | ||
0285c67d NC |
238 | @c man begin DESCRIPTION |
239 | ||
ff5dcc92 | 240 | The @sc{gnu} linker @command{ld} is meant to cover a broad range of situations, |
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241 | and to be as compatible as possible with other linkers. As a result, |
242 | you have many choices to control its behavior. | |
243 | ||
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244 | @c man end |
245 | ||
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246 | @ifset UsesEnvVars |
247 | @menu | |
248 | * Options:: Command Line Options | |
249 | * Environment:: Environment Variables | |
250 | @end menu | |
251 | ||
252 | @node Options | |
253 | @section Command Line Options | |
254 | @end ifset | |
255 | ||
256 | @cindex command line | |
257 | @cindex options | |
0285c67d NC |
258 | |
259 | @c man begin OPTIONS | |
260 | ||
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261 | The linker supports a plethora of command-line options, but in actual |
262 | practice few of them are used in any particular context. | |
263 | @cindex standard Unix system | |
ff5dcc92 | 264 | For instance, a frequent use of @command{ld} is to link standard Unix |
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265 | object files on a standard, supported Unix system. On such a system, to |
266 | link a file @code{hello.o}: | |
267 | ||
268 | @smallexample | |
269 | ld -o @var{output} /lib/crt0.o hello.o -lc | |
270 | @end smallexample | |
271 | ||
ff5dcc92 | 272 | This tells @command{ld} to produce a file called @var{output} as the |
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273 | result of linking the file @code{/lib/crt0.o} with @code{hello.o} and |
274 | the library @code{libc.a}, which will come from the standard search | |
275 | directories. (See the discussion of the @samp{-l} option below.) | |
276 | ||
ff5dcc92 | 277 | Some of the command-line options to @command{ld} may be specified at any |
511ab9e9 ILT |
278 | point in the command line. However, options which refer to files, such |
279 | as @samp{-l} or @samp{-T}, cause the file to be read at the point at | |
280 | which the option appears in the command line, relative to the object | |
281 | files and other file options. Repeating non-file options with a | |
282 | different argument will either have no further effect, or override prior | |
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283 | occurrences (those further to the left on the command line) of that |
284 | option. Options which may be meaningfully specified more than once are | |
285 | noted in the descriptions below. | |
286 | ||
287 | @cindex object files | |
511ab9e9 ILT |
288 | Non-option arguments are object files or archives which are to be linked |
289 | together. They may follow, precede, or be mixed in with command-line | |
290 | options, except that an object file argument may not be placed between | |
291 | an option and its argument. | |
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292 | |
293 | Usually the linker is invoked with at least one object file, but you can | |
294 | specify other forms of binary input files using @samp{-l}, @samp{-R}, | |
295 | and the script command language. If @emph{no} binary input files at all | |
296 | are specified, the linker does not produce any output, and issues the | |
297 | message @samp{No input files}. | |
298 | ||
36f63dca | 299 | If the linker cannot recognize the format of an object file, it will |
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300 | assume that it is a linker script. A script specified in this way |
301 | augments the main linker script used for the link (either the default | |
302 | linker script or the one specified by using @samp{-T}). This feature | |
303 | permits the linker to link against a file which appears to be an object | |
304 | or an archive, but actually merely defines some symbol values, or uses | |
53d25da6 AM |
305 | @code{INPUT} or @code{GROUP} to load other objects. Specifying a |
306 | script in this way merely augments the main linker script, with the | |
307 | extra commands placed after the main script; use the @samp{-T} option | |
308 | to replace the default linker script entirely, but note the effect of | |
309 | the @code{INSERT} command. @xref{Scripts}. | |
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310 | |
311 | For options whose names are a single letter, | |
312 | option arguments must either follow the option letter without intervening | |
313 | whitespace, or be given as separate arguments immediately following the | |
314 | option that requires them. | |
315 | ||
316 | For options whose names are multiple letters, either one dash or two can | |
e4897a32 | 317 | precede the option name; for example, @samp{-trace-symbol} and |
36f63dca | 318 | @samp{--trace-symbol} are equivalent. Note---there is one exception to |
e4897a32 | 319 | this rule. Multiple letter options that start with a lower case 'o' can |
ba1be17e | 320 | only be preceded by two dashes. This is to reduce confusion with the |
e4897a32 NC |
321 | @samp{-o} option. So for example @samp{-omagic} sets the output file |
322 | name to @samp{magic} whereas @samp{--omagic} sets the NMAGIC flag on the | |
323 | output. | |
324 | ||
325 | Arguments to multiple-letter options must either be separated from the | |
326 | option name by an equals sign, or be given as separate arguments | |
327 | immediately following the option that requires them. For example, | |
328 | @samp{--trace-symbol foo} and @samp{--trace-symbol=foo} are equivalent. | |
329 | Unique abbreviations of the names of multiple-letter options are | |
330 | accepted. | |
252b5132 | 331 | |
36f63dca NC |
332 | Note---if the linker is being invoked indirectly, via a compiler driver |
333 | (e.g. @samp{gcc}) then all the linker command line options should be | |
fa19fce0 NC |
334 | prefixed by @samp{-Wl,} (or whatever is appropriate for the particular |
335 | compiler driver) like this: | |
4e53152f NC |
336 | |
337 | @smallexample | |
2509a395 | 338 | gcc -Wl,--start-group foo.o bar.o -Wl,--end-group |
4e53152f NC |
339 | @end smallexample |
340 | ||
341 | This is important, because otherwise the compiler driver program may | |
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342 | silently drop the linker options, resulting in a bad link. Confusion |
343 | may also arise when passing options that require values through a | |
344 | driver, as the use of a space between option and argument acts as | |
345 | a separator, and causes the driver to pass only the option to the linker | |
346 | and the argument to the compiler. In this case, it is simplest to use | |
347 | the joined forms of both single- and multiple-letter options, such as: | |
348 | ||
349 | @smallexample | |
350 | gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map | |
351 | @end smallexample | |
4e53152f NC |
352 | |
353 | Here is a table of the generic command line switches accepted by the GNU | |
354 | linker: | |
355 | ||
ff5dcc92 | 356 | @table @gcctabopt |
38fc1cb1 | 357 | @include at-file.texi |
dff70155 | 358 | |
2509a395 SL |
359 | @kindex -a @var{keyword} |
360 | @item -a @var{keyword} | |
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361 | This option is supported for HP/UX compatibility. The @var{keyword} |
362 | argument must be one of the strings @samp{archive}, @samp{shared}, or | |
363 | @samp{default}. @samp{-aarchive} is functionally equivalent to | |
364 | @samp{-Bstatic}, and the other two keywords are functionally equivalent | |
365 | to @samp{-Bdynamic}. This option may be used any number of times. | |
366 | ||
7ee314fa AM |
367 | @kindex --audit @var{AUDITLIB} |
368 | @item --audit @var{AUDITLIB} | |
369 | Adds @var{AUDITLIB} to the @code{DT_AUDIT} entry of the dynamic section. | |
370 | @var{AUDITLIB} is not checked for existence, nor will it use the DT_SONAME | |
371 | specified in the library. If specified multiple times @code{DT_AUDIT} | |
372 | will contain a colon separated list of audit interfaces to use. If the linker | |
373 | finds an object with an audit entry while searching for shared libraries, | |
9d5777a3 | 374 | it will add a corresponding @code{DT_DEPAUDIT} entry in the output file. |
7ee314fa | 375 | This option is only meaningful on ELF platforms supporting the rtld-audit |
9d5777a3 | 376 | interface. |
7ee314fa | 377 | |
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378 | @ifset I960 |
379 | @cindex architectures | |
2509a395 SL |
380 | @kindex -A @var{arch} |
381 | @item -A @var{architecture} | |
252b5132 RH |
382 | @kindex --architecture=@var{arch} |
383 | @itemx --architecture=@var{architecture} | |
ff5dcc92 SC |
384 | In the current release of @command{ld}, this option is useful only for the |
385 | Intel 960 family of architectures. In that @command{ld} configuration, the | |
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386 | @var{architecture} argument identifies the particular architecture in |
387 | the 960 family, enabling some safeguards and modifying the | |
ff5dcc92 | 388 | archive-library search path. @xref{i960,,@command{ld} and the Intel 960 |
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389 | family}, for details. |
390 | ||
ff5dcc92 | 391 | Future releases of @command{ld} may support similar functionality for |
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392 | other architecture families. |
393 | @end ifset | |
394 | ||
395 | @ifclear SingleFormat | |
396 | @cindex binary input format | |
397 | @kindex -b @var{format} | |
398 | @kindex --format=@var{format} | |
399 | @cindex input format | |
400 | @cindex input format | |
401 | @item -b @var{input-format} | |
402 | @itemx --format=@var{input-format} | |
ff5dcc92 SC |
403 | @command{ld} may be configured to support more than one kind of object |
404 | file. If your @command{ld} is configured this way, you can use the | |
252b5132 | 405 | @samp{-b} option to specify the binary format for input object files |
ff5dcc92 | 406 | that follow this option on the command line. Even when @command{ld} is |
252b5132 | 407 | configured to support alternative object formats, you don't usually need |
ff5dcc92 | 408 | to specify this, as @command{ld} should be configured to expect as a |
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409 | default input format the most usual format on each machine. |
410 | @var{input-format} is a text string, the name of a particular format | |
411 | supported by the BFD libraries. (You can list the available binary | |
412 | formats with @samp{objdump -i}.) | |
413 | @xref{BFD}. | |
414 | ||
415 | You may want to use this option if you are linking files with an unusual | |
416 | binary format. You can also use @samp{-b} to switch formats explicitly (when | |
417 | linking object files of different formats), by including | |
418 | @samp{-b @var{input-format}} before each group of object files in a | |
a1ab1d2a | 419 | particular format. |
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420 | |
421 | The default format is taken from the environment variable | |
422 | @code{GNUTARGET}. | |
423 | @ifset UsesEnvVars | |
424 | @xref{Environment}. | |
425 | @end ifset | |
426 | You can also define the input format from a script, using the command | |
0285c67d NC |
427 | @code{TARGET}; |
428 | @ifclear man | |
429 | see @ref{Format Commands}. | |
430 | @end ifclear | |
252b5132 RH |
431 | @end ifclear |
432 | ||
433 | @kindex -c @var{MRI-cmdfile} | |
434 | @kindex --mri-script=@var{MRI-cmdfile} | |
435 | @cindex compatibility, MRI | |
436 | @item -c @var{MRI-commandfile} | |
437 | @itemx --mri-script=@var{MRI-commandfile} | |
ff5dcc92 | 438 | For compatibility with linkers produced by MRI, @command{ld} accepts script |
252b5132 | 439 | files written in an alternate, restricted command language, described in |
0285c67d NC |
440 | @ifclear man |
441 | @ref{MRI,,MRI Compatible Script Files}. | |
442 | @end ifclear | |
443 | @ifset man | |
444 | the MRI Compatible Script Files section of GNU ld documentation. | |
445 | @end ifset | |
446 | Introduce MRI script files with | |
252b5132 | 447 | the option @samp{-c}; use the @samp{-T} option to run linker |
ff5dcc92 SC |
448 | scripts written in the general-purpose @command{ld} scripting language. |
449 | If @var{MRI-cmdfile} does not exist, @command{ld} looks for it in the directories | |
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450 | specified by any @samp{-L} options. |
451 | ||
452 | @cindex common allocation | |
453 | @kindex -d | |
454 | @kindex -dc | |
455 | @kindex -dp | |
a1ab1d2a | 456 | @item -d |
252b5132 RH |
457 | @itemx -dc |
458 | @itemx -dp | |
459 | These three options are equivalent; multiple forms are supported for | |
460 | compatibility with other linkers. They assign space to common symbols | |
461 | even if a relocatable output file is specified (with @samp{-r}). The | |
462 | script command @code{FORCE_COMMON_ALLOCATION} has the same effect. | |
463 | @xref{Miscellaneous Commands}. | |
464 | ||
7ee314fa AM |
465 | @kindex --depaudit @var{AUDITLIB} |
466 | @kindex -P @var{AUDITLIB} | |
467 | @item --depaudit @var{AUDITLIB} | |
468 | @itemx -P @var{AUDITLIB} | |
469 | Adds @var{AUDITLIB} to the @code{DT_DEPAUDIT} entry of the dynamic section. | |
470 | @var{AUDITLIB} is not checked for existence, nor will it use the DT_SONAME | |
471 | specified in the library. If specified multiple times @code{DT_DEPAUDIT} | |
472 | will contain a colon separated list of audit interfaces to use. This | |
473 | option is only meaningful on ELF platforms supporting the rtld-audit interface. | |
9d5777a3 | 474 | The -P option is provided for Solaris compatibility. |
7ee314fa | 475 | |
252b5132 RH |
476 | @cindex entry point, from command line |
477 | @kindex -e @var{entry} | |
478 | @kindex --entry=@var{entry} | |
a1ab1d2a | 479 | @item -e @var{entry} |
252b5132 RH |
480 | @itemx --entry=@var{entry} |
481 | Use @var{entry} as the explicit symbol for beginning execution of your | |
482 | program, rather than the default entry point. If there is no symbol | |
483 | named @var{entry}, the linker will try to parse @var{entry} as a number, | |
484 | and use that as the entry address (the number will be interpreted in | |
485 | base 10; you may use a leading @samp{0x} for base 16, or a leading | |
486 | @samp{0} for base 8). @xref{Entry Point}, for a discussion of defaults | |
487 | and other ways of specifying the entry point. | |
488 | ||
b58f81ae DJ |
489 | @kindex --exclude-libs |
490 | @item --exclude-libs @var{lib},@var{lib},... | |
491 | Specifies a list of archive libraries from which symbols should not be automatically | |
e1c37eb5 | 492 | exported. The library names may be delimited by commas or colons. Specifying |
b58f81ae DJ |
493 | @code{--exclude-libs ALL} excludes symbols in all archive libraries from |
494 | automatic export. This option is available only for the i386 PE targeted | |
495 | port of the linker and for ELF targeted ports. For i386 PE, symbols | |
496 | explicitly listed in a .def file are still exported, regardless of this | |
497 | option. For ELF targeted ports, symbols affected by this option will | |
498 | be treated as hidden. | |
499 | ||
e1c37eb5 DK |
500 | @kindex --exclude-modules-for-implib |
501 | @item --exclude-modules-for-implib @var{module},@var{module},... | |
502 | Specifies a list of object files or archive members, from which symbols | |
503 | should not be automatically exported, but which should be copied wholesale | |
504 | into the import library being generated during the link. The module names | |
505 | may be delimited by commas or colons, and must match exactly the filenames | |
506 | used by @command{ld} to open the files; for archive members, this is simply | |
507 | the member name, but for object files the name listed must include and | |
508 | match precisely any path used to specify the input file on the linker's | |
509 | command-line. This option is available only for the i386 PE targeted port | |
510 | of the linker. Symbols explicitly listed in a .def file are still exported, | |
511 | regardless of this option. | |
512 | ||
252b5132 RH |
513 | @cindex dynamic symbol table |
514 | @kindex -E | |
515 | @kindex --export-dynamic | |
267e2722 | 516 | @kindex --no-export-dynamic |
252b5132 RH |
517 | @item -E |
518 | @itemx --export-dynamic | |
267e2722 CD |
519 | @itemx --no-export-dynamic |
520 | When creating a dynamically linked executable, using the @option{-E} | |
521 | option or the @option{--export-dynamic} option causes the linker to add | |
522 | all symbols to the dynamic symbol table. The dynamic symbol table is the | |
523 | set of symbols which are visible from dynamic objects at run time. | |
524 | ||
525 | If you do not use either of these options (or use the | |
526 | @option{--no-export-dynamic} option to restore the default behavior), the | |
527 | dynamic symbol table will normally contain only those symbols which are | |
528 | referenced by some dynamic object mentioned in the link. | |
252b5132 RH |
529 | |
530 | If you use @code{dlopen} to load a dynamic object which needs to refer | |
531 | back to the symbols defined by the program, rather than some other | |
532 | dynamic object, then you will probably need to use this option when | |
533 | linking the program itself. | |
534 | ||
55255dae | 535 | You can also use the dynamic list to control what symbols should |
cb840a31 | 536 | be added to the dynamic symbol table if the output format supports it. |
55255dae | 537 | See the description of @samp{--dynamic-list}. |
cb840a31 | 538 | |
8b747e1a DK |
539 | Note that this option is specific to ELF targeted ports. PE targets |
540 | support a similar function to export all symbols from a DLL or EXE; see | |
541 | the description of @samp{--export-all-symbols} below. | |
542 | ||
36f63dca | 543 | @ifclear SingleFormat |
252b5132 RH |
544 | @cindex big-endian objects |
545 | @cindex endianness | |
546 | @kindex -EB | |
547 | @item -EB | |
548 | Link big-endian objects. This affects the default output format. | |
549 | ||
550 | @cindex little-endian objects | |
551 | @kindex -EL | |
552 | @item -EL | |
553 | Link little-endian objects. This affects the default output format. | |
36f63dca | 554 | @end ifclear |
252b5132 | 555 | |
2509a395 SL |
556 | @kindex -f @var{name} |
557 | @kindex --auxiliary=@var{name} | |
558 | @item -f @var{name} | |
559 | @itemx --auxiliary=@var{name} | |
252b5132 RH |
560 | When creating an ELF shared object, set the internal DT_AUXILIARY field |
561 | to the specified name. This tells the dynamic linker that the symbol | |
562 | table of the shared object should be used as an auxiliary filter on the | |
563 | symbol table of the shared object @var{name}. | |
564 | ||
565 | If you later link a program against this filter object, then, when you | |
566 | run the program, the dynamic linker will see the DT_AUXILIARY field. If | |
567 | the dynamic linker resolves any symbols from the filter object, it will | |
568 | first check whether there is a definition in the shared object | |
569 | @var{name}. If there is one, it will be used instead of the definition | |
570 | in the filter object. The shared object @var{name} need not exist. | |
571 | Thus the shared object @var{name} may be used to provide an alternative | |
572 | implementation of certain functions, perhaps for debugging or for | |
573 | machine specific performance. | |
574 | ||
575 | This option may be specified more than once. The DT_AUXILIARY entries | |
576 | will be created in the order in which they appear on the command line. | |
577 | ||
2509a395 SL |
578 | @kindex -F @var{name} |
579 | @kindex --filter=@var{name} | |
252b5132 | 580 | @item -F @var{name} |
2509a395 | 581 | @itemx --filter=@var{name} |
252b5132 RH |
582 | When creating an ELF shared object, set the internal DT_FILTER field to |
583 | the specified name. This tells the dynamic linker that the symbol table | |
584 | of the shared object which is being created should be used as a filter | |
585 | on the symbol table of the shared object @var{name}. | |
586 | ||
587 | If you later link a program against this filter object, then, when you | |
588 | run the program, the dynamic linker will see the DT_FILTER field. The | |
589 | dynamic linker will resolve symbols according to the symbol table of the | |
590 | filter object as usual, but it will actually link to the definitions | |
591 | found in the shared object @var{name}. Thus the filter object can be | |
592 | used to select a subset of the symbols provided by the object | |
593 | @var{name}. | |
594 | ||
ff5dcc92 | 595 | Some older linkers used the @option{-F} option throughout a compilation |
252b5132 | 596 | toolchain for specifying object-file format for both input and output |
36f63dca NC |
597 | object files. |
598 | @ifclear SingleFormat | |
599 | The @sc{gnu} linker uses other mechanisms for this purpose: the | |
ece2d90e | 600 | @option{-b}, @option{--format}, @option{--oformat} options, the |
252b5132 | 601 | @code{TARGET} command in linker scripts, and the @code{GNUTARGET} |
36f63dca NC |
602 | environment variable. |
603 | @end ifclear | |
604 | The @sc{gnu} linker will ignore the @option{-F} option when not | |
605 | creating an ELF shared object. | |
252b5132 | 606 | |
3dbf70a2 | 607 | @cindex finalization function |
2509a395 SL |
608 | @kindex -fini=@var{name} |
609 | @item -fini=@var{name} | |
3dbf70a2 MM |
610 | When creating an ELF executable or shared object, call NAME when the |
611 | executable or shared object is unloaded, by setting DT_FINI to the | |
612 | address of the function. By default, the linker uses @code{_fini} as | |
613 | the function to call. | |
614 | ||
252b5132 RH |
615 | @kindex -g |
616 | @item -g | |
617 | Ignored. Provided for compatibility with other tools. | |
618 | ||
2509a395 SL |
619 | @kindex -G @var{value} |
620 | @kindex --gpsize=@var{value} | |
252b5132 | 621 | @cindex object size |
2509a395 | 622 | @item -G @var{value} |
252b5132 RH |
623 | @itemx --gpsize=@var{value} |
624 | Set the maximum size of objects to be optimized using the GP register to | |
625 | @var{size}. This is only meaningful for object file formats such as | |
e8044f35 | 626 | MIPS ELF that support putting large and small objects into different |
252b5132 RH |
627 | sections. This is ignored for other object file formats. |
628 | ||
629 | @cindex runtime library name | |
2509a395 | 630 | @kindex -h @var{name} |
252b5132 | 631 | @kindex -soname=@var{name} |
2509a395 | 632 | @item -h @var{name} |
252b5132 RH |
633 | @itemx -soname=@var{name} |
634 | When creating an ELF shared object, set the internal DT_SONAME field to | |
635 | the specified name. When an executable is linked with a shared object | |
636 | which has a DT_SONAME field, then when the executable is run the dynamic | |
637 | linker will attempt to load the shared object specified by the DT_SONAME | |
638 | field rather than the using the file name given to the linker. | |
639 | ||
640 | @kindex -i | |
641 | @cindex incremental link | |
642 | @item -i | |
643 | Perform an incremental link (same as option @samp{-r}). | |
644 | ||
3dbf70a2 | 645 | @cindex initialization function |
2509a395 SL |
646 | @kindex -init=@var{name} |
647 | @item -init=@var{name} | |
3dbf70a2 MM |
648 | When creating an ELF executable or shared object, call NAME when the |
649 | executable or shared object is loaded, by setting DT_INIT to the address | |
650 | of the function. By default, the linker uses @code{_init} as the | |
651 | function to call. | |
652 | ||
252b5132 | 653 | @cindex archive files, from cmd line |
2509a395 | 654 | @kindex -l @var{namespec} |
bcb674cf | 655 | @kindex --library=@var{namespec} |
2509a395 | 656 | @item -l @var{namespec} |
bcb674cf RS |
657 | @itemx --library=@var{namespec} |
658 | Add the archive or object file specified by @var{namespec} to the | |
659 | list of files to link. This option may be used any number of times. | |
660 | If @var{namespec} is of the form @file{:@var{filename}}, @command{ld} | |
07d8eb55 | 661 | will search the library path for a file called @var{filename}, otherwise it |
bcb674cf | 662 | will search the library path for a file called @file{lib@var{namespec}.a}. |
252b5132 | 663 | |
ff5dcc92 | 664 | On systems which support shared libraries, @command{ld} may also search for |
bcb674cf RS |
665 | files other than @file{lib@var{namespec}.a}. Specifically, on ELF |
666 | and SunOS systems, @command{ld} will search a directory for a library | |
667 | called @file{lib@var{namespec}.so} before searching for one called | |
668 | @file{lib@var{namespec}.a}. (By convention, a @code{.so} extension | |
669 | indicates a shared library.) Note that this behavior does not apply | |
670 | to @file{:@var{filename}}, which always specifies a file called | |
671 | @var{filename}. | |
252b5132 RH |
672 | |
673 | The linker will search an archive only once, at the location where it is | |
674 | specified on the command line. If the archive defines a symbol which | |
675 | was undefined in some object which appeared before the archive on the | |
676 | command line, the linker will include the appropriate file(s) from the | |
677 | archive. However, an undefined symbol in an object appearing later on | |
678 | the command line will not cause the linker to search the archive again. | |
679 | ||
ff5dcc92 | 680 | See the @option{-(} option for a way to force the linker to search |
252b5132 RH |
681 | archives multiple times. |
682 | ||
683 | You may list the same archive multiple times on the command line. | |
684 | ||
685 | @ifset GENERIC | |
686 | This type of archive searching is standard for Unix linkers. However, | |
ff5dcc92 | 687 | if you are using @command{ld} on AIX, note that it is different from the |
252b5132 RH |
688 | behaviour of the AIX linker. |
689 | @end ifset | |
690 | ||
691 | @cindex search directory, from cmd line | |
2509a395 | 692 | @kindex -L @var{dir} |
252b5132 | 693 | @kindex --library-path=@var{dir} |
2509a395 | 694 | @item -L @var{searchdir} |
252b5132 | 695 | @itemx --library-path=@var{searchdir} |
ff5dcc92 SC |
696 | Add path @var{searchdir} to the list of paths that @command{ld} will search |
697 | for archive libraries and @command{ld} control scripts. You may use this | |
252b5132 RH |
698 | option any number of times. The directories are searched in the order |
699 | in which they are specified on the command line. Directories specified | |
700 | on the command line are searched before the default directories. All | |
ff5dcc92 | 701 | @option{-L} options apply to all @option{-l} options, regardless of the |
7d24f02c KH |
702 | order in which the options appear. @option{-L} options do not affect |
703 | how @command{ld} searches for a linker script unless @option{-T} | |
704 | option is specified. | |
252b5132 | 705 | |
9c8ebd6a DJ |
706 | If @var{searchdir} begins with @code{=}, then the @code{=} will be replaced |
707 | by the @dfn{sysroot prefix}, a path specified when the linker is configured. | |
708 | ||
252b5132 RH |
709 | @ifset UsesEnvVars |
710 | The default set of paths searched (without being specified with | |
ff5dcc92 | 711 | @samp{-L}) depends on which emulation mode @command{ld} is using, and in |
252b5132 RH |
712 | some cases also on how it was configured. @xref{Environment}. |
713 | @end ifset | |
714 | ||
715 | The paths can also be specified in a link script with the | |
716 | @code{SEARCH_DIR} command. Directories specified this way are searched | |
717 | at the point in which the linker script appears in the command line. | |
718 | ||
719 | @cindex emulation | |
720 | @kindex -m @var{emulation} | |
2509a395 | 721 | @item -m @var{emulation} |
252b5132 RH |
722 | Emulate the @var{emulation} linker. You can list the available |
723 | emulations with the @samp{--verbose} or @samp{-V} options. | |
724 | ||
725 | If the @samp{-m} option is not used, the emulation is taken from the | |
726 | @code{LDEMULATION} environment variable, if that is defined. | |
727 | ||
728 | Otherwise, the default emulation depends upon how the linker was | |
729 | configured. | |
730 | ||
731 | @cindex link map | |
732 | @kindex -M | |
733 | @kindex --print-map | |
734 | @item -M | |
735 | @itemx --print-map | |
736 | Print a link map to the standard output. A link map provides | |
737 | information about the link, including the following: | |
738 | ||
739 | @itemize @bullet | |
740 | @item | |
3b83e13a | 741 | Where object files are mapped into memory. |
252b5132 RH |
742 | @item |
743 | How common symbols are allocated. | |
744 | @item | |
745 | All archive members included in the link, with a mention of the symbol | |
746 | which caused the archive member to be brought in. | |
3b83e13a NC |
747 | @item |
748 | The values assigned to symbols. | |
749 | ||
750 | Note - symbols whose values are computed by an expression which | |
751 | involves a reference to a previous value of the same symbol may not | |
752 | have correct result displayed in the link map. This is because the | |
753 | linker discards intermediate results and only retains the final value | |
754 | of an expression. Under such circumstances the linker will display | |
755 | the final value enclosed by square brackets. Thus for example a | |
756 | linker script containing: | |
757 | ||
758 | @smallexample | |
759 | foo = 1 | |
760 | foo = foo * 4 | |
761 | foo = foo + 8 | |
762 | @end smallexample | |
763 | ||
764 | will produce the following output in the link map if the @option{-M} | |
765 | option is used: | |
766 | ||
767 | @smallexample | |
768 | 0x00000001 foo = 0x1 | |
769 | [0x0000000c] foo = (foo * 0x4) | |
770 | [0x0000000c] foo = (foo + 0x8) | |
771 | @end smallexample | |
772 | ||
773 | See @ref{Expressions} for more information about expressions in linker | |
774 | scripts. | |
252b5132 RH |
775 | @end itemize |
776 | ||
777 | @kindex -n | |
778 | @cindex read-only text | |
779 | @cindex NMAGIC | |
780 | @kindex --nmagic | |
781 | @item -n | |
782 | @itemx --nmagic | |
90f5d9d9 JZ |
783 | Turn off page alignment of sections, and disable linking against shared |
784 | libraries. If the output format supports Unix style magic numbers, | |
785 | mark the output as @code{NMAGIC}. | |
252b5132 RH |
786 | |
787 | @kindex -N | |
788 | @kindex --omagic | |
789 | @cindex read/write from cmd line | |
790 | @cindex OMAGIC | |
a1ab1d2a | 791 | @item -N |
252b5132 RH |
792 | @itemx --omagic |
793 | Set the text and data sections to be readable and writable. Also, do | |
63fd3b82 NC |
794 | not page-align the data segment, and disable linking against shared |
795 | libraries. If the output format supports Unix style magic numbers, | |
4d8907ac DS |
796 | mark the output as @code{OMAGIC}. Note: Although a writable text section |
797 | is allowed for PE-COFF targets, it does not conform to the format | |
798 | specification published by Microsoft. | |
63fd3b82 NC |
799 | |
800 | @kindex --no-omagic | |
801 | @cindex OMAGIC | |
802 | @item --no-omagic | |
803 | This option negates most of the effects of the @option{-N} option. It | |
804 | sets the text section to be read-only, and forces the data segment to | |
805 | be page-aligned. Note - this option does not enable linking against | |
806 | shared libraries. Use @option{-Bdynamic} for this. | |
252b5132 RH |
807 | |
808 | @kindex -o @var{output} | |
809 | @kindex --output=@var{output} | |
810 | @cindex naming the output file | |
811 | @item -o @var{output} | |
812 | @itemx --output=@var{output} | |
ff5dcc92 | 813 | Use @var{output} as the name for the program produced by @command{ld}; if this |
252b5132 RH |
814 | option is not specified, the name @file{a.out} is used by default. The |
815 | script command @code{OUTPUT} can also specify the output file name. | |
816 | ||
817 | @kindex -O @var{level} | |
818 | @cindex generating optimized output | |
819 | @item -O @var{level} | |
ff5dcc92 | 820 | If @var{level} is a numeric values greater than zero @command{ld} optimizes |
252b5132 | 821 | the output. This might take significantly longer and therefore probably |
98c503ac NC |
822 | should only be enabled for the final binary. At the moment this |
823 | option only affects ELF shared library generation. Future releases of | |
824 | the linker may make more use of this option. Also currently there is | |
825 | no difference in the linker's behaviour for different non-zero values | |
826 | of this option. Again this may change with future releases. | |
252b5132 | 827 | |
a712da20 NC |
828 | @kindex -q |
829 | @kindex --emit-relocs | |
830 | @cindex retain relocations in final executable | |
831 | @item -q | |
832 | @itemx --emit-relocs | |
ba1be17e | 833 | Leave relocation sections and contents in fully linked executables. |
a712da20 NC |
834 | Post link analysis and optimization tools may need this information in |
835 | order to perform correct modifications of executables. This results | |
836 | in larger executables. | |
837 | ||
dbab7a7b NC |
838 | This option is currently only supported on ELF platforms. |
839 | ||
4f471f39 RS |
840 | @kindex --force-dynamic |
841 | @cindex forcing the creation of dynamic sections | |
842 | @item --force-dynamic | |
843 | Force the output file to have dynamic sections. This option is specific | |
844 | to VxWorks targets. | |
845 | ||
252b5132 RH |
846 | @cindex partial link |
847 | @cindex relocatable output | |
848 | @kindex -r | |
1049f94e | 849 | @kindex --relocatable |
252b5132 | 850 | @item -r |
1049f94e | 851 | @itemx --relocatable |
252b5132 | 852 | Generate relocatable output---i.e., generate an output file that can in |
ff5dcc92 | 853 | turn serve as input to @command{ld}. This is often called @dfn{partial |
252b5132 RH |
854 | linking}. As a side effect, in environments that support standard Unix |
855 | magic numbers, this option also sets the output file's magic number to | |
856 | @code{OMAGIC}. | |
ff5dcc92 | 857 | @c ; see @option{-N}. |
252b5132 RH |
858 | If this option is not specified, an absolute file is produced. When |
859 | linking C++ programs, this option @emph{will not} resolve references to | |
860 | constructors; to do that, use @samp{-Ur}. | |
861 | ||
62bf86b4 HPN |
862 | When an input file does not have the same format as the output file, |
863 | partial linking is only supported if that input file does not contain any | |
864 | relocations. Different output formats can have further restrictions; for | |
865 | example some @code{a.out}-based formats do not support partial linking | |
866 | with input files in other formats at all. | |
867 | ||
252b5132 RH |
868 | This option does the same thing as @samp{-i}. |
869 | ||
870 | @kindex -R @var{file} | |
871 | @kindex --just-symbols=@var{file} | |
872 | @cindex symbol-only input | |
873 | @item -R @var{filename} | |
874 | @itemx --just-symbols=@var{filename} | |
875 | Read symbol names and their addresses from @var{filename}, but do not | |
876 | relocate it or include it in the output. This allows your output file | |
877 | to refer symbolically to absolute locations of memory defined in other | |
878 | programs. You may use this option more than once. | |
879 | ||
ff5dcc92 | 880 | For compatibility with other ELF linkers, if the @option{-R} option is |
252b5132 | 881 | followed by a directory name, rather than a file name, it is treated as |
ff5dcc92 | 882 | the @option{-rpath} option. |
252b5132 RH |
883 | |
884 | @kindex -s | |
885 | @kindex --strip-all | |
886 | @cindex strip all symbols | |
a1ab1d2a | 887 | @item -s |
252b5132 RH |
888 | @itemx --strip-all |
889 | Omit all symbol information from the output file. | |
890 | ||
891 | @kindex -S | |
892 | @kindex --strip-debug | |
893 | @cindex strip debugger symbols | |
a1ab1d2a | 894 | @item -S |
252b5132 RH |
895 | @itemx --strip-debug |
896 | Omit debugger symbol information (but not all symbols) from the output file. | |
897 | ||
898 | @kindex -t | |
899 | @kindex --trace | |
900 | @cindex input files, displaying | |
a1ab1d2a | 901 | @item -t |
252b5132 | 902 | @itemx --trace |
ff5dcc92 | 903 | Print the names of the input files as @command{ld} processes them. |
252b5132 RH |
904 | |
905 | @kindex -T @var{script} | |
906 | @kindex --script=@var{script} | |
907 | @cindex script files | |
908 | @item -T @var{scriptfile} | |
909 | @itemx --script=@var{scriptfile} | |
910 | Use @var{scriptfile} as the linker script. This script replaces | |
ff5dcc92 | 911 | @command{ld}'s default linker script (rather than adding to it), so |
252b5132 | 912 | @var{commandfile} must specify everything necessary to describe the |
114283d8 NC |
913 | output file. @xref{Scripts}. If @var{scriptfile} does not exist in |
914 | the current directory, @code{ld} looks for it in the directories | |
915 | specified by any preceding @samp{-L} options. Multiple @samp{-T} | |
916 | options accumulate. | |
252b5132 | 917 | |
14be8564 L |
918 | @kindex -dT @var{script} |
919 | @kindex --default-script=@var{script} | |
920 | @cindex script files | |
921 | @item -dT @var{scriptfile} | |
922 | @itemx --default-script=@var{scriptfile} | |
923 | Use @var{scriptfile} as the default linker script. @xref{Scripts}. | |
924 | ||
925 | This option is similar to the @option{--script} option except that | |
926 | processing of the script is delayed until after the rest of the | |
927 | command line has been processed. This allows options placed after the | |
928 | @option{--default-script} option on the command line to affect the | |
929 | behaviour of the linker script, which can be important when the linker | |
930 | command line cannot be directly controlled by the user. (eg because | |
931 | the command line is being constructed by another tool, such as | |
932 | @samp{gcc}). | |
933 | ||
252b5132 RH |
934 | @kindex -u @var{symbol} |
935 | @kindex --undefined=@var{symbol} | |
936 | @cindex undefined symbol | |
937 | @item -u @var{symbol} | |
938 | @itemx --undefined=@var{symbol} | |
939 | Force @var{symbol} to be entered in the output file as an undefined | |
940 | symbol. Doing this may, for example, trigger linking of additional | |
941 | modules from standard libraries. @samp{-u} may be repeated with | |
942 | different option arguments to enter additional undefined symbols. This | |
943 | option is equivalent to the @code{EXTERN} linker script command. | |
944 | ||
945 | @kindex -Ur | |
946 | @cindex constructors | |
a1ab1d2a | 947 | @item -Ur |
252b5132 RH |
948 | For anything other than C++ programs, this option is equivalent to |
949 | @samp{-r}: it generates relocatable output---i.e., an output file that can in | |
ff5dcc92 | 950 | turn serve as input to @command{ld}. When linking C++ programs, @samp{-Ur} |
252b5132 RH |
951 | @emph{does} resolve references to constructors, unlike @samp{-r}. |
952 | It does not work to use @samp{-Ur} on files that were themselves linked | |
953 | with @samp{-Ur}; once the constructor table has been built, it cannot | |
954 | be added to. Use @samp{-Ur} only for the last partial link, and | |
955 | @samp{-r} for the others. | |
956 | ||
577a0623 AM |
957 | @kindex --unique[=@var{SECTION}] |
958 | @item --unique[=@var{SECTION}] | |
959 | Creates a separate output section for every input section matching | |
960 | @var{SECTION}, or if the optional wildcard @var{SECTION} argument is | |
961 | missing, for every orphan input section. An orphan section is one not | |
962 | specifically mentioned in a linker script. You may use this option | |
963 | multiple times on the command line; It prevents the normal merging of | |
964 | input sections with the same name, overriding output section assignments | |
965 | in a linker script. | |
a854a4a7 | 966 | |
252b5132 RH |
967 | @kindex -v |
968 | @kindex -V | |
969 | @kindex --version | |
970 | @cindex version | |
971 | @item -v | |
972 | @itemx --version | |
973 | @itemx -V | |
ff5dcc92 | 974 | Display the version number for @command{ld}. The @option{-V} option also |
252b5132 RH |
975 | lists the supported emulations. |
976 | ||
977 | @kindex -x | |
978 | @kindex --discard-all | |
979 | @cindex deleting local symbols | |
980 | @item -x | |
981 | @itemx --discard-all | |
982 | Delete all local symbols. | |
983 | ||
984 | @kindex -X | |
985 | @kindex --discard-locals | |
986 | @cindex local symbols, deleting | |
a1ab1d2a | 987 | @item -X |
252b5132 | 988 | @itemx --discard-locals |
3c68c38f BW |
989 | Delete all temporary local symbols. (These symbols start with |
990 | system-specific local label prefixes, typically @samp{.L} for ELF systems | |
991 | or @samp{L} for traditional a.out systems.) | |
252b5132 RH |
992 | |
993 | @kindex -y @var{symbol} | |
994 | @kindex --trace-symbol=@var{symbol} | |
995 | @cindex symbol tracing | |
996 | @item -y @var{symbol} | |
997 | @itemx --trace-symbol=@var{symbol} | |
998 | Print the name of each linked file in which @var{symbol} appears. This | |
999 | option may be given any number of times. On many systems it is necessary | |
1000 | to prepend an underscore. | |
1001 | ||
1002 | This option is useful when you have an undefined symbol in your link but | |
1003 | don't know where the reference is coming from. | |
1004 | ||
1005 | @kindex -Y @var{path} | |
1006 | @item -Y @var{path} | |
1007 | Add @var{path} to the default library search path. This option exists | |
1008 | for Solaris compatibility. | |
1009 | ||
1010 | @kindex -z @var{keyword} | |
1011 | @item -z @var{keyword} | |
cd6d6c15 NC |
1012 | The recognized keywords are: |
1013 | @table @samp | |
1014 | ||
1015 | @item combreloc | |
1016 | Combines multiple reloc sections and sorts them to make dynamic symbol | |
1017 | lookup caching possible. | |
1018 | ||
1019 | @item defs | |
560e09e9 | 1020 | Disallows undefined symbols in object files. Undefined symbols in |
07f3b6ad | 1021 | shared libraries are still allowed. |
cd6d6c15 | 1022 | |
6aa29e7b JJ |
1023 | @item execstack |
1024 | Marks the object as requiring executable stack. | |
1025 | ||
b039ef04 L |
1026 | @item global |
1027 | This option is only meaningful when building a shared object. It makes | |
1028 | the symbols defined by this shared object available for symbol resolution | |
1029 | of subsequently loaded libraries. | |
1030 | ||
cd6d6c15 NC |
1031 | @item initfirst |
1032 | This option is only meaningful when building a shared object. | |
1033 | It marks the object so that its runtime initialization will occur | |
1034 | before the runtime initialization of any other objects brought into | |
1035 | the process at the same time. Similarly the runtime finalization of | |
1036 | the object will occur after the runtime finalization of any other | |
1037 | objects. | |
1038 | ||
1039 | @item interpose | |
1040 | Marks the object that its symbol table interposes before all symbols | |
1041 | but the primary executable. | |
1042 | ||
5fa222e4 AM |
1043 | @item lazy |
1044 | When generating an executable or shared library, mark it to tell the | |
1045 | dynamic linker to defer function call resolution to the point when | |
1046 | the function is called (lazy binding), rather than at load time. | |
1047 | Lazy binding is the default. | |
1048 | ||
cd6d6c15 NC |
1049 | @item loadfltr |
1050 | Marks the object that its filters be processed immediately at | |
1051 | runtime. | |
1052 | ||
1053 | @item muldefs | |
1054 | Allows multiple definitions. | |
1055 | ||
1056 | @item nocombreloc | |
1057 | Disables multiple reloc sections combining. | |
1058 | ||
1059 | @item nocopyreloc | |
1060 | Disables production of copy relocs. | |
1061 | ||
1062 | @item nodefaultlib | |
1063 | Marks the object that the search for dependencies of this object will | |
1064 | ignore any default library search paths. | |
1065 | ||
1066 | @item nodelete | |
1067 | Marks the object shouldn't be unloaded at runtime. | |
1068 | ||
1069 | @item nodlopen | |
1070 | Marks the object not available to @code{dlopen}. | |
1071 | ||
1072 | @item nodump | |
1073 | Marks the object can not be dumped by @code{dldump}. | |
1074 | ||
6aa29e7b JJ |
1075 | @item noexecstack |
1076 | Marks the object as not requiring executable stack. | |
1077 | ||
1078 | @item norelro | |
1079 | Don't create an ELF @code{PT_GNU_RELRO} segment header in the object. | |
1080 | ||
cd6d6c15 NC |
1081 | @item now |
1082 | When generating an executable or shared library, mark it to tell the | |
1083 | dynamic linker to resolve all symbols when the program is started, or | |
1084 | when the shared library is linked to using dlopen, instead of | |
1085 | deferring function call resolution to the point when the function is | |
1086 | first called. | |
1087 | ||
1088 | @item origin | |
1089 | Marks the object may contain $ORIGIN. | |
1090 | ||
6aa29e7b JJ |
1091 | @item relro |
1092 | Create an ELF @code{PT_GNU_RELRO} segment header in the object. | |
1093 | ||
24718e3b L |
1094 | @item max-page-size=@var{value} |
1095 | Set the emulation maximum page size to @var{value}. | |
1096 | ||
1097 | @item common-page-size=@var{value} | |
1098 | Set the emulation common page size to @var{value}. | |
1099 | ||
04c3a755 NS |
1100 | @item stack-size=@var{value} |
1101 | Specify a stack size for in an ELF @code{PT_GNU_STACK} segment. | |
1102 | Specifying zero will override any default non-zero sized | |
1103 | @code{PT_GNU_STACK} segment creation. | |
1104 | ||
cd6d6c15 NC |
1105 | @end table |
1106 | ||
ece2d90e | 1107 | Other keywords are ignored for Solaris compatibility. |
252b5132 RH |
1108 | |
1109 | @kindex -( | |
1110 | @cindex groups of archives | |
1111 | @item -( @var{archives} -) | |
1112 | @itemx --start-group @var{archives} --end-group | |
1113 | The @var{archives} should be a list of archive files. They may be | |
1114 | either explicit file names, or @samp{-l} options. | |
1115 | ||
1116 | The specified archives are searched repeatedly until no new undefined | |
1117 | references are created. Normally, an archive is searched only once in | |
1118 | the order that it is specified on the command line. If a symbol in that | |
1119 | archive is needed to resolve an undefined symbol referred to by an | |
1120 | object in an archive that appears later on the command line, the linker | |
1121 | would not be able to resolve that reference. By grouping the archives, | |
1122 | they all be searched repeatedly until all possible references are | |
1123 | resolved. | |
1124 | ||
1125 | Using this option has a significant performance cost. It is best to use | |
1126 | it only when there are unavoidable circular references between two or | |
1127 | more archives. | |
1128 | ||
69da35b5 NC |
1129 | @kindex --accept-unknown-input-arch |
1130 | @kindex --no-accept-unknown-input-arch | |
1131 | @item --accept-unknown-input-arch | |
1132 | @itemx --no-accept-unknown-input-arch | |
1133 | Tells the linker to accept input files whose architecture cannot be | |
2ca22b03 | 1134 | recognised. The assumption is that the user knows what they are doing |
69da35b5 NC |
1135 | and deliberately wants to link in these unknown input files. This was |
1136 | the default behaviour of the linker, before release 2.14. The default | |
1137 | behaviour from release 2.14 onwards is to reject such input files, and | |
1138 | so the @samp{--accept-unknown-input-arch} option has been added to | |
1139 | restore the old behaviour. | |
2ca22b03 | 1140 | |
4a43e768 AM |
1141 | @kindex --as-needed |
1142 | @kindex --no-as-needed | |
1143 | @item --as-needed | |
1144 | @itemx --no-as-needed | |
1145 | This option affects ELF DT_NEEDED tags for dynamic libraries mentioned | |
ddbb8a31 | 1146 | on the command line after the @option{--as-needed} option. Normally |
4a43e768 AM |
1147 | the linker will add a DT_NEEDED tag for each dynamic library mentioned |
1148 | on the command line, regardless of whether the library is actually | |
ddbb8a31 | 1149 | needed or not. @option{--as-needed} causes a DT_NEEDED tag to only be |
ffa9430d AM |
1150 | emitted for a library that @emph{at that point in the link} satisfies a |
1151 | non-weak undefined symbol reference from a regular object file or, if | |
1152 | the library is not found in the DT_NEEDED lists of other libraries, a | |
1153 | non-weak undefined symbol reference from another dynamic library. | |
1154 | Object files or libraries appearing on the command line @emph{after} | |
1155 | the library in question do not affect whether the library is seen as | |
1156 | needed. This is similar to the rules for extraction of object files | |
1157 | from archives. @option{--no-as-needed} restores the default behaviour. | |
4a43e768 | 1158 | |
e56f61be L |
1159 | @kindex --add-needed |
1160 | @kindex --no-add-needed | |
1161 | @item --add-needed | |
1162 | @itemx --no-add-needed | |
ddbb8a31 NC |
1163 | These two options have been deprecated because of the similarity of |
1164 | their names to the @option{--as-needed} and @option{--no-as-needed} | |
1165 | options. They have been replaced by @option{--copy-dt-needed-entries} | |
1166 | and @option{--no-copy-dt-needed-entries}. | |
e56f61be | 1167 | |
252b5132 RH |
1168 | @kindex -assert @var{keyword} |
1169 | @item -assert @var{keyword} | |
1170 | This option is ignored for SunOS compatibility. | |
1171 | ||
1172 | @kindex -Bdynamic | |
1173 | @kindex -dy | |
1174 | @kindex -call_shared | |
1175 | @item -Bdynamic | |
1176 | @itemx -dy | |
1177 | @itemx -call_shared | |
1178 | Link against dynamic libraries. This is only meaningful on platforms | |
1179 | for which shared libraries are supported. This option is normally the | |
1180 | default on such platforms. The different variants of this option are | |
1181 | for compatibility with various systems. You may use this option | |
1182 | multiple times on the command line: it affects library searching for | |
da8bce14 | 1183 | @option{-l} options which follow it. |
252b5132 | 1184 | |
a1ab1d2a UD |
1185 | @kindex -Bgroup |
1186 | @item -Bgroup | |
1187 | Set the @code{DF_1_GROUP} flag in the @code{DT_FLAGS_1} entry in the dynamic | |
1188 | section. This causes the runtime linker to handle lookups in this | |
1189 | object and its dependencies to be performed only inside the group. | |
560e09e9 NC |
1190 | @option{--unresolved-symbols=report-all} is implied. This option is |
1191 | only meaningful on ELF platforms which support shared libraries. | |
a1ab1d2a | 1192 | |
252b5132 RH |
1193 | @kindex -Bstatic |
1194 | @kindex -dn | |
1195 | @kindex -non_shared | |
1196 | @kindex -static | |
a1ab1d2a | 1197 | @item -Bstatic |
252b5132 RH |
1198 | @itemx -dn |
1199 | @itemx -non_shared | |
1200 | @itemx -static | |
1201 | Do not link against shared libraries. This is only meaningful on | |
1202 | platforms for which shared libraries are supported. The different | |
1203 | variants of this option are for compatibility with various systems. You | |
1204 | may use this option multiple times on the command line: it affects | |
560e09e9 | 1205 | library searching for @option{-l} options which follow it. This |
e9156f74 NC |
1206 | option also implies @option{--unresolved-symbols=report-all}. This |
1207 | option can be used with @option{-shared}. Doing so means that a | |
1208 | shared library is being created but that all of the library's external | |
1209 | references must be resolved by pulling in entries from static | |
ece2d90e | 1210 | libraries. |
252b5132 RH |
1211 | |
1212 | @kindex -Bsymbolic | |
1213 | @item -Bsymbolic | |
1214 | When creating a shared library, bind references to global symbols to the | |
1215 | definition within the shared library, if any. Normally, it is possible | |
1216 | for a program linked against a shared library to override the definition | |
1217 | within the shared library. This option is only meaningful on ELF | |
1218 | platforms which support shared libraries. | |
1219 | ||
40b36307 L |
1220 | @kindex -Bsymbolic-functions |
1221 | @item -Bsymbolic-functions | |
1222 | When creating a shared library, bind references to global function | |
c0065db7 | 1223 | symbols to the definition within the shared library, if any. |
40b36307 L |
1224 | This option is only meaningful on ELF platforms which support shared |
1225 | libraries. | |
1226 | ||
55255dae L |
1227 | @kindex --dynamic-list=@var{dynamic-list-file} |
1228 | @item --dynamic-list=@var{dynamic-list-file} | |
1229 | Specify the name of a dynamic list file to the linker. This is | |
1230 | typically used when creating shared libraries to specify a list of | |
1231 | global symbols whose references shouldn't be bound to the definition | |
1232 | within the shared library, or creating dynamically linked executables | |
1233 | to specify a list of symbols which should be added to the symbol table | |
1234 | in the executable. This option is only meaningful on ELF platforms | |
1235 | which support shared libraries. | |
1236 | ||
1237 | The format of the dynamic list is the same as the version node without | |
1238 | scope and node name. See @ref{VERSION} for more information. | |
1239 | ||
40b36307 L |
1240 | @kindex --dynamic-list-data |
1241 | @item --dynamic-list-data | |
1242 | Include all global data symbols to the dynamic list. | |
1243 | ||
1244 | @kindex --dynamic-list-cpp-new | |
1245 | @item --dynamic-list-cpp-new | |
1246 | Provide the builtin dynamic list for C++ operator new and delete. It | |
1247 | is mainly useful for building shared libstdc++. | |
1248 | ||
0b8a70d9 L |
1249 | @kindex --dynamic-list-cpp-typeinfo |
1250 | @item --dynamic-list-cpp-typeinfo | |
1251 | Provide the builtin dynamic list for C++ runtime type identification. | |
1252 | ||
252b5132 RH |
1253 | @kindex --check-sections |
1254 | @kindex --no-check-sections | |
1255 | @item --check-sections | |
308b1ffd | 1256 | @itemx --no-check-sections |
252b5132 | 1257 | Asks the linker @emph{not} to check section addresses after they have |
7d816a17 | 1258 | been assigned to see if there are any overlaps. Normally the linker will |
252b5132 RH |
1259 | perform this check, and if it finds any overlaps it will produce |
1260 | suitable error messages. The linker does know about, and does make | |
1261 | allowances for sections in overlays. The default behaviour can be | |
560e09e9 | 1262 | restored by using the command line switch @option{--check-sections}. |
02b0b1aa NS |
1263 | Section overlap is not usually checked for relocatable links. You can |
1264 | force checking in that case by using the @option{--check-sections} | |
1265 | option. | |
252b5132 | 1266 | |
ddbb8a31 NC |
1267 | @kindex --copy-dt-needed-entries |
1268 | @kindex --no-copy-dt-needed-entries | |
1269 | @item --copy-dt-needed-entries | |
1270 | @itemx --no-copy-dt-needed-entries | |
9d5777a3 | 1271 | This option affects the treatment of dynamic libraries referred to |
ddbb8a31 | 1272 | by DT_NEEDED tags @emph{inside} ELF dynamic libraries mentioned on the |
08efffb8 | 1273 | command line. Normally the linker won't add a DT_NEEDED tag to the |
ddbb8a31 | 1274 | output binary for each library mentioned in a DT_NEEDED tag in an |
08efffb8 | 1275 | input dynamic library. With @option{--copy-dt-needed-entries} |
ddbb8a31 | 1276 | specified on the command line however any dynamic libraries that |
08efffb8 MM |
1277 | follow it will have their DT_NEEDED entries added. The default |
1278 | behaviour can be restored with @option{--no-copy-dt-needed-entries}. | |
ddbb8a31 NC |
1279 | |
1280 | This option also has an effect on the resolution of symbols in dynamic | |
08efffb8 MM |
1281 | libraries. With @option{--copy-dt-needed-entries} dynamic libraries |
1282 | mentioned on the command line will be recursively searched, following | |
1283 | their DT_NEEDED tags to other libraries, in order to resolve symbols | |
1284 | required by the output binary. With the default setting however | |
1285 | the searching of dynamic libraries that follow it will stop with the | |
1286 | dynamic library itself. No DT_NEEDED links will be traversed to resolve | |
ddbb8a31 NC |
1287 | symbols. |
1288 | ||
252b5132 RH |
1289 | @cindex cross reference table |
1290 | @kindex --cref | |
1291 | @item --cref | |
1292 | Output a cross reference table. If a linker map file is being | |
1293 | generated, the cross reference table is printed to the map file. | |
1294 | Otherwise, it is printed on the standard output. | |
1295 | ||
1296 | The format of the table is intentionally simple, so that it may be | |
1297 | easily processed by a script if necessary. The symbols are printed out, | |
1298 | sorted by name. For each symbol, a list of file names is given. If the | |
1299 | symbol is defined, the first file listed is the location of the | |
049c1c8e NC |
1300 | definition. If the symbol is defined as a common value then any files |
1301 | where this happens appear next. Finally any files that reference the | |
1302 | symbol are listed. | |
252b5132 | 1303 | |
4818e05f AM |
1304 | @cindex common allocation |
1305 | @kindex --no-define-common | |
1306 | @item --no-define-common | |
1307 | This option inhibits the assignment of addresses to common symbols. | |
1308 | The script command @code{INHIBIT_COMMON_ALLOCATION} has the same effect. | |
1309 | @xref{Miscellaneous Commands}. | |
1310 | ||
1311 | The @samp{--no-define-common} option allows decoupling | |
1312 | the decision to assign addresses to Common symbols from the choice | |
1313 | of the output file type; otherwise a non-Relocatable output type | |
1314 | forces assigning addresses to Common symbols. | |
1315 | Using @samp{--no-define-common} allows Common symbols that are referenced | |
1316 | from a shared library to be assigned addresses only in the main program. | |
1317 | This eliminates the unused duplicate space in the shared library, | |
1318 | and also prevents any possible confusion over resolving to the wrong | |
1319 | duplicate when there are many dynamic modules with specialized search | |
1320 | paths for runtime symbol resolution. | |
1321 | ||
252b5132 | 1322 | @cindex symbols, from command line |
2509a395 SL |
1323 | @kindex --defsym=@var{symbol}=@var{exp} |
1324 | @item --defsym=@var{symbol}=@var{expression} | |
252b5132 RH |
1325 | Create a global symbol in the output file, containing the absolute |
1326 | address given by @var{expression}. You may use this option as many | |
1327 | times as necessary to define multiple symbols in the command line. A | |
1328 | limited form of arithmetic is supported for the @var{expression} in this | |
1329 | context: you may give a hexadecimal constant or the name of an existing | |
1330 | symbol, or use @code{+} and @code{-} to add or subtract hexadecimal | |
1331 | constants or symbols. If you need more elaborate expressions, consider | |
1332 | using the linker command language from a script (@pxref{Assignments,, | |
1333 | Assignment: Symbol Definitions}). @emph{Note:} there should be no white | |
1334 | space between @var{symbol}, the equals sign (``@key{=}''), and | |
1335 | @var{expression}. | |
1336 | ||
1337 | @cindex demangling, from command line | |
28c309a2 | 1338 | @kindex --demangle[=@var{style}] |
252b5132 | 1339 | @kindex --no-demangle |
28c309a2 | 1340 | @item --demangle[=@var{style}] |
252b5132 RH |
1341 | @itemx --no-demangle |
1342 | These options control whether to demangle symbol names in error messages | |
1343 | and other output. When the linker is told to demangle, it tries to | |
1344 | present symbol names in a readable fashion: it strips leading | |
1345 | underscores if they are used by the object file format, and converts C++ | |
a1ab1d2a UD |
1346 | mangled symbol names into user readable names. Different compilers have |
1347 | different mangling styles. The optional demangling style argument can be used | |
1348 | to choose an appropriate demangling style for your compiler. The linker will | |
28c309a2 NC |
1349 | demangle by default unless the environment variable @samp{COLLECT_NO_DEMANGLE} |
1350 | is set. These options may be used to override the default. | |
252b5132 RH |
1351 | |
1352 | @cindex dynamic linker, from command line | |
506eee22 | 1353 | @kindex -I@var{file} |
2509a395 SL |
1354 | @kindex --dynamic-linker=@var{file} |
1355 | @item -I@var{file} | |
1356 | @itemx --dynamic-linker=@var{file} | |
252b5132 RH |
1357 | Set the name of the dynamic linker. This is only meaningful when |
1358 | generating dynamically linked ELF executables. The default dynamic | |
1359 | linker is normally correct; don't use this unless you know what you are | |
1360 | doing. | |
1361 | ||
7ce691ae | 1362 | @kindex --fatal-warnings |
0fe58ccd | 1363 | @kindex --no-fatal-warnings |
7ce691ae | 1364 | @item --fatal-warnings |
0fe58ccd NC |
1365 | @itemx --no-fatal-warnings |
1366 | Treat all warnings as errors. The default behaviour can be restored | |
1367 | with the option @option{--no-fatal-warnings}. | |
7ce691ae | 1368 | |
252b5132 RH |
1369 | @kindex --force-exe-suffix |
1370 | @item --force-exe-suffix | |
1371 | Make sure that an output file has a .exe suffix. | |
1372 | ||
1373 | If a successfully built fully linked output file does not have a | |
1374 | @code{.exe} or @code{.dll} suffix, this option forces the linker to copy | |
1375 | the output file to one of the same name with a @code{.exe} suffix. This | |
1376 | option is useful when using unmodified Unix makefiles on a Microsoft | |
1377 | Windows host, since some versions of Windows won't run an image unless | |
1378 | it ends in a @code{.exe} suffix. | |
1379 | ||
1380 | @kindex --gc-sections | |
1381 | @kindex --no-gc-sections | |
1382 | @cindex garbage collection | |
c17d87de NC |
1383 | @item --gc-sections |
1384 | @itemx --no-gc-sections | |
252b5132 | 1385 | Enable garbage collection of unused input sections. It is ignored on |
ac69cbc6 | 1386 | targets that do not support this option. The default behaviour (of not |
b3549761 NC |
1387 | performing this garbage collection) can be restored by specifying |
1388 | @samp{--no-gc-sections} on the command line. | |
252b5132 | 1389 | |
d5465ba2 AM |
1390 | @samp{--gc-sections} decides which input sections are used by |
1391 | examining symbols and relocations. The section containing the entry | |
1392 | symbol and all sections containing symbols undefined on the | |
1393 | command-line will be kept, as will sections containing symbols | |
1394 | referenced by dynamic objects. Note that when building shared | |
1395 | libraries, the linker must assume that any visible symbol is | |
1396 | referenced. Once this initial set of sections has been determined, | |
1397 | the linker recursively marks as used any section referenced by their | |
1398 | relocations. See @samp{--entry} and @samp{--undefined}. | |
1399 | ||
ac69cbc6 | 1400 | This option can be set when doing a partial link (enabled with option |
9d5777a3 | 1401 | @samp{-r}). In this case the root of symbols kept must be explicitly |
ac69cbc6 TG |
1402 | specified either by an @samp{--entry} or @samp{--undefined} option or by |
1403 | a @code{ENTRY} command in the linker script. | |
1404 | ||
c17d87de NC |
1405 | @kindex --print-gc-sections |
1406 | @kindex --no-print-gc-sections | |
1407 | @cindex garbage collection | |
1408 | @item --print-gc-sections | |
1409 | @itemx --no-print-gc-sections | |
1410 | List all sections removed by garbage collection. The listing is | |
1411 | printed on stderr. This option is only effective if garbage | |
1412 | collection has been enabled via the @samp{--gc-sections}) option. The | |
1413 | default behaviour (of not listing the sections that are removed) can | |
1414 | be restored by specifying @samp{--no-print-gc-sections} on the command | |
1415 | line. | |
1416 | ||
30824704 RM |
1417 | @kindex --print-output-format |
1418 | @cindex output format | |
1419 | @item --print-output-format | |
1420 | Print the name of the default output format (perhaps influenced by | |
1421 | other command-line options). This is the string that would appear | |
1422 | in an @code{OUTPUT_FORMAT} linker script command (@pxref{File Commands}). | |
1423 | ||
252b5132 RH |
1424 | @cindex help |
1425 | @cindex usage | |
1426 | @kindex --help | |
1427 | @item --help | |
1428 | Print a summary of the command-line options on the standard output and exit. | |
1429 | ||
ea20a7da CC |
1430 | @kindex --target-help |
1431 | @item --target-help | |
1432 | Print a summary of all target specific options on the standard output and exit. | |
1433 | ||
2509a395 SL |
1434 | @kindex -Map=@var{mapfile} |
1435 | @item -Map=@var{mapfile} | |
252b5132 | 1436 | Print a link map to the file @var{mapfile}. See the description of the |
560e09e9 | 1437 | @option{-M} option, above. |
252b5132 RH |
1438 | |
1439 | @cindex memory usage | |
1440 | @kindex --no-keep-memory | |
1441 | @item --no-keep-memory | |
ff5dcc92 SC |
1442 | @command{ld} normally optimizes for speed over memory usage by caching the |
1443 | symbol tables of input files in memory. This option tells @command{ld} to | |
252b5132 | 1444 | instead optimize for memory usage, by rereading the symbol tables as |
ff5dcc92 | 1445 | necessary. This may be required if @command{ld} runs out of memory space |
252b5132 RH |
1446 | while linking a large executable. |
1447 | ||
1448 | @kindex --no-undefined | |
a1ab1d2a | 1449 | @kindex -z defs |
252b5132 | 1450 | @item --no-undefined |
a1ab1d2a | 1451 | @itemx -z defs |
560e09e9 NC |
1452 | Report unresolved symbol references from regular object files. This |
1453 | is done even if the linker is creating a non-symbolic shared library. | |
1454 | The switch @option{--[no-]allow-shlib-undefined} controls the | |
1455 | behaviour for reporting unresolved references found in shared | |
ece2d90e | 1456 | libraries being linked in. |
252b5132 | 1457 | |
aa713662 L |
1458 | @kindex --allow-multiple-definition |
1459 | @kindex -z muldefs | |
1460 | @item --allow-multiple-definition | |
1461 | @itemx -z muldefs | |
1462 | Normally when a symbol is defined multiple times, the linker will | |
1463 | report a fatal error. These options allow multiple definitions and the | |
1464 | first definition will be used. | |
1465 | ||
b79e8c78 | 1466 | @kindex --allow-shlib-undefined |
ae9a127f | 1467 | @kindex --no-allow-shlib-undefined |
b79e8c78 | 1468 | @item --allow-shlib-undefined |
ae9a127f | 1469 | @itemx --no-allow-shlib-undefined |
903249d7 | 1470 | Allows or disallows undefined symbols in shared libraries. |
560e09e9 NC |
1471 | This switch is similar to @option{--no-undefined} except that it |
1472 | determines the behaviour when the undefined symbols are in a | |
1473 | shared library rather than a regular object file. It does not affect | |
1474 | how undefined symbols in regular object files are handled. | |
1475 | ||
903249d7 NC |
1476 | The default behaviour is to report errors for any undefined symbols |
1477 | referenced in shared libraries if the linker is being used to create | |
1478 | an executable, but to allow them if the linker is being used to create | |
1479 | a shared library. | |
1480 | ||
1481 | The reasons for allowing undefined symbol references in shared | |
1482 | libraries specified at link time are that: | |
1483 | ||
1484 | @itemize @bullet | |
1485 | @item | |
1486 | A shared library specified at link time may not be the same as the one | |
1487 | that is available at load time, so the symbol might actually be | |
1488 | resolvable at load time. | |
1489 | @item | |
1490 | There are some operating systems, eg BeOS and HPPA, where undefined | |
1491 | symbols in shared libraries are normal. | |
1492 | ||
1493 | The BeOS kernel for example patches shared libraries at load time to | |
1494 | select whichever function is most appropriate for the current | |
1495 | architecture. This is used, for example, to dynamically select an | |
1496 | appropriate memset function. | |
1497 | @end itemize | |
b79e8c78 | 1498 | |
31941635 L |
1499 | @kindex --no-undefined-version |
1500 | @item --no-undefined-version | |
1501 | Normally when a symbol has an undefined version, the linker will ignore | |
1502 | it. This option disallows symbols with undefined version and a fatal error | |
1503 | will be issued instead. | |
1504 | ||
3e3b46e5 PB |
1505 | @kindex --default-symver |
1506 | @item --default-symver | |
1507 | Create and use a default symbol version (the soname) for unversioned | |
fc0e6df6 PB |
1508 | exported symbols. |
1509 | ||
1510 | @kindex --default-imported-symver | |
1511 | @item --default-imported-symver | |
1512 | Create and use a default symbol version (the soname) for unversioned | |
1513 | imported symbols. | |
3e3b46e5 | 1514 | |
252b5132 RH |
1515 | @kindex --no-warn-mismatch |
1516 | @item --no-warn-mismatch | |
ff5dcc92 | 1517 | Normally @command{ld} will give an error if you try to link together input |
252b5132 RH |
1518 | files that are mismatched for some reason, perhaps because they have |
1519 | been compiled for different processors or for different endiannesses. | |
ff5dcc92 | 1520 | This option tells @command{ld} that it should silently permit such possible |
252b5132 RH |
1521 | errors. This option should only be used with care, in cases when you |
1522 | have taken some special action that ensures that the linker errors are | |
1523 | inappropriate. | |
1524 | ||
fe7929ce AM |
1525 | @kindex --no-warn-search-mismatch |
1526 | @item --no-warn-search-mismatch | |
1527 | Normally @command{ld} will give a warning if it finds an incompatible | |
1528 | library during a library search. This option silences the warning. | |
1529 | ||
252b5132 RH |
1530 | @kindex --no-whole-archive |
1531 | @item --no-whole-archive | |
ff5dcc92 | 1532 | Turn off the effect of the @option{--whole-archive} option for subsequent |
252b5132 RH |
1533 | archive files. |
1534 | ||
1535 | @cindex output file after errors | |
1536 | @kindex --noinhibit-exec | |
1537 | @item --noinhibit-exec | |
1538 | Retain the executable output file whenever it is still usable. | |
1539 | Normally, the linker will not produce an output file if it encounters | |
1540 | errors during the link process; it exits without writing an output file | |
1541 | when it issues any error whatsoever. | |
1542 | ||
0a9c1c8e CD |
1543 | @kindex -nostdlib |
1544 | @item -nostdlib | |
1545 | Only search library directories explicitly specified on the | |
1546 | command line. Library directories specified in linker scripts | |
1547 | (including linker scripts specified on the command line) are ignored. | |
1548 | ||
252b5132 | 1549 | @ifclear SingleFormat |
2509a395 SL |
1550 | @kindex --oformat=@var{output-format} |
1551 | @item --oformat=@var{output-format} | |
ff5dcc92 SC |
1552 | @command{ld} may be configured to support more than one kind of object |
1553 | file. If your @command{ld} is configured this way, you can use the | |
252b5132 | 1554 | @samp{--oformat} option to specify the binary format for the output |
ff5dcc92 SC |
1555 | object file. Even when @command{ld} is configured to support alternative |
1556 | object formats, you don't usually need to specify this, as @command{ld} | |
252b5132 RH |
1557 | should be configured to produce as a default output format the most |
1558 | usual format on each machine. @var{output-format} is a text string, the | |
1559 | name of a particular format supported by the BFD libraries. (You can | |
1560 | list the available binary formats with @samp{objdump -i}.) The script | |
1561 | command @code{OUTPUT_FORMAT} can also specify the output format, but | |
1562 | this option overrides it. @xref{BFD}. | |
1563 | @end ifclear | |
1564 | ||
36af4a4e JJ |
1565 | @kindex -pie |
1566 | @kindex --pic-executable | |
1567 | @item -pie | |
1568 | @itemx --pic-executable | |
1569 | @cindex position independent executables | |
1570 | Create a position independent executable. This is currently only supported on | |
1571 | ELF platforms. Position independent executables are similar to shared | |
1572 | libraries in that they are relocated by the dynamic linker to the virtual | |
7e7d5768 | 1573 | address the OS chooses for them (which can vary between invocations). Like |
36af4a4e JJ |
1574 | normal dynamically linked executables they can be executed and symbols |
1575 | defined in the executable cannot be overridden by shared libraries. | |
1576 | ||
252b5132 RH |
1577 | @kindex -qmagic |
1578 | @item -qmagic | |
1579 | This option is ignored for Linux compatibility. | |
1580 | ||
1581 | @kindex -Qy | |
1582 | @item -Qy | |
1583 | This option is ignored for SVR4 compatibility. | |
1584 | ||
1585 | @kindex --relax | |
1586 | @cindex synthesizing linker | |
1587 | @cindex relaxing addressing modes | |
28d5f677 | 1588 | @cindex --no-relax |
252b5132 | 1589 | @item --relax |
28d5f677 | 1590 | @itemx --no-relax |
a1ab1d2a | 1591 | An option with machine dependent effects. |
252b5132 RH |
1592 | @ifset GENERIC |
1593 | This option is only supported on a few targets. | |
1594 | @end ifset | |
1595 | @ifset H8300 | |
ff5dcc92 | 1596 | @xref{H8/300,,@command{ld} and the H8/300}. |
252b5132 RH |
1597 | @end ifset |
1598 | @ifset I960 | |
ff5dcc92 | 1599 | @xref{i960,, @command{ld} and the Intel 960 family}. |
252b5132 | 1600 | @end ifset |
e0001a05 NC |
1601 | @ifset XTENSA |
1602 | @xref{Xtensa,, @command{ld} and Xtensa Processors}. | |
1603 | @end ifset | |
93fd0973 SC |
1604 | @ifset M68HC11 |
1605 | @xref{M68HC11/68HC12,,@command{ld} and the 68HC11 and 68HC12}. | |
1606 | @end ifset | |
2a60a7a8 AM |
1607 | @ifset POWERPC |
1608 | @xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}. | |
1609 | @end ifset | |
252b5132 | 1610 | |
28d5f677 NC |
1611 | On some platforms the @samp{--relax} option performs target specific, |
1612 | global optimizations that become possible when the linker resolves | |
1613 | addressing in the program, such as relaxing address modes, | |
1614 | synthesizing new instructions, selecting shorter version of current | |
11e7fd74 | 1615 | instructions, and combining constant values. |
252b5132 RH |
1616 | |
1617 | On some platforms these link time global optimizations may make symbolic | |
1618 | debugging of the resulting executable impossible. | |
1619 | @ifset GENERIC | |
28d5f677 NC |
1620 | This is known to be the case for the Matsushita MN10200 and MN10300 |
1621 | family of processors. | |
252b5132 RH |
1622 | @end ifset |
1623 | ||
1624 | @ifset GENERIC | |
1625 | On platforms where this is not supported, @samp{--relax} is accepted, | |
1626 | but ignored. | |
1627 | @end ifset | |
1628 | ||
28d5f677 NC |
1629 | On platforms where @samp{--relax} is accepted the option |
1630 | @samp{--no-relax} can be used to disable the feature. | |
1631 | ||
252b5132 RH |
1632 | @cindex retaining specified symbols |
1633 | @cindex stripping all but some symbols | |
1634 | @cindex symbols, retaining selectively | |
2509a395 SL |
1635 | @kindex --retain-symbols-file=@var{filename} |
1636 | @item --retain-symbols-file=@var{filename} | |
252b5132 RH |
1637 | Retain @emph{only} the symbols listed in the file @var{filename}, |
1638 | discarding all others. @var{filename} is simply a flat file, with one | |
1639 | symbol name per line. This option is especially useful in environments | |
1640 | @ifset GENERIC | |
1641 | (such as VxWorks) | |
1642 | @end ifset | |
1643 | where a large global symbol table is accumulated gradually, to conserve | |
1644 | run-time memory. | |
1645 | ||
1646 | @samp{--retain-symbols-file} does @emph{not} discard undefined symbols, | |
1647 | or symbols needed for relocations. | |
1648 | ||
1649 | You may only specify @samp{--retain-symbols-file} once in the command | |
1650 | line. It overrides @samp{-s} and @samp{-S}. | |
1651 | ||
1652 | @ifset GENERIC | |
2509a395 | 1653 | @item -rpath=@var{dir} |
252b5132 | 1654 | @cindex runtime library search path |
2509a395 | 1655 | @kindex -rpath=@var{dir} |
252b5132 | 1656 | Add a directory to the runtime library search path. This is used when |
ff5dcc92 | 1657 | linking an ELF executable with shared objects. All @option{-rpath} |
252b5132 | 1658 | arguments are concatenated and passed to the runtime linker, which uses |
ff5dcc92 | 1659 | them to locate shared objects at runtime. The @option{-rpath} option is |
252b5132 RH |
1660 | also used when locating shared objects which are needed by shared |
1661 | objects explicitly included in the link; see the description of the | |
ff5dcc92 | 1662 | @option{-rpath-link} option. If @option{-rpath} is not used when linking an |
252b5132 RH |
1663 | ELF executable, the contents of the environment variable |
1664 | @code{LD_RUN_PATH} will be used if it is defined. | |
1665 | ||
ff5dcc92 | 1666 | The @option{-rpath} option may also be used on SunOS. By default, on |
252b5132 | 1667 | SunOS, the linker will form a runtime search patch out of all the |
ff5dcc92 SC |
1668 | @option{-L} options it is given. If a @option{-rpath} option is used, the |
1669 | runtime search path will be formed exclusively using the @option{-rpath} | |
1670 | options, ignoring the @option{-L} options. This can be useful when using | |
1671 | gcc, which adds many @option{-L} options which may be on NFS mounted | |
b45619c0 | 1672 | file systems. |
252b5132 | 1673 | |
ff5dcc92 | 1674 | For compatibility with other ELF linkers, if the @option{-R} option is |
252b5132 | 1675 | followed by a directory name, rather than a file name, it is treated as |
ff5dcc92 | 1676 | the @option{-rpath} option. |
252b5132 RH |
1677 | @end ifset |
1678 | ||
1679 | @ifset GENERIC | |
1680 | @cindex link-time runtime library search path | |
2509a395 SL |
1681 | @kindex -rpath-link=@var{dir} |
1682 | @item -rpath-link=@var{dir} | |
252b5132 RH |
1683 | When using ELF or SunOS, one shared library may require another. This |
1684 | happens when an @code{ld -shared} link includes a shared library as one | |
1685 | of the input files. | |
1686 | ||
1687 | When the linker encounters such a dependency when doing a non-shared, | |
1688 | non-relocatable link, it will automatically try to locate the required | |
1689 | shared library and include it in the link, if it is not included | |
ff5dcc92 | 1690 | explicitly. In such a case, the @option{-rpath-link} option |
252b5132 | 1691 | specifies the first set of directories to search. The |
ff5dcc92 | 1692 | @option{-rpath-link} option may specify a sequence of directory names |
252b5132 RH |
1693 | either by specifying a list of names separated by colons, or by |
1694 | appearing multiple times. | |
1695 | ||
28c309a2 NC |
1696 | This option should be used with caution as it overrides the search path |
1697 | that may have been hard compiled into a shared library. In such a case it | |
1698 | is possible to use unintentionally a different search path than the | |
1699 | runtime linker would do. | |
1700 | ||
252b5132 | 1701 | The linker uses the following search paths to locate required shared |
ece2d90e | 1702 | libraries: |
252b5132 RH |
1703 | @enumerate |
1704 | @item | |
ff5dcc92 | 1705 | Any directories specified by @option{-rpath-link} options. |
252b5132 | 1706 | @item |
ff5dcc92 SC |
1707 | Any directories specified by @option{-rpath} options. The difference |
1708 | between @option{-rpath} and @option{-rpath-link} is that directories | |
1709 | specified by @option{-rpath} options are included in the executable and | |
1710 | used at runtime, whereas the @option{-rpath-link} option is only effective | |
ece2d90e NC |
1711 | at link time. Searching @option{-rpath} in this way is only supported |
1712 | by native linkers and cross linkers which have been configured with | |
1713 | the @option{--with-sysroot} option. | |
252b5132 | 1714 | @item |
e2a83dd0 NC |
1715 | On an ELF system, for native linkers, if the @option{-rpath} and |
1716 | @option{-rpath-link} options were not used, search the contents of the | |
1717 | environment variable @code{LD_RUN_PATH}. | |
252b5132 | 1718 | @item |
ff5dcc92 SC |
1719 | On SunOS, if the @option{-rpath} option was not used, search any |
1720 | directories specified using @option{-L} options. | |
252b5132 | 1721 | @item |
a1b8d843 | 1722 | For a native linker, search the contents of the environment |
e2a83dd0 | 1723 | variable @code{LD_LIBRARY_PATH}. |
252b5132 | 1724 | @item |
ec4eb78a L |
1725 | For a native ELF linker, the directories in @code{DT_RUNPATH} or |
1726 | @code{DT_RPATH} of a shared library are searched for shared | |
1727 | libraries needed by it. The @code{DT_RPATH} entries are ignored if | |
1728 | @code{DT_RUNPATH} entries exist. | |
1729 | @item | |
252b5132 RH |
1730 | The default directories, normally @file{/lib} and @file{/usr/lib}. |
1731 | @item | |
1732 | For a native linker on an ELF system, if the file @file{/etc/ld.so.conf} | |
1733 | exists, the list of directories found in that file. | |
1734 | @end enumerate | |
1735 | ||
1736 | If the required shared library is not found, the linker will issue a | |
1737 | warning and continue with the link. | |
1738 | @end ifset | |
1739 | ||
1740 | @kindex -shared | |
1741 | @kindex -Bshareable | |
1742 | @item -shared | |
1743 | @itemx -Bshareable | |
1744 | @cindex shared libraries | |
1745 | Create a shared library. This is currently only supported on ELF, XCOFF | |
1746 | and SunOS platforms. On SunOS, the linker will automatically create a | |
ff5dcc92 | 1747 | shared library if the @option{-e} option is not used and there are |
252b5132 RH |
1748 | undefined symbols in the link. |
1749 | ||
252b5132 | 1750 | @kindex --sort-common |
2509a395 SL |
1751 | @item --sort-common |
1752 | @itemx --sort-common=ascending | |
1753 | @itemx --sort-common=descending | |
de7dd2bd NC |
1754 | This option tells @command{ld} to sort the common symbols by alignment in |
1755 | ascending or descending order when it places them in the appropriate output | |
1756 | sections. The symbol alignments considered are sixteen-byte or larger, | |
1757 | eight-byte, four-byte, two-byte, and one-byte. This is to prevent gaps | |
1758 | between symbols due to alignment constraints. If no sorting order is | |
1759 | specified, then descending order is assumed. | |
252b5132 | 1760 | |
2509a395 SL |
1761 | @kindex --sort-section=name |
1762 | @item --sort-section=name | |
bcaa7b3e L |
1763 | This option will apply @code{SORT_BY_NAME} to all wildcard section |
1764 | patterns in the linker script. | |
1765 | ||
2509a395 SL |
1766 | @kindex --sort-section=alignment |
1767 | @item --sort-section=alignment | |
bcaa7b3e L |
1768 | This option will apply @code{SORT_BY_ALIGNMENT} to all wildcard section |
1769 | patterns in the linker script. | |
1770 | ||
252b5132 | 1771 | @kindex --split-by-file |
2509a395 | 1772 | @item --split-by-file[=@var{size}] |
ff5dcc92 | 1773 | Similar to @option{--split-by-reloc} but creates a new output section for |
a854a4a7 AM |
1774 | each input file when @var{size} is reached. @var{size} defaults to a |
1775 | size of 1 if not given. | |
252b5132 RH |
1776 | |
1777 | @kindex --split-by-reloc | |
2509a395 | 1778 | @item --split-by-reloc[=@var{count}] |
a854a4a7 | 1779 | Tries to creates extra sections in the output file so that no single |
252b5132 | 1780 | output section in the file contains more than @var{count} relocations. |
a854a4a7 | 1781 | This is useful when generating huge relocatable files for downloading into |
252b5132 RH |
1782 | certain real time kernels with the COFF object file format; since COFF |
1783 | cannot represent more than 65535 relocations in a single section. Note | |
1784 | that this will fail to work with object file formats which do not | |
1785 | support arbitrary sections. The linker will not split up individual | |
1786 | input sections for redistribution, so if a single input section contains | |
1787 | more than @var{count} relocations one output section will contain that | |
a854a4a7 | 1788 | many relocations. @var{count} defaults to a value of 32768. |
252b5132 RH |
1789 | |
1790 | @kindex --stats | |
1791 | @item --stats | |
1792 | Compute and display statistics about the operation of the linker, such | |
1793 | as execution time and memory usage. | |
1794 | ||
2509a395 | 1795 | @kindex --sysroot=@var{directory} |
e2243057 RS |
1796 | @item --sysroot=@var{directory} |
1797 | Use @var{directory} as the location of the sysroot, overriding the | |
1798 | configure-time default. This option is only supported by linkers | |
1799 | that were configured using @option{--with-sysroot}. | |
1800 | ||
252b5132 RH |
1801 | @kindex --traditional-format |
1802 | @cindex traditional format | |
1803 | @item --traditional-format | |
ff5dcc92 SC |
1804 | For some targets, the output of @command{ld} is different in some ways from |
1805 | the output of some existing linker. This switch requests @command{ld} to | |
252b5132 RH |
1806 | use the traditional format instead. |
1807 | ||
1808 | @cindex dbx | |
ff5dcc92 | 1809 | For example, on SunOS, @command{ld} combines duplicate entries in the |
252b5132 RH |
1810 | symbol string table. This can reduce the size of an output file with |
1811 | full debugging information by over 30 percent. Unfortunately, the SunOS | |
1812 | @code{dbx} program can not read the resulting program (@code{gdb} has no | |
ff5dcc92 | 1813 | trouble). The @samp{--traditional-format} switch tells @command{ld} to not |
252b5132 RH |
1814 | combine duplicate entries. |
1815 | ||
2509a395 SL |
1816 | @kindex --section-start=@var{sectionname}=@var{org} |
1817 | @item --section-start=@var{sectionname}=@var{org} | |
176355da NC |
1818 | Locate a section in the output file at the absolute |
1819 | address given by @var{org}. You may use this option as many | |
1820 | times as necessary to locate multiple sections in the command | |
1821 | line. | |
1822 | @var{org} must be a single hexadecimal integer; | |
1823 | for compatibility with other linkers, you may omit the leading | |
1824 | @samp{0x} usually associated with hexadecimal values. @emph{Note:} there | |
1825 | should be no white space between @var{sectionname}, the equals | |
1826 | sign (``@key{=}''), and @var{org}. | |
1827 | ||
2509a395 SL |
1828 | @kindex -Tbss=@var{org} |
1829 | @kindex -Tdata=@var{org} | |
1830 | @kindex -Ttext=@var{org} | |
252b5132 | 1831 | @cindex segment origins, cmd line |
2509a395 SL |
1832 | @item -Tbss=@var{org} |
1833 | @itemx -Tdata=@var{org} | |
1834 | @itemx -Ttext=@var{org} | |
1835 | Same as @option{--section-start}, with @code{.bss}, @code{.data} or | |
a6e02871 | 1836 | @code{.text} as the @var{sectionname}. |
252b5132 | 1837 | |
2509a395 SL |
1838 | @kindex -Ttext-segment=@var{org} |
1839 | @item -Ttext-segment=@var{org} | |
258795f5 L |
1840 | @cindex text segment origin, cmd line |
1841 | When creating an ELF executable or shared object, it will set the address | |
1842 | of the first byte of the text segment. | |
1843 | ||
9d5777a3 RM |
1844 | @kindex -Trodata-segment=@var{org} |
1845 | @item -Trodata-segment=@var{org} | |
1846 | @cindex rodata segment origin, cmd line | |
1847 | When creating an ELF executable or shared object for a target where | |
1848 | the read-only data is in its own segment separate from the executable | |
1849 | text, it will set the address of the first byte of the read-only data segment. | |
1850 | ||
0d705e9f AM |
1851 | @kindex -Tldata-segment=@var{org} |
1852 | @item -Tldata-segment=@var{org} | |
1853 | @cindex ldata segment origin, cmd line | |
1854 | When creating an ELF executable or shared object for x86-64 medium memory | |
1855 | model, it will set the address of the first byte of the ldata segment. | |
1856 | ||
560e09e9 NC |
1857 | @kindex --unresolved-symbols |
1858 | @item --unresolved-symbols=@var{method} | |
1859 | Determine how to handle unresolved symbols. There are four possible | |
1860 | values for @samp{method}: | |
1861 | ||
1862 | @table @samp | |
1863 | @item ignore-all | |
da8bce14 | 1864 | Do not report any unresolved symbols. |
560e09e9 NC |
1865 | |
1866 | @item report-all | |
da8bce14 | 1867 | Report all unresolved symbols. This is the default. |
560e09e9 NC |
1868 | |
1869 | @item ignore-in-object-files | |
1870 | Report unresolved symbols that are contained in shared libraries, but | |
1871 | ignore them if they come from regular object files. | |
1872 | ||
1873 | @item ignore-in-shared-libs | |
1874 | Report unresolved symbols that come from regular object files, but | |
1875 | ignore them if they come from shared libraries. This can be useful | |
1876 | when creating a dynamic binary and it is known that all the shared | |
1877 | libraries that it should be referencing are included on the linker's | |
1878 | command line. | |
1879 | @end table | |
1880 | ||
1881 | The behaviour for shared libraries on their own can also be controlled | |
1882 | by the @option{--[no-]allow-shlib-undefined} option. | |
1883 | ||
1884 | Normally the linker will generate an error message for each reported | |
1885 | unresolved symbol but the option @option{--warn-unresolved-symbols} | |
1886 | can change this to a warning. | |
1887 | ||
1715a13c L |
1888 | @kindex --verbose[=@var{NUMBER}] |
1889 | @cindex verbose[=@var{NUMBER}] | |
252b5132 | 1890 | @item --dll-verbose |
1715a13c | 1891 | @itemx --verbose[=@var{NUMBER}] |
ff5dcc92 | 1892 | Display the version number for @command{ld} and list the linker emulations |
252b5132 | 1893 | supported. Display which input files can and cannot be opened. Display |
1715a13c L |
1894 | the linker script being used by the linker. If the optional @var{NUMBER} |
1895 | argument > 1, plugin symbol status will also be displayed. | |
252b5132 RH |
1896 | |
1897 | @kindex --version-script=@var{version-scriptfile} | |
1898 | @cindex version script, symbol versions | |
2509a395 | 1899 | @item --version-script=@var{version-scriptfile} |
252b5132 RH |
1900 | Specify the name of a version script to the linker. This is typically |
1901 | used when creating shared libraries to specify additional information | |
36f63dca | 1902 | about the version hierarchy for the library being created. This option |
09e2aba4 DK |
1903 | is only fully supported on ELF platforms which support shared libraries; |
1904 | see @ref{VERSION}. It is partially supported on PE platforms, which can | |
1905 | use version scripts to filter symbol visibility in auto-export mode: any | |
1906 | symbols marked @samp{local} in the version script will not be exported. | |
1907 | @xref{WIN32}. | |
252b5132 | 1908 | |
7ce691ae | 1909 | @kindex --warn-common |
252b5132 RH |
1910 | @cindex warnings, on combining symbols |
1911 | @cindex combining symbols, warnings on | |
1912 | @item --warn-common | |
1913 | Warn when a common symbol is combined with another common symbol or with | |
11e7fd74 | 1914 | a symbol definition. Unix linkers allow this somewhat sloppy practice, |
252b5132 RH |
1915 | but linkers on some other operating systems do not. This option allows |
1916 | you to find potential problems from combining global symbols. | |
11e7fd74 | 1917 | Unfortunately, some C libraries use this practice, so you may get some |
252b5132 RH |
1918 | warnings about symbols in the libraries as well as in your programs. |
1919 | ||
1920 | There are three kinds of global symbols, illustrated here by C examples: | |
1921 | ||
1922 | @table @samp | |
1923 | @item int i = 1; | |
1924 | A definition, which goes in the initialized data section of the output | |
1925 | file. | |
1926 | ||
1927 | @item extern int i; | |
1928 | An undefined reference, which does not allocate space. | |
1929 | There must be either a definition or a common symbol for the | |
1930 | variable somewhere. | |
1931 | ||
1932 | @item int i; | |
1933 | A common symbol. If there are only (one or more) common symbols for a | |
1934 | variable, it goes in the uninitialized data area of the output file. | |
1935 | The linker merges multiple common symbols for the same variable into a | |
1936 | single symbol. If they are of different sizes, it picks the largest | |
1937 | size. The linker turns a common symbol into a declaration, if there is | |
1938 | a definition of the same variable. | |
1939 | @end table | |
1940 | ||
1941 | The @samp{--warn-common} option can produce five kinds of warnings. | |
1942 | Each warning consists of a pair of lines: the first describes the symbol | |
1943 | just encountered, and the second describes the previous symbol | |
1944 | encountered with the same name. One or both of the two symbols will be | |
1945 | a common symbol. | |
1946 | ||
1947 | @enumerate | |
1948 | @item | |
1949 | Turning a common symbol into a reference, because there is already a | |
1950 | definition for the symbol. | |
1951 | @smallexample | |
1952 | @var{file}(@var{section}): warning: common of `@var{symbol}' | |
1953 | overridden by definition | |
1954 | @var{file}(@var{section}): warning: defined here | |
1955 | @end smallexample | |
1956 | ||
1957 | @item | |
1958 | Turning a common symbol into a reference, because a later definition for | |
1959 | the symbol is encountered. This is the same as the previous case, | |
1960 | except that the symbols are encountered in a different order. | |
1961 | @smallexample | |
1962 | @var{file}(@var{section}): warning: definition of `@var{symbol}' | |
1963 | overriding common | |
1964 | @var{file}(@var{section}): warning: common is here | |
1965 | @end smallexample | |
1966 | ||
1967 | @item | |
1968 | Merging a common symbol with a previous same-sized common symbol. | |
1969 | @smallexample | |
1970 | @var{file}(@var{section}): warning: multiple common | |
1971 | of `@var{symbol}' | |
1972 | @var{file}(@var{section}): warning: previous common is here | |
1973 | @end smallexample | |
1974 | ||
1975 | @item | |
1976 | Merging a common symbol with a previous larger common symbol. | |
1977 | @smallexample | |
1978 | @var{file}(@var{section}): warning: common of `@var{symbol}' | |
1979 | overridden by larger common | |
1980 | @var{file}(@var{section}): warning: larger common is here | |
1981 | @end smallexample | |
1982 | ||
1983 | @item | |
1984 | Merging a common symbol with a previous smaller common symbol. This is | |
1985 | the same as the previous case, except that the symbols are | |
1986 | encountered in a different order. | |
1987 | @smallexample | |
1988 | @var{file}(@var{section}): warning: common of `@var{symbol}' | |
1989 | overriding smaller common | |
1990 | @var{file}(@var{section}): warning: smaller common is here | |
1991 | @end smallexample | |
1992 | @end enumerate | |
1993 | ||
1994 | @kindex --warn-constructors | |
1995 | @item --warn-constructors | |
1996 | Warn if any global constructors are used. This is only useful for a few | |
1997 | object file formats. For formats like COFF or ELF, the linker can not | |
1998 | detect the use of global constructors. | |
1999 | ||
2000 | @kindex --warn-multiple-gp | |
2001 | @item --warn-multiple-gp | |
2002 | Warn if multiple global pointer values are required in the output file. | |
2003 | This is only meaningful for certain processors, such as the Alpha. | |
2004 | Specifically, some processors put large-valued constants in a special | |
2005 | section. A special register (the global pointer) points into the middle | |
2006 | of this section, so that constants can be loaded efficiently via a | |
2007 | base-register relative addressing mode. Since the offset in | |
2008 | base-register relative mode is fixed and relatively small (e.g., 16 | |
2009 | bits), this limits the maximum size of the constant pool. Thus, in | |
2010 | large programs, it is often necessary to use multiple global pointer | |
2011 | values in order to be able to address all possible constants. This | |
2012 | option causes a warning to be issued whenever this case occurs. | |
2013 | ||
2014 | @kindex --warn-once | |
2015 | @cindex warnings, on undefined symbols | |
2016 | @cindex undefined symbols, warnings on | |
2017 | @item --warn-once | |
2018 | Only warn once for each undefined symbol, rather than once per module | |
2019 | which refers to it. | |
2020 | ||
2021 | @kindex --warn-section-align | |
2022 | @cindex warnings, on section alignment | |
2023 | @cindex section alignment, warnings on | |
2024 | @item --warn-section-align | |
2025 | Warn if the address of an output section is changed because of | |
2026 | alignment. Typically, the alignment will be set by an input section. | |
2027 | The address will only be changed if it not explicitly specified; that | |
2028 | is, if the @code{SECTIONS} command does not specify a start address for | |
2029 | the section (@pxref{SECTIONS}). | |
2030 | ||
8fdd7217 NC |
2031 | @kindex --warn-shared-textrel |
2032 | @item --warn-shared-textrel | |
ece2d90e | 2033 | Warn if the linker adds a DT_TEXTREL to a shared object. |
8fdd7217 | 2034 | |
a0c402a5 L |
2035 | @kindex --warn-alternate-em |
2036 | @item --warn-alternate-em | |
2037 | Warn if an object has alternate ELF machine code. | |
2038 | ||
560e09e9 NC |
2039 | @kindex --warn-unresolved-symbols |
2040 | @item --warn-unresolved-symbols | |
2041 | If the linker is going to report an unresolved symbol (see the option | |
2042 | @option{--unresolved-symbols}) it will normally generate an error. | |
2043 | This option makes it generate a warning instead. | |
2044 | ||
2045 | @kindex --error-unresolved-symbols | |
2046 | @item --error-unresolved-symbols | |
2047 | This restores the linker's default behaviour of generating errors when | |
2048 | it is reporting unresolved symbols. | |
2049 | ||
252b5132 RH |
2050 | @kindex --whole-archive |
2051 | @cindex including an entire archive | |
2052 | @item --whole-archive | |
2053 | For each archive mentioned on the command line after the | |
ff5dcc92 | 2054 | @option{--whole-archive} option, include every object file in the archive |
252b5132 RH |
2055 | in the link, rather than searching the archive for the required object |
2056 | files. This is normally used to turn an archive file into a shared | |
2057 | library, forcing every object to be included in the resulting shared | |
2058 | library. This option may be used more than once. | |
2059 | ||
7ec229ce | 2060 | Two notes when using this option from gcc: First, gcc doesn't know |
ff5dcc92 SC |
2061 | about this option, so you have to use @option{-Wl,-whole-archive}. |
2062 | Second, don't forget to use @option{-Wl,-no-whole-archive} after your | |
7ec229ce DD |
2063 | list of archives, because gcc will add its own list of archives to |
2064 | your link and you may not want this flag to affect those as well. | |
2065 | ||
2509a395 SL |
2066 | @kindex --wrap=@var{symbol} |
2067 | @item --wrap=@var{symbol} | |
252b5132 RH |
2068 | Use a wrapper function for @var{symbol}. Any undefined reference to |
2069 | @var{symbol} will be resolved to @code{__wrap_@var{symbol}}. Any | |
2070 | undefined reference to @code{__real_@var{symbol}} will be resolved to | |
2071 | @var{symbol}. | |
2072 | ||
2073 | This can be used to provide a wrapper for a system function. The | |
2074 | wrapper function should be called @code{__wrap_@var{symbol}}. If it | |
2075 | wishes to call the system function, it should call | |
2076 | @code{__real_@var{symbol}}. | |
2077 | ||
2078 | Here is a trivial example: | |
2079 | ||
2080 | @smallexample | |
2081 | void * | |
cc2f008e | 2082 | __wrap_malloc (size_t c) |
252b5132 | 2083 | @{ |
cc2f008e | 2084 | printf ("malloc called with %zu\n", c); |
252b5132 RH |
2085 | return __real_malloc (c); |
2086 | @} | |
2087 | @end smallexample | |
2088 | ||
ff5dcc92 | 2089 | If you link other code with this file using @option{--wrap malloc}, then |
252b5132 RH |
2090 | all calls to @code{malloc} will call the function @code{__wrap_malloc} |
2091 | instead. The call to @code{__real_malloc} in @code{__wrap_malloc} will | |
2092 | call the real @code{malloc} function. | |
2093 | ||
2094 | You may wish to provide a @code{__real_malloc} function as well, so that | |
ff5dcc92 | 2095 | links without the @option{--wrap} option will succeed. If you do this, |
252b5132 RH |
2096 | you should not put the definition of @code{__real_malloc} in the same |
2097 | file as @code{__wrap_malloc}; if you do, the assembler may resolve the | |
2098 | call before the linker has a chance to wrap it to @code{malloc}. | |
2099 | ||
6aa29e7b JJ |
2100 | @kindex --eh-frame-hdr |
2101 | @item --eh-frame-hdr | |
2102 | Request creation of @code{.eh_frame_hdr} section and ELF | |
2103 | @code{PT_GNU_EH_FRAME} segment header. | |
2104 | ||
e41b3a13 JJ |
2105 | @kindex --ld-generated-unwind-info |
2106 | @item --no-ld-generated-unwind-info | |
2107 | Request creation of @code{.eh_frame} unwind info for linker | |
2108 | generated code sections like PLT. This option is on by default | |
2109 | if linker generated unwind info is supported. | |
2110 | ||
6c1439be L |
2111 | @kindex --enable-new-dtags |
2112 | @kindex --disable-new-dtags | |
2113 | @item --enable-new-dtags | |
2114 | @itemx --disable-new-dtags | |
2115 | This linker can create the new dynamic tags in ELF. But the older ELF | |
2116 | systems may not understand them. If you specify | |
b1b00fcc MF |
2117 | @option{--enable-new-dtags}, the new dynamic tags will be created as needed |
2118 | and older dynamic tags will be omitted. | |
ff5dcc92 | 2119 | If you specify @option{--disable-new-dtags}, no new dynamic tags will be |
6c1439be L |
2120 | created. By default, the new dynamic tags are not created. Note that |
2121 | those options are only available for ELF systems. | |
2122 | ||
2d643429 | 2123 | @kindex --hash-size=@var{number} |
e185dd51 | 2124 | @item --hash-size=@var{number} |
2d643429 NC |
2125 | Set the default size of the linker's hash tables to a prime number |
2126 | close to @var{number}. Increasing this value can reduce the length of | |
2127 | time it takes the linker to perform its tasks, at the expense of | |
2128 | increasing the linker's memory requirements. Similarly reducing this | |
2129 | value can reduce the memory requirements at the expense of speed. | |
2130 | ||
fdc90cb4 JJ |
2131 | @kindex --hash-style=@var{style} |
2132 | @item --hash-style=@var{style} | |
2133 | Set the type of linker's hash table(s). @var{style} can be either | |
2134 | @code{sysv} for classic ELF @code{.hash} section, @code{gnu} for | |
2135 | new style GNU @code{.gnu.hash} section or @code{both} for both | |
2136 | the classic ELF @code{.hash} and new style GNU @code{.gnu.hash} | |
2137 | hash tables. The default is @code{sysv}. | |
2138 | ||
35835446 JR |
2139 | @kindex --reduce-memory-overheads |
2140 | @item --reduce-memory-overheads | |
2141 | This option reduces memory requirements at ld runtime, at the expense of | |
f2a8f148 | 2142 | linking speed. This was introduced to select the old O(n^2) algorithm |
35835446 | 2143 | for link map file generation, rather than the new O(n) algorithm which uses |
2d643429 NC |
2144 | about 40% more memory for symbol storage. |
2145 | ||
4f9c04f7 | 2146 | Another effect of the switch is to set the default hash table size to |
2d643429 | 2147 | 1021, which again saves memory at the cost of lengthening the linker's |
a85785bc | 2148 | run time. This is not done however if the @option{--hash-size} switch |
2d643429 NC |
2149 | has been used. |
2150 | ||
2151 | The @option{--reduce-memory-overheads} switch may be also be used to | |
2152 | enable other tradeoffs in future versions of the linker. | |
35835446 | 2153 | |
c0065db7 RM |
2154 | @kindex --build-id |
2155 | @kindex --build-id=@var{style} | |
2156 | @item --build-id | |
2157 | @itemx --build-id=@var{style} | |
2158 | Request creation of @code{.note.gnu.build-id} ELF note section. | |
2159 | The contents of the note are unique bits identifying this linked | |
2160 | file. @var{style} can be @code{uuid} to use 128 random bits, | |
24382dca RM |
2161 | @code{sha1} to use a 160-bit @sc{SHA1} hash on the normative |
2162 | parts of the output contents, @code{md5} to use a 128-bit | |
2163 | @sc{MD5} hash on the normative parts of the output contents, or | |
2164 | @code{0x@var{hexstring}} to use a chosen bit string specified as | |
2165 | an even number of hexadecimal digits (@code{-} and @code{:} | |
2166 | characters between digit pairs are ignored). If @var{style} is | |
2167 | omitted, @code{sha1} is used. | |
2168 | ||
2169 | The @code{md5} and @code{sha1} styles produces an identifier | |
2170 | that is always the same in an identical output file, but will be | |
2171 | unique among all nonidentical output files. It is not intended | |
2172 | to be compared as a checksum for the file's contents. A linked | |
2173 | file may be changed later by other tools, but the build ID bit | |
2174 | string identifying the original linked file does not change. | |
c0065db7 RM |
2175 | |
2176 | Passing @code{none} for @var{style} disables the setting from any | |
2177 | @code{--build-id} options earlier on the command line. | |
252b5132 RH |
2178 | @end table |
2179 | ||
0285c67d NC |
2180 | @c man end |
2181 | ||
36f63dca | 2182 | @subsection Options Specific to i386 PE Targets |
252b5132 | 2183 | |
0285c67d NC |
2184 | @c man begin OPTIONS |
2185 | ||
ff5dcc92 | 2186 | The i386 PE linker supports the @option{-shared} option, which causes |
252b5132 RH |
2187 | the output to be a dynamically linked library (DLL) instead of a |
2188 | normal executable. You should name the output @code{*.dll} when you | |
2189 | use this option. In addition, the linker fully supports the standard | |
2190 | @code{*.def} files, which may be specified on the linker command line | |
2191 | like an object file (in fact, it should precede archives it exports | |
2192 | symbols from, to ensure that they get linked in, just like a normal | |
2193 | object file). | |
2194 | ||
2195 | In addition to the options common to all targets, the i386 PE linker | |
2196 | support additional command line options that are specific to the i386 | |
2197 | PE target. Options that take values may be separated from their | |
2198 | values by either a space or an equals sign. | |
2199 | ||
ff5dcc92 | 2200 | @table @gcctabopt |
252b5132 RH |
2201 | |
2202 | @kindex --add-stdcall-alias | |
2203 | @item --add-stdcall-alias | |
2204 | If given, symbols with a stdcall suffix (@@@var{nn}) will be exported | |
2205 | as-is and also with the suffix stripped. | |
bb10df36 | 2206 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2207 | |
2208 | @kindex --base-file | |
2209 | @item --base-file @var{file} | |
2210 | Use @var{file} as the name of a file in which to save the base | |
2211 | addresses of all the relocations needed for generating DLLs with | |
2212 | @file{dlltool}. | |
bb10df36 | 2213 | [This is an i386 PE specific option] |
252b5132 RH |
2214 | |
2215 | @kindex --dll | |
2216 | @item --dll | |
2217 | Create a DLL instead of a regular executable. You may also use | |
ff5dcc92 | 2218 | @option{-shared} or specify a @code{LIBRARY} in a given @code{.def} |
252b5132 | 2219 | file. |
bb10df36 | 2220 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 | 2221 | |
88183869 DK |
2222 | @kindex --enable-long-section-names |
2223 | @kindex --disable-long-section-names | |
2224 | @item --enable-long-section-names | |
2225 | @itemx --disable-long-section-names | |
2226 | The PE variants of the Coff object format add an extension that permits | |
2227 | the use of section names longer than eight characters, the normal limit | |
2228 | for Coff. By default, these names are only allowed in object files, as | |
2229 | fully-linked executable images do not carry the Coff string table required | |
2230 | to support the longer names. As a GNU extension, it is possible to | |
2231 | allow their use in executable images as well, or to (probably pointlessly!) | |
2232 | disallow it in object files, by using these two options. Executable images | |
2233 | generated with these long section names are slightly non-standard, carrying | |
2234 | as they do a string table, and may generate confusing output when examined | |
9d5777a3 RM |
2235 | with non-GNU PE-aware tools, such as file viewers and dumpers. However, |
2236 | GDB relies on the use of PE long section names to find Dwarf-2 debug | |
3efd345c DK |
2237 | information sections in an executable image at runtime, and so if neither |
2238 | option is specified on the command-line, @command{ld} will enable long | |
2239 | section names, overriding the default and technically correct behaviour, | |
2240 | when it finds the presence of debug information while linking an executable | |
2241 | image and not stripping symbols. | |
88183869 DK |
2242 | [This option is valid for all PE targeted ports of the linker] |
2243 | ||
252b5132 RH |
2244 | @kindex --enable-stdcall-fixup |
2245 | @kindex --disable-stdcall-fixup | |
2246 | @item --enable-stdcall-fixup | |
2247 | @itemx --disable-stdcall-fixup | |
2248 | If the link finds a symbol that it cannot resolve, it will attempt to | |
36f63dca | 2249 | do ``fuzzy linking'' by looking for another defined symbol that differs |
252b5132 RH |
2250 | only in the format of the symbol name (cdecl vs stdcall) and will |
2251 | resolve that symbol by linking to the match. For example, the | |
2252 | undefined symbol @code{_foo} might be linked to the function | |
2253 | @code{_foo@@12}, or the undefined symbol @code{_bar@@16} might be linked | |
2254 | to the function @code{_bar}. When the linker does this, it prints a | |
2255 | warning, since it normally should have failed to link, but sometimes | |
2256 | import libraries generated from third-party dlls may need this feature | |
ff5dcc92 | 2257 | to be usable. If you specify @option{--enable-stdcall-fixup}, this |
252b5132 | 2258 | feature is fully enabled and warnings are not printed. If you specify |
ff5dcc92 | 2259 | @option{--disable-stdcall-fixup}, this feature is disabled and such |
252b5132 | 2260 | mismatches are considered to be errors. |
bb10df36 | 2261 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 | 2262 | |
522f09cd KT |
2263 | @kindex --leading-underscore |
2264 | @kindex --no-leading-underscore | |
2265 | @item --leading-underscore | |
2266 | @itemx --no-leading-underscore | |
2267 | For most targets default symbol-prefix is an underscore and is defined | |
2268 | in target's description. By this option it is possible to | |
2269 | disable/enable the default underscore symbol-prefix. | |
2270 | ||
252b5132 RH |
2271 | @cindex DLLs, creating |
2272 | @kindex --export-all-symbols | |
2273 | @item --export-all-symbols | |
2274 | If given, all global symbols in the objects used to build a DLL will | |
2275 | be exported by the DLL. Note that this is the default if there | |
2276 | otherwise wouldn't be any exported symbols. When symbols are | |
2277 | explicitly exported via DEF files or implicitly exported via function | |
2278 | attributes, the default is to not export anything else unless this | |
2279 | option is given. Note that the symbols @code{DllMain@@12}, | |
ece2d90e | 2280 | @code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and |
b044cda1 | 2281 | @code{impure_ptr} will not be automatically |
ece2d90e NC |
2282 | exported. Also, symbols imported from other DLLs will not be |
2283 | re-exported, nor will symbols specifying the DLL's internal layout | |
2284 | such as those beginning with @code{_head_} or ending with | |
2285 | @code{_iname}. In addition, no symbols from @code{libgcc}, | |
b044cda1 CW |
2286 | @code{libstd++}, @code{libmingw32}, or @code{crtX.o} will be exported. |
2287 | Symbols whose names begin with @code{__rtti_} or @code{__builtin_} will | |
2288 | not be exported, to help with C++ DLLs. Finally, there is an | |
ece2d90e | 2289 | extensive list of cygwin-private symbols that are not exported |
b044cda1 | 2290 | (obviously, this applies on when building DLLs for cygwin targets). |
ece2d90e | 2291 | These cygwin-excludes are: @code{_cygwin_dll_entry@@12}, |
b044cda1 | 2292 | @code{_cygwin_crt0_common@@8}, @code{_cygwin_noncygwin_dll_entry@@12}, |
ece2d90e | 2293 | @code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll}, |
b044cda1 | 2294 | @code{cygwin_premain0}, @code{cygwin_premain1}, @code{cygwin_premain2}, |
ece2d90e | 2295 | @code{cygwin_premain3}, and @code{environ}. |
bb10df36 | 2296 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2297 | |
2298 | @kindex --exclude-symbols | |
1d0a3c9c | 2299 | @item --exclude-symbols @var{symbol},@var{symbol},... |
252b5132 RH |
2300 | Specifies a list of symbols which should not be automatically |
2301 | exported. The symbol names may be delimited by commas or colons. | |
bb10df36 | 2302 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 | 2303 | |
2927aaca NC |
2304 | @kindex --exclude-all-symbols |
2305 | @item --exclude-all-symbols | |
2306 | Specifies no symbols should be automatically exported. | |
2307 | [This option is specific to the i386 PE targeted port of the linker] | |
2308 | ||
252b5132 RH |
2309 | @kindex --file-alignment |
2310 | @item --file-alignment | |
2311 | Specify the file alignment. Sections in the file will always begin at | |
2312 | file offsets which are multiples of this number. This defaults to | |
2313 | 512. | |
bb10df36 | 2314 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2315 | |
2316 | @cindex heap size | |
2317 | @kindex --heap | |
2318 | @item --heap @var{reserve} | |
2319 | @itemx --heap @var{reserve},@var{commit} | |
a00b50c5 | 2320 | Specify the number of bytes of memory to reserve (and optionally commit) |
fe6d7d6a | 2321 | to be used as heap for this program. The default is 1MB reserved, 4K |
252b5132 | 2322 | committed. |
bb10df36 | 2323 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2324 | |
2325 | @cindex image base | |
2326 | @kindex --image-base | |
2327 | @item --image-base @var{value} | |
2328 | Use @var{value} as the base address of your program or dll. This is | |
2329 | the lowest memory location that will be used when your program or dll | |
2330 | is loaded. To reduce the need to relocate and improve performance of | |
2331 | your dlls, each should have a unique base address and not overlap any | |
2332 | other dlls. The default is 0x400000 for executables, and 0x10000000 | |
2333 | for dlls. | |
bb10df36 | 2334 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2335 | |
2336 | @kindex --kill-at | |
2337 | @item --kill-at | |
2338 | If given, the stdcall suffixes (@@@var{nn}) will be stripped from | |
2339 | symbols before they are exported. | |
bb10df36 | 2340 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 | 2341 | |
26d2d8a2 BF |
2342 | @kindex --large-address-aware |
2343 | @item --large-address-aware | |
b45619c0 | 2344 | If given, the appropriate bit in the ``Characteristics'' field of the COFF |
26d2d8a2 | 2345 | header is set to indicate that this executable supports virtual addresses |
b45619c0 | 2346 | greater than 2 gigabytes. This should be used in conjunction with the /3GB |
26d2d8a2 BF |
2347 | or /USERVA=@var{value} megabytes switch in the ``[operating systems]'' |
2348 | section of the BOOT.INI. Otherwise, this bit has no effect. | |
2349 | [This option is specific to PE targeted ports of the linker] | |
2350 | ||
f69a2f97 NC |
2351 | @kindex --disable-large-address-aware |
2352 | @item --disable-large-address-aware | |
2353 | Reverts the effect of a previous @samp{--large-address-aware} option. | |
2354 | This is useful if @samp{--large-address-aware} is always set by the compiler | |
2355 | driver (e.g. Cygwin gcc) and the executable does not support virtual | |
2356 | addresses greater than 2 gigabytes. | |
2357 | [This option is specific to PE targeted ports of the linker] | |
2358 | ||
252b5132 RH |
2359 | @kindex --major-image-version |
2360 | @item --major-image-version @var{value} | |
36f63dca | 2361 | Sets the major number of the ``image version''. Defaults to 1. |
bb10df36 | 2362 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2363 | |
2364 | @kindex --major-os-version | |
2365 | @item --major-os-version @var{value} | |
36f63dca | 2366 | Sets the major number of the ``os version''. Defaults to 4. |
bb10df36 | 2367 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2368 | |
2369 | @kindex --major-subsystem-version | |
2370 | @item --major-subsystem-version @var{value} | |
36f63dca | 2371 | Sets the major number of the ``subsystem version''. Defaults to 4. |
bb10df36 | 2372 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2373 | |
2374 | @kindex --minor-image-version | |
2375 | @item --minor-image-version @var{value} | |
36f63dca | 2376 | Sets the minor number of the ``image version''. Defaults to 0. |
bb10df36 | 2377 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2378 | |
2379 | @kindex --minor-os-version | |
2380 | @item --minor-os-version @var{value} | |
36f63dca | 2381 | Sets the minor number of the ``os version''. Defaults to 0. |
bb10df36 | 2382 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2383 | |
2384 | @kindex --minor-subsystem-version | |
2385 | @item --minor-subsystem-version @var{value} | |
36f63dca | 2386 | Sets the minor number of the ``subsystem version''. Defaults to 0. |
bb10df36 | 2387 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2388 | |
2389 | @cindex DEF files, creating | |
2390 | @cindex DLLs, creating | |
2391 | @kindex --output-def | |
2392 | @item --output-def @var{file} | |
2393 | The linker will create the file @var{file} which will contain a DEF | |
2394 | file corresponding to the DLL the linker is generating. This DEF file | |
2395 | (which should be called @code{*.def}) may be used to create an import | |
2396 | library with @code{dlltool} or may be used as a reference to | |
2397 | automatically or implicitly exported symbols. | |
bb10df36 | 2398 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 | 2399 | |
b044cda1 CW |
2400 | @cindex DLLs, creating |
2401 | @kindex --out-implib | |
2402 | @item --out-implib @var{file} | |
2403 | The linker will create the file @var{file} which will contain an | |
2404 | import lib corresponding to the DLL the linker is generating. This | |
2405 | import lib (which should be called @code{*.dll.a} or @code{*.a} | |
560e09e9 | 2406 | may be used to link clients against the generated DLL; this behaviour |
b044cda1 CW |
2407 | makes it possible to skip a separate @code{dlltool} import library |
2408 | creation step. | |
bb10df36 | 2409 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 CW |
2410 | |
2411 | @kindex --enable-auto-image-base | |
2412 | @item --enable-auto-image-base | |
2413 | Automatically choose the image base for DLLs, unless one is specified | |
2414 | using the @code{--image-base} argument. By using a hash generated | |
2415 | from the dllname to create unique image bases for each DLL, in-memory | |
2416 | collisions and relocations which can delay program execution are | |
2417 | avoided. | |
bb10df36 | 2418 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 CW |
2419 | |
2420 | @kindex --disable-auto-image-base | |
2421 | @item --disable-auto-image-base | |
2422 | Do not automatically generate a unique image base. If there is no | |
2423 | user-specified image base (@code{--image-base}) then use the platform | |
2424 | default. | |
bb10df36 | 2425 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 CW |
2426 | |
2427 | @cindex DLLs, linking to | |
2428 | @kindex --dll-search-prefix | |
2429 | @item --dll-search-prefix @var{string} | |
489d0400 | 2430 | When linking dynamically to a dll without an import library, |
ece2d90e | 2431 | search for @code{<string><basename>.dll} in preference to |
560e09e9 | 2432 | @code{lib<basename>.dll}. This behaviour allows easy distinction |
b044cda1 CW |
2433 | between DLLs built for the various "subplatforms": native, cygwin, |
2434 | uwin, pw, etc. For instance, cygwin DLLs typically use | |
ece2d90e | 2435 | @code{--dll-search-prefix=cyg}. |
bb10df36 | 2436 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 CW |
2437 | |
2438 | @kindex --enable-auto-import | |
2439 | @item --enable-auto-import | |
ece2d90e NC |
2440 | Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for |
2441 | DATA imports from DLLs, and create the necessary thunking symbols when | |
4d8907ac DS |
2442 | building the import libraries with those DATA exports. Note: Use of the |
2443 | 'auto-import' extension will cause the text section of the image file | |
2444 | to be made writable. This does not conform to the PE-COFF format | |
2445 | specification published by Microsoft. | |
2446 | ||
e2a83dd0 NC |
2447 | Note - use of the 'auto-import' extension will also cause read only |
2448 | data which would normally be placed into the .rdata section to be | |
2449 | placed into the .data section instead. This is in order to work | |
2450 | around a problem with consts that is described here: | |
2451 | http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html | |
2452 | ||
4d8907ac DS |
2453 | Using 'auto-import' generally will 'just work' -- but sometimes you may |
2454 | see this message: | |
0d888aac | 2455 | |
ece2d90e | 2456 | "variable '<var>' can't be auto-imported. Please read the |
0d888aac CW |
2457 | documentation for ld's @code{--enable-auto-import} for details." |
2458 | ||
ece2d90e NC |
2459 | This message occurs when some (sub)expression accesses an address |
2460 | ultimately given by the sum of two constants (Win32 import tables only | |
c0065db7 RM |
2461 | allow one). Instances where this may occur include accesses to member |
2462 | fields of struct variables imported from a DLL, as well as using a | |
2463 | constant index into an array variable imported from a DLL. Any | |
2f8d8971 NC |
2464 | multiword variable (arrays, structs, long long, etc) may trigger |
2465 | this error condition. However, regardless of the exact data type | |
2466 | of the offending exported variable, ld will always detect it, issue | |
2467 | the warning, and exit. | |
2468 | ||
2469 | There are several ways to address this difficulty, regardless of the | |
2470 | data type of the exported variable: | |
0d888aac | 2471 | |
2fa9fc65 NC |
2472 | One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task |
2473 | of adjusting references in your client code for runtime environment, so | |
560e09e9 | 2474 | this method works only when runtime environment supports this feature. |
2fa9fc65 | 2475 | |
c0065db7 RM |
2476 | A second solution is to force one of the 'constants' to be a variable -- |
2477 | that is, unknown and un-optimizable at compile time. For arrays, | |
2478 | there are two possibilities: a) make the indexee (the array's address) | |
0d888aac CW |
2479 | a variable, or b) make the 'constant' index a variable. Thus: |
2480 | ||
2481 | @example | |
2482 | extern type extern_array[]; | |
c0065db7 | 2483 | extern_array[1] --> |
0d888aac CW |
2484 | @{ volatile type *t=extern_array; t[1] @} |
2485 | @end example | |
2486 | ||
2487 | or | |
2488 | ||
2489 | @example | |
2490 | extern type extern_array[]; | |
c0065db7 | 2491 | extern_array[1] --> |
0d888aac CW |
2492 | @{ volatile int t=1; extern_array[t] @} |
2493 | @end example | |
2494 | ||
c0065db7 | 2495 | For structs (and most other multiword data types) the only option |
2f8d8971 | 2496 | is to make the struct itself (or the long long, or the ...) variable: |
0d888aac CW |
2497 | |
2498 | @example | |
2499 | extern struct s extern_struct; | |
c0065db7 | 2500 | extern_struct.field --> |
0d888aac CW |
2501 | @{ volatile struct s *t=&extern_struct; t->field @} |
2502 | @end example | |
2503 | ||
c406afaf NC |
2504 | or |
2505 | ||
2506 | @example | |
2507 | extern long long extern_ll; | |
2508 | extern_ll --> | |
2509 | @{ volatile long long * local_ll=&extern_ll; *local_ll @} | |
2510 | @end example | |
2511 | ||
2fa9fc65 | 2512 | A third method of dealing with this difficulty is to abandon |
c0065db7 | 2513 | 'auto-import' for the offending symbol and mark it with |
11e7fd74 | 2514 | @code{__declspec(dllimport)}. However, in practice that |
0d888aac | 2515 | requires using compile-time #defines to indicate whether you are |
c0065db7 RM |
2516 | building a DLL, building client code that will link to the DLL, or |
2517 | merely building/linking to a static library. In making the choice | |
2518 | between the various methods of resolving the 'direct address with | |
0d888aac CW |
2519 | constant offset' problem, you should consider typical real-world usage: |
2520 | ||
2521 | Original: | |
2522 | @example | |
2523 | --foo.h | |
2524 | extern int arr[]; | |
2525 | --foo.c | |
2526 | #include "foo.h" | |
2527 | void main(int argc, char **argv)@{ | |
2528 | printf("%d\n",arr[1]); | |
2529 | @} | |
2530 | @end example | |
2531 | ||
2532 | Solution 1: | |
2533 | @example | |
2534 | --foo.h | |
2535 | extern int arr[]; | |
2536 | --foo.c | |
2537 | #include "foo.h" | |
2538 | void main(int argc, char **argv)@{ | |
2539 | /* This workaround is for win32 and cygwin; do not "optimize" */ | |
2540 | volatile int *parr = arr; | |
2541 | printf("%d\n",parr[1]); | |
2542 | @} | |
2543 | @end example | |
2544 | ||
2545 | Solution 2: | |
2546 | @example | |
2547 | --foo.h | |
2548 | /* Note: auto-export is assumed (no __declspec(dllexport)) */ | |
2549 | #if (defined(_WIN32) || defined(__CYGWIN__)) && \ | |
2550 | !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC)) | |
2551 | #define FOO_IMPORT __declspec(dllimport) | |
2552 | #else | |
2553 | #define FOO_IMPORT | |
2554 | #endif | |
2555 | extern FOO_IMPORT int arr[]; | |
2556 | --foo.c | |
2557 | #include "foo.h" | |
2558 | void main(int argc, char **argv)@{ | |
2559 | printf("%d\n",arr[1]); | |
2560 | @} | |
2561 | @end example | |
2562 | ||
c0065db7 | 2563 | A fourth way to avoid this problem is to re-code your |
0d888aac CW |
2564 | library to use a functional interface rather than a data interface |
2565 | for the offending variables (e.g. set_foo() and get_foo() accessor | |
2566 | functions). | |
bb10df36 | 2567 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 CW |
2568 | |
2569 | @kindex --disable-auto-import | |
2570 | @item --disable-auto-import | |
c0065db7 | 2571 | Do not attempt to do sophisticated linking of @code{_symbol} to |
b044cda1 | 2572 | @code{__imp__symbol} for DATA imports from DLLs. |
bb10df36 | 2573 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 | 2574 | |
2fa9fc65 NC |
2575 | @kindex --enable-runtime-pseudo-reloc |
2576 | @item --enable-runtime-pseudo-reloc | |
2577 | If your code contains expressions described in --enable-auto-import section, | |
2578 | that is, DATA imports from DLL with non-zero offset, this switch will create | |
2579 | a vector of 'runtime pseudo relocations' which can be used by runtime | |
c0065db7 | 2580 | environment to adjust references to such data in your client code. |
bb10df36 | 2581 | [This option is specific to the i386 PE targeted port of the linker] |
2fa9fc65 NC |
2582 | |
2583 | @kindex --disable-runtime-pseudo-reloc | |
2584 | @item --disable-runtime-pseudo-reloc | |
2585 | Do not create pseudo relocations for non-zero offset DATA imports from | |
676ee43b | 2586 | DLLs. |
bb10df36 | 2587 | [This option is specific to the i386 PE targeted port of the linker] |
2fa9fc65 | 2588 | |
b044cda1 CW |
2589 | @kindex --enable-extra-pe-debug |
2590 | @item --enable-extra-pe-debug | |
2591 | Show additional debug info related to auto-import symbol thunking. | |
bb10df36 | 2592 | [This option is specific to the i386 PE targeted port of the linker] |
b044cda1 | 2593 | |
252b5132 RH |
2594 | @kindex --section-alignment |
2595 | @item --section-alignment | |
2596 | Sets the section alignment. Sections in memory will always begin at | |
2597 | addresses which are a multiple of this number. Defaults to 0x1000. | |
bb10df36 | 2598 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2599 | |
2600 | @cindex stack size | |
2601 | @kindex --stack | |
2602 | @item --stack @var{reserve} | |
2603 | @itemx --stack @var{reserve},@var{commit} | |
a00b50c5 | 2604 | Specify the number of bytes of memory to reserve (and optionally commit) |
fe6d7d6a | 2605 | to be used as stack for this program. The default is 2MB reserved, 4K |
252b5132 | 2606 | committed. |
bb10df36 | 2607 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 RH |
2608 | |
2609 | @kindex --subsystem | |
2610 | @item --subsystem @var{which} | |
2611 | @itemx --subsystem @var{which}:@var{major} | |
2612 | @itemx --subsystem @var{which}:@var{major}.@var{minor} | |
2613 | Specifies the subsystem under which your program will execute. The | |
2614 | legal values for @var{which} are @code{native}, @code{windows}, | |
33f362e1 NC |
2615 | @code{console}, @code{posix}, and @code{xbox}. You may optionally set |
2616 | the subsystem version also. Numeric values are also accepted for | |
2617 | @var{which}. | |
bb10df36 | 2618 | [This option is specific to the i386 PE targeted port of the linker] |
252b5132 | 2619 | |
2f563b51 DK |
2620 | The following options set flags in the @code{DllCharacteristics} field |
2621 | of the PE file header: | |
2622 | [These options are specific to PE targeted ports of the linker] | |
2623 | ||
2624 | @kindex --dynamicbase | |
2625 | @item --dynamicbase | |
2626 | The image base address may be relocated using address space layout | |
2627 | randomization (ASLR). This feature was introduced with MS Windows | |
2628 | Vista for i386 PE targets. | |
2629 | ||
2630 | @kindex --forceinteg | |
2631 | @item --forceinteg | |
2632 | Code integrity checks are enforced. | |
2633 | ||
2634 | @kindex --nxcompat | |
2635 | @item --nxcompat | |
2636 | The image is compatible with the Data Execution Prevention. | |
2637 | This feature was introduced with MS Windows XP SP2 for i386 PE targets. | |
2638 | ||
2639 | @kindex --no-isolation | |
2640 | @item --no-isolation | |
2641 | Although the image understands isolation, do not isolate the image. | |
2642 | ||
2643 | @kindex --no-seh | |
2644 | @item --no-seh | |
2645 | The image does not use SEH. No SE handler may be called from | |
2646 | this image. | |
2647 | ||
2648 | @kindex --no-bind | |
2649 | @item --no-bind | |
2650 | Do not bind this image. | |
2651 | ||
2652 | @kindex --wdmdriver | |
2653 | @item --wdmdriver | |
2654 | The driver uses the MS Windows Driver Model. | |
9d5777a3 | 2655 | |
2f563b51 DK |
2656 | @kindex --tsaware |
2657 | @item --tsaware | |
2658 | The image is Terminal Server aware. | |
2659 | ||
0cb112f7 CF |
2660 | @kindex --insert-timestamp |
2661 | @item --insert-timestamp | |
2662 | Insert a real timestamp into the image, rather than the default value | |
2663 | of zero. This will result in a slightly different results with each | |
2664 | invocation, which could be helpful for distributing unique images. | |
252b5132 RH |
2665 | @end table |
2666 | ||
0285c67d NC |
2667 | @c man end |
2668 | ||
ac145307 BS |
2669 | @ifset C6X |
2670 | @subsection Options specific to C6X uClinux targets | |
2671 | ||
2672 | @c man begin OPTIONS | |
2673 | ||
2674 | The C6X uClinux target uses a binary format called DSBT to support shared | |
2675 | libraries. Each shared library in the system needs to have a unique index; | |
2676 | all executables use an index of 0. | |
2677 | ||
2678 | @table @gcctabopt | |
2679 | ||
2680 | @kindex --dsbt-size | |
2681 | @item --dsbt-size @var{size} | |
2682 | This option sets the number of entires in the DSBT of the current executable | |
2683 | or shared library to @var{size}. The default is to create a table with 64 | |
2684 | entries. | |
2685 | ||
2686 | @kindex --dsbt-index | |
2687 | @item --dsbt-index @var{index} | |
2688 | This option sets the DSBT index of the current executable or shared library | |
2689 | to @var{index}. The default is 0, which is appropriate for generating | |
2690 | executables. If a shared library is generated with a DSBT index of 0, the | |
2691 | @code{R_C6000_DSBT_INDEX} relocs are copied into the output file. | |
2692 | ||
fbd9ad90 PB |
2693 | @kindex --no-merge-exidx-entries |
2694 | The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent | |
2695 | exidx entries in frame unwind info. | |
2696 | ||
ac145307 BS |
2697 | @end table |
2698 | ||
2699 | @c man end | |
2700 | @end ifset | |
2701 | ||
93fd0973 SC |
2702 | @ifset M68HC11 |
2703 | @subsection Options specific to Motorola 68HC11 and 68HC12 targets | |
2704 | ||
2705 | @c man begin OPTIONS | |
2706 | ||
2707 | The 68HC11 and 68HC12 linkers support specific options to control the | |
2708 | memory bank switching mapping and trampoline code generation. | |
2709 | ||
2710 | @table @gcctabopt | |
2711 | ||
2712 | @kindex --no-trampoline | |
2713 | @item --no-trampoline | |
2714 | This option disables the generation of trampoline. By default a trampoline | |
2715 | is generated for each far function which is called using a @code{jsr} | |
2716 | instruction (this happens when a pointer to a far function is taken). | |
2717 | ||
2718 | @kindex --bank-window | |
2719 | @item --bank-window @var{name} | |
2720 | This option indicates to the linker the name of the memory region in | |
2721 | the @samp{MEMORY} specification that describes the memory bank window. | |
2722 | The definition of such region is then used by the linker to compute | |
2723 | paging and addresses within the memory window. | |
2724 | ||
2725 | @end table | |
2726 | ||
2727 | @c man end | |
2728 | @end ifset | |
2729 | ||
7fb9f789 NC |
2730 | @ifset M68K |
2731 | @subsection Options specific to Motorola 68K target | |
2732 | ||
2733 | @c man begin OPTIONS | |
2734 | ||
2735 | The following options are supported to control handling of GOT generation | |
2736 | when linking for 68K targets. | |
2737 | ||
2738 | @table @gcctabopt | |
2739 | ||
2740 | @kindex --got | |
2741 | @item --got=@var{type} | |
2742 | This option tells the linker which GOT generation scheme to use. | |
2743 | @var{type} should be one of @samp{single}, @samp{negative}, | |
2744 | @samp{multigot} or @samp{target}. For more information refer to the | |
2745 | Info entry for @file{ld}. | |
2746 | ||
2747 | @end table | |
2748 | ||
2749 | @c man end | |
2750 | @end ifset | |
2751 | ||
833794fc MR |
2752 | @ifset MIPS |
2753 | @subsection Options specific to MIPS targets | |
2754 | ||
2755 | @c man begin OPTIONS | |
2756 | ||
2757 | The following options are supported to control microMIPS instruction | |
2758 | generation when linking for MIPS targets. | |
2759 | ||
2760 | @table @gcctabopt | |
2761 | ||
2762 | @kindex --insn32 | |
2763 | @item --insn32 | |
2764 | @kindex --no-insn32 | |
2765 | @itemx --no-insn32 | |
2766 | These options control the choice of microMIPS instructions used in code | |
2767 | generated by the linker, such as that in the PLT or lazy binding stubs, | |
2768 | or in relaxation. If @samp{--insn32} is used, then the linker only uses | |
2769 | 32-bit instruction encodings. By default or if @samp{--no-insn32} is | |
2770 | used, all instruction encodings are used, including 16-bit ones where | |
2771 | possible. | |
2772 | ||
2773 | @end table | |
2774 | ||
2775 | @c man end | |
2776 | @end ifset | |
2777 | ||
252b5132 RH |
2778 | @ifset UsesEnvVars |
2779 | @node Environment | |
2780 | @section Environment Variables | |
2781 | ||
0285c67d NC |
2782 | @c man begin ENVIRONMENT |
2783 | ||
560e09e9 | 2784 | You can change the behaviour of @command{ld} with the environment variables |
36f63dca NC |
2785 | @ifclear SingleFormat |
2786 | @code{GNUTARGET}, | |
2787 | @end ifclear | |
2788 | @code{LDEMULATION} and @code{COLLECT_NO_DEMANGLE}. | |
252b5132 | 2789 | |
36f63dca | 2790 | @ifclear SingleFormat |
252b5132 RH |
2791 | @kindex GNUTARGET |
2792 | @cindex default input format | |
2793 | @code{GNUTARGET} determines the input-file object format if you don't | |
2794 | use @samp{-b} (or its synonym @samp{--format}). Its value should be one | |
2795 | of the BFD names for an input format (@pxref{BFD}). If there is no | |
ff5dcc92 | 2796 | @code{GNUTARGET} in the environment, @command{ld} uses the natural format |
252b5132 RH |
2797 | of the target. If @code{GNUTARGET} is set to @code{default} then BFD |
2798 | attempts to discover the input format by examining binary input files; | |
2799 | this method often succeeds, but there are potential ambiguities, since | |
2800 | there is no method of ensuring that the magic number used to specify | |
2801 | object-file formats is unique. However, the configuration procedure for | |
2802 | BFD on each system places the conventional format for that system first | |
2803 | in the search-list, so ambiguities are resolved in favor of convention. | |
36f63dca | 2804 | @end ifclear |
252b5132 RH |
2805 | |
2806 | @kindex LDEMULATION | |
2807 | @cindex default emulation | |
2808 | @cindex emulation, default | |
2809 | @code{LDEMULATION} determines the default emulation if you don't use the | |
2810 | @samp{-m} option. The emulation can affect various aspects of linker | |
2811 | behaviour, particularly the default linker script. You can list the | |
2812 | available emulations with the @samp{--verbose} or @samp{-V} options. If | |
2813 | the @samp{-m} option is not used, and the @code{LDEMULATION} environment | |
2814 | variable is not defined, the default emulation depends upon how the | |
2815 | linker was configured. | |
252b5132 RH |
2816 | |
2817 | @kindex COLLECT_NO_DEMANGLE | |
2818 | @cindex demangling, default | |
2819 | Normally, the linker will default to demangling symbols. However, if | |
2820 | @code{COLLECT_NO_DEMANGLE} is set in the environment, then it will | |
2821 | default to not demangling symbols. This environment variable is used in | |
2822 | a similar fashion by the @code{gcc} linker wrapper program. The default | |
2823 | may be overridden by the @samp{--demangle} and @samp{--no-demangle} | |
2824 | options. | |
2825 | ||
0285c67d NC |
2826 | @c man end |
2827 | @end ifset | |
2828 | ||
252b5132 RH |
2829 | @node Scripts |
2830 | @chapter Linker Scripts | |
2831 | ||
2832 | @cindex scripts | |
2833 | @cindex linker scripts | |
2834 | @cindex command files | |
2835 | Every link is controlled by a @dfn{linker script}. This script is | |
2836 | written in the linker command language. | |
2837 | ||
2838 | The main purpose of the linker script is to describe how the sections in | |
2839 | the input files should be mapped into the output file, and to control | |
2840 | the memory layout of the output file. Most linker scripts do nothing | |
2841 | more than this. However, when necessary, the linker script can also | |
2842 | direct the linker to perform many other operations, using the commands | |
2843 | described below. | |
2844 | ||
2845 | The linker always uses a linker script. If you do not supply one | |
2846 | yourself, the linker will use a default script that is compiled into the | |
2847 | linker executable. You can use the @samp{--verbose} command line option | |
2848 | to display the default linker script. Certain command line options, | |
2849 | such as @samp{-r} or @samp{-N}, will affect the default linker script. | |
2850 | ||
2851 | You may supply your own linker script by using the @samp{-T} command | |
2852 | line option. When you do this, your linker script will replace the | |
2853 | default linker script. | |
2854 | ||
2855 | You may also use linker scripts implicitly by naming them as input files | |
2856 | to the linker, as though they were files to be linked. @xref{Implicit | |
2857 | Linker Scripts}. | |
2858 | ||
2859 | @menu | |
2860 | * Basic Script Concepts:: Basic Linker Script Concepts | |
2861 | * Script Format:: Linker Script Format | |
2862 | * Simple Example:: Simple Linker Script Example | |
2863 | * Simple Commands:: Simple Linker Script Commands | |
2864 | * Assignments:: Assigning Values to Symbols | |
2865 | * SECTIONS:: SECTIONS Command | |
2866 | * MEMORY:: MEMORY Command | |
2867 | * PHDRS:: PHDRS Command | |
2868 | * VERSION:: VERSION Command | |
2869 | * Expressions:: Expressions in Linker Scripts | |
2870 | * Implicit Linker Scripts:: Implicit Linker Scripts | |
2871 | @end menu | |
2872 | ||
2873 | @node Basic Script Concepts | |
2874 | @section Basic Linker Script Concepts | |
2875 | @cindex linker script concepts | |
2876 | We need to define some basic concepts and vocabulary in order to | |
2877 | describe the linker script language. | |
2878 | ||
2879 | The linker combines input files into a single output file. The output | |
2880 | file and each input file are in a special data format known as an | |
2881 | @dfn{object file format}. Each file is called an @dfn{object file}. | |
2882 | The output file is often called an @dfn{executable}, but for our | |
2883 | purposes we will also call it an object file. Each object file has, | |
2884 | among other things, a list of @dfn{sections}. We sometimes refer to a | |
2885 | section in an input file as an @dfn{input section}; similarly, a section | |
2886 | in the output file is an @dfn{output section}. | |
2887 | ||
2888 | Each section in an object file has a name and a size. Most sections | |
2889 | also have an associated block of data, known as the @dfn{section | |
56dd11f0 | 2890 | contents}. A section may be marked as @dfn{loadable}, which means that |
252b5132 RH |
2891 | the contents should be loaded into memory when the output file is run. |
2892 | A section with no contents may be @dfn{allocatable}, which means that an | |
2893 | area in memory should be set aside, but nothing in particular should be | |
2894 | loaded there (in some cases this memory must be zeroed out). A section | |
2895 | which is neither loadable nor allocatable typically contains some sort | |
2896 | of debugging information. | |
2897 | ||
2898 | Every loadable or allocatable output section has two addresses. The | |
2899 | first is the @dfn{VMA}, or virtual memory address. This is the address | |
2900 | the section will have when the output file is run. The second is the | |
2901 | @dfn{LMA}, or load memory address. This is the address at which the | |
2902 | section will be loaded. In most cases the two addresses will be the | |
2903 | same. An example of when they might be different is when a data section | |
2904 | is loaded into ROM, and then copied into RAM when the program starts up | |
2905 | (this technique is often used to initialize global variables in a ROM | |
2906 | based system). In this case the ROM address would be the LMA, and the | |
2907 | RAM address would be the VMA. | |
2908 | ||
2909 | You can see the sections in an object file by using the @code{objdump} | |
2910 | program with the @samp{-h} option. | |
2911 | ||
2912 | Every object file also has a list of @dfn{symbols}, known as the | |
2913 | @dfn{symbol table}. A symbol may be defined or undefined. Each symbol | |
2914 | has a name, and each defined symbol has an address, among other | |
2915 | information. If you compile a C or C++ program into an object file, you | |
2916 | will get a defined symbol for every defined function and global or | |
2917 | static variable. Every undefined function or global variable which is | |
2918 | referenced in the input file will become an undefined symbol. | |
2919 | ||
2920 | You can see the symbols in an object file by using the @code{nm} | |
2921 | program, or by using the @code{objdump} program with the @samp{-t} | |
2922 | option. | |
2923 | ||
2924 | @node Script Format | |
2925 | @section Linker Script Format | |
2926 | @cindex linker script format | |
2927 | Linker scripts are text files. | |
2928 | ||
2929 | You write a linker script as a series of commands. Each command is | |
2930 | either a keyword, possibly followed by arguments, or an assignment to a | |
2931 | symbol. You may separate commands using semicolons. Whitespace is | |
2932 | generally ignored. | |
2933 | ||
2934 | Strings such as file or format names can normally be entered directly. | |
2935 | If the file name contains a character such as a comma which would | |
2936 | otherwise serve to separate file names, you may put the file name in | |
2937 | double quotes. There is no way to use a double quote character in a | |
2938 | file name. | |
2939 | ||
2940 | You may include comments in linker scripts just as in C, delimited by | |
2941 | @samp{/*} and @samp{*/}. As in C, comments are syntactically equivalent | |
2942 | to whitespace. | |
2943 | ||
2944 | @node Simple Example | |
2945 | @section Simple Linker Script Example | |
2946 | @cindex linker script example | |
2947 | @cindex example of linker script | |
2948 | Many linker scripts are fairly simple. | |
2949 | ||
2950 | The simplest possible linker script has just one command: | |
2951 | @samp{SECTIONS}. You use the @samp{SECTIONS} command to describe the | |
2952 | memory layout of the output file. | |
2953 | ||
2954 | The @samp{SECTIONS} command is a powerful command. Here we will | |
2955 | describe a simple use of it. Let's assume your program consists only of | |
2956 | code, initialized data, and uninitialized data. These will be in the | |
2957 | @samp{.text}, @samp{.data}, and @samp{.bss} sections, respectively. | |
2958 | Let's assume further that these are the only sections which appear in | |
2959 | your input files. | |
2960 | ||
2961 | For this example, let's say that the code should be loaded at address | |
2962 | 0x10000, and that the data should start at address 0x8000000. Here is a | |
2963 | linker script which will do that: | |
2964 | @smallexample | |
2965 | SECTIONS | |
2966 | @{ | |
2967 | . = 0x10000; | |
2968 | .text : @{ *(.text) @} | |
2969 | . = 0x8000000; | |
2970 | .data : @{ *(.data) @} | |
2971 | .bss : @{ *(.bss) @} | |
2972 | @} | |
2973 | @end smallexample | |
2974 | ||
2975 | You write the @samp{SECTIONS} command as the keyword @samp{SECTIONS}, | |
2976 | followed by a series of symbol assignments and output section | |
2977 | descriptions enclosed in curly braces. | |
2978 | ||
252b5132 RH |
2979 | The first line inside the @samp{SECTIONS} command of the above example |
2980 | sets the value of the special symbol @samp{.}, which is the location | |
2981 | counter. If you do not specify the address of an output section in some | |
2982 | other way (other ways are described later), the address is set from the | |
2983 | current value of the location counter. The location counter is then | |
2984 | incremented by the size of the output section. At the start of the | |
2985 | @samp{SECTIONS} command, the location counter has the value @samp{0}. | |
2986 | ||
2987 | The second line defines an output section, @samp{.text}. The colon is | |
2988 | required syntax which may be ignored for now. Within the curly braces | |
2989 | after the output section name, you list the names of the input sections | |
2990 | which should be placed into this output section. The @samp{*} is a | |
2991 | wildcard which matches any file name. The expression @samp{*(.text)} | |
2992 | means all @samp{.text} input sections in all input files. | |
2993 | ||
2994 | Since the location counter is @samp{0x10000} when the output section | |
2995 | @samp{.text} is defined, the linker will set the address of the | |
2996 | @samp{.text} section in the output file to be @samp{0x10000}. | |
2997 | ||
2998 | The remaining lines define the @samp{.data} and @samp{.bss} sections in | |
2999 | the output file. The linker will place the @samp{.data} output section | |
3000 | at address @samp{0x8000000}. After the linker places the @samp{.data} | |
3001 | output section, the value of the location counter will be | |
3002 | @samp{0x8000000} plus the size of the @samp{.data} output section. The | |
3003 | effect is that the linker will place the @samp{.bss} output section | |
58434bc1 | 3004 | immediately after the @samp{.data} output section in memory. |
252b5132 RH |
3005 | |
3006 | The linker will ensure that each output section has the required | |
3007 | alignment, by increasing the location counter if necessary. In this | |
3008 | example, the specified addresses for the @samp{.text} and @samp{.data} | |
3009 | sections will probably satisfy any alignment constraints, but the linker | |
3010 | may have to create a small gap between the @samp{.data} and @samp{.bss} | |
3011 | sections. | |
3012 | ||
3013 | That's it! That's a simple and complete linker script. | |
3014 | ||
3015 | @node Simple Commands | |
3016 | @section Simple Linker Script Commands | |
3017 | @cindex linker script simple commands | |
3018 | In this section we describe the simple linker script commands. | |
3019 | ||
3020 | @menu | |
3021 | * Entry Point:: Setting the entry point | |
3022 | * File Commands:: Commands dealing with files | |
3023 | @ifclear SingleFormat | |
3024 | * Format Commands:: Commands dealing with object file formats | |
3025 | @end ifclear | |
3026 | ||
4a93e180 | 3027 | * REGION_ALIAS:: Assign alias names to memory regions |
252b5132 RH |
3028 | * Miscellaneous Commands:: Other linker script commands |
3029 | @end menu | |
3030 | ||
3031 | @node Entry Point | |
36f63dca | 3032 | @subsection Setting the Entry Point |
252b5132 RH |
3033 | @kindex ENTRY(@var{symbol}) |
3034 | @cindex start of execution | |
3035 | @cindex first instruction | |
3036 | @cindex entry point | |
3037 | The first instruction to execute in a program is called the @dfn{entry | |
3038 | point}. You can use the @code{ENTRY} linker script command to set the | |
3039 | entry point. The argument is a symbol name: | |
3040 | @smallexample | |
3041 | ENTRY(@var{symbol}) | |
3042 | @end smallexample | |
3043 | ||
3044 | There are several ways to set the entry point. The linker will set the | |
3045 | entry point by trying each of the following methods in order, and | |
3046 | stopping when one of them succeeds: | |
3047 | @itemize @bullet | |
a1ab1d2a | 3048 | @item |
252b5132 | 3049 | the @samp{-e} @var{entry} command-line option; |
a1ab1d2a | 3050 | @item |
252b5132 | 3051 | the @code{ENTRY(@var{symbol})} command in a linker script; |
a1ab1d2a | 3052 | @item |
3ab904c4 NC |
3053 | the value of a target specific symbol, if it is defined; For many |
3054 | targets this is @code{start}, but PE and BeOS based systems for example | |
3055 | check a list of possible entry symbols, matching the first one found. | |
a1ab1d2a | 3056 | @item |
252b5132 | 3057 | the address of the first byte of the @samp{.text} section, if present; |
a1ab1d2a | 3058 | @item |
252b5132 RH |
3059 | The address @code{0}. |
3060 | @end itemize | |
3061 | ||
3062 | @node File Commands | |
36f63dca | 3063 | @subsection Commands Dealing with Files |
252b5132 RH |
3064 | @cindex linker script file commands |
3065 | Several linker script commands deal with files. | |
3066 | ||
3067 | @table @code | |
3068 | @item INCLUDE @var{filename} | |
3069 | @kindex INCLUDE @var{filename} | |
3070 | @cindex including a linker script | |
3071 | Include the linker script @var{filename} at this point. The file will | |
3072 | be searched for in the current directory, and in any directory specified | |
ff5dcc92 | 3073 | with the @option{-L} option. You can nest calls to @code{INCLUDE} up to |
252b5132 RH |
3074 | 10 levels deep. |
3075 | ||
4006703d NS |
3076 | You can place @code{INCLUDE} directives at the top level, in @code{MEMORY} or |
3077 | @code{SECTIONS} commands, or in output section descriptions. | |
3078 | ||
252b5132 RH |
3079 | @item INPUT(@var{file}, @var{file}, @dots{}) |
3080 | @itemx INPUT(@var{file} @var{file} @dots{}) | |
3081 | @kindex INPUT(@var{files}) | |
3082 | @cindex input files in linker scripts | |
3083 | @cindex input object files in linker scripts | |
3084 | @cindex linker script input object files | |
3085 | The @code{INPUT} command directs the linker to include the named files | |
3086 | in the link, as though they were named on the command line. | |
3087 | ||
3088 | For example, if you always want to include @file{subr.o} any time you do | |
3089 | a link, but you can't be bothered to put it on every link command line, | |
3090 | then you can put @samp{INPUT (subr.o)} in your linker script. | |
3091 | ||
3092 | In fact, if you like, you can list all of your input files in the linker | |
3093 | script, and then invoke the linker with nothing but a @samp{-T} option. | |
3094 | ||
e3f2db7f AO |
3095 | In case a @dfn{sysroot prefix} is configured, and the filename starts |
3096 | with the @samp{/} character, and the script being processed was | |
3097 | located inside the @dfn{sysroot prefix}, the filename will be looked | |
3098 | for in the @dfn{sysroot prefix}. Otherwise, the linker will try to | |
3099 | open the file in the current directory. If it is not found, the | |
3100 | linker will search through the archive library search path. See the | |
3101 | description of @samp{-L} in @ref{Options,,Command Line Options}. | |
252b5132 | 3102 | |
ff5dcc92 | 3103 | If you use @samp{INPUT (-l@var{file})}, @command{ld} will transform the |
252b5132 RH |
3104 | name to @code{lib@var{file}.a}, as with the command line argument |
3105 | @samp{-l}. | |
3106 | ||
3107 | When you use the @code{INPUT} command in an implicit linker script, the | |
3108 | files will be included in the link at the point at which the linker | |
3109 | script file is included. This can affect archive searching. | |
3110 | ||
3111 | @item GROUP(@var{file}, @var{file}, @dots{}) | |
3112 | @itemx GROUP(@var{file} @var{file} @dots{}) | |
3113 | @kindex GROUP(@var{files}) | |
3114 | @cindex grouping input files | |
3115 | The @code{GROUP} command is like @code{INPUT}, except that the named | |
3116 | files should all be archives, and they are searched repeatedly until no | |
3117 | new undefined references are created. See the description of @samp{-(} | |
3118 | in @ref{Options,,Command Line Options}. | |
3119 | ||
b717d30e JJ |
3120 | @item AS_NEEDED(@var{file}, @var{file}, @dots{}) |
3121 | @itemx AS_NEEDED(@var{file} @var{file} @dots{}) | |
3122 | @kindex AS_NEEDED(@var{files}) | |
3123 | This construct can appear only inside of the @code{INPUT} or @code{GROUP} | |
3124 | commands, among other filenames. The files listed will be handled | |
3125 | as if they appear directly in the @code{INPUT} or @code{GROUP} commands, | |
3126 | with the exception of ELF shared libraries, that will be added only | |
3127 | when they are actually needed. This construct essentially enables | |
3128 | @option{--as-needed} option for all the files listed inside of it | |
3129 | and restores previous @option{--as-needed} resp. @option{--no-as-needed} | |
3130 | setting afterwards. | |
3131 | ||
252b5132 RH |
3132 | @item OUTPUT(@var{filename}) |
3133 | @kindex OUTPUT(@var{filename}) | |
b45619c0 | 3134 | @cindex output file name in linker script |
252b5132 RH |
3135 | The @code{OUTPUT} command names the output file. Using |
3136 | @code{OUTPUT(@var{filename})} in the linker script is exactly like using | |
3137 | @samp{-o @var{filename}} on the command line (@pxref{Options,,Command | |
3138 | Line Options}). If both are used, the command line option takes | |
3139 | precedence. | |
3140 | ||
3141 | You can use the @code{OUTPUT} command to define a default name for the | |
3142 | output file other than the usual default of @file{a.out}. | |
3143 | ||
3144 | @item SEARCH_DIR(@var{path}) | |
3145 | @kindex SEARCH_DIR(@var{path}) | |
3146 | @cindex library search path in linker script | |
3147 | @cindex archive search path in linker script | |
3148 | @cindex search path in linker script | |
3149 | The @code{SEARCH_DIR} command adds @var{path} to the list of paths where | |
ff5dcc92 | 3150 | @command{ld} looks for archive libraries. Using |
252b5132 RH |
3151 | @code{SEARCH_DIR(@var{path})} is exactly like using @samp{-L @var{path}} |
3152 | on the command line (@pxref{Options,,Command Line Options}). If both | |
3153 | are used, then the linker will search both paths. Paths specified using | |
3154 | the command line option are searched first. | |
3155 | ||
3156 | @item STARTUP(@var{filename}) | |
3157 | @kindex STARTUP(@var{filename}) | |
3158 | @cindex first input file | |
3159 | The @code{STARTUP} command is just like the @code{INPUT} command, except | |
3160 | that @var{filename} will become the first input file to be linked, as | |
3161 | though it were specified first on the command line. This may be useful | |
3162 | when using a system in which the entry point is always the start of the | |
3163 | first file. | |
3164 | @end table | |
3165 | ||
3166 | @ifclear SingleFormat | |
3167 | @node Format Commands | |
36f63dca | 3168 | @subsection Commands Dealing with Object File Formats |
252b5132 RH |
3169 | A couple of linker script commands deal with object file formats. |
3170 | ||
3171 | @table @code | |
3172 | @item OUTPUT_FORMAT(@var{bfdname}) | |
3173 | @itemx OUTPUT_FORMAT(@var{default}, @var{big}, @var{little}) | |
3174 | @kindex OUTPUT_FORMAT(@var{bfdname}) | |
3175 | @cindex output file format in linker script | |
3176 | The @code{OUTPUT_FORMAT} command names the BFD format to use for the | |
3177 | output file (@pxref{BFD}). Using @code{OUTPUT_FORMAT(@var{bfdname})} is | |
024531e2 | 3178 | exactly like using @samp{--oformat @var{bfdname}} on the command line |
252b5132 RH |
3179 | (@pxref{Options,,Command Line Options}). If both are used, the command |
3180 | line option takes precedence. | |
3181 | ||
3182 | You can use @code{OUTPUT_FORMAT} with three arguments to use different | |
3183 | formats based on the @samp{-EB} and @samp{-EL} command line options. | |
3184 | This permits the linker script to set the output format based on the | |
3185 | desired endianness. | |
3186 | ||
3187 | If neither @samp{-EB} nor @samp{-EL} are used, then the output format | |
3188 | will be the first argument, @var{default}. If @samp{-EB} is used, the | |
3189 | output format will be the second argument, @var{big}. If @samp{-EL} is | |
3190 | used, the output format will be the third argument, @var{little}. | |
3191 | ||
3192 | For example, the default linker script for the MIPS ELF target uses this | |
3193 | command: | |
3194 | @smallexample | |
3195 | OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips) | |
3196 | @end smallexample | |
3197 | This says that the default format for the output file is | |
3198 | @samp{elf32-bigmips}, but if the user uses the @samp{-EL} command line | |
3199 | option, the output file will be created in the @samp{elf32-littlemips} | |
3200 | format. | |
3201 | ||
3202 | @item TARGET(@var{bfdname}) | |
3203 | @kindex TARGET(@var{bfdname}) | |
3204 | @cindex input file format in linker script | |
3205 | The @code{TARGET} command names the BFD format to use when reading input | |
3206 | files. It affects subsequent @code{INPUT} and @code{GROUP} commands. | |
3207 | This command is like using @samp{-b @var{bfdname}} on the command line | |
3208 | (@pxref{Options,,Command Line Options}). If the @code{TARGET} command | |
3209 | is used but @code{OUTPUT_FORMAT} is not, then the last @code{TARGET} | |
3210 | command is also used to set the format for the output file. @xref{BFD}. | |
3211 | @end table | |
3212 | @end ifclear | |
3213 | ||
4a93e180 NC |
3214 | @node REGION_ALIAS |
3215 | @subsection Assign alias names to memory regions | |
3216 | @kindex REGION_ALIAS(@var{alias}, @var{region}) | |
3217 | @cindex region alias | |
3218 | @cindex region names | |
3219 | ||
3220 | Alias names can be added to existing memory regions created with the | |
3221 | @ref{MEMORY} command. Each name corresponds to at most one memory region. | |
3222 | ||
3223 | @smallexample | |
3224 | REGION_ALIAS(@var{alias}, @var{region}) | |
3225 | @end smallexample | |
3226 | ||
3227 | The @code{REGION_ALIAS} function creates an alias name @var{alias} for the | |
3228 | memory region @var{region}. This allows a flexible mapping of output sections | |
3229 | to memory regions. An example follows. | |
3230 | ||
3231 | Suppose we have an application for embedded systems which come with various | |
3232 | memory storage devices. All have a general purpose, volatile memory @code{RAM} | |
3233 | that allows code execution or data storage. Some may have a read-only, | |
3234 | non-volatile memory @code{ROM} that allows code execution and read-only data | |
3235 | access. The last variant is a read-only, non-volatile memory @code{ROM2} with | |
3236 | read-only data access and no code execution capability. We have four output | |
3237 | sections: | |
3238 | ||
3239 | @itemize @bullet | |
3240 | @item | |
3241 | @code{.text} program code; | |
3242 | @item | |
3243 | @code{.rodata} read-only data; | |
3244 | @item | |
3245 | @code{.data} read-write initialized data; | |
3246 | @item | |
3247 | @code{.bss} read-write zero initialized data. | |
3248 | @end itemize | |
3249 | ||
3250 | The goal is to provide a linker command file that contains a system independent | |
3251 | part defining the output sections and a system dependent part mapping the | |
3252 | output sections to the memory regions available on the system. Our embedded | |
3253 | systems come with three different memory setups @code{A}, @code{B} and | |
3254 | @code{C}: | |
3255 | @multitable @columnfractions .25 .25 .25 .25 | |
3256 | @item Section @tab Variant A @tab Variant B @tab Variant C | |
9d5777a3 | 3257 | @item .text @tab RAM @tab ROM @tab ROM |
4a93e180 NC |
3258 | @item .rodata @tab RAM @tab ROM @tab ROM2 |
3259 | @item .data @tab RAM @tab RAM/ROM @tab RAM/ROM2 | |
3260 | @item .bss @tab RAM @tab RAM @tab RAM | |
3261 | @end multitable | |
3262 | The notation @code{RAM/ROM} or @code{RAM/ROM2} means that this section is | |
3263 | loaded into region @code{ROM} or @code{ROM2} respectively. Please note that | |
3264 | the load address of the @code{.data} section starts in all three variants at | |
3265 | the end of the @code{.rodata} section. | |
3266 | ||
3267 | The base linker script that deals with the output sections follows. It | |
3268 | includes the system dependent @code{linkcmds.memory} file that describes the | |
3269 | memory layout: | |
3270 | @smallexample | |
3271 | INCLUDE linkcmds.memory | |
3272 | ||
3273 | SECTIONS | |
3274 | @{ | |
3275 | .text : | |
3276 | @{ | |
3277 | *(.text) | |
3278 | @} > REGION_TEXT | |
3279 | .rodata : | |
3280 | @{ | |
3281 | *(.rodata) | |
3282 | rodata_end = .; | |
3283 | @} > REGION_RODATA | |
3284 | .data : AT (rodata_end) | |
3285 | @{ | |
3286 | data_start = .; | |
3287 | *(.data) | |
3288 | @} > REGION_DATA | |
3289 | data_size = SIZEOF(.data); | |
3290 | data_load_start = LOADADDR(.data); | |
3291 | .bss : | |
3292 | @{ | |
3293 | *(.bss) | |
3294 | @} > REGION_BSS | |
3295 | @} | |
3296 | @end smallexample | |
3297 | ||
3298 | Now we need three different @code{linkcmds.memory} files to define memory | |
3299 | regions and alias names. The content of @code{linkcmds.memory} for the three | |
3300 | variants @code{A}, @code{B} and @code{C}: | |
3301 | @table @code | |
3302 | @item A | |
3303 | Here everything goes into the @code{RAM}. | |
3304 | @smallexample | |
3305 | MEMORY | |
3306 | @{ | |
3307 | RAM : ORIGIN = 0, LENGTH = 4M | |
3308 | @} | |
3309 | ||
3310 | REGION_ALIAS("REGION_TEXT", RAM); | |
3311 | REGION_ALIAS("REGION_RODATA", RAM); | |
3312 | REGION_ALIAS("REGION_DATA", RAM); | |
3313 | REGION_ALIAS("REGION_BSS", RAM); | |
3314 | @end smallexample | |
3315 | @item B | |
3316 | Program code and read-only data go into the @code{ROM}. Read-write data goes | |
3317 | into the @code{RAM}. An image of the initialized data is loaded into the | |
3318 | @code{ROM} and will be copied during system start into the @code{RAM}. | |
3319 | @smallexample | |
3320 | MEMORY | |
3321 | @{ | |
3322 | ROM : ORIGIN = 0, LENGTH = 3M | |
3323 | RAM : ORIGIN = 0x10000000, LENGTH = 1M | |
3324 | @} | |
3325 | ||
3326 | REGION_ALIAS("REGION_TEXT", ROM); | |
3327 | REGION_ALIAS("REGION_RODATA", ROM); | |
3328 | REGION_ALIAS("REGION_DATA", RAM); | |
3329 | REGION_ALIAS("REGION_BSS", RAM); | |
3330 | @end smallexample | |
3331 | @item C | |
3332 | Program code goes into the @code{ROM}. Read-only data goes into the | |
3333 | @code{ROM2}. Read-write data goes into the @code{RAM}. An image of the | |
3334 | initialized data is loaded into the @code{ROM2} and will be copied during | |
3335 | system start into the @code{RAM}. | |
3336 | @smallexample | |
3337 | MEMORY | |
3338 | @{ | |
3339 | ROM : ORIGIN = 0, LENGTH = 2M | |
3340 | ROM2 : ORIGIN = 0x10000000, LENGTH = 1M | |
3341 | RAM : ORIGIN = 0x20000000, LENGTH = 1M | |
3342 | @} | |
3343 | ||
3344 | REGION_ALIAS("REGION_TEXT", ROM); | |
3345 | REGION_ALIAS("REGION_RODATA", ROM2); | |
3346 | REGION_ALIAS("REGION_DATA", RAM); | |
3347 | REGION_ALIAS("REGION_BSS", RAM); | |
3348 | @end smallexample | |
3349 | @end table | |
3350 | ||
3351 | It is possible to write a common system initialization routine to copy the | |
3352 | @code{.data} section from @code{ROM} or @code{ROM2} into the @code{RAM} if | |
3353 | necessary: | |
3354 | @smallexample | |
3355 | #include <string.h> | |
3356 | ||
3357 | extern char data_start []; | |
3358 | extern char data_size []; | |
3359 | extern char data_load_start []; | |
3360 | ||
3361 | void copy_data(void) | |
3362 | @{ | |
3363 | if (data_start != data_load_start) | |
3364 | @{ | |
3365 | memcpy(data_start, data_load_start, (size_t) data_size); | |
3366 | @} | |
3367 | @} | |
3368 | @end smallexample | |
3369 | ||
252b5132 | 3370 | @node Miscellaneous Commands |
36f63dca | 3371 | @subsection Other Linker Script Commands |
252b5132 RH |
3372 | There are a few other linker scripts commands. |
3373 | ||
3374 | @table @code | |
3375 | @item ASSERT(@var{exp}, @var{message}) | |
3376 | @kindex ASSERT | |
3377 | @cindex assertion in linker script | |
3378 | Ensure that @var{exp} is non-zero. If it is zero, then exit the linker | |
3379 | with an error code, and print @var{message}. | |
3380 | ||
3381 | @item EXTERN(@var{symbol} @var{symbol} @dots{}) | |
3382 | @kindex EXTERN | |
3383 | @cindex undefined symbol in linker script | |
3384 | Force @var{symbol} to be entered in the output file as an undefined | |
3385 | symbol. Doing this may, for example, trigger linking of additional | |
3386 | modules from standard libraries. You may list several @var{symbol}s for | |
3387 | each @code{EXTERN}, and you may use @code{EXTERN} multiple times. This | |
3388 | command has the same effect as the @samp{-u} command-line option. | |
3389 | ||
3390 | @item FORCE_COMMON_ALLOCATION | |
3391 | @kindex FORCE_COMMON_ALLOCATION | |
3392 | @cindex common allocation in linker script | |
3393 | This command has the same effect as the @samp{-d} command-line option: | |
ff5dcc92 | 3394 | to make @command{ld} assign space to common symbols even if a relocatable |
252b5132 RH |
3395 | output file is specified (@samp{-r}). |
3396 | ||
4818e05f AM |
3397 | @item INHIBIT_COMMON_ALLOCATION |
3398 | @kindex INHIBIT_COMMON_ALLOCATION | |
3399 | @cindex common allocation in linker script | |
3400 | This command has the same effect as the @samp{--no-define-common} | |
3401 | command-line option: to make @code{ld} omit the assignment of addresses | |
3402 | to common symbols even for a non-relocatable output file. | |
3403 | ||
53d25da6 AM |
3404 | @item INSERT [ AFTER | BEFORE ] @var{output_section} |
3405 | @kindex INSERT | |
3406 | @cindex insert user script into default script | |
3407 | This command is typically used in a script specified by @samp{-T} to | |
3408 | augment the default @code{SECTIONS} with, for example, overlays. It | |
3409 | inserts all prior linker script statements after (or before) | |
3410 | @var{output_section}, and also causes @samp{-T} to not override the | |
3411 | default linker script. The exact insertion point is as for orphan | |
3412 | sections. @xref{Location Counter}. The insertion happens after the | |
3413 | linker has mapped input sections to output sections. Prior to the | |
3414 | insertion, since @samp{-T} scripts are parsed before the default | |
3415 | linker script, statements in the @samp{-T} script occur before the | |
3416 | default linker script statements in the internal linker representation | |
3417 | of the script. In particular, input section assignments will be made | |
3418 | to @samp{-T} output sections before those in the default script. Here | |
3419 | is an example of how a @samp{-T} script using @code{INSERT} might look: | |
3420 | ||
3421 | @smallexample | |
3422 | SECTIONS | |
3423 | @{ | |
3424 | OVERLAY : | |
3425 | @{ | |
3426 | .ov1 @{ ov1*(.text) @} | |
3427 | .ov2 @{ ov2*(.text) @} | |
3428 | @} | |
3429 | @} | |
3430 | INSERT AFTER .text; | |
3431 | @end smallexample | |
3432 | ||
252b5132 RH |
3433 | @item NOCROSSREFS(@var{section} @var{section} @dots{}) |
3434 | @kindex NOCROSSREFS(@var{sections}) | |
3435 | @cindex cross references | |
ff5dcc92 | 3436 | This command may be used to tell @command{ld} to issue an error about any |
252b5132 RH |
3437 | references among certain output sections. |
3438 | ||
3439 | In certain types of programs, particularly on embedded systems when | |
3440 | using overlays, when one section is loaded into memory, another section | |
3441 | will not be. Any direct references between the two sections would be | |
3442 | errors. For example, it would be an error if code in one section called | |
3443 | a function defined in the other section. | |
3444 | ||
3445 | The @code{NOCROSSREFS} command takes a list of output section names. If | |
ff5dcc92 | 3446 | @command{ld} detects any cross references between the sections, it reports |
252b5132 RH |
3447 | an error and returns a non-zero exit status. Note that the |
3448 | @code{NOCROSSREFS} command uses output section names, not input section | |
3449 | names. | |
3450 | ||
3451 | @ifclear SingleFormat | |
3452 | @item OUTPUT_ARCH(@var{bfdarch}) | |
3453 | @kindex OUTPUT_ARCH(@var{bfdarch}) | |
3454 | @cindex machine architecture | |
3455 | @cindex architecture | |
3456 | Specify a particular output machine architecture. The argument is one | |
3457 | of the names used by the BFD library (@pxref{BFD}). You can see the | |
3458 | architecture of an object file by using the @code{objdump} program with | |
3459 | the @samp{-f} option. | |
3460 | @end ifclear | |
01554a74 AM |
3461 | |
3462 | @item LD_FEATURE(@var{string}) | |
3463 | @kindex LD_FEATURE(@var{string}) | |
3464 | This command may be used to modify @command{ld} behavior. If | |
3465 | @var{string} is @code{"SANE_EXPR"} then absolute symbols and numbers | |
3466 | in a script are simply treated as numbers everywhere. | |
3467 | @xref{Expression Section}. | |
252b5132 RH |
3468 | @end table |
3469 | ||
3470 | @node Assignments | |
3471 | @section Assigning Values to Symbols | |
3472 | @cindex assignment in scripts | |
3473 | @cindex symbol definition, scripts | |
3474 | @cindex variables, defining | |
3475 | You may assign a value to a symbol in a linker script. This will define | |
73ae6183 | 3476 | the symbol and place it into the symbol table with a global scope. |
252b5132 RH |
3477 | |
3478 | @menu | |
3479 | * Simple Assignments:: Simple Assignments | |
eb8476a6 | 3480 | * HIDDEN:: HIDDEN |
252b5132 | 3481 | * PROVIDE:: PROVIDE |
7af8e998 | 3482 | * PROVIDE_HIDDEN:: PROVIDE_HIDDEN |
73ae6183 | 3483 | * Source Code Reference:: How to use a linker script defined symbol in source code |
252b5132 RH |
3484 | @end menu |
3485 | ||
3486 | @node Simple Assignments | |
3487 | @subsection Simple Assignments | |
3488 | ||
3489 | You may assign to a symbol using any of the C assignment operators: | |
3490 | ||
3491 | @table @code | |
3492 | @item @var{symbol} = @var{expression} ; | |
3493 | @itemx @var{symbol} += @var{expression} ; | |
3494 | @itemx @var{symbol} -= @var{expression} ; | |
3495 | @itemx @var{symbol} *= @var{expression} ; | |
3496 | @itemx @var{symbol} /= @var{expression} ; | |
3497 | @itemx @var{symbol} <<= @var{expression} ; | |
3498 | @itemx @var{symbol} >>= @var{expression} ; | |
3499 | @itemx @var{symbol} &= @var{expression} ; | |
3500 | @itemx @var{symbol} |= @var{expression} ; | |
3501 | @end table | |
3502 | ||
3503 | The first case will define @var{symbol} to the value of | |
3504 | @var{expression}. In the other cases, @var{symbol} must already be | |
3505 | defined, and the value will be adjusted accordingly. | |
3506 | ||
3507 | The special symbol name @samp{.} indicates the location counter. You | |
b5666f2f | 3508 | may only use this within a @code{SECTIONS} command. @xref{Location Counter}. |
252b5132 RH |
3509 | |
3510 | The semicolon after @var{expression} is required. | |
3511 | ||
3512 | Expressions are defined below; see @ref{Expressions}. | |
3513 | ||
3514 | You may write symbol assignments as commands in their own right, or as | |
3515 | statements within a @code{SECTIONS} command, or as part of an output | |
3516 | section description in a @code{SECTIONS} command. | |
3517 | ||
3518 | The section of the symbol will be set from the section of the | |
3519 | expression; for more information, see @ref{Expression Section}. | |
3520 | ||
3521 | Here is an example showing the three different places that symbol | |
3522 | assignments may be used: | |
3523 | ||
3524 | @smallexample | |
3525 | floating_point = 0; | |
3526 | SECTIONS | |
3527 | @{ | |
3528 | .text : | |
3529 | @{ | |
3530 | *(.text) | |
3531 | _etext = .; | |
3532 | @} | |
156e34dd | 3533 | _bdata = (. + 3) & ~ 3; |
252b5132 RH |
3534 | .data : @{ *(.data) @} |
3535 | @} | |
3536 | @end smallexample | |
3537 | @noindent | |
3538 | In this example, the symbol @samp{floating_point} will be defined as | |
3539 | zero. The symbol @samp{_etext} will be defined as the address following | |
3540 | the last @samp{.text} input section. The symbol @samp{_bdata} will be | |
3541 | defined as the address following the @samp{.text} output section aligned | |
3542 | upward to a 4 byte boundary. | |
3543 | ||
eb8476a6 MR |
3544 | @node HIDDEN |
3545 | @subsection HIDDEN | |
3546 | @cindex HIDDEN | |
3547 | For ELF targeted ports, define a symbol that will be hidden and won't be | |
3548 | exported. The syntax is @code{HIDDEN(@var{symbol} = @var{expression})}. | |
3549 | ||
3550 | Here is the example from @ref{Simple Assignments}, rewritten to use | |
3551 | @code{HIDDEN}: | |
3552 | ||
3553 | @smallexample | |
3554 | HIDDEN(floating_point = 0); | |
3555 | SECTIONS | |
3556 | @{ | |
3557 | .text : | |
3558 | @{ | |
3559 | *(.text) | |
3560 | HIDDEN(_etext = .); | |
3561 | @} | |
3562 | HIDDEN(_bdata = (. + 3) & ~ 3); | |
3563 | .data : @{ *(.data) @} | |
3564 | @} | |
3565 | @end smallexample | |
3566 | @noindent | |
3567 | In this case none of the three symbols will be visible outside this module. | |
3568 | ||
252b5132 RH |
3569 | @node PROVIDE |
3570 | @subsection PROVIDE | |
3571 | @cindex PROVIDE | |
3572 | In some cases, it is desirable for a linker script to define a symbol | |
3573 | only if it is referenced and is not defined by any object included in | |
3574 | the link. For example, traditional linkers defined the symbol | |
3575 | @samp{etext}. However, ANSI C requires that the user be able to use | |
3576 | @samp{etext} as a function name without encountering an error. The | |
3577 | @code{PROVIDE} keyword may be used to define a symbol, such as | |
3578 | @samp{etext}, only if it is referenced but not defined. The syntax is | |
3579 | @code{PROVIDE(@var{symbol} = @var{expression})}. | |
3580 | ||
3581 | Here is an example of using @code{PROVIDE} to define @samp{etext}: | |
3582 | @smallexample | |
3583 | SECTIONS | |
3584 | @{ | |
3585 | .text : | |
3586 | @{ | |
3587 | *(.text) | |
3588 | _etext = .; | |
3589 | PROVIDE(etext = .); | |
3590 | @} | |
3591 | @} | |
3592 | @end smallexample | |
3593 | ||
3594 | In this example, if the program defines @samp{_etext} (with a leading | |
3595 | underscore), the linker will give a multiple definition error. If, on | |
3596 | the other hand, the program defines @samp{etext} (with no leading | |
3597 | underscore), the linker will silently use the definition in the program. | |
3598 | If the program references @samp{etext} but does not define it, the | |
3599 | linker will use the definition in the linker script. | |
3600 | ||
7af8e998 L |
3601 | @node PROVIDE_HIDDEN |
3602 | @subsection PROVIDE_HIDDEN | |
3603 | @cindex PROVIDE_HIDDEN | |
3604 | Similar to @code{PROVIDE}. For ELF targeted ports, the symbol will be | |
3605 | hidden and won't be exported. | |
3606 | ||
73ae6183 NC |
3607 | @node Source Code Reference |
3608 | @subsection Source Code Reference | |
3609 | ||
3610 | Accessing a linker script defined variable from source code is not | |
3611 | intuitive. In particular a linker script symbol is not equivalent to | |
3612 | a variable declaration in a high level language, it is instead a | |
3613 | symbol that does not have a value. | |
3614 | ||
3615 | Before going further, it is important to note that compilers often | |
3616 | transform names in the source code into different names when they are | |
3617 | stored in the symbol table. For example, Fortran compilers commonly | |
3618 | prepend or append an underscore, and C++ performs extensive @samp{name | |
3619 | mangling}. Therefore there might be a discrepancy between the name | |
3620 | of a variable as it is used in source code and the name of the same | |
3621 | variable as it is defined in a linker script. For example in C a | |
3622 | linker script variable might be referred to as: | |
3623 | ||
3624 | @smallexample | |
3625 | extern int foo; | |
3626 | @end smallexample | |
3627 | ||
3628 | But in the linker script it might be defined as: | |
3629 | ||
3630 | @smallexample | |
3631 | _foo = 1000; | |
3632 | @end smallexample | |
3633 | ||
3634 | In the remaining examples however it is assumed that no name | |
3635 | transformation has taken place. | |
3636 | ||
3637 | When a symbol is declared in a high level language such as C, two | |
3638 | things happen. The first is that the compiler reserves enough space | |
3639 | in the program's memory to hold the @emph{value} of the symbol. The | |
3640 | second is that the compiler creates an entry in the program's symbol | |
3641 | table which holds the symbol's @emph{address}. ie the symbol table | |
3642 | contains the address of the block of memory holding the symbol's | |
3643 | value. So for example the following C declaration, at file scope: | |
3644 | ||
3645 | @smallexample | |
3646 | int foo = 1000; | |
3647 | @end smallexample | |
3648 | ||
10bf6894 | 3649 | creates an entry called @samp{foo} in the symbol table. This entry |
73ae6183 NC |
3650 | holds the address of an @samp{int} sized block of memory where the |
3651 | number 1000 is initially stored. | |
3652 | ||
3653 | When a program references a symbol the compiler generates code that | |
3654 | first accesses the symbol table to find the address of the symbol's | |
3655 | memory block and then code to read the value from that memory block. | |
3656 | So: | |
3657 | ||
3658 | @smallexample | |
3659 | foo = 1; | |
3660 | @end smallexample | |
3661 | ||
3662 | looks up the symbol @samp{foo} in the symbol table, gets the address | |
3663 | associated with this symbol and then writes the value 1 into that | |
3664 | address. Whereas: | |
3665 | ||
3666 | @smallexample | |
3667 | int * a = & foo; | |
3668 | @end smallexample | |
3669 | ||
10bf6894 | 3670 | looks up the symbol @samp{foo} in the symbol table, gets its address |
73ae6183 NC |
3671 | and then copies this address into the block of memory associated with |
3672 | the variable @samp{a}. | |
3673 | ||
3674 | Linker scripts symbol declarations, by contrast, create an entry in | |
3675 | the symbol table but do not assign any memory to them. Thus they are | |
3676 | an address without a value. So for example the linker script definition: | |
3677 | ||
3678 | @smallexample | |
3679 | foo = 1000; | |
3680 | @end smallexample | |
3681 | ||
3682 | creates an entry in the symbol table called @samp{foo} which holds | |
3683 | the address of memory location 1000, but nothing special is stored at | |
3684 | address 1000. This means that you cannot access the @emph{value} of a | |
3685 | linker script defined symbol - it has no value - all you can do is | |
3686 | access the @emph{address} of a linker script defined symbol. | |
3687 | ||
3688 | Hence when you are using a linker script defined symbol in source code | |
3689 | you should always take the address of the symbol, and never attempt to | |
3690 | use its value. For example suppose you want to copy the contents of a | |
3691 | section of memory called .ROM into a section called .FLASH and the | |
3692 | linker script contains these declarations: | |
3693 | ||
3694 | @smallexample | |
3695 | @group | |
3696 | start_of_ROM = .ROM; | |
3697 | end_of_ROM = .ROM + sizeof (.ROM) - 1; | |
3698 | start_of_FLASH = .FLASH; | |
3699 | @end group | |
3700 | @end smallexample | |
3701 | ||
3702 | Then the C source code to perform the copy would be: | |
3703 | ||
3704 | @smallexample | |
3705 | @group | |
3706 | extern char start_of_ROM, end_of_ROM, start_of_FLASH; | |
c0065db7 | 3707 | |
73ae6183 NC |
3708 | memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM); |
3709 | @end group | |
3710 | @end smallexample | |
3711 | ||
3712 | Note the use of the @samp{&} operators. These are correct. | |
3713 | ||
252b5132 | 3714 | @node SECTIONS |
36f63dca | 3715 | @section SECTIONS Command |
252b5132 RH |
3716 | @kindex SECTIONS |
3717 | The @code{SECTIONS} command tells the linker how to map input sections | |
3718 | into output sections, and how to place the output sections in memory. | |
3719 | ||
3720 | The format of the @code{SECTIONS} command is: | |
3721 | @smallexample | |
3722 | SECTIONS | |
3723 | @{ | |
3724 | @var{sections-command} | |
3725 | @var{sections-command} | |
3726 | @dots{} | |
3727 | @} | |
3728 | @end smallexample | |
3729 | ||
3730 | Each @var{sections-command} may of be one of the following: | |
3731 | ||
3732 | @itemize @bullet | |
3733 | @item | |
3734 | an @code{ENTRY} command (@pxref{Entry Point,,Entry command}) | |
3735 | @item | |
3736 | a symbol assignment (@pxref{Assignments}) | |
3737 | @item | |
3738 | an output section description | |
3739 | @item | |
3740 | an overlay description | |
3741 | @end itemize | |
3742 | ||
3743 | The @code{ENTRY} command and symbol assignments are permitted inside the | |
3744 | @code{SECTIONS} command for convenience in using the location counter in | |
3745 | those commands. This can also make the linker script easier to | |
3746 | understand because you can use those commands at meaningful points in | |
3747 | the layout of the output file. | |
3748 | ||
3749 | Output section descriptions and overlay descriptions are described | |
3750 | below. | |
3751 | ||
3752 | If you do not use a @code{SECTIONS} command in your linker script, the | |
3753 | linker will place each input section into an identically named output | |
3754 | section in the order that the sections are first encountered in the | |
3755 | input files. If all input sections are present in the first file, for | |
3756 | example, the order of sections in the output file will match the order | |
3757 | in the first input file. The first section will be at address zero. | |
3758 | ||
3759 | @menu | |
3760 | * Output Section Description:: Output section description | |
3761 | * Output Section Name:: Output section name | |
3762 | * Output Section Address:: Output section address | |
3763 | * Input Section:: Input section description | |
3764 | * Output Section Data:: Output section data | |
3765 | * Output Section Keywords:: Output section keywords | |
3766 | * Output Section Discarding:: Output section discarding | |
3767 | * Output Section Attributes:: Output section attributes | |
3768 | * Overlay Description:: Overlay description | |
3769 | @end menu | |
3770 | ||
3771 | @node Output Section Description | |
36f63dca | 3772 | @subsection Output Section Description |
252b5132 RH |
3773 | The full description of an output section looks like this: |
3774 | @smallexample | |
a1ab1d2a | 3775 | @group |
7e7d5768 | 3776 | @var{section} [@var{address}] [(@var{type})] : |
0c71d759 | 3777 | [AT(@var{lma})] |
1eec346e | 3778 | [ALIGN(@var{section_align}) | ALIGN_WITH_INPUT] |
0c71d759 NC |
3779 | [SUBALIGN(@var{subsection_align})] |
3780 | [@var{constraint}] | |
252b5132 RH |
3781 | @{ |
3782 | @var{output-section-command} | |
3783 | @var{output-section-command} | |
3784 | @dots{} | |
562d3460 | 3785 | @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}] |
252b5132 RH |
3786 | @end group |
3787 | @end smallexample | |
3788 | ||
3789 | Most output sections do not use most of the optional section attributes. | |
3790 | ||
3791 | The whitespace around @var{section} is required, so that the section | |
3792 | name is unambiguous. The colon and the curly braces are also required. | |
3793 | The line breaks and other white space are optional. | |
3794 | ||
3795 | Each @var{output-section-command} may be one of the following: | |
3796 | ||
3797 | @itemize @bullet | |
3798 | @item | |
3799 | a symbol assignment (@pxref{Assignments}) | |
3800 | @item | |
3801 | an input section description (@pxref{Input Section}) | |
3802 | @item | |
3803 | data values to include directly (@pxref{Output Section Data}) | |
3804 | @item | |
3805 | a special output section keyword (@pxref{Output Section Keywords}) | |
3806 | @end itemize | |
3807 | ||
3808 | @node Output Section Name | |
36f63dca | 3809 | @subsection Output Section Name |
252b5132 RH |
3810 | @cindex name, section |
3811 | @cindex section name | |
3812 | The name of the output section is @var{section}. @var{section} must | |
3813 | meet the constraints of your output format. In formats which only | |
3814 | support a limited number of sections, such as @code{a.out}, the name | |
3815 | must be one of the names supported by the format (@code{a.out}, for | |
3816 | example, allows only @samp{.text}, @samp{.data} or @samp{.bss}). If the | |
3817 | output format supports any number of sections, but with numbers and not | |
3818 | names (as is the case for Oasys), the name should be supplied as a | |
3819 | quoted numeric string. A section name may consist of any sequence of | |
3820 | characters, but a name which contains any unusual characters such as | |
3821 | commas must be quoted. | |
3822 | ||
3823 | The output section name @samp{/DISCARD/} is special; @ref{Output Section | |
3824 | Discarding}. | |
3825 | ||
3826 | @node Output Section Address | |
2a16d82a | 3827 | @subsection Output Section Address |
252b5132 RH |
3828 | @cindex address, section |
3829 | @cindex section address | |
3830 | The @var{address} is an expression for the VMA (the virtual memory | |
ea5cae92 NC |
3831 | address) of the output section. This address is optional, but if it |
3832 | is provided then the output address will be set exactly as specified. | |
3833 | ||
3834 | If the output address is not specified then one will be chosen for the | |
3835 | section, based on the heuristic below. This address will be adjusted | |
3836 | to fit the alignment requirement of the output section. The | |
3837 | alignment requirement is the strictest alignment of any input section | |
3838 | contained within the output section. | |
3839 | ||
3840 | The output section address heuristic is as follows: | |
3841 | ||
3842 | @itemize @bullet | |
3843 | @item | |
3844 | If an output memory @var{region} is set for the section then it | |
3845 | is added to this region and its address will be the next free address | |
3846 | in that region. | |
3847 | ||
3848 | @item | |
3849 | If the MEMORY command has been used to create a list of memory | |
3850 | regions then the first region which has attributes compatible with the | |
3851 | section is selected to contain it. The section's output address will | |
3852 | be the next free address in that region; @ref{MEMORY}. | |
3853 | ||
3854 | @item | |
3855 | If no memory regions were specified, or none match the section then | |
3856 | the output address will be based on the current value of the location | |
3857 | counter. | |
3858 | @end itemize | |
3859 | ||
3860 | @noindent | |
3861 | For example: | |
3862 | ||
252b5132 RH |
3863 | @smallexample |
3864 | .text . : @{ *(.text) @} | |
3865 | @end smallexample | |
ea5cae92 | 3866 | |
252b5132 RH |
3867 | @noindent |
3868 | and | |
ea5cae92 | 3869 | |
252b5132 RH |
3870 | @smallexample |
3871 | .text : @{ *(.text) @} | |
3872 | @end smallexample | |
ea5cae92 | 3873 | |
252b5132 RH |
3874 | @noindent |
3875 | are subtly different. The first will set the address of the | |
3876 | @samp{.text} output section to the current value of the location | |
3877 | counter. The second will set it to the current value of the location | |
ea5cae92 NC |
3878 | counter aligned to the strictest alignment of any of the @samp{.text} |
3879 | input sections. | |
252b5132 RH |
3880 | |
3881 | The @var{address} may be an arbitrary expression; @ref{Expressions}. | |
3882 | For example, if you want to align the section on a 0x10 byte boundary, | |
3883 | so that the lowest four bits of the section address are zero, you could | |
3884 | do something like this: | |
3885 | @smallexample | |
3886 | .text ALIGN(0x10) : @{ *(.text) @} | |
3887 | @end smallexample | |
3888 | @noindent | |
3889 | This works because @code{ALIGN} returns the current location counter | |
3890 | aligned upward to the specified value. | |
3891 | ||
3892 | Specifying @var{address} for a section will change the value of the | |
6ce340f1 NC |
3893 | location counter, provided that the section is non-empty. (Empty |
3894 | sections are ignored). | |
252b5132 RH |
3895 | |
3896 | @node Input Section | |
36f63dca | 3897 | @subsection Input Section Description |
252b5132 RH |
3898 | @cindex input sections |
3899 | @cindex mapping input sections to output sections | |
3900 | The most common output section command is an input section description. | |
3901 | ||
3902 | The input section description is the most basic linker script operation. | |
3903 | You use output sections to tell the linker how to lay out your program | |
3904 | in memory. You use input section descriptions to tell the linker how to | |
3905 | map the input files into your memory layout. | |
3906 | ||
3907 | @menu | |
3908 | * Input Section Basics:: Input section basics | |
3909 | * Input Section Wildcards:: Input section wildcard patterns | |
3910 | * Input Section Common:: Input section for common symbols | |
3911 | * Input Section Keep:: Input section and garbage collection | |
3912 | * Input Section Example:: Input section example | |
3913 | @end menu | |
3914 | ||
3915 | @node Input Section Basics | |
36f63dca | 3916 | @subsubsection Input Section Basics |
252b5132 RH |
3917 | @cindex input section basics |
3918 | An input section description consists of a file name optionally followed | |
3919 | by a list of section names in parentheses. | |
3920 | ||
3921 | The file name and the section name may be wildcard patterns, which we | |
3922 | describe further below (@pxref{Input Section Wildcards}). | |
3923 | ||
3924 | The most common input section description is to include all input | |
3925 | sections with a particular name in the output section. For example, to | |
3926 | include all input @samp{.text} sections, you would write: | |
3927 | @smallexample | |
3928 | *(.text) | |
3929 | @end smallexample | |
3930 | @noindent | |
18625d54 CM |
3931 | Here the @samp{*} is a wildcard which matches any file name. To exclude a list |
3932 | of files from matching the file name wildcard, EXCLUDE_FILE may be used to | |
3933 | match all files except the ones specified in the EXCLUDE_FILE list. For | |
3934 | example: | |
252b5132 | 3935 | @smallexample |
b4346c09 | 3936 | *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors) |
252b5132 | 3937 | @end smallexample |
765b7cbe JB |
3938 | will cause all .ctors sections from all files except @file{crtend.o} and |
3939 | @file{otherfile.o} to be included. | |
252b5132 RH |
3940 | |
3941 | There are two ways to include more than one section: | |
3942 | @smallexample | |
3943 | *(.text .rdata) | |
3944 | *(.text) *(.rdata) | |
3945 | @end smallexample | |
3946 | @noindent | |
3947 | The difference between these is the order in which the @samp{.text} and | |
3948 | @samp{.rdata} input sections will appear in the output section. In the | |
b6bf44ba AM |
3949 | first example, they will be intermingled, appearing in the same order as |
3950 | they are found in the linker input. In the second example, all | |
252b5132 RH |
3951 | @samp{.text} input sections will appear first, followed by all |
3952 | @samp{.rdata} input sections. | |
3953 | ||
3954 | You can specify a file name to include sections from a particular file. | |
3955 | You would do this if one or more of your files contain special data that | |
3956 | needs to be at a particular location in memory. For example: | |
3957 | @smallexample | |
3958 | data.o(.data) | |
3959 | @end smallexample | |
3960 | ||
ae17ab41 CM |
3961 | To refine the sections that are included based on the section flags |
3962 | of an input section, INPUT_SECTION_FLAGS may be used. | |
3963 | ||
3964 | Here is a simple example for using Section header flags for ELF sections: | |
3965 | ||
3966 | @smallexample | |
3967 | @group | |
3968 | SECTIONS @{ | |
3969 | .text : @{ INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) @} | |
3970 | .text2 : @{ INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) @} | |
3971 | @} | |
3972 | @end group | |
3973 | @end smallexample | |
3974 | ||
3975 | In this example, the output section @samp{.text} will be comprised of any | |
3976 | input section matching the name *(.text) whose section header flags | |
3977 | @code{SHF_MERGE} and @code{SHF_STRINGS} are set. The output section | |
3978 | @samp{.text2} will be comprised of any input section matching the name *(.text) | |
3979 | whose section header flag @code{SHF_WRITE} is clear. | |
3980 | ||
967928e9 AM |
3981 | You can also specify files within archives by writing a pattern |
3982 | matching the archive, a colon, then the pattern matching the file, | |
3983 | with no whitespace around the colon. | |
3984 | ||
3985 | @table @samp | |
3986 | @item archive:file | |
3987 | matches file within archive | |
3988 | @item archive: | |
3989 | matches the whole archive | |
3990 | @item :file | |
3991 | matches file but not one in an archive | |
3992 | @end table | |
3993 | ||
3994 | Either one or both of @samp{archive} and @samp{file} can contain shell | |
3995 | wildcards. On DOS based file systems, the linker will assume that a | |
3996 | single letter followed by a colon is a drive specifier, so | |
3997 | @samp{c:myfile.o} is a simple file specification, not @samp{myfile.o} | |
3998 | within an archive called @samp{c}. @samp{archive:file} filespecs may | |
3999 | also be used within an @code{EXCLUDE_FILE} list, but may not appear in | |
4000 | other linker script contexts. For instance, you cannot extract a file | |
4001 | from an archive by using @samp{archive:file} in an @code{INPUT} | |
4002 | command. | |
4003 | ||
252b5132 RH |
4004 | If you use a file name without a list of sections, then all sections in |
4005 | the input file will be included in the output section. This is not | |
4006 | commonly done, but it may by useful on occasion. For example: | |
4007 | @smallexample | |
4008 | data.o | |
4009 | @end smallexample | |
4010 | ||
967928e9 AM |
4011 | When you use a file name which is not an @samp{archive:file} specifier |
4012 | and does not contain any wild card | |
252b5132 RH |
4013 | characters, the linker will first see if you also specified the file |
4014 | name on the linker command line or in an @code{INPUT} command. If you | |
4015 | did not, the linker will attempt to open the file as an input file, as | |
4016 | though it appeared on the command line. Note that this differs from an | |
4017 | @code{INPUT} command, because the linker will not search for the file in | |
4018 | the archive search path. | |
4019 | ||
4020 | @node Input Section Wildcards | |
36f63dca | 4021 | @subsubsection Input Section Wildcard Patterns |
252b5132 RH |
4022 | @cindex input section wildcards |
4023 | @cindex wildcard file name patterns | |
4024 | @cindex file name wildcard patterns | |
4025 | @cindex section name wildcard patterns | |
4026 | In an input section description, either the file name or the section | |
4027 | name or both may be wildcard patterns. | |
4028 | ||
4029 | The file name of @samp{*} seen in many examples is a simple wildcard | |
4030 | pattern for the file name. | |
4031 | ||
4032 | The wildcard patterns are like those used by the Unix shell. | |
4033 | ||
4034 | @table @samp | |
4035 | @item * | |
4036 | matches any number of characters | |
4037 | @item ? | |
4038 | matches any single character | |
4039 | @item [@var{chars}] | |
4040 | matches a single instance of any of the @var{chars}; the @samp{-} | |
4041 | character may be used to specify a range of characters, as in | |
4042 | @samp{[a-z]} to match any lower case letter | |
4043 | @item \ | |
4044 | quotes the following character | |
4045 | @end table | |
4046 | ||
4047 | When a file name is matched with a wildcard, the wildcard characters | |
4048 | will not match a @samp{/} character (used to separate directory names on | |
4049 | Unix). A pattern consisting of a single @samp{*} character is an | |
4050 | exception; it will always match any file name, whether it contains a | |
4051 | @samp{/} or not. In a section name, the wildcard characters will match | |
4052 | a @samp{/} character. | |
4053 | ||
4054 | File name wildcard patterns only match files which are explicitly | |
4055 | specified on the command line or in an @code{INPUT} command. The linker | |
4056 | does not search directories to expand wildcards. | |
4057 | ||
4058 | If a file name matches more than one wildcard pattern, or if a file name | |
4059 | appears explicitly and is also matched by a wildcard pattern, the linker | |
4060 | will use the first match in the linker script. For example, this | |
4061 | sequence of input section descriptions is probably in error, because the | |
4062 | @file{data.o} rule will not be used: | |
4063 | @smallexample | |
4064 | .data : @{ *(.data) @} | |
4065 | .data1 : @{ data.o(.data) @} | |
4066 | @end smallexample | |
4067 | ||
bcaa7b3e | 4068 | @cindex SORT_BY_NAME |
252b5132 RH |
4069 | Normally, the linker will place files and sections matched by wildcards |
4070 | in the order in which they are seen during the link. You can change | |
bcaa7b3e L |
4071 | this by using the @code{SORT_BY_NAME} keyword, which appears before a wildcard |
4072 | pattern in parentheses (e.g., @code{SORT_BY_NAME(.text*)}). When the | |
4073 | @code{SORT_BY_NAME} keyword is used, the linker will sort the files or sections | |
252b5132 RH |
4074 | into ascending order by name before placing them in the output file. |
4075 | ||
bcaa7b3e L |
4076 | @cindex SORT_BY_ALIGNMENT |
4077 | @code{SORT_BY_ALIGNMENT} is very similar to @code{SORT_BY_NAME}. The | |
4078 | difference is @code{SORT_BY_ALIGNMENT} will sort sections into | |
1ae5c3ae | 4079 | descending order by alignment before placing them in the output file. |
ee83b8a6 NC |
4080 | Larger alignments are placed before smaller alignments in order to |
4081 | reduce the amount of padding necessary. | |
bcaa7b3e | 4082 | |
02ecc8e9 L |
4083 | @cindex SORT_BY_INIT_PRIORITY |
4084 | @code{SORT_BY_INIT_PRIORITY} is very similar to @code{SORT_BY_NAME}. The | |
4085 | difference is @code{SORT_BY_INIT_PRIORITY} will sort sections into | |
4086 | ascending order by numerical value of the GCC init_priority attribute | |
4087 | encoded in the section name before placing them in the output file. | |
4088 | ||
bcaa7b3e L |
4089 | @cindex SORT |
4090 | @code{SORT} is an alias for @code{SORT_BY_NAME}. | |
4091 | ||
4092 | When there are nested section sorting commands in linker script, there | |
4093 | can be at most 1 level of nesting for section sorting commands. | |
4094 | ||
4095 | @enumerate | |
4096 | @item | |
4097 | @code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)). | |
1ae5c3ae | 4098 | It will sort the input sections by name first, then by alignment if two |
bcaa7b3e L |
4099 | sections have the same name. |
4100 | @item | |
4101 | @code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)). | |
1ae5c3ae | 4102 | It will sort the input sections by alignment first, then by name if two |
bcaa7b3e L |
4103 | sections have the same alignment. |
4104 | @item | |
c0065db7 | 4105 | @code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is |
bcaa7b3e L |
4106 | treated the same as @code{SORT_BY_NAME} (wildcard section pattern). |
4107 | @item | |
4108 | @code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)) | |
4109 | is treated the same as @code{SORT_BY_ALIGNMENT} (wildcard section pattern). | |
4110 | @item | |
4111 | All other nested section sorting commands are invalid. | |
4112 | @end enumerate | |
4113 | ||
4114 | When both command line section sorting option and linker script | |
4115 | section sorting command are used, section sorting command always | |
4116 | takes precedence over the command line option. | |
4117 | ||
4118 | If the section sorting command in linker script isn't nested, the | |
4119 | command line option will make the section sorting command to be | |
4120 | treated as nested sorting command. | |
4121 | ||
4122 | @enumerate | |
4123 | @item | |
4124 | @code{SORT_BY_NAME} (wildcard section pattern ) with | |
4125 | @option{--sort-sections alignment} is equivalent to | |
4126 | @code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)). | |
4127 | @item | |
4128 | @code{SORT_BY_ALIGNMENT} (wildcard section pattern) with | |
4129 | @option{--sort-section name} is equivalent to | |
4130 | @code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)). | |
4131 | @end enumerate | |
4132 | ||
4133 | If the section sorting command in linker script is nested, the | |
4134 | command line option will be ignored. | |
4135 | ||
eda680f8 L |
4136 | @cindex SORT_NONE |
4137 | @code{SORT_NONE} disables section sorting by ignoring the command line | |
4138 | section sorting option. | |
4139 | ||
252b5132 RH |
4140 | If you ever get confused about where input sections are going, use the |
4141 | @samp{-M} linker option to generate a map file. The map file shows | |
4142 | precisely how input sections are mapped to output sections. | |
4143 | ||
4144 | This example shows how wildcard patterns might be used to partition | |
4145 | files. This linker script directs the linker to place all @samp{.text} | |
4146 | sections in @samp{.text} and all @samp{.bss} sections in @samp{.bss}. | |
4147 | The linker will place the @samp{.data} section from all files beginning | |
4148 | with an upper case character in @samp{.DATA}; for all other files, the | |
4149 | linker will place the @samp{.data} section in @samp{.data}. | |
4150 | @smallexample | |
4151 | @group | |
4152 | SECTIONS @{ | |
4153 | .text : @{ *(.text) @} | |
4154 | .DATA : @{ [A-Z]*(.data) @} | |
4155 | .data : @{ *(.data) @} | |
4156 | .bss : @{ *(.bss) @} | |
4157 | @} | |
4158 | @end group | |
4159 | @end smallexample | |
4160 | ||
4161 | @node Input Section Common | |
36f63dca | 4162 | @subsubsection Input Section for Common Symbols |
252b5132 RH |
4163 | @cindex common symbol placement |
4164 | @cindex uninitialized data placement | |
4165 | A special notation is needed for common symbols, because in many object | |
4166 | file formats common symbols do not have a particular input section. The | |
4167 | linker treats common symbols as though they are in an input section | |
4168 | named @samp{COMMON}. | |
4169 | ||
4170 | You may use file names with the @samp{COMMON} section just as with any | |
4171 | other input sections. You can use this to place common symbols from a | |
4172 | particular input file in one section while common symbols from other | |
4173 | input files are placed in another section. | |
4174 | ||
4175 | In most cases, common symbols in input files will be placed in the | |
4176 | @samp{.bss} section in the output file. For example: | |
4177 | @smallexample | |
4178 | .bss @{ *(.bss) *(COMMON) @} | |
4179 | @end smallexample | |
4180 | ||
4181 | @cindex scommon section | |
4182 | @cindex small common symbols | |
4183 | Some object file formats have more than one type of common symbol. For | |
4184 | example, the MIPS ELF object file format distinguishes standard common | |
4185 | symbols and small common symbols. In this case, the linker will use a | |
4186 | different special section name for other types of common symbols. In | |
4187 | the case of MIPS ELF, the linker uses @samp{COMMON} for standard common | |
4188 | symbols and @samp{.scommon} for small common symbols. This permits you | |
4189 | to map the different types of common symbols into memory at different | |
4190 | locations. | |
4191 | ||
4192 | @cindex [COMMON] | |
4193 | You will sometimes see @samp{[COMMON]} in old linker scripts. This | |
4194 | notation is now considered obsolete. It is equivalent to | |
4195 | @samp{*(COMMON)}. | |
4196 | ||
4197 | @node Input Section Keep | |
36f63dca | 4198 | @subsubsection Input Section and Garbage Collection |
252b5132 RH |
4199 | @cindex KEEP |
4200 | @cindex garbage collection | |
4201 | When link-time garbage collection is in use (@samp{--gc-sections}), | |
a1ab1d2a | 4202 | it is often useful to mark sections that should not be eliminated. |
252b5132 RH |
4203 | This is accomplished by surrounding an input section's wildcard entry |
4204 | with @code{KEEP()}, as in @code{KEEP(*(.init))} or | |
bcaa7b3e | 4205 | @code{KEEP(SORT_BY_NAME(*)(.ctors))}. |
252b5132 RH |
4206 | |
4207 | @node Input Section Example | |
36f63dca | 4208 | @subsubsection Input Section Example |
252b5132 RH |
4209 | The following example is a complete linker script. It tells the linker |
4210 | to read all of the sections from file @file{all.o} and place them at the | |
4211 | start of output section @samp{outputa} which starts at location | |
4212 | @samp{0x10000}. All of section @samp{.input1} from file @file{foo.o} | |
4213 | follows immediately, in the same output section. All of section | |
4214 | @samp{.input2} from @file{foo.o} goes into output section | |
4215 | @samp{outputb}, followed by section @samp{.input1} from @file{foo1.o}. | |
4216 | All of the remaining @samp{.input1} and @samp{.input2} sections from any | |
4217 | files are written to output section @samp{outputc}. | |
4218 | ||
4219 | @smallexample | |
4220 | @group | |
4221 | SECTIONS @{ | |
4222 | outputa 0x10000 : | |
4223 | @{ | |
4224 | all.o | |
4225 | foo.o (.input1) | |
4226 | @} | |
36f63dca NC |
4227 | @end group |
4228 | @group | |
252b5132 RH |
4229 | outputb : |
4230 | @{ | |
4231 | foo.o (.input2) | |
4232 | foo1.o (.input1) | |
4233 | @} | |
36f63dca NC |
4234 | @end group |
4235 | @group | |
252b5132 RH |
4236 | outputc : |
4237 | @{ | |
4238 | *(.input1) | |
4239 | *(.input2) | |
4240 | @} | |
4241 | @} | |
4242 | @end group | |
a1ab1d2a | 4243 | @end smallexample |
252b5132 RH |
4244 | |
4245 | @node Output Section Data | |
36f63dca | 4246 | @subsection Output Section Data |
252b5132 RH |
4247 | @cindex data |
4248 | @cindex section data | |
4249 | @cindex output section data | |
4250 | @kindex BYTE(@var{expression}) | |
4251 | @kindex SHORT(@var{expression}) | |
4252 | @kindex LONG(@var{expression}) | |
4253 | @kindex QUAD(@var{expression}) | |
4254 | @kindex SQUAD(@var{expression}) | |
4255 | You can include explicit bytes of data in an output section by using | |
4256 | @code{BYTE}, @code{SHORT}, @code{LONG}, @code{QUAD}, or @code{SQUAD} as | |
4257 | an output section command. Each keyword is followed by an expression in | |
4258 | parentheses providing the value to store (@pxref{Expressions}). The | |
4259 | value of the expression is stored at the current value of the location | |
4260 | counter. | |
4261 | ||
4262 | The @code{BYTE}, @code{SHORT}, @code{LONG}, and @code{QUAD} commands | |
4263 | store one, two, four, and eight bytes (respectively). After storing the | |
4264 | bytes, the location counter is incremented by the number of bytes | |
4265 | stored. | |
4266 | ||
4267 | For example, this will store the byte 1 followed by the four byte value | |
4268 | of the symbol @samp{addr}: | |
4269 | @smallexample | |
4270 | BYTE(1) | |
4271 | LONG(addr) | |
4272 | @end smallexample | |
4273 | ||
4274 | When using a 64 bit host or target, @code{QUAD} and @code{SQUAD} are the | |
4275 | same; they both store an 8 byte, or 64 bit, value. When both host and | |
4276 | target are 32 bits, an expression is computed as 32 bits. In this case | |
4277 | @code{QUAD} stores a 32 bit value zero extended to 64 bits, and | |
4278 | @code{SQUAD} stores a 32 bit value sign extended to 64 bits. | |
4279 | ||
4280 | If the object file format of the output file has an explicit endianness, | |
4281 | which is the normal case, the value will be stored in that endianness. | |
4282 | When the object file format does not have an explicit endianness, as is | |
4283 | true of, for example, S-records, the value will be stored in the | |
4284 | endianness of the first input object file. | |
4285 | ||
36f63dca | 4286 | Note---these commands only work inside a section description and not |
2b5fc1f5 NC |
4287 | between them, so the following will produce an error from the linker: |
4288 | @smallexample | |
4289 | SECTIONS @{@ .text : @{@ *(.text) @}@ LONG(1) .data : @{@ *(.data) @}@ @}@ | |
4290 | @end smallexample | |
4291 | whereas this will work: | |
4292 | @smallexample | |
4293 | SECTIONS @{@ .text : @{@ *(.text) ; LONG(1) @}@ .data : @{@ *(.data) @}@ @}@ | |
4294 | @end smallexample | |
4295 | ||
252b5132 RH |
4296 | @kindex FILL(@var{expression}) |
4297 | @cindex holes, filling | |
4298 | @cindex unspecified memory | |
4299 | You may use the @code{FILL} command to set the fill pattern for the | |
4300 | current section. It is followed by an expression in parentheses. Any | |
4301 | otherwise unspecified regions of memory within the section (for example, | |
4302 | gaps left due to the required alignment of input sections) are filled | |
a139d329 | 4303 | with the value of the expression, repeated as |
252b5132 RH |
4304 | necessary. A @code{FILL} statement covers memory locations after the |
4305 | point at which it occurs in the section definition; by including more | |
4306 | than one @code{FILL} statement, you can have different fill patterns in | |
4307 | different parts of an output section. | |
4308 | ||
4309 | This example shows how to fill unspecified regions of memory with the | |
563e308f | 4310 | value @samp{0x90}: |
252b5132 | 4311 | @smallexample |
563e308f | 4312 | FILL(0x90909090) |
252b5132 RH |
4313 | @end smallexample |
4314 | ||
4315 | The @code{FILL} command is similar to the @samp{=@var{fillexp}} output | |
9673c93c | 4316 | section attribute, but it only affects the |
252b5132 RH |
4317 | part of the section following the @code{FILL} command, rather than the |
4318 | entire section. If both are used, the @code{FILL} command takes | |
9673c93c | 4319 | precedence. @xref{Output Section Fill}, for details on the fill |
a139d329 | 4320 | expression. |
252b5132 RH |
4321 | |
4322 | @node Output Section Keywords | |
36f63dca | 4323 | @subsection Output Section Keywords |
252b5132 RH |
4324 | There are a couple of keywords which can appear as output section |
4325 | commands. | |
4326 | ||
4327 | @table @code | |
4328 | @kindex CREATE_OBJECT_SYMBOLS | |
4329 | @cindex input filename symbols | |
4330 | @cindex filename symbols | |
4331 | @item CREATE_OBJECT_SYMBOLS | |
4332 | The command tells the linker to create a symbol for each input file. | |
4333 | The name of each symbol will be the name of the corresponding input | |
4334 | file. The section of each symbol will be the output section in which | |
4335 | the @code{CREATE_OBJECT_SYMBOLS} command appears. | |
4336 | ||
4337 | This is conventional for the a.out object file format. It is not | |
4338 | normally used for any other object file format. | |
4339 | ||
4340 | @kindex CONSTRUCTORS | |
4341 | @cindex C++ constructors, arranging in link | |
4342 | @cindex constructors, arranging in link | |
4343 | @item CONSTRUCTORS | |
4344 | When linking using the a.out object file format, the linker uses an | |
4345 | unusual set construct to support C++ global constructors and | |
4346 | destructors. When linking object file formats which do not support | |
4347 | arbitrary sections, such as ECOFF and XCOFF, the linker will | |
4348 | automatically recognize C++ global constructors and destructors by name. | |
4349 | For these object file formats, the @code{CONSTRUCTORS} command tells the | |
4350 | linker to place constructor information in the output section where the | |
4351 | @code{CONSTRUCTORS} command appears. The @code{CONSTRUCTORS} command is | |
4352 | ignored for other object file formats. | |
4353 | ||
4354 | The symbol @w{@code{__CTOR_LIST__}} marks the start of the global | |
7e69709c AM |
4355 | constructors, and the symbol @w{@code{__CTOR_END__}} marks the end. |
4356 | Similarly, @w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_END__}} mark | |
4357 | the start and end of the global destructors. The | |
252b5132 RH |
4358 | first word in the list is the number of entries, followed by the address |
4359 | of each constructor or destructor, followed by a zero word. The | |
4360 | compiler must arrange to actually run the code. For these object file | |
4361 | formats @sc{gnu} C++ normally calls constructors from a subroutine | |
4362 | @code{__main}; a call to @code{__main} is automatically inserted into | |
4363 | the startup code for @code{main}. @sc{gnu} C++ normally runs | |
4364 | destructors either by using @code{atexit}, or directly from the function | |
4365 | @code{exit}. | |
4366 | ||
4367 | For object file formats such as @code{COFF} or @code{ELF} which support | |
4368 | arbitrary section names, @sc{gnu} C++ will normally arrange to put the | |
4369 | addresses of global constructors and destructors into the @code{.ctors} | |
4370 | and @code{.dtors} sections. Placing the following sequence into your | |
4371 | linker script will build the sort of table which the @sc{gnu} C++ | |
4372 | runtime code expects to see. | |
4373 | ||
4374 | @smallexample | |
4375 | __CTOR_LIST__ = .; | |
4376 | LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) | |
4377 | *(.ctors) | |
4378 | LONG(0) | |
4379 | __CTOR_END__ = .; | |
4380 | __DTOR_LIST__ = .; | |
4381 | LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) | |
4382 | *(.dtors) | |
4383 | LONG(0) | |
4384 | __DTOR_END__ = .; | |
4385 | @end smallexample | |
4386 | ||
4387 | If you are using the @sc{gnu} C++ support for initialization priority, | |
4388 | which provides some control over the order in which global constructors | |
4389 | are run, you must sort the constructors at link time to ensure that they | |
4390 | are executed in the correct order. When using the @code{CONSTRUCTORS} | |
bcaa7b3e L |
4391 | command, use @samp{SORT_BY_NAME(CONSTRUCTORS)} instead. When using the |
4392 | @code{.ctors} and @code{.dtors} sections, use @samp{*(SORT_BY_NAME(.ctors))} and | |
4393 | @samp{*(SORT_BY_NAME(.dtors))} instead of just @samp{*(.ctors)} and | |
252b5132 RH |
4394 | @samp{*(.dtors)}. |
4395 | ||
4396 | Normally the compiler and linker will handle these issues automatically, | |
4397 | and you will not need to concern yourself with them. However, you may | |
4398 | need to consider this if you are using C++ and writing your own linker | |
4399 | scripts. | |
4400 | ||
4401 | @end table | |
4402 | ||
4403 | @node Output Section Discarding | |
36f63dca | 4404 | @subsection Output Section Discarding |
252b5132 RH |
4405 | @cindex discarding sections |
4406 | @cindex sections, discarding | |
4407 | @cindex removing sections | |
74541ad4 AM |
4408 | The linker will not create output sections with no contents. This is |
4409 | for convenience when referring to input sections that may or may not | |
4410 | be present in any of the input files. For example: | |
252b5132 | 4411 | @smallexample |
49c13adb | 4412 | .foo : @{ *(.foo) @} |
252b5132 RH |
4413 | @end smallexample |
4414 | @noindent | |
4415 | will only create a @samp{.foo} section in the output file if there is a | |
74541ad4 AM |
4416 | @samp{.foo} section in at least one input file, and if the input |
4417 | sections are not all empty. Other link script directives that allocate | |
4418 | space in an output section will also create the output section. | |
4419 | ||
a0976ea4 | 4420 | The linker will ignore address assignments (@pxref{Output Section Address}) |
74541ad4 AM |
4421 | on discarded output sections, except when the linker script defines |
4422 | symbols in the output section. In that case the linker will obey | |
a0976ea4 AM |
4423 | the address assignments, possibly advancing dot even though the |
4424 | section is discarded. | |
252b5132 RH |
4425 | |
4426 | @cindex /DISCARD/ | |
4427 | The special output section name @samp{/DISCARD/} may be used to discard | |
4428 | input sections. Any input sections which are assigned to an output | |
4429 | section named @samp{/DISCARD/} are not included in the output file. | |
4430 | ||
4431 | @node Output Section Attributes | |
36f63dca | 4432 | @subsection Output Section Attributes |
252b5132 RH |
4433 | @cindex output section attributes |
4434 | We showed above that the full description of an output section looked | |
4435 | like this: | |
0c71d759 | 4436 | |
252b5132 | 4437 | @smallexample |
a1ab1d2a | 4438 | @group |
7e7d5768 | 4439 | @var{section} [@var{address}] [(@var{type})] : |
0c71d759 NC |
4440 | [AT(@var{lma})] |
4441 | [ALIGN(@var{section_align})] | |
4442 | [SUBALIGN(@var{subsection_align})] | |
4443 | [@var{constraint}] | |
252b5132 RH |
4444 | @{ |
4445 | @var{output-section-command} | |
4446 | @var{output-section-command} | |
4447 | @dots{} | |
562d3460 | 4448 | @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}] |
252b5132 RH |
4449 | @end group |
4450 | @end smallexample | |
0c71d759 | 4451 | |
252b5132 RH |
4452 | We've already described @var{section}, @var{address}, and |
4453 | @var{output-section-command}. In this section we will describe the | |
4454 | remaining section attributes. | |
4455 | ||
a1ab1d2a | 4456 | @menu |
252b5132 RH |
4457 | * Output Section Type:: Output section type |
4458 | * Output Section LMA:: Output section LMA | |
bbf115d3 | 4459 | * Forced Output Alignment:: Forced Output Alignment |
7e7d5768 | 4460 | * Forced Input Alignment:: Forced Input Alignment |
0c71d759 | 4461 | * Output Section Constraint:: Output section constraint |
252b5132 RH |
4462 | * Output Section Region:: Output section region |
4463 | * Output Section Phdr:: Output section phdr | |
4464 | * Output Section Fill:: Output section fill | |
4465 | @end menu | |
4466 | ||
4467 | @node Output Section Type | |
36f63dca | 4468 | @subsubsection Output Section Type |
252b5132 RH |
4469 | Each output section may have a type. The type is a keyword in |
4470 | parentheses. The following types are defined: | |
4471 | ||
4472 | @table @code | |
4473 | @item NOLOAD | |
4474 | The section should be marked as not loadable, so that it will not be | |
4475 | loaded into memory when the program is run. | |
4476 | @item DSECT | |
4477 | @itemx COPY | |
4478 | @itemx INFO | |
4479 | @itemx OVERLAY | |
4480 | These type names are supported for backward compatibility, and are | |
4481 | rarely used. They all have the same effect: the section should be | |
4482 | marked as not allocatable, so that no memory is allocated for the | |
4483 | section when the program is run. | |
4484 | @end table | |
4485 | ||
4486 | @kindex NOLOAD | |
4487 | @cindex prevent unnecessary loading | |
4488 | @cindex loading, preventing | |
4489 | The linker normally sets the attributes of an output section based on | |
4490 | the input sections which map into it. You can override this by using | |
4491 | the section type. For example, in the script sample below, the | |
4492 | @samp{ROM} section is addressed at memory location @samp{0} and does not | |
2e76e85a | 4493 | need to be loaded when the program is run. |
252b5132 RH |
4494 | @smallexample |
4495 | @group | |
4496 | SECTIONS @{ | |
4497 | ROM 0 (NOLOAD) : @{ @dots{} @} | |
4498 | @dots{} | |
4499 | @} | |
4500 | @end group | |
4501 | @end smallexample | |
4502 | ||
4503 | @node Output Section LMA | |
36f63dca | 4504 | @subsubsection Output Section LMA |
562d3460 | 4505 | @kindex AT>@var{lma_region} |
252b5132 RH |
4506 | @kindex AT(@var{lma}) |
4507 | @cindex load address | |
4508 | @cindex section load address | |
4509 | Every section has a virtual address (VMA) and a load address (LMA); see | |
ea5cae92 NC |
4510 | @ref{Basic Script Concepts}. The virtual address is specified by the |
4511 | @pxref{Output Section Address} described earlier. The load address is | |
4512 | specified by the @code{AT} or @code{AT>} keywords. Specifying a load | |
4513 | address is optional. | |
6bdafbeb | 4514 | |
ea5cae92 NC |
4515 | The @code{AT} keyword takes an expression as an argument. This |
4516 | specifies the exact load address of the section. The @code{AT>} keyword | |
4517 | takes the name of a memory region as an argument. @xref{MEMORY}. The | |
4518 | load address of the section is set to the next free address in the | |
4519 | region, aligned to the section's alignment requirements. | |
dc0b6aa0 AM |
4520 | |
4521 | If neither @code{AT} nor @code{AT>} is specified for an allocatable | |
ea5cae92 NC |
4522 | section, the linker will use the following heuristic to determine the |
4523 | load address: | |
4524 | ||
4525 | @itemize @bullet | |
4526 | @item | |
4527 | If the section has a specific VMA address, then this is used as | |
4528 | the LMA address as well. | |
4529 | ||
4530 | @item | |
4531 | If the section is not allocatable then its LMA is set to its VMA. | |
4532 | ||
4533 | @item | |
4534 | Otherwise if a memory region can be found that is compatible | |
4535 | with the current section, and this region contains at least one | |
4536 | section, then the LMA is set so the difference between the | |
4537 | VMA and LMA is the same as the difference between the VMA and LMA of | |
4538 | the last section in the located region. | |
4539 | ||
4540 | @item | |
4541 | If no memory regions have been declared then a default region | |
4542 | that covers the entire address space is used in the previous step. | |
4543 | ||
4544 | @item | |
4545 | If no suitable region could be found, or there was no previous | |
4546 | section then the LMA is set equal to the VMA. | |
4547 | @end itemize | |
252b5132 RH |
4548 | |
4549 | @cindex ROM initialized data | |
4550 | @cindex initialized data in ROM | |
4551 | This feature is designed to make it easy to build a ROM image. For | |
4552 | example, the following linker script creates three output sections: one | |
4553 | called @samp{.text}, which starts at @code{0x1000}, one called | |
4554 | @samp{.mdata}, which is loaded at the end of the @samp{.text} section | |
4555 | even though its VMA is @code{0x2000}, and one called @samp{.bss} to hold | |
4556 | uninitialized data at address @code{0x3000}. The symbol @code{_data} is | |
4557 | defined with the value @code{0x2000}, which shows that the location | |
4558 | counter holds the VMA value, not the LMA value. | |
4559 | ||
4560 | @smallexample | |
4561 | @group | |
4562 | SECTIONS | |
4563 | @{ | |
4564 | .text 0x1000 : @{ *(.text) _etext = . ; @} | |
a1ab1d2a | 4565 | .mdata 0x2000 : |
252b5132 RH |
4566 | AT ( ADDR (.text) + SIZEOF (.text) ) |
4567 | @{ _data = . ; *(.data); _edata = . ; @} | |
4568 | .bss 0x3000 : | |
4569 | @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@} | |
4570 | @} | |
4571 | @end group | |
4572 | @end smallexample | |
4573 | ||
4574 | The run-time initialization code for use with a program generated with | |
4575 | this linker script would include something like the following, to copy | |
4576 | the initialized data from the ROM image to its runtime address. Notice | |
4577 | how this code takes advantage of the symbols defined by the linker | |
4578 | script. | |
4579 | ||
4580 | @smallexample | |
4581 | @group | |
4582 | extern char _etext, _data, _edata, _bstart, _bend; | |
4583 | char *src = &_etext; | |
4584 | char *dst = &_data; | |
4585 | ||
ea5cae92 NC |
4586 | /* ROM has data at end of text; copy it. */ |
4587 | while (dst < &_edata) | |
252b5132 | 4588 | *dst++ = *src++; |
252b5132 | 4589 | |
ea5cae92 | 4590 | /* Zero bss. */ |
252b5132 RH |
4591 | for (dst = &_bstart; dst< &_bend; dst++) |
4592 | *dst = 0; | |
4593 | @end group | |
4594 | @end smallexample | |
4595 | ||
bbf115d3 L |
4596 | @node Forced Output Alignment |
4597 | @subsubsection Forced Output Alignment | |
4598 | @kindex ALIGN(@var{section_align}) | |
4599 | @cindex forcing output section alignment | |
4600 | @cindex output section alignment | |
1eec346e NC |
4601 | You can increase an output section's alignment by using ALIGN. As an |
4602 | alternative you can force the output section alignment to the maximum alignment | |
4603 | of all its input sections with ALIGN_WITH_INPUT. The alignment forced by | |
4604 | ALIGN_WITH_INPUT is used even in case the load and virtual memory regions are | |
4605 | different. | |
bbf115d3 | 4606 | |
7e7d5768 AM |
4607 | @node Forced Input Alignment |
4608 | @subsubsection Forced Input Alignment | |
4609 | @kindex SUBALIGN(@var{subsection_align}) | |
4610 | @cindex forcing input section alignment | |
4611 | @cindex input section alignment | |
4612 | You can force input section alignment within an output section by using | |
4613 | SUBALIGN. The value specified overrides any alignment given by input | |
4614 | sections, whether larger or smaller. | |
4615 | ||
0c71d759 NC |
4616 | @node Output Section Constraint |
4617 | @subsubsection Output Section Constraint | |
4618 | @kindex ONLY_IF_RO | |
4619 | @kindex ONLY_IF_RW | |
4620 | @cindex constraints on output sections | |
4621 | You can specify that an output section should only be created if all | |
4622 | of its input sections are read-only or all of its input sections are | |
4623 | read-write by using the keyword @code{ONLY_IF_RO} and | |
4624 | @code{ONLY_IF_RW} respectively. | |
4625 | ||
252b5132 | 4626 | @node Output Section Region |
36f63dca | 4627 | @subsubsection Output Section Region |
252b5132 RH |
4628 | @kindex >@var{region} |
4629 | @cindex section, assigning to memory region | |
4630 | @cindex memory regions and sections | |
4631 | You can assign a section to a previously defined region of memory by | |
4632 | using @samp{>@var{region}}. @xref{MEMORY}. | |
4633 | ||
4634 | Here is a simple example: | |
4635 | @smallexample | |
4636 | @group | |
4637 | MEMORY @{ rom : ORIGIN = 0x1000, LENGTH = 0x1000 @} | |
4638 | SECTIONS @{ ROM : @{ *(.text) @} >rom @} | |
4639 | @end group | |
4640 | @end smallexample | |
4641 | ||
4642 | @node Output Section Phdr | |
36f63dca | 4643 | @subsubsection Output Section Phdr |
252b5132 RH |
4644 | @kindex :@var{phdr} |
4645 | @cindex section, assigning to program header | |
4646 | @cindex program headers and sections | |
4647 | You can assign a section to a previously defined program segment by | |
4648 | using @samp{:@var{phdr}}. @xref{PHDRS}. If a section is assigned to | |
4649 | one or more segments, then all subsequent allocated sections will be | |
4650 | assigned to those segments as well, unless they use an explicitly | |
4651 | @code{:@var{phdr}} modifier. You can use @code{:NONE} to tell the | |
4652 | linker to not put the section in any segment at all. | |
4653 | ||
4654 | Here is a simple example: | |
4655 | @smallexample | |
4656 | @group | |
4657 | PHDRS @{ text PT_LOAD ; @} | |
4658 | SECTIONS @{ .text : @{ *(.text) @} :text @} | |
4659 | @end group | |
4660 | @end smallexample | |
4661 | ||
4662 | @node Output Section Fill | |
36f63dca | 4663 | @subsubsection Output Section Fill |
252b5132 RH |
4664 | @kindex =@var{fillexp} |
4665 | @cindex section fill pattern | |
4666 | @cindex fill pattern, entire section | |
4667 | You can set the fill pattern for an entire section by using | |
4668 | @samp{=@var{fillexp}}. @var{fillexp} is an expression | |
4669 | (@pxref{Expressions}). Any otherwise unspecified regions of memory | |
4670 | within the output section (for example, gaps left due to the required | |
a139d329 AM |
4671 | alignment of input sections) will be filled with the value, repeated as |
4672 | necessary. If the fill expression is a simple hex number, ie. a string | |
9673c93c | 4673 | of hex digit starting with @samp{0x} and without a trailing @samp{k} or @samp{M}, then |
a139d329 AM |
4674 | an arbitrarily long sequence of hex digits can be used to specify the |
4675 | fill pattern; Leading zeros become part of the pattern too. For all | |
9673c93c | 4676 | other cases, including extra parentheses or a unary @code{+}, the fill |
a139d329 AM |
4677 | pattern is the four least significant bytes of the value of the |
4678 | expression. In all cases, the number is big-endian. | |
252b5132 RH |
4679 | |
4680 | You can also change the fill value with a @code{FILL} command in the | |
9673c93c | 4681 | output section commands; (@pxref{Output Section Data}). |
252b5132 RH |
4682 | |
4683 | Here is a simple example: | |
4684 | @smallexample | |
4685 | @group | |
563e308f | 4686 | SECTIONS @{ .text : @{ *(.text) @} =0x90909090 @} |
252b5132 RH |
4687 | @end group |
4688 | @end smallexample | |
4689 | ||
4690 | @node Overlay Description | |
36f63dca | 4691 | @subsection Overlay Description |
252b5132 RH |
4692 | @kindex OVERLAY |
4693 | @cindex overlays | |
4694 | An overlay description provides an easy way to describe sections which | |
4695 | are to be loaded as part of a single memory image but are to be run at | |
4696 | the same memory address. At run time, some sort of overlay manager will | |
4697 | copy the overlaid sections in and out of the runtime memory address as | |
4698 | required, perhaps by simply manipulating addressing bits. This approach | |
4699 | can be useful, for example, when a certain region of memory is faster | |
4700 | than another. | |
4701 | ||
4702 | Overlays are described using the @code{OVERLAY} command. The | |
4703 | @code{OVERLAY} command is used within a @code{SECTIONS} command, like an | |
4704 | output section description. The full syntax of the @code{OVERLAY} | |
4705 | command is as follows: | |
4706 | @smallexample | |
4707 | @group | |
4708 | OVERLAY [@var{start}] : [NOCROSSREFS] [AT ( @var{ldaddr} )] | |
4709 | @{ | |
4710 | @var{secname1} | |
4711 | @{ | |
4712 | @var{output-section-command} | |
4713 | @var{output-section-command} | |
4714 | @dots{} | |
4715 | @} [:@var{phdr}@dots{}] [=@var{fill}] | |
4716 | @var{secname2} | |
4717 | @{ | |
4718 | @var{output-section-command} | |
4719 | @var{output-section-command} | |
4720 | @dots{} | |
4721 | @} [:@var{phdr}@dots{}] [=@var{fill}] | |
4722 | @dots{} | |
4723 | @} [>@var{region}] [:@var{phdr}@dots{}] [=@var{fill}] | |
4724 | @end group | |
4725 | @end smallexample | |
4726 | ||
4727 | Everything is optional except @code{OVERLAY} (a keyword), and each | |
4728 | section must have a name (@var{secname1} and @var{secname2} above). The | |
4729 | section definitions within the @code{OVERLAY} construct are identical to | |
11e7fd74 | 4730 | those within the general @code{SECTIONS} construct (@pxref{SECTIONS}), |
252b5132 RH |
4731 | except that no addresses and no memory regions may be defined for |
4732 | sections within an @code{OVERLAY}. | |
4733 | ||
4734 | The sections are all defined with the same starting address. The load | |
4735 | addresses of the sections are arranged such that they are consecutive in | |
4736 | memory starting at the load address used for the @code{OVERLAY} as a | |
4737 | whole (as with normal section definitions, the load address is optional, | |
4738 | and defaults to the start address; the start address is also optional, | |
4739 | and defaults to the current value of the location counter). | |
4740 | ||
56dd11f0 NC |
4741 | If the @code{NOCROSSREFS} keyword is used, and there are any |
4742 | references among the sections, the linker will report an error. Since | |
4743 | the sections all run at the same address, it normally does not make | |
4744 | sense for one section to refer directly to another. | |
4745 | @xref{Miscellaneous Commands, NOCROSSREFS}. | |
252b5132 RH |
4746 | |
4747 | For each section within the @code{OVERLAY}, the linker automatically | |
34711ca3 | 4748 | provides two symbols. The symbol @code{__load_start_@var{secname}} is |
252b5132 RH |
4749 | defined as the starting load address of the section. The symbol |
4750 | @code{__load_stop_@var{secname}} is defined as the final load address of | |
4751 | the section. Any characters within @var{secname} which are not legal | |
4752 | within C identifiers are removed. C (or assembler) code may use these | |
4753 | symbols to move the overlaid sections around as necessary. | |
4754 | ||
4755 | At the end of the overlay, the value of the location counter is set to | |
4756 | the start address of the overlay plus the size of the largest section. | |
4757 | ||
4758 | Here is an example. Remember that this would appear inside a | |
4759 | @code{SECTIONS} construct. | |
4760 | @smallexample | |
4761 | @group | |
4762 | OVERLAY 0x1000 : AT (0x4000) | |
4763 | @{ | |
4764 | .text0 @{ o1/*.o(.text) @} | |
4765 | .text1 @{ o2/*.o(.text) @} | |
4766 | @} | |
4767 | @end group | |
4768 | @end smallexample | |
4769 | @noindent | |
4770 | This will define both @samp{.text0} and @samp{.text1} to start at | |
4771 | address 0x1000. @samp{.text0} will be loaded at address 0x4000, and | |
4772 | @samp{.text1} will be loaded immediately after @samp{.text0}. The | |
34711ca3 | 4773 | following symbols will be defined if referenced: @code{__load_start_text0}, |
252b5132 RH |
4774 | @code{__load_stop_text0}, @code{__load_start_text1}, |
4775 | @code{__load_stop_text1}. | |
4776 | ||
4777 | C code to copy overlay @code{.text1} into the overlay area might look | |
4778 | like the following. | |
4779 | ||
4780 | @smallexample | |
4781 | @group | |
4782 | extern char __load_start_text1, __load_stop_text1; | |
4783 | memcpy ((char *) 0x1000, &__load_start_text1, | |
4784 | &__load_stop_text1 - &__load_start_text1); | |
4785 | @end group | |
4786 | @end smallexample | |
4787 | ||
4788 | Note that the @code{OVERLAY} command is just syntactic sugar, since | |
4789 | everything it does can be done using the more basic commands. The above | |
4790 | example could have been written identically as follows. | |
4791 | ||
4792 | @smallexample | |
4793 | @group | |
4794 | .text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @} | |
34711ca3 AM |
4795 | PROVIDE (__load_start_text0 = LOADADDR (.text0)); |
4796 | PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0)); | |
252b5132 | 4797 | .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @} |
34711ca3 AM |
4798 | PROVIDE (__load_start_text1 = LOADADDR (.text1)); |
4799 | PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1)); | |
252b5132 RH |
4800 | . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1)); |
4801 | @end group | |
4802 | @end smallexample | |
4803 | ||
4804 | @node MEMORY | |
36f63dca | 4805 | @section MEMORY Command |
252b5132 RH |
4806 | @kindex MEMORY |
4807 | @cindex memory regions | |
4808 | @cindex regions of memory | |
4809 | @cindex allocating memory | |
4810 | @cindex discontinuous memory | |
4811 | The linker's default configuration permits allocation of all available | |
4812 | memory. You can override this by using the @code{MEMORY} command. | |
4813 | ||
4814 | The @code{MEMORY} command describes the location and size of blocks of | |
4815 | memory in the target. You can use it to describe which memory regions | |
4816 | may be used by the linker, and which memory regions it must avoid. You | |
4817 | can then assign sections to particular memory regions. The linker will | |
4818 | set section addresses based on the memory regions, and will warn about | |
4819 | regions that become too full. The linker will not shuffle sections | |
4820 | around to fit into the available regions. | |
4821 | ||
4822 | A linker script may contain at most one use of the @code{MEMORY} | |
4823 | command. However, you can define as many blocks of memory within it as | |
4824 | you wish. The syntax is: | |
4825 | @smallexample | |
4826 | @group | |
a1ab1d2a | 4827 | MEMORY |
252b5132 RH |
4828 | @{ |
4829 | @var{name} [(@var{attr})] : ORIGIN = @var{origin}, LENGTH = @var{len} | |
4830 | @dots{} | |
4831 | @} | |
4832 | @end group | |
4833 | @end smallexample | |
4834 | ||
4835 | The @var{name} is a name used in the linker script to refer to the | |
4836 | region. The region name has no meaning outside of the linker script. | |
4837 | Region names are stored in a separate name space, and will not conflict | |
4838 | with symbol names, file names, or section names. Each memory region | |
4a93e180 NC |
4839 | must have a distinct name within the @code{MEMORY} command. However you can |
4840 | add later alias names to existing memory regions with the @ref{REGION_ALIAS} | |
9d5777a3 | 4841 | command. |
252b5132 RH |
4842 | |
4843 | @cindex memory region attributes | |
4844 | The @var{attr} string is an optional list of attributes that specify | |
4845 | whether to use a particular memory region for an input section which is | |
4846 | not explicitly mapped in the linker script. As described in | |
4847 | @ref{SECTIONS}, if you do not specify an output section for some input | |
4848 | section, the linker will create an output section with the same name as | |
4849 | the input section. If you define region attributes, the linker will use | |
4850 | them to select the memory region for the output section that it creates. | |
4851 | ||
4852 | The @var{attr} string must consist only of the following characters: | |
4853 | @table @samp | |
4854 | @item R | |
4855 | Read-only section | |
4856 | @item W | |
4857 | Read/write section | |
4858 | @item X | |
4859 | Executable section | |
4860 | @item A | |
4861 | Allocatable section | |
4862 | @item I | |
4863 | Initialized section | |
4864 | @item L | |
4865 | Same as @samp{I} | |
4866 | @item ! | |
c09e9a8c | 4867 | Invert the sense of any of the attributes that follow |
252b5132 RH |
4868 | @end table |
4869 | ||
4870 | If a unmapped section matches any of the listed attributes other than | |
4871 | @samp{!}, it will be placed in the memory region. The @samp{!} | |
4872 | attribute reverses this test, so that an unmapped section will be placed | |
4873 | in the memory region only if it does not match any of the listed | |
4874 | attributes. | |
4875 | ||
4876 | @kindex ORIGIN = | |
4877 | @kindex o = | |
4878 | @kindex org = | |
9cd6d51a NC |
4879 | The @var{origin} is an numerical expression for the start address of |
4880 | the memory region. The expression must evaluate to a constant and it | |
4881 | cannot involve any symbols. The keyword @code{ORIGIN} may be | |
4882 | abbreviated to @code{org} or @code{o} (but not, for example, | |
4883 | @code{ORG}). | |
252b5132 RH |
4884 | |
4885 | @kindex LENGTH = | |
4886 | @kindex len = | |
4887 | @kindex l = | |
4888 | The @var{len} is an expression for the size in bytes of the memory | |
4889 | region. As with the @var{origin} expression, the expression must | |
9cd6d51a NC |
4890 | be numerical only and must evaluate to a constant. The keyword |
4891 | @code{LENGTH} may be abbreviated to @code{len} or @code{l}. | |
252b5132 RH |
4892 | |
4893 | In the following example, we specify that there are two memory regions | |
4894 | available for allocation: one starting at @samp{0} for 256 kilobytes, | |
4895 | and the other starting at @samp{0x40000000} for four megabytes. The | |
4896 | linker will place into the @samp{rom} memory region every section which | |
4897 | is not explicitly mapped into a memory region, and is either read-only | |
4898 | or executable. The linker will place other sections which are not | |
4899 | explicitly mapped into a memory region into the @samp{ram} memory | |
4900 | region. | |
4901 | ||
4902 | @smallexample | |
4903 | @group | |
a1ab1d2a | 4904 | MEMORY |
252b5132 RH |
4905 | @{ |
4906 | rom (rx) : ORIGIN = 0, LENGTH = 256K | |
4907 | ram (!rx) : org = 0x40000000, l = 4M | |
4908 | @} | |
4909 | @end group | |
4910 | @end smallexample | |
4911 | ||
4912 | Once you define a memory region, you can direct the linker to place | |
4913 | specific output sections into that memory region by using the | |
4914 | @samp{>@var{region}} output section attribute. For example, if you have | |
4915 | a memory region named @samp{mem}, you would use @samp{>mem} in the | |
4916 | output section definition. @xref{Output Section Region}. If no address | |
4917 | was specified for the output section, the linker will set the address to | |
4918 | the next available address within the memory region. If the combined | |
4919 | output sections directed to a memory region are too large for the | |
4920 | region, the linker will issue an error message. | |
4921 | ||
3ec57632 | 4922 | It is possible to access the origin and length of a memory in an |
c0065db7 | 4923 | expression via the @code{ORIGIN(@var{memory})} and |
3ec57632 NC |
4924 | @code{LENGTH(@var{memory})} functions: |
4925 | ||
4926 | @smallexample | |
4927 | @group | |
c0065db7 | 4928 | _fstack = ORIGIN(ram) + LENGTH(ram) - 4; |
3ec57632 NC |
4929 | @end group |
4930 | @end smallexample | |
4931 | ||
252b5132 RH |
4932 | @node PHDRS |
4933 | @section PHDRS Command | |
4934 | @kindex PHDRS | |
4935 | @cindex program headers | |
4936 | @cindex ELF program headers | |
4937 | @cindex program segments | |
4938 | @cindex segments, ELF | |
4939 | The ELF object file format uses @dfn{program headers}, also knows as | |
4940 | @dfn{segments}. The program headers describe how the program should be | |
4941 | loaded into memory. You can print them out by using the @code{objdump} | |
4942 | program with the @samp{-p} option. | |
4943 | ||
4944 | When you run an ELF program on a native ELF system, the system loader | |
4945 | reads the program headers in order to figure out how to load the | |
4946 | program. This will only work if the program headers are set correctly. | |
4947 | This manual does not describe the details of how the system loader | |
4948 | interprets program headers; for more information, see the ELF ABI. | |
4949 | ||
4950 | The linker will create reasonable program headers by default. However, | |
4951 | in some cases, you may need to specify the program headers more | |
4952 | precisely. You may use the @code{PHDRS} command for this purpose. When | |
4953 | the linker sees the @code{PHDRS} command in the linker script, it will | |
4954 | not create any program headers other than the ones specified. | |
4955 | ||
4956 | The linker only pays attention to the @code{PHDRS} command when | |
4957 | generating an ELF output file. In other cases, the linker will simply | |
4958 | ignore @code{PHDRS}. | |
4959 | ||
4960 | This is the syntax of the @code{PHDRS} command. The words @code{PHDRS}, | |
4961 | @code{FILEHDR}, @code{AT}, and @code{FLAGS} are keywords. | |
4962 | ||
4963 | @smallexample | |
4964 | @group | |
4965 | PHDRS | |
4966 | @{ | |
4967 | @var{name} @var{type} [ FILEHDR ] [ PHDRS ] [ AT ( @var{address} ) ] | |
4968 | [ FLAGS ( @var{flags} ) ] ; | |
4969 | @} | |
4970 | @end group | |
4971 | @end smallexample | |
4972 | ||
4973 | The @var{name} is used only for reference in the @code{SECTIONS} command | |
4974 | of the linker script. It is not put into the output file. Program | |
4975 | header names are stored in a separate name space, and will not conflict | |
4976 | with symbol names, file names, or section names. Each program header | |
5c1a3f0f NS |
4977 | must have a distinct name. The headers are processed in order and it |
4978 | is usual for them to map to sections in ascending load address order. | |
252b5132 RH |
4979 | |
4980 | Certain program header types describe segments of memory which the | |
4981 | system loader will load from the file. In the linker script, you | |
4982 | specify the contents of these segments by placing allocatable output | |
4983 | sections in the segments. You use the @samp{:@var{phdr}} output section | |
4984 | attribute to place a section in a particular segment. @xref{Output | |
4985 | Section Phdr}. | |
4986 | ||
4987 | It is normal to put certain sections in more than one segment. This | |
4988 | merely implies that one segment of memory contains another. You may | |
4989 | repeat @samp{:@var{phdr}}, using it once for each segment which should | |
4990 | contain the section. | |
4991 | ||
4992 | If you place a section in one or more segments using @samp{:@var{phdr}}, | |
4993 | then the linker will place all subsequent allocatable sections which do | |
4994 | not specify @samp{:@var{phdr}} in the same segments. This is for | |
4995 | convenience, since generally a whole set of contiguous sections will be | |
4996 | placed in a single segment. You can use @code{:NONE} to override the | |
4997 | default segment and tell the linker to not put the section in any | |
4998 | segment at all. | |
4999 | ||
5000 | @kindex FILEHDR | |
5001 | @kindex PHDRS | |
5c1a3f0f | 5002 | You may use the @code{FILEHDR} and @code{PHDRS} keywords after |
252b5132 RH |
5003 | the program header type to further describe the contents of the segment. |
5004 | The @code{FILEHDR} keyword means that the segment should include the ELF | |
5005 | file header. The @code{PHDRS} keyword means that the segment should | |
5c1a3f0f | 5006 | include the ELF program headers themselves. If applied to a loadable |
4100cea3 AM |
5007 | segment (@code{PT_LOAD}), all prior loadable segments must have one of |
5008 | these keywords. | |
252b5132 RH |
5009 | |
5010 | The @var{type} may be one of the following. The numbers indicate the | |
5011 | value of the keyword. | |
5012 | ||
5013 | @table @asis | |
5014 | @item @code{PT_NULL} (0) | |
5015 | Indicates an unused program header. | |
5016 | ||
5017 | @item @code{PT_LOAD} (1) | |
5018 | Indicates that this program header describes a segment to be loaded from | |
5019 | the file. | |
5020 | ||
5021 | @item @code{PT_DYNAMIC} (2) | |
5022 | Indicates a segment where dynamic linking information can be found. | |
5023 | ||
5024 | @item @code{PT_INTERP} (3) | |
5025 | Indicates a segment where the name of the program interpreter may be | |
5026 | found. | |
5027 | ||
5028 | @item @code{PT_NOTE} (4) | |
5029 | Indicates a segment holding note information. | |
5030 | ||
5031 | @item @code{PT_SHLIB} (5) | |
5032 | A reserved program header type, defined but not specified by the ELF | |
5033 | ABI. | |
5034 | ||
5035 | @item @code{PT_PHDR} (6) | |
5036 | Indicates a segment where the program headers may be found. | |
5037 | ||
5038 | @item @var{expression} | |
5039 | An expression giving the numeric type of the program header. This may | |
5040 | be used for types not defined above. | |
5041 | @end table | |
5042 | ||
5043 | You can specify that a segment should be loaded at a particular address | |
5044 | in memory by using an @code{AT} expression. This is identical to the | |
5045 | @code{AT} command used as an output section attribute (@pxref{Output | |
5046 | Section LMA}). The @code{AT} command for a program header overrides the | |
5047 | output section attribute. | |
5048 | ||
5049 | The linker will normally set the segment flags based on the sections | |
5050 | which comprise the segment. You may use the @code{FLAGS} keyword to | |
5051 | explicitly specify the segment flags. The value of @var{flags} must be | |
5052 | an integer. It is used to set the @code{p_flags} field of the program | |
5053 | header. | |
5054 | ||
5055 | Here is an example of @code{PHDRS}. This shows a typical set of program | |
5056 | headers used on a native ELF system. | |
5057 | ||
5058 | @example | |
5059 | @group | |
5060 | PHDRS | |
5061 | @{ | |
5062 | headers PT_PHDR PHDRS ; | |
5063 | interp PT_INTERP ; | |
5064 | text PT_LOAD FILEHDR PHDRS ; | |
5065 | data PT_LOAD ; | |
5066 | dynamic PT_DYNAMIC ; | |
5067 | @} | |
5068 | ||
5069 | SECTIONS | |
5070 | @{ | |
5071 | . = SIZEOF_HEADERS; | |
5072 | .interp : @{ *(.interp) @} :text :interp | |
5073 | .text : @{ *(.text) @} :text | |
5074 | .rodata : @{ *(.rodata) @} /* defaults to :text */ | |
5075 | @dots{} | |
5076 | . = . + 0x1000; /* move to a new page in memory */ | |
5077 | .data : @{ *(.data) @} :data | |
5078 | .dynamic : @{ *(.dynamic) @} :data :dynamic | |
5079 | @dots{} | |
5080 | @} | |
5081 | @end group | |
5082 | @end example | |
5083 | ||
5084 | @node VERSION | |
5085 | @section VERSION Command | |
5086 | @kindex VERSION @{script text@} | |
5087 | @cindex symbol versions | |
5088 | @cindex version script | |
5089 | @cindex versions of symbols | |
5090 | The linker supports symbol versions when using ELF. Symbol versions are | |
5091 | only useful when using shared libraries. The dynamic linker can use | |
5092 | symbol versions to select a specific version of a function when it runs | |
5093 | a program that may have been linked against an earlier version of the | |
5094 | shared library. | |
5095 | ||
5096 | You can include a version script directly in the main linker script, or | |
5097 | you can supply the version script as an implicit linker script. You can | |
5098 | also use the @samp{--version-script} linker option. | |
5099 | ||
5100 | The syntax of the @code{VERSION} command is simply | |
5101 | @smallexample | |
5102 | VERSION @{ version-script-commands @} | |
5103 | @end smallexample | |
5104 | ||
5105 | The format of the version script commands is identical to that used by | |
5106 | Sun's linker in Solaris 2.5. The version script defines a tree of | |
5107 | version nodes. You specify the node names and interdependencies in the | |
5108 | version script. You can specify which symbols are bound to which | |
5109 | version nodes, and you can reduce a specified set of symbols to local | |
5110 | scope so that they are not globally visible outside of the shared | |
5111 | library. | |
5112 | ||
5113 | The easiest way to demonstrate the version script language is with a few | |
5114 | examples. | |
5115 | ||
5116 | @smallexample | |
5117 | VERS_1.1 @{ | |
5118 | global: | |
5119 | foo1; | |
5120 | local: | |
a1ab1d2a UD |
5121 | old*; |
5122 | original*; | |
5123 | new*; | |
252b5132 RH |
5124 | @}; |
5125 | ||
5126 | VERS_1.2 @{ | |
5127 | foo2; | |
5128 | @} VERS_1.1; | |
5129 | ||
5130 | VERS_2.0 @{ | |
5131 | bar1; bar2; | |
c0065db7 | 5132 | extern "C++" @{ |
86043bbb | 5133 | ns::*; |
bb1515f2 MF |
5134 | "f(int, double)"; |
5135 | @}; | |
252b5132 RH |
5136 | @} VERS_1.2; |
5137 | @end smallexample | |
5138 | ||
5139 | This example version script defines three version nodes. The first | |
5140 | version node defined is @samp{VERS_1.1}; it has no other dependencies. | |
5141 | The script binds the symbol @samp{foo1} to @samp{VERS_1.1}. It reduces | |
5142 | a number of symbols to local scope so that they are not visible outside | |
313e35ee AM |
5143 | of the shared library; this is done using wildcard patterns, so that any |
5144 | symbol whose name begins with @samp{old}, @samp{original}, or @samp{new} | |
5145 | is matched. The wildcard patterns available are the same as those used | |
5146 | in the shell when matching filenames (also known as ``globbing''). | |
86043bbb MM |
5147 | However, if you specify the symbol name inside double quotes, then the |
5148 | name is treated as literal, rather than as a glob pattern. | |
252b5132 RH |
5149 | |
5150 | Next, the version script defines node @samp{VERS_1.2}. This node | |
5151 | depends upon @samp{VERS_1.1}. The script binds the symbol @samp{foo2} | |
5152 | to the version node @samp{VERS_1.2}. | |
5153 | ||
5154 | Finally, the version script defines node @samp{VERS_2.0}. This node | |
5155 | depends upon @samp{VERS_1.2}. The scripts binds the symbols @samp{bar1} | |
5156 | and @samp{bar2} are bound to the version node @samp{VERS_2.0}. | |
5157 | ||
5158 | When the linker finds a symbol defined in a library which is not | |
5159 | specifically bound to a version node, it will effectively bind it to an | |
5160 | unspecified base version of the library. You can bind all otherwise | |
a981ed6f | 5161 | unspecified symbols to a given version node by using @samp{global: *;} |
ae5a3597 AM |
5162 | somewhere in the version script. Note that it's slightly crazy to use |
5163 | wildcards in a global spec except on the last version node. Global | |
5164 | wildcards elsewhere run the risk of accidentally adding symbols to the | |
5165 | set exported for an old version. That's wrong since older versions | |
5166 | ought to have a fixed set of symbols. | |
252b5132 RH |
5167 | |
5168 | The names of the version nodes have no specific meaning other than what | |
5169 | they might suggest to the person reading them. The @samp{2.0} version | |
5170 | could just as well have appeared in between @samp{1.1} and @samp{1.2}. | |
5171 | However, this would be a confusing way to write a version script. | |
5172 | ||
0f6bf451 | 5173 | Node name can be omitted, provided it is the only version node |
6b9b879a JJ |
5174 | in the version script. Such version script doesn't assign any versions to |
5175 | symbols, only selects which symbols will be globally visible out and which | |
5176 | won't. | |
5177 | ||
5178 | @smallexample | |
7c9c73be | 5179 | @{ global: foo; bar; local: *; @}; |
9d201f2f | 5180 | @end smallexample |
6b9b879a | 5181 | |
252b5132 RH |
5182 | When you link an application against a shared library that has versioned |
5183 | symbols, the application itself knows which version of each symbol it | |
5184 | requires, and it also knows which version nodes it needs from each | |
5185 | shared library it is linked against. Thus at runtime, the dynamic | |
5186 | loader can make a quick check to make sure that the libraries you have | |
5187 | linked against do in fact supply all of the version nodes that the | |
5188 | application will need to resolve all of the dynamic symbols. In this | |
5189 | way it is possible for the dynamic linker to know with certainty that | |
5190 | all external symbols that it needs will be resolvable without having to | |
5191 | search for each symbol reference. | |
5192 | ||
5193 | The symbol versioning is in effect a much more sophisticated way of | |
5194 | doing minor version checking that SunOS does. The fundamental problem | |
5195 | that is being addressed here is that typically references to external | |
5196 | functions are bound on an as-needed basis, and are not all bound when | |
5197 | the application starts up. If a shared library is out of date, a | |
5198 | required interface may be missing; when the application tries to use | |
5199 | that interface, it may suddenly and unexpectedly fail. With symbol | |
5200 | versioning, the user will get a warning when they start their program if | |
5201 | the libraries being used with the application are too old. | |
5202 | ||
5203 | There are several GNU extensions to Sun's versioning approach. The | |
5204 | first of these is the ability to bind a symbol to a version node in the | |
5205 | source file where the symbol is defined instead of in the versioning | |
5206 | script. This was done mainly to reduce the burden on the library | |
5207 | maintainer. You can do this by putting something like: | |
5208 | @smallexample | |
5209 | __asm__(".symver original_foo,foo@@VERS_1.1"); | |
5210 | @end smallexample | |
5211 | @noindent | |
5212 | in the C source file. This renames the function @samp{original_foo} to | |
5213 | be an alias for @samp{foo} bound to the version node @samp{VERS_1.1}. | |
5214 | The @samp{local:} directive can be used to prevent the symbol | |
96a94295 L |
5215 | @samp{original_foo} from being exported. A @samp{.symver} directive |
5216 | takes precedence over a version script. | |
252b5132 RH |
5217 | |
5218 | The second GNU extension is to allow multiple versions of the same | |
5219 | function to appear in a given shared library. In this way you can make | |
5220 | an incompatible change to an interface without increasing the major | |
5221 | version number of the shared library, while still allowing applications | |
5222 | linked against the old interface to continue to function. | |
5223 | ||
5224 | To do this, you must use multiple @samp{.symver} directives in the | |
5225 | source file. Here is an example: | |
5226 | ||
5227 | @smallexample | |
5228 | __asm__(".symver original_foo,foo@@"); | |
5229 | __asm__(".symver old_foo,foo@@VERS_1.1"); | |
5230 | __asm__(".symver old_foo1,foo@@VERS_1.2"); | |
5231 | __asm__(".symver new_foo,foo@@@@VERS_2.0"); | |
5232 | @end smallexample | |
5233 | ||
5234 | In this example, @samp{foo@@} represents the symbol @samp{foo} bound to the | |
5235 | unspecified base version of the symbol. The source file that contains this | |
5236 | example would define 4 C functions: @samp{original_foo}, @samp{old_foo}, | |
5237 | @samp{old_foo1}, and @samp{new_foo}. | |
5238 | ||
5239 | When you have multiple definitions of a given symbol, there needs to be | |
5240 | some way to specify a default version to which external references to | |
5241 | this symbol will be bound. You can do this with the | |
5242 | @samp{foo@@@@VERS_2.0} type of @samp{.symver} directive. You can only | |
5243 | declare one version of a symbol as the default in this manner; otherwise | |
5244 | you would effectively have multiple definitions of the same symbol. | |
5245 | ||
5246 | If you wish to bind a reference to a specific version of the symbol | |
5247 | within the shared library, you can use the aliases of convenience | |
36f63dca | 5248 | (i.e., @samp{old_foo}), or you can use the @samp{.symver} directive to |
252b5132 RH |
5249 | specifically bind to an external version of the function in question. |
5250 | ||
cb840a31 L |
5251 | You can also specify the language in the version script: |
5252 | ||
5253 | @smallexample | |
5254 | VERSION extern "lang" @{ version-script-commands @} | |
5255 | @end smallexample | |
5256 | ||
c0065db7 | 5257 | The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}. |
cb840a31 L |
5258 | The linker will iterate over the list of symbols at the link time and |
5259 | demangle them according to @samp{lang} before matching them to the | |
bb1515f2 MF |
5260 | patterns specified in @samp{version-script-commands}. The default |
5261 | @samp{lang} is @samp{C}. | |
cb840a31 | 5262 | |
86043bbb MM |
5263 | Demangled names may contains spaces and other special characters. As |
5264 | described above, you can use a glob pattern to match demangled names, | |
5265 | or you can use a double-quoted string to match the string exactly. In | |
5266 | the latter case, be aware that minor differences (such as differing | |
5267 | whitespace) between the version script and the demangler output will | |
5268 | cause a mismatch. As the exact string generated by the demangler | |
5269 | might change in the future, even if the mangled name does not, you | |
5270 | should check that all of your version directives are behaving as you | |
5271 | expect when you upgrade. | |
5272 | ||
252b5132 RH |
5273 | @node Expressions |
5274 | @section Expressions in Linker Scripts | |
5275 | @cindex expressions | |
5276 | @cindex arithmetic | |
5277 | The syntax for expressions in the linker script language is identical to | |
5278 | that of C expressions. All expressions are evaluated as integers. All | |
5279 | expressions are evaluated in the same size, which is 32 bits if both the | |
5280 | host and target are 32 bits, and is otherwise 64 bits. | |
5281 | ||
5282 | You can use and set symbol values in expressions. | |
5283 | ||
5284 | The linker defines several special purpose builtin functions for use in | |
5285 | expressions. | |
5286 | ||
5287 | @menu | |
5288 | * Constants:: Constants | |
0c71d759 | 5289 | * Symbolic Constants:: Symbolic constants |
252b5132 | 5290 | * Symbols:: Symbol Names |
ecca9871 | 5291 | * Orphan Sections:: Orphan Sections |
252b5132 RH |
5292 | * Location Counter:: The Location Counter |
5293 | * Operators:: Operators | |
5294 | * Evaluation:: Evaluation | |
5295 | * Expression Section:: The Section of an Expression | |
5296 | * Builtin Functions:: Builtin Functions | |
5297 | @end menu | |
5298 | ||
5299 | @node Constants | |
5300 | @subsection Constants | |
5301 | @cindex integer notation | |
5302 | @cindex constants in linker scripts | |
5303 | All constants are integers. | |
5304 | ||
5305 | As in C, the linker considers an integer beginning with @samp{0} to be | |
5306 | octal, and an integer beginning with @samp{0x} or @samp{0X} to be | |
8a308ae8 | 5307 | hexadecimal. Alternatively the linker accepts suffixes of @samp{h} or |
11e7fd74 | 5308 | @samp{H} for hexadecimal, @samp{o} or @samp{O} for octal, @samp{b} or |
8a308ae8 NC |
5309 | @samp{B} for binary and @samp{d} or @samp{D} for decimal. Any integer |
5310 | value without a prefix or a suffix is considered to be decimal. | |
252b5132 RH |
5311 | |
5312 | @cindex scaled integers | |
5313 | @cindex K and M integer suffixes | |
5314 | @cindex M and K integer suffixes | |
5315 | @cindex suffixes for integers | |
5316 | @cindex integer suffixes | |
5317 | In addition, you can use the suffixes @code{K} and @code{M} to scale a | |
5318 | constant by | |
5319 | @c TEXI2ROFF-KILL | |
36f63dca | 5320 | @ifnottex |
252b5132 RH |
5321 | @c END TEXI2ROFF-KILL |
5322 | @code{1024} or @code{1024*1024} | |
5323 | @c TEXI2ROFF-KILL | |
36f63dca | 5324 | @end ifnottex |
252b5132 RH |
5325 | @tex |
5326 | ${\rm 1024}$ or ${\rm 1024}^2$ | |
5327 | @end tex | |
5328 | @c END TEXI2ROFF-KILL | |
8a308ae8 NC |
5329 | respectively. For example, the following |
5330 | all refer to the same quantity: | |
5331 | ||
252b5132 | 5332 | @smallexample |
36f63dca NC |
5333 | _fourk_1 = 4K; |
5334 | _fourk_2 = 4096; | |
5335 | _fourk_3 = 0x1000; | |
8a308ae8 | 5336 | _fourk_4 = 10000o; |
252b5132 RH |
5337 | @end smallexample |
5338 | ||
8a308ae8 NC |
5339 | Note - the @code{K} and @code{M} suffixes cannot be used in |
5340 | conjunction with the base suffixes mentioned above. | |
5341 | ||
0c71d759 NC |
5342 | @node Symbolic Constants |
5343 | @subsection Symbolic Constants | |
5344 | @cindex symbolic constants | |
5345 | @kindex CONSTANT | |
5346 | It is possible to refer to target specific constants via the use of | |
5347 | the @code{CONSTANT(@var{name})} operator, where @var{name} is one of: | |
5348 | ||
5349 | @table @code | |
5350 | @item MAXPAGESIZE | |
5351 | @kindex MAXPAGESIZE | |
5352 | The target's maximum page size. | |
5353 | ||
5354 | @item COMMONPAGESIZE | |
5355 | @kindex COMMONPAGESIZE | |
5356 | The target's default page size. | |
5357 | @end table | |
5358 | ||
5359 | So for example: | |
5360 | ||
5361 | @smallexample | |
9d5777a3 | 5362 | .text ALIGN (CONSTANT (MAXPAGESIZE)) : @{ *(.text) @} |
0c71d759 NC |
5363 | @end smallexample |
5364 | ||
5365 | will create a text section aligned to the largest page boundary | |
5366 | supported by the target. | |
5367 | ||
252b5132 RH |
5368 | @node Symbols |
5369 | @subsection Symbol Names | |
5370 | @cindex symbol names | |
5371 | @cindex names | |
5372 | @cindex quoted symbol names | |
5373 | @kindex " | |
5374 | Unless quoted, symbol names start with a letter, underscore, or period | |
5375 | and may include letters, digits, underscores, periods, and hyphens. | |
5376 | Unquoted symbol names must not conflict with any keywords. You can | |
5377 | specify a symbol which contains odd characters or has the same name as a | |
5378 | keyword by surrounding the symbol name in double quotes: | |
5379 | @smallexample | |
36f63dca NC |
5380 | "SECTION" = 9; |
5381 | "with a space" = "also with a space" + 10; | |
252b5132 RH |
5382 | @end smallexample |
5383 | ||
5384 | Since symbols can contain many non-alphabetic characters, it is safest | |
5385 | to delimit symbols with spaces. For example, @samp{A-B} is one symbol, | |
5386 | whereas @samp{A - B} is an expression involving subtraction. | |
5387 | ||
ecca9871 L |
5388 | @node Orphan Sections |
5389 | @subsection Orphan Sections | |
5390 | @cindex orphan | |
5391 | Orphan sections are sections present in the input files which | |
5392 | are not explicitly placed into the output file by the linker | |
5393 | script. The linker will still copy these sections into the | |
5394 | output file, but it has to guess as to where they should be | |
5395 | placed. The linker uses a simple heuristic to do this. It | |
5396 | attempts to place orphan sections after non-orphan sections of the | |
5397 | same attribute, such as code vs data, loadable vs non-loadable, etc. | |
5398 | If there is not enough room to do this then it places | |
5399 | at the end of the file. | |
5400 | ||
5401 | For ELF targets, the attribute of the section includes section type as | |
5402 | well as section flag. | |
5403 | ||
41911f68 | 5404 | If an orphaned section's name is representable as a C identifier then |
a61ca861 | 5405 | the linker will automatically @pxref{PROVIDE} two symbols: |
9aec8434 | 5406 | __start_SECNAME and __stop_SECNAME, where SECNAME is the name of the |
41911f68 NC |
5407 | section. These indicate the start address and end address of the |
5408 | orphaned section respectively. Note: most section names are not | |
5409 | representable as C identifiers because they contain a @samp{.} | |
5410 | character. | |
5411 | ||
252b5132 RH |
5412 | @node Location Counter |
5413 | @subsection The Location Counter | |
5414 | @kindex . | |
5415 | @cindex dot | |
5416 | @cindex location counter | |
5417 | @cindex current output location | |
5418 | The special linker variable @dfn{dot} @samp{.} always contains the | |
5419 | current output location counter. Since the @code{.} always refers to a | |
5420 | location in an output section, it may only appear in an expression | |
5421 | within a @code{SECTIONS} command. The @code{.} symbol may appear | |
5422 | anywhere that an ordinary symbol is allowed in an expression. | |
5423 | ||
5424 | @cindex holes | |
5425 | Assigning a value to @code{.} will cause the location counter to be | |
5426 | moved. This may be used to create holes in the output section. The | |
dc0b6aa0 AM |
5427 | location counter may not be moved backwards inside an output section, |
5428 | and may not be moved backwards outside of an output section if so | |
5429 | doing creates areas with overlapping LMAs. | |
252b5132 RH |
5430 | |
5431 | @smallexample | |
5432 | SECTIONS | |
5433 | @{ | |
5434 | output : | |
5435 | @{ | |
5436 | file1(.text) | |
5437 | . = . + 1000; | |
5438 | file2(.text) | |
5439 | . += 1000; | |
5440 | file3(.text) | |
563e308f | 5441 | @} = 0x12345678; |
252b5132 RH |
5442 | @} |
5443 | @end smallexample | |
5444 | @noindent | |
5445 | In the previous example, the @samp{.text} section from @file{file1} is | |
5446 | located at the beginning of the output section @samp{output}. It is | |
5447 | followed by a 1000 byte gap. Then the @samp{.text} section from | |
5448 | @file{file2} appears, also with a 1000 byte gap following before the | |
563e308f | 5449 | @samp{.text} section from @file{file3}. The notation @samp{= 0x12345678} |
252b5132 RH |
5450 | specifies what data to write in the gaps (@pxref{Output Section Fill}). |
5451 | ||
5c6bbab8 NC |
5452 | @cindex dot inside sections |
5453 | Note: @code{.} actually refers to the byte offset from the start of the | |
5454 | current containing object. Normally this is the @code{SECTIONS} | |
69da35b5 | 5455 | statement, whose start address is 0, hence @code{.} can be used as an |
5c6bbab8 NC |
5456 | absolute address. If @code{.} is used inside a section description |
5457 | however, it refers to the byte offset from the start of that section, | |
5458 | not an absolute address. Thus in a script like this: | |
5459 | ||
5460 | @smallexample | |
5461 | SECTIONS | |
5462 | @{ | |
5463 | . = 0x100 | |
5464 | .text: @{ | |
5465 | *(.text) | |
5466 | . = 0x200 | |
5467 | @} | |
5468 | . = 0x500 | |
5469 | .data: @{ | |
5470 | *(.data) | |
5471 | . += 0x600 | |
5472 | @} | |
5473 | @} | |
5474 | @end smallexample | |
5475 | ||
5476 | The @samp{.text} section will be assigned a starting address of 0x100 | |
5477 | and a size of exactly 0x200 bytes, even if there is not enough data in | |
5478 | the @samp{.text} input sections to fill this area. (If there is too | |
5479 | much data, an error will be produced because this would be an attempt to | |
5480 | move @code{.} backwards). The @samp{.data} section will start at 0x500 | |
5481 | and it will have an extra 0x600 bytes worth of space after the end of | |
5482 | the values from the @samp{.data} input sections and before the end of | |
5483 | the @samp{.data} output section itself. | |
5484 | ||
b5666f2f AM |
5485 | @cindex dot outside sections |
5486 | Setting symbols to the value of the location counter outside of an | |
5487 | output section statement can result in unexpected values if the linker | |
5488 | needs to place orphan sections. For example, given the following: | |
5489 | ||
5490 | @smallexample | |
5491 | SECTIONS | |
5492 | @{ | |
5493 | start_of_text = . ; | |
5494 | .text: @{ *(.text) @} | |
5495 | end_of_text = . ; | |
5496 | ||
5497 | start_of_data = . ; | |
5498 | .data: @{ *(.data) @} | |
5499 | end_of_data = . ; | |
5500 | @} | |
5501 | @end smallexample | |
5502 | ||
5503 | If the linker needs to place some input section, e.g. @code{.rodata}, | |
5504 | not mentioned in the script, it might choose to place that section | |
5505 | between @code{.text} and @code{.data}. You might think the linker | |
5506 | should place @code{.rodata} on the blank line in the above script, but | |
5507 | blank lines are of no particular significance to the linker. As well, | |
5508 | the linker doesn't associate the above symbol names with their | |
5509 | sections. Instead, it assumes that all assignments or other | |
5510 | statements belong to the previous output section, except for the | |
5511 | special case of an assignment to @code{.}. I.e., the linker will | |
5512 | place the orphan @code{.rodata} section as if the script was written | |
5513 | as follows: | |
5514 | ||
5515 | @smallexample | |
5516 | SECTIONS | |
5517 | @{ | |
5518 | start_of_text = . ; | |
5519 | .text: @{ *(.text) @} | |
5520 | end_of_text = . ; | |
5521 | ||
5522 | start_of_data = . ; | |
5523 | .rodata: @{ *(.rodata) @} | |
5524 | .data: @{ *(.data) @} | |
5525 | end_of_data = . ; | |
5526 | @} | |
5527 | @end smallexample | |
5528 | ||
5529 | This may or may not be the script author's intention for the value of | |
5530 | @code{start_of_data}. One way to influence the orphan section | |
5531 | placement is to assign the location counter to itself, as the linker | |
5532 | assumes that an assignment to @code{.} is setting the start address of | |
5533 | a following output section and thus should be grouped with that | |
5534 | section. So you could write: | |
5535 | ||
5536 | @smallexample | |
5537 | SECTIONS | |
5538 | @{ | |
5539 | start_of_text = . ; | |
5540 | .text: @{ *(.text) @} | |
5541 | end_of_text = . ; | |
5542 | ||
5543 | . = . ; | |
5544 | start_of_data = . ; | |
5545 | .data: @{ *(.data) @} | |
5546 | end_of_data = . ; | |
5547 | @} | |
5548 | @end smallexample | |
5549 | ||
5550 | Now, the orphan @code{.rodata} section will be placed between | |
5551 | @code{end_of_text} and @code{start_of_data}. | |
5552 | ||
252b5132 RH |
5553 | @need 2000 |
5554 | @node Operators | |
5555 | @subsection Operators | |
5556 | @cindex operators for arithmetic | |
5557 | @cindex arithmetic operators | |
5558 | @cindex precedence in expressions | |
5559 | The linker recognizes the standard C set of arithmetic operators, with | |
5560 | the standard bindings and precedence levels: | |
5561 | @c TEXI2ROFF-KILL | |
36f63dca | 5562 | @ifnottex |
252b5132 RH |
5563 | @c END TEXI2ROFF-KILL |
5564 | @smallexample | |
5565 | precedence associativity Operators Notes | |
5566 | (highest) | |
5567 | 1 left ! - ~ (1) | |
5568 | 2 left * / % | |
5569 | 3 left + - | |
5570 | 4 left >> << | |
5571 | 5 left == != > < <= >= | |
5572 | 6 left & | |
5573 | 7 left | | |
5574 | 8 left && | |
5575 | 9 left || | |
5576 | 10 right ? : | |
5577 | 11 right &= += -= *= /= (2) | |
5578 | (lowest) | |
5579 | @end smallexample | |
5580 | Notes: | |
a1ab1d2a | 5581 | (1) Prefix operators |
252b5132 RH |
5582 | (2) @xref{Assignments}. |
5583 | @c TEXI2ROFF-KILL | |
36f63dca | 5584 | @end ifnottex |
252b5132 RH |
5585 | @tex |
5586 | \vskip \baselineskip | |
5587 | %"lispnarrowing" is the extra indent used generally for smallexample | |
5588 | \hskip\lispnarrowing\vbox{\offinterlineskip | |
5589 | \hrule | |
5590 | \halign | |
5591 | {\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr | |
5592 | height2pt&\omit&&\omit&&\omit&\cr | |
5593 | &Precedence&& Associativity &&{\rm Operators}&\cr | |
5594 | height2pt&\omit&&\omit&&\omit&\cr | |
5595 | \noalign{\hrule} | |
5596 | height2pt&\omit&&\omit&&\omit&\cr | |
5597 | &highest&&&&&\cr | |
5598 | % '176 is tilde, '~' in tt font | |
a1ab1d2a | 5599 | &1&&left&&\qquad- \char'176\ !\qquad\dag&\cr |
252b5132 RH |
5600 | &2&&left&&* / \%&\cr |
5601 | &3&&left&&+ -&\cr | |
5602 | &4&&left&&>> <<&\cr | |
5603 | &5&&left&&== != > < <= >=&\cr | |
5604 | &6&&left&&\&&\cr | |
5605 | &7&&left&&|&\cr | |
5606 | &8&&left&&{\&\&}&\cr | |
5607 | &9&&left&&||&\cr | |
5608 | &10&&right&&? :&\cr | |
5609 | &11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr | |
5610 | &lowest&&&&&\cr | |
5611 | height2pt&\omit&&\omit&&\omit&\cr} | |
5612 | \hrule} | |
5613 | @end tex | |
5614 | @iftex | |
5615 | { | |
5616 | @obeylines@parskip=0pt@parindent=0pt | |
5617 | @dag@quad Prefix operators. | |
5618 | @ddag@quad @xref{Assignments}. | |
5619 | } | |
5620 | @end iftex | |
5621 | @c END TEXI2ROFF-KILL | |
5622 | ||
5623 | @node Evaluation | |
5624 | @subsection Evaluation | |
5625 | @cindex lazy evaluation | |
5626 | @cindex expression evaluation order | |
5627 | The linker evaluates expressions lazily. It only computes the value of | |
5628 | an expression when absolutely necessary. | |
5629 | ||
5630 | The linker needs some information, such as the value of the start | |
5631 | address of the first section, and the origins and lengths of memory | |
5632 | regions, in order to do any linking at all. These values are computed | |
5633 | as soon as possible when the linker reads in the linker script. | |
5634 | ||
5635 | However, other values (such as symbol values) are not known or needed | |
5636 | until after storage allocation. Such values are evaluated later, when | |
5637 | other information (such as the sizes of output sections) is available | |
5638 | for use in the symbol assignment expression. | |
5639 | ||
5640 | The sizes of sections cannot be known until after allocation, so | |
5641 | assignments dependent upon these are not performed until after | |
5642 | allocation. | |
5643 | ||
5644 | Some expressions, such as those depending upon the location counter | |
5645 | @samp{.}, must be evaluated during section allocation. | |
5646 | ||
5647 | If the result of an expression is required, but the value is not | |
5648 | available, then an error results. For example, a script like the | |
5649 | following | |
5650 | @smallexample | |
5651 | @group | |
5652 | SECTIONS | |
5653 | @{ | |
a1ab1d2a | 5654 | .text 9+this_isnt_constant : |
252b5132 RH |
5655 | @{ *(.text) @} |
5656 | @} | |
5657 | @end group | |
5658 | @end smallexample | |
5659 | @noindent | |
5660 | will cause the error message @samp{non constant expression for initial | |
5661 | address}. | |
5662 | ||
5663 | @node Expression Section | |
5664 | @subsection The Section of an Expression | |
5665 | @cindex expression sections | |
5666 | @cindex absolute expressions | |
5667 | @cindex relative expressions | |
5668 | @cindex absolute and relocatable symbols | |
5669 | @cindex relocatable and absolute symbols | |
5670 | @cindex symbols, relocatable and absolute | |
7542af2a AM |
5671 | Addresses and symbols may be section relative, or absolute. A section |
5672 | relative symbol is relocatable. If you request relocatable output | |
5673 | using the @samp{-r} option, a further link operation may change the | |
5674 | value of a section relative symbol. On the other hand, an absolute | |
5675 | symbol will retain the same value throughout any further link | |
5676 | operations. | |
5677 | ||
abf4be64 AM |
5678 | Some terms in linker expressions are addresses. This is true of |
5679 | section relative symbols and for builtin functions that return an | |
5680 | address, such as @code{ADDR}, @code{LOADADDR}, @code{ORIGIN} and | |
5681 | @code{SEGMENT_START}. Other terms are simply numbers, or are builtin | |
5682 | functions that return a non-address value, such as @code{LENGTH}. | |
01554a74 AM |
5683 | One complication is that unless you set @code{LD_FEATURE ("SANE_EXPR")} |
5684 | (@pxref{Miscellaneous Commands}), numbers and absolute symbols are treated | |
5c3049d2 AM |
5685 | differently depending on their location, for compatibility with older |
5686 | versions of @code{ld}. Expressions appearing outside an output | |
5687 | section definition treat all numbers as absolute addresses. | |
5688 | Expressions appearing inside an output section definition treat | |
01554a74 AM |
5689 | absolute symbols as numbers. If @code{LD_FEATURE ("SANE_EXPR")} is |
5690 | given, then absolute symbols and numbers are simply treated as numbers | |
5691 | everywhere. | |
5c3049d2 AM |
5692 | |
5693 | In the following simple example, | |
252b5132 | 5694 | |
7542af2a AM |
5695 | @smallexample |
5696 | @group | |
5697 | SECTIONS | |
5698 | @{ | |
5699 | . = 0x100; | |
5700 | __executable_start = 0x100; | |
5701 | .data : | |
5702 | @{ | |
5703 | . = 0x10; | |
5704 | __data_start = 0x10; | |
5705 | *(.data) | |
5706 | @} | |
5707 | @dots{} | |
5708 | @} | |
5709 | @end group | |
5710 | @end smallexample | |
252b5132 | 5711 | |
7542af2a AM |
5712 | both @code{.} and @code{__executable_start} are set to the absolute |
5713 | address 0x100 in the first two assignments, then both @code{.} and | |
5714 | @code{__data_start} are set to 0x10 relative to the @code{.data} | |
5715 | section in the second two assignments. | |
252b5132 | 5716 | |
5c3049d2 AM |
5717 | For expressions involving numbers, relative addresses and absolute |
5718 | addresses, ld follows these rules to evaluate terms: | |
7542af2a AM |
5719 | |
5720 | @itemize @bullet | |
5721 | @item | |
c05f749e AM |
5722 | Unary operations on an absolute address or number, and binary |
5723 | operations on two absolute addresses or two numbers, or between one | |
5724 | absolute address and a number, apply the operator to the value(s). | |
5725 | @item | |
7542af2a AM |
5726 | Unary operations on a relative address, and binary operations on two |
5727 | relative addresses in the same section or between one relative address | |
5728 | and a number, apply the operator to the offset part of the address(es). | |
5729 | @item | |
c05f749e AM |
5730 | Other binary operations, that is, between two relative addresses not |
5731 | in the same section, or between a relative address and an absolute | |
5732 | address, first convert any non-absolute term to an absolute address | |
5733 | before applying the operator. | |
7542af2a AM |
5734 | @end itemize |
5735 | ||
5736 | The result section of each sub-expression is as follows: | |
5737 | ||
5738 | @itemize @bullet | |
5739 | @item | |
5740 | An operation involving only numbers results in a number. | |
5741 | @item | |
5742 | The result of comparisons, @samp{&&} and @samp{||} is also a number. | |
5743 | @item | |
9bc8bb33 | 5744 | The result of other binary arithmetic and logical operations on two |
11e7fd74 | 5745 | relative addresses in the same section or two absolute addresses |
9bc8bb33 AM |
5746 | (after above conversions) is also a number. |
5747 | @item | |
5748 | The result of other operations on relative addresses or one | |
5749 | relative address and a number, is a relative address in the same | |
5750 | section as the relative operand(s). | |
7542af2a AM |
5751 | @item |
5752 | The result of other operations on absolute addresses (after above | |
5753 | conversions) is an absolute address. | |
5754 | @end itemize | |
252b5132 RH |
5755 | |
5756 | You can use the builtin function @code{ABSOLUTE} to force an expression | |
5757 | to be absolute when it would otherwise be relative. For example, to | |
5758 | create an absolute symbol set to the address of the end of the output | |
5759 | section @samp{.data}: | |
5760 | @smallexample | |
5761 | SECTIONS | |
5762 | @{ | |
5763 | .data : @{ *(.data) _edata = ABSOLUTE(.); @} | |
5764 | @} | |
5765 | @end smallexample | |
5766 | @noindent | |
5767 | If @samp{ABSOLUTE} were not used, @samp{_edata} would be relative to the | |
5768 | @samp{.data} section. | |
5769 | ||
7542af2a AM |
5770 | Using @code{LOADADDR} also forces an expression absolute, since this |
5771 | particular builtin function returns an absolute address. | |
5772 | ||
252b5132 RH |
5773 | @node Builtin Functions |
5774 | @subsection Builtin Functions | |
5775 | @cindex functions in expressions | |
5776 | The linker script language includes a number of builtin functions for | |
5777 | use in linker script expressions. | |
5778 | ||
5779 | @table @code | |
5780 | @item ABSOLUTE(@var{exp}) | |
5781 | @kindex ABSOLUTE(@var{exp}) | |
5782 | @cindex expression, absolute | |
5783 | Return the absolute (non-relocatable, as opposed to non-negative) value | |
5784 | of the expression @var{exp}. Primarily useful to assign an absolute | |
5785 | value to a symbol within a section definition, where symbol values are | |
5786 | normally section relative. @xref{Expression Section}. | |
5787 | ||
5788 | @item ADDR(@var{section}) | |
5789 | @kindex ADDR(@var{section}) | |
5790 | @cindex section address in expression | |
7542af2a | 5791 | Return the address (VMA) of the named @var{section}. Your |
252b5132 | 5792 | script must previously have defined the location of that section. In |
7542af2a AM |
5793 | the following example, @code{start_of_output_1}, @code{symbol_1} and |
5794 | @code{symbol_2} are assigned equivalent values, except that | |
5795 | @code{symbol_1} will be relative to the @code{.output1} section while | |
5796 | the other two will be absolute: | |
252b5132 RH |
5797 | @smallexample |
5798 | @group | |
5799 | SECTIONS @{ @dots{} | |
5800 | .output1 : | |
a1ab1d2a | 5801 | @{ |
252b5132 RH |
5802 | start_of_output_1 = ABSOLUTE(.); |
5803 | @dots{} | |
5804 | @} | |
5805 | .output : | |
5806 | @{ | |
5807 | symbol_1 = ADDR(.output1); | |
5808 | symbol_2 = start_of_output_1; | |
5809 | @} | |
5810 | @dots{} @} | |
5811 | @end group | |
5812 | @end smallexample | |
5813 | ||
876f4090 NS |
5814 | @item ALIGN(@var{align}) |
5815 | @itemx ALIGN(@var{exp},@var{align}) | |
5816 | @kindex ALIGN(@var{align}) | |
5817 | @kindex ALIGN(@var{exp},@var{align}) | |
252b5132 RH |
5818 | @cindex round up location counter |
5819 | @cindex align location counter | |
876f4090 NS |
5820 | @cindex round up expression |
5821 | @cindex align expression | |
5822 | Return the location counter (@code{.}) or arbitrary expression aligned | |
5823 | to the next @var{align} boundary. The single operand @code{ALIGN} | |
5824 | doesn't change the value of the location counter---it just does | |
5825 | arithmetic on it. The two operand @code{ALIGN} allows an arbitrary | |
5826 | expression to be aligned upwards (@code{ALIGN(@var{align})} is | |
5827 | equivalent to @code{ALIGN(., @var{align})}). | |
5828 | ||
5829 | Here is an example which aligns the output @code{.data} section to the | |
5830 | next @code{0x2000} byte boundary after the preceding section and sets a | |
5831 | variable within the section to the next @code{0x8000} boundary after the | |
5832 | input sections: | |
252b5132 RH |
5833 | @smallexample |
5834 | @group | |
5835 | SECTIONS @{ @dots{} | |
5836 | .data ALIGN(0x2000): @{ | |
5837 | *(.data) | |
5838 | variable = ALIGN(0x8000); | |
5839 | @} | |
5840 | @dots{} @} | |
5841 | @end group | |
5842 | @end smallexample | |
5843 | @noindent | |
5844 | The first use of @code{ALIGN} in this example specifies the location of | |
5845 | a section because it is used as the optional @var{address} attribute of | |
5846 | a section definition (@pxref{Output Section Address}). The second use | |
5847 | of @code{ALIGN} is used to defines the value of a symbol. | |
5848 | ||
5849 | The builtin function @code{NEXT} is closely related to @code{ALIGN}. | |
5850 | ||
362c1d1a NS |
5851 | @item ALIGNOF(@var{section}) |
5852 | @kindex ALIGNOF(@var{section}) | |
5853 | @cindex section alignment | |
5854 | Return the alignment in bytes of the named @var{section}, if that section has | |
5855 | been allocated. If the section has not been allocated when this is | |
5856 | evaluated, the linker will report an error. In the following example, | |
5857 | the alignment of the @code{.output} section is stored as the first | |
5858 | value in that section. | |
5859 | @smallexample | |
5860 | @group | |
5861 | SECTIONS@{ @dots{} | |
5862 | .output @{ | |
5863 | LONG (ALIGNOF (.output)) | |
5864 | @dots{} | |
5865 | @} | |
5866 | @dots{} @} | |
5867 | @end group | |
5868 | @end smallexample | |
5869 | ||
252b5132 RH |
5870 | @item BLOCK(@var{exp}) |
5871 | @kindex BLOCK(@var{exp}) | |
5872 | This is a synonym for @code{ALIGN}, for compatibility with older linker | |
5873 | scripts. It is most often seen when setting the address of an output | |
5874 | section. | |
5875 | ||
2d20f7bf JJ |
5876 | @item DATA_SEGMENT_ALIGN(@var{maxpagesize}, @var{commonpagesize}) |
5877 | @kindex DATA_SEGMENT_ALIGN(@var{maxpagesize}, @var{commonpagesize}) | |
5878 | This is equivalent to either | |
5879 | @smallexample | |
5880 | (ALIGN(@var{maxpagesize}) + (. & (@var{maxpagesize} - 1))) | |
5881 | @end smallexample | |
5882 | or | |
5883 | @smallexample | |
5884 | (ALIGN(@var{maxpagesize}) + (. & (@var{maxpagesize} - @var{commonpagesize}))) | |
5885 | @end smallexample | |
5886 | @noindent | |
5887 | depending on whether the latter uses fewer @var{commonpagesize} sized pages | |
5888 | for the data segment (area between the result of this expression and | |
5889 | @code{DATA_SEGMENT_END}) than the former or not. | |
5890 | If the latter form is used, it means @var{commonpagesize} bytes of runtime | |
5891 | memory will be saved at the expense of up to @var{commonpagesize} wasted | |
5892 | bytes in the on-disk file. | |
5893 | ||
5894 | This expression can only be used directly in @code{SECTIONS} commands, not in | |
5895 | any output section descriptions and only once in the linker script. | |
5896 | @var{commonpagesize} should be less or equal to @var{maxpagesize} and should | |
5897 | be the system page size the object wants to be optimized for (while still | |
5898 | working on system page sizes up to @var{maxpagesize}). | |
5899 | ||
5900 | @noindent | |
5901 | Example: | |
5902 | @smallexample | |
5903 | . = DATA_SEGMENT_ALIGN(0x10000, 0x2000); | |
5904 | @end smallexample | |
5905 | ||
5906 | @item DATA_SEGMENT_END(@var{exp}) | |
5907 | @kindex DATA_SEGMENT_END(@var{exp}) | |
5908 | This defines the end of data segment for @code{DATA_SEGMENT_ALIGN} | |
5909 | evaluation purposes. | |
5910 | ||
5911 | @smallexample | |
5912 | . = DATA_SEGMENT_END(.); | |
5913 | @end smallexample | |
5914 | ||
a4f5ad88 JJ |
5915 | @item DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp}) |
5916 | @kindex DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp}) | |
5917 | This defines the end of the @code{PT_GNU_RELRO} segment when | |
5918 | @samp{-z relro} option is used. Second argument is returned. | |
5919 | When @samp{-z relro} option is not present, @code{DATA_SEGMENT_RELRO_END} | |
5920 | does nothing, otherwise @code{DATA_SEGMENT_ALIGN} is padded so that | |
5921 | @var{exp} + @var{offset} is aligned to the most commonly used page | |
5922 | boundary for particular target. If present in the linker script, | |
5923 | it must always come in between @code{DATA_SEGMENT_ALIGN} and | |
5924 | @code{DATA_SEGMENT_END}. | |
5925 | ||
5926 | @smallexample | |
5927 | . = DATA_SEGMENT_RELRO_END(24, .); | |
5928 | @end smallexample | |
5929 | ||
252b5132 RH |
5930 | @item DEFINED(@var{symbol}) |
5931 | @kindex DEFINED(@var{symbol}) | |
5932 | @cindex symbol defaults | |
5933 | Return 1 if @var{symbol} is in the linker global symbol table and is | |
420e579c HPN |
5934 | defined before the statement using DEFINED in the script, otherwise |
5935 | return 0. You can use this function to provide | |
252b5132 RH |
5936 | default values for symbols. For example, the following script fragment |
5937 | shows how to set a global symbol @samp{begin} to the first location in | |
5938 | the @samp{.text} section---but if a symbol called @samp{begin} already | |
5939 | existed, its value is preserved: | |
5940 | ||
5941 | @smallexample | |
5942 | @group | |
5943 | SECTIONS @{ @dots{} | |
5944 | .text : @{ | |
5945 | begin = DEFINED(begin) ? begin : . ; | |
5946 | @dots{} | |
5947 | @} | |
5948 | @dots{} | |
5949 | @} | |
5950 | @end group | |
5951 | @end smallexample | |
5952 | ||
3ec57632 NC |
5953 | @item LENGTH(@var{memory}) |
5954 | @kindex LENGTH(@var{memory}) | |
5955 | Return the length of the memory region named @var{memory}. | |
5956 | ||
252b5132 RH |
5957 | @item LOADADDR(@var{section}) |
5958 | @kindex LOADADDR(@var{section}) | |
5959 | @cindex section load address in expression | |
7542af2a | 5960 | Return the absolute LMA of the named @var{section}. (@pxref{Output |
252b5132 RH |
5961 | Section LMA}). |
5962 | ||
2e53f7d6 NC |
5963 | @item LOG2CEIL(@var{exp}) |
5964 | @kindex LOG2CEIL(@var{exp}) | |
5965 | Return the binary logarithm of @var{exp} rounded towards infinity. | |
5966 | @code{LOG2CEIL(0)} returns 0. | |
5967 | ||
252b5132 RH |
5968 | @kindex MAX |
5969 | @item MAX(@var{exp1}, @var{exp2}) | |
5970 | Returns the maximum of @var{exp1} and @var{exp2}. | |
5971 | ||
5972 | @kindex MIN | |
5973 | @item MIN(@var{exp1}, @var{exp2}) | |
5974 | Returns the minimum of @var{exp1} and @var{exp2}. | |
5975 | ||
5976 | @item NEXT(@var{exp}) | |
5977 | @kindex NEXT(@var{exp}) | |
5978 | @cindex unallocated address, next | |
5979 | Return the next unallocated address that is a multiple of @var{exp}. | |
5980 | This function is closely related to @code{ALIGN(@var{exp})}; unless you | |
5981 | use the @code{MEMORY} command to define discontinuous memory for the | |
5982 | output file, the two functions are equivalent. | |
5983 | ||
3ec57632 NC |
5984 | @item ORIGIN(@var{memory}) |
5985 | @kindex ORIGIN(@var{memory}) | |
5986 | Return the origin of the memory region named @var{memory}. | |
5987 | ||
ba916c8a MM |
5988 | @item SEGMENT_START(@var{segment}, @var{default}) |
5989 | @kindex SEGMENT_START(@var{segment}, @var{default}) | |
5990 | Return the base address of the named @var{segment}. If an explicit | |
c5da8c7d NC |
5991 | value has already been given for this segment (with a command-line |
5992 | @samp{-T} option) then that value will be returned otherwise the value | |
5993 | will be @var{default}. At present, the @samp{-T} command-line option | |
5994 | can only be used to set the base address for the ``text'', ``data'', and | |
7542af2a | 5995 | ``bss'' sections, but you can use @code{SEGMENT_START} with any segment |
ba916c8a MM |
5996 | name. |
5997 | ||
252b5132 RH |
5998 | @item SIZEOF(@var{section}) |
5999 | @kindex SIZEOF(@var{section}) | |
6000 | @cindex section size | |
6001 | Return the size in bytes of the named @var{section}, if that section has | |
6002 | been allocated. If the section has not been allocated when this is | |
6003 | evaluated, the linker will report an error. In the following example, | |
6004 | @code{symbol_1} and @code{symbol_2} are assigned identical values: | |
6005 | @smallexample | |
6006 | @group | |
6007 | SECTIONS@{ @dots{} | |
6008 | .output @{ | |
6009 | .start = . ; | |
6010 | @dots{} | |
6011 | .end = . ; | |
6012 | @} | |
6013 | symbol_1 = .end - .start ; | |
6014 | symbol_2 = SIZEOF(.output); | |
6015 | @dots{} @} | |
6016 | @end group | |
6017 | @end smallexample | |
6018 | ||
6019 | @item SIZEOF_HEADERS | |
6020 | @itemx sizeof_headers | |
6021 | @kindex SIZEOF_HEADERS | |
6022 | @cindex header size | |
6023 | Return the size in bytes of the output file's headers. This is | |
6024 | information which appears at the start of the output file. You can use | |
6025 | this number when setting the start address of the first section, if you | |
6026 | choose, to facilitate paging. | |
6027 | ||
6028 | @cindex not enough room for program headers | |
6029 | @cindex program headers, not enough room | |
6030 | When producing an ELF output file, if the linker script uses the | |
6031 | @code{SIZEOF_HEADERS} builtin function, the linker must compute the | |
6032 | number of program headers before it has determined all the section | |
6033 | addresses and sizes. If the linker later discovers that it needs | |
6034 | additional program headers, it will report an error @samp{not enough | |
6035 | room for program headers}. To avoid this error, you must avoid using | |
6036 | the @code{SIZEOF_HEADERS} function, or you must rework your linker | |
6037 | script to avoid forcing the linker to use additional program headers, or | |
6038 | you must define the program headers yourself using the @code{PHDRS} | |
6039 | command (@pxref{PHDRS}). | |
6040 | @end table | |
6041 | ||
6042 | @node Implicit Linker Scripts | |
6043 | @section Implicit Linker Scripts | |
6044 | @cindex implicit linker scripts | |
6045 | If you specify a linker input file which the linker can not recognize as | |
6046 | an object file or an archive file, it will try to read the file as a | |
6047 | linker script. If the file can not be parsed as a linker script, the | |
6048 | linker will report an error. | |
6049 | ||
6050 | An implicit linker script will not replace the default linker script. | |
6051 | ||
6052 | Typically an implicit linker script would contain only symbol | |
6053 | assignments, or the @code{INPUT}, @code{GROUP}, or @code{VERSION} | |
6054 | commands. | |
6055 | ||
6056 | Any input files read because of an implicit linker script will be read | |
6057 | at the position in the command line where the implicit linker script was | |
6058 | read. This can affect archive searching. | |
6059 | ||
6060 | @ifset GENERIC | |
6061 | @node Machine Dependent | |
6062 | @chapter Machine Dependent Features | |
6063 | ||
6064 | @cindex machine dependencies | |
ff5dcc92 SC |
6065 | @command{ld} has additional features on some platforms; the following |
6066 | sections describe them. Machines where @command{ld} has no additional | |
252b5132 RH |
6067 | functionality are not listed. |
6068 | ||
6069 | @menu | |
36f63dca NC |
6070 | @ifset H8300 |
6071 | * H8/300:: @command{ld} and the H8/300 | |
6072 | @end ifset | |
6073 | @ifset I960 | |
6074 | * i960:: @command{ld} and the Intel 960 family | |
6075 | @end ifset | |
7ca01ed9 NC |
6076 | @ifset M68HC11 |
6077 | * M68HC11/68HC12:: @code{ld} and the Motorola 68HC11 and 68HC12 families | |
6078 | @end ifset | |
36f63dca NC |
6079 | @ifset ARM |
6080 | * ARM:: @command{ld} and the ARM family | |
6081 | @end ifset | |
6082 | @ifset HPPA | |
6083 | * HPPA ELF32:: @command{ld} and HPPA 32-bit ELF | |
6084 | @end ifset | |
7fb9f789 NC |
6085 | @ifset M68K |
6086 | * M68K:: @command{ld} and the Motorola 68K family | |
6087 | @end ifset | |
833794fc MR |
6088 | @ifset MIPS |
6089 | * MIPS:: @command{ld} and the MIPS family | |
6090 | @end ifset | |
3c3bdf30 | 6091 | @ifset MMIX |
36f63dca | 6092 | * MMIX:: @command{ld} and MMIX |
3c3bdf30 | 6093 | @end ifset |
2469cfa2 | 6094 | @ifset MSP430 |
36f63dca | 6095 | * MSP430:: @command{ld} and MSP430 |
2469cfa2 | 6096 | @end ifset |
2a60a7a8 AM |
6097 | @ifset POWERPC |
6098 | * PowerPC ELF32:: @command{ld} and PowerPC 32-bit ELF Support | |
6099 | @end ifset | |
6100 | @ifset POWERPC64 | |
6101 | * PowerPC64 ELF64:: @command{ld} and PowerPC64 64-bit ELF Support | |
6102 | @end ifset | |
49fa1e15 AM |
6103 | @ifset SPU |
6104 | * SPU ELF:: @command{ld} and SPU ELF Support | |
6105 | @end ifset | |
74459f0e | 6106 | @ifset TICOFF |
ff5dcc92 | 6107 | * TI COFF:: @command{ld} and TI COFF |
74459f0e | 6108 | @end ifset |
2ca22b03 NC |
6109 | @ifset WIN32 |
6110 | * WIN32:: @command{ld} and WIN32 (cygwin/mingw) | |
6111 | @end ifset | |
e0001a05 NC |
6112 | @ifset XTENSA |
6113 | * Xtensa:: @command{ld} and Xtensa Processors | |
6114 | @end ifset | |
252b5132 RH |
6115 | @end menu |
6116 | @end ifset | |
6117 | ||
252b5132 RH |
6118 | @ifset H8300 |
6119 | @ifclear GENERIC | |
6120 | @raisesections | |
6121 | @end ifclear | |
6122 | ||
6123 | @node H8/300 | |
ff5dcc92 | 6124 | @section @command{ld} and the H8/300 |
252b5132 RH |
6125 | |
6126 | @cindex H8/300 support | |
ff5dcc92 | 6127 | For the H8/300, @command{ld} can perform these global optimizations when |
252b5132 RH |
6128 | you specify the @samp{--relax} command-line option. |
6129 | ||
6130 | @table @emph | |
6131 | @cindex relaxing on H8/300 | |
6132 | @item relaxing address modes | |
ff5dcc92 | 6133 | @command{ld} finds all @code{jsr} and @code{jmp} instructions whose |
252b5132 RH |
6134 | targets are within eight bits, and turns them into eight-bit |
6135 | program-counter relative @code{bsr} and @code{bra} instructions, | |
6136 | respectively. | |
6137 | ||
6138 | @cindex synthesizing on H8/300 | |
6139 | @item synthesizing instructions | |
81f5558e | 6140 | @c FIXME: specifically mov.b, or any mov instructions really? -> mov.b only, at least on H8, H8H, H8S |
ff5dcc92 | 6141 | @command{ld} finds all @code{mov.b} instructions which use the |
252b5132 RH |
6142 | sixteen-bit absolute address form, but refer to the top |
6143 | page of memory, and changes them to use the eight-bit address form. | |
6144 | (That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into | |
6145 | @samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the | |
6146 | top page of memory). | |
1502569c | 6147 | |
81f5558e NC |
6148 | @command{ld} finds all @code{mov} instructions which use the register |
6149 | indirect with 32-bit displacement addressing mode, but use a small | |
6150 | displacement inside 16-bit displacement range, and changes them to use | |
6151 | the 16-bit displacement form. (That is: the linker turns @samp{mov.b | |
6152 | @code{@@}@var{d}:32,ERx} into @samp{mov.b @code{@@}@var{d}:16,ERx} | |
6153 | whenever the displacement @var{d} is in the 16 bit signed integer | |
6154 | range. Only implemented in ELF-format ld). | |
6155 | ||
1502569c | 6156 | @item bit manipulation instructions |
c0065db7 | 6157 | @command{ld} finds all bit manipulation instructions like @code{band, bclr, |
1502569c | 6158 | biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor} |
c0065db7 | 6159 | which use 32 bit and 16 bit absolute address form, but refer to the top |
1502569c NC |
6160 | page of memory, and changes them to use the 8 bit address form. |
6161 | (That is: the linker turns @samp{bset #xx:3,@code{@@}@var{aa}:32} into | |
c0065db7 | 6162 | @samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in |
1502569c NC |
6163 | the top page of memory). |
6164 | ||
6165 | @item system control instructions | |
c0065db7 RM |
6166 | @command{ld} finds all @code{ldc.w, stc.w} instructions which use the |
6167 | 32 bit absolute address form, but refer to the top page of memory, and | |
1502569c NC |
6168 | changes them to use 16 bit address form. |
6169 | (That is: the linker turns @samp{ldc.w @code{@@}@var{aa}:32,ccr} into | |
c0065db7 | 6170 | @samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in |
1502569c | 6171 | the top page of memory). |
252b5132 RH |
6172 | @end table |
6173 | ||
6174 | @ifclear GENERIC | |
6175 | @lowersections | |
6176 | @end ifclear | |
6177 | @end ifset | |
6178 | ||
36f63dca | 6179 | @ifclear GENERIC |
c2dcd04e | 6180 | @ifset Renesas |
36f63dca | 6181 | @c This stuff is pointless to say unless you're especially concerned |
c2dcd04e NC |
6182 | @c with Renesas chips; don't enable it for generic case, please. |
6183 | @node Renesas | |
6184 | @chapter @command{ld} and Other Renesas Chips | |
36f63dca | 6185 | |
c2dcd04e NC |
6186 | @command{ld} also supports the Renesas (formerly Hitachi) H8/300H, |
6187 | H8/500, and SH chips. No special features, commands, or command-line | |
6188 | options are required for these chips. | |
36f63dca NC |
6189 | @end ifset |
6190 | @end ifclear | |
6191 | ||
6192 | @ifset I960 | |
6193 | @ifclear GENERIC | |
6194 | @raisesections | |
6195 | @end ifclear | |
6196 | ||
6197 | @node i960 | |
6198 | @section @command{ld} and the Intel 960 Family | |
6199 | ||
6200 | @cindex i960 support | |
6201 | ||
6202 | You can use the @samp{-A@var{architecture}} command line option to | |
6203 | specify one of the two-letter names identifying members of the 960 | |
6204 | family; the option specifies the desired output target, and warns of any | |
6205 | incompatible instructions in the input files. It also modifies the | |
6206 | linker's search strategy for archive libraries, to support the use of | |
6207 | libraries specific to each particular architecture, by including in the | |
6208 | search loop names suffixed with the string identifying the architecture. | |
6209 | ||
6210 | For example, if your @command{ld} command line included @w{@samp{-ACA}} as | |
6211 | well as @w{@samp{-ltry}}, the linker would look (in its built-in search | |
6212 | paths, and in any paths you specify with @samp{-L}) for a library with | |
6213 | the names | |
6214 | ||
6215 | @smallexample | |
6216 | @group | |
6217 | try | |
6218 | libtry.a | |
6219 | tryca | |
6220 | libtryca.a | |
6221 | @end group | |
6222 | @end smallexample | |
6223 | ||
6224 | @noindent | |
6225 | The first two possibilities would be considered in any event; the last | |
6226 | two are due to the use of @w{@samp{-ACA}}. | |
6227 | ||
6228 | You can meaningfully use @samp{-A} more than once on a command line, since | |
6229 | the 960 architecture family allows combination of target architectures; each | |
6230 | use will add another pair of name variants to search for when @w{@samp{-l}} | |
6231 | specifies a library. | |
6232 | ||
6233 | @cindex @option{--relax} on i960 | |
6234 | @cindex relaxing on i960 | |
6235 | @command{ld} supports the @samp{--relax} option for the i960 family. If | |
6236 | you specify @samp{--relax}, @command{ld} finds all @code{balx} and | |
6237 | @code{calx} instructions whose targets are within 24 bits, and turns | |
6238 | them into 24-bit program-counter relative @code{bal} and @code{cal} | |
6239 | instructions, respectively. @command{ld} also turns @code{cal} | |
6240 | instructions into @code{bal} instructions when it determines that the | |
6241 | target subroutine is a leaf routine (that is, the target subroutine does | |
6242 | not itself call any subroutines). | |
6243 | ||
48229727 JB |
6244 | @cindex Cortex-A8 erratum workaround |
6245 | @kindex --fix-cortex-a8 | |
6246 | @kindex --no-fix-cortex-a8 | |
6247 | The @samp{--fix-cortex-a8} switch enables a link-time workaround for an erratum in certain Cortex-A8 processors. The workaround is enabled by default if you are targeting the ARM v7-A architecture profile. It can be enabled otherwise by specifying @samp{--fix-cortex-a8}, or disabled unconditionally by specifying @samp{--no-fix-cortex-a8}. | |
6248 | ||
6249 | The erratum only affects Thumb-2 code. Please contact ARM for further details. | |
6250 | ||
85fdf906 AH |
6251 | @kindex --merge-exidx-entries |
6252 | @kindex --no-merge-exidx-entries | |
6253 | The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent exidx entries in debuginfo. | |
6254 | ||
36f63dca NC |
6255 | @ifclear GENERIC |
6256 | @lowersections | |
6257 | @end ifclear | |
6258 | @end ifset | |
6259 | ||
6260 | @ifset ARM | |
6261 | @ifclear GENERIC | |
6262 | @raisesections | |
6263 | @end ifclear | |
6264 | ||
93fd0973 SC |
6265 | @ifset M68HC11 |
6266 | @ifclear GENERIC | |
6267 | @raisesections | |
6268 | @end ifclear | |
6269 | ||
6270 | @node M68HC11/68HC12 | |
6271 | @section @command{ld} and the Motorola 68HC11 and 68HC12 families | |
6272 | ||
6273 | @cindex M68HC11 and 68HC12 support | |
6274 | ||
6275 | @subsection Linker Relaxation | |
6276 | ||
6277 | For the Motorola 68HC11, @command{ld} can perform these global | |
6278 | optimizations when you specify the @samp{--relax} command-line option. | |
6279 | ||
6280 | @table @emph | |
6281 | @cindex relaxing on M68HC11 | |
6282 | @item relaxing address modes | |
6283 | @command{ld} finds all @code{jsr} and @code{jmp} instructions whose | |
6284 | targets are within eight bits, and turns them into eight-bit | |
6285 | program-counter relative @code{bsr} and @code{bra} instructions, | |
6286 | respectively. | |
6287 | ||
6288 | @command{ld} also looks at all 16-bit extended addressing modes and | |
6289 | transforms them in a direct addressing mode when the address is in | |
6290 | page 0 (between 0 and 0x0ff). | |
6291 | ||
6292 | @item relaxing gcc instruction group | |
6293 | When @command{gcc} is called with @option{-mrelax}, it can emit group | |
6294 | of instructions that the linker can optimize to use a 68HC11 direct | |
6295 | addressing mode. These instructions consists of @code{bclr} or | |
6296 | @code{bset} instructions. | |
6297 | ||
6298 | @end table | |
6299 | ||
6300 | @subsection Trampoline Generation | |
6301 | ||
6302 | @cindex trampoline generation on M68HC11 | |
6303 | @cindex trampoline generation on M68HC12 | |
6304 | For 68HC11 and 68HC12, @command{ld} can generate trampoline code to | |
6305 | call a far function using a normal @code{jsr} instruction. The linker | |
c0065db7 | 6306 | will also change the relocation to some far function to use the |
93fd0973 SC |
6307 | trampoline address instead of the function address. This is typically the |
6308 | case when a pointer to a function is taken. The pointer will in fact | |
6309 | point to the function trampoline. | |
6310 | ||
6311 | @ifclear GENERIC | |
6312 | @lowersections | |
6313 | @end ifclear | |
6314 | @end ifset | |
6315 | ||
36f63dca | 6316 | @node ARM |
3674e28a | 6317 | @section @command{ld} and the ARM family |
36f63dca NC |
6318 | |
6319 | @cindex ARM interworking support | |
6320 | @kindex --support-old-code | |
6321 | For the ARM, @command{ld} will generate code stubs to allow functions calls | |
b45619c0 | 6322 | between ARM and Thumb code. These stubs only work with code that has |
36f63dca NC |
6323 | been compiled and assembled with the @samp{-mthumb-interwork} command |
6324 | line option. If it is necessary to link with old ARM object files or | |
6325 | libraries, which have not been compiled with the -mthumb-interwork | |
6326 | option then the @samp{--support-old-code} command line switch should be | |
6327 | given to the linker. This will make it generate larger stub functions | |
6328 | which will work with non-interworking aware ARM code. Note, however, | |
6329 | the linker does not support generating stubs for function calls to | |
6330 | non-interworking aware Thumb code. | |
6331 | ||
6332 | @cindex thumb entry point | |
6333 | @cindex entry point, thumb | |
6334 | @kindex --thumb-entry=@var{entry} | |
6335 | The @samp{--thumb-entry} switch is a duplicate of the generic | |
6336 | @samp{--entry} switch, in that it sets the program's starting address. | |
6337 | But it also sets the bottom bit of the address, so that it can be | |
6338 | branched to using a BX instruction, and the program will start | |
6339 | executing in Thumb mode straight away. | |
6340 | ||
ce11ba6c KT |
6341 | @cindex PE import table prefixing |
6342 | @kindex --use-nul-prefixed-import-tables | |
6343 | The @samp{--use-nul-prefixed-import-tables} switch is specifying, that | |
6344 | the import tables idata4 and idata5 have to be generated with a zero | |
11e7fd74 | 6345 | element prefix for import libraries. This is the old style to generate |
ce11ba6c KT |
6346 | import tables. By default this option is turned off. |
6347 | ||
e489d0ae PB |
6348 | @cindex BE8 |
6349 | @kindex --be8 | |
6350 | The @samp{--be8} switch instructs @command{ld} to generate BE8 format | |
6351 | executables. This option is only valid when linking big-endian objects. | |
6352 | The resulting image will contain big-endian data and little-endian code. | |
6353 | ||
3674e28a PB |
6354 | @cindex TARGET1 |
6355 | @kindex --target1-rel | |
6356 | @kindex --target1-abs | |
6357 | The @samp{R_ARM_TARGET1} relocation is typically used for entries in the | |
6358 | @samp{.init_array} section. It is interpreted as either @samp{R_ARM_REL32} | |
6359 | or @samp{R_ARM_ABS32}, depending on the target. The @samp{--target1-rel} | |
6360 | and @samp{--target1-abs} switches override the default. | |
6361 | ||
6362 | @cindex TARGET2 | |
6363 | @kindex --target2=@var{type} | |
6364 | The @samp{--target2=type} switch overrides the default definition of the | |
6365 | @samp{R_ARM_TARGET2} relocation. Valid values for @samp{type}, their | |
6366 | meanings, and target defaults are as follows: | |
6367 | @table @samp | |
6368 | @item rel | |
eeac373a PB |
6369 | @samp{R_ARM_REL32} (arm*-*-elf, arm*-*-eabi) |
6370 | @item abs | |
6371 | @samp{R_ARM_ABS32} (arm*-*-symbianelf) | |
3674e28a PB |
6372 | @item got-rel |
6373 | @samp{R_ARM_GOT_PREL} (arm*-*-linux, arm*-*-*bsd) | |
6374 | @end table | |
6375 | ||
319850b4 JB |
6376 | @cindex FIX_V4BX |
6377 | @kindex --fix-v4bx | |
6378 | The @samp{R_ARM_V4BX} relocation (defined by the ARM AAELF | |
6379 | specification) enables objects compiled for the ARMv4 architecture to be | |
6380 | interworking-safe when linked with other objects compiled for ARMv4t, but | |
6381 | also allows pure ARMv4 binaries to be built from the same ARMv4 objects. | |
6382 | ||
6383 | In the latter case, the switch @option{--fix-v4bx} must be passed to the | |
6384 | linker, which causes v4t @code{BX rM} instructions to be rewritten as | |
6385 | @code{MOV PC,rM}, since v4 processors do not have a @code{BX} instruction. | |
6386 | ||
6387 | In the former case, the switch should not be used, and @samp{R_ARM_V4BX} | |
6388 | relocations are ignored. | |
6389 | ||
845b51d6 PB |
6390 | @cindex FIX_V4BX_INTERWORKING |
6391 | @kindex --fix-v4bx-interworking | |
6392 | Replace @code{BX rM} instructions identified by @samp{R_ARM_V4BX} | |
6393 | relocations with a branch to the following veneer: | |
6394 | ||
6395 | @smallexample | |
6396 | TST rM, #1 | |
6397 | MOVEQ PC, rM | |
6398 | BX Rn | |
6399 | @end smallexample | |
6400 | ||
6401 | This allows generation of libraries/applications that work on ARMv4 cores | |
6402 | and are still interworking safe. Note that the above veneer clobbers the | |
11e7fd74 | 6403 | condition flags, so may cause incorrect program behavior in rare cases. |
845b51d6 | 6404 | |
33bfe774 JB |
6405 | @cindex USE_BLX |
6406 | @kindex --use-blx | |
6407 | The @samp{--use-blx} switch enables the linker to use ARM/Thumb | |
6408 | BLX instructions (available on ARMv5t and above) in various | |
6409 | situations. Currently it is used to perform calls via the PLT from Thumb | |
6410 | code using BLX rather than using BX and a mode-switching stub before | |
6411 | each PLT entry. This should lead to such calls executing slightly faster. | |
6412 | ||
6413 | This option is enabled implicitly for SymbianOS, so there is no need to | |
6414 | specify it if you are using that target. | |
6415 | ||
c6dd86c6 JB |
6416 | @cindex VFP11_DENORM_FIX |
6417 | @kindex --vfp11-denorm-fix | |
6418 | The @samp{--vfp11-denorm-fix} switch enables a link-time workaround for a | |
6419 | bug in certain VFP11 coprocessor hardware, which sometimes allows | |
6420 | instructions with denorm operands (which must be handled by support code) | |
6421 | to have those operands overwritten by subsequent instructions before | |
6422 | the support code can read the intended values. | |
6423 | ||
6424 | The bug may be avoided in scalar mode if you allow at least one | |
6425 | intervening instruction between a VFP11 instruction which uses a register | |
6426 | and another instruction which writes to the same register, or at least two | |
6427 | intervening instructions if vector mode is in use. The bug only affects | |
6428 | full-compliance floating-point mode: you do not need this workaround if | |
6429 | you are using "runfast" mode. Please contact ARM for further details. | |
6430 | ||
6431 | If you know you are using buggy VFP11 hardware, you can | |
6432 | enable this workaround by specifying the linker option | |
6433 | @samp{--vfp-denorm-fix=scalar} if you are using the VFP11 scalar | |
6434 | mode only, or @samp{--vfp-denorm-fix=vector} if you are using | |
6435 | vector mode (the latter also works for scalar code). The default is | |
6436 | @samp{--vfp-denorm-fix=none}. | |
6437 | ||
6438 | If the workaround is enabled, instructions are scanned for | |
6439 | potentially-troublesome sequences, and a veneer is created for each | |
6440 | such sequence which may trigger the erratum. The veneer consists of the | |
6441 | first instruction of the sequence and a branch back to the subsequent | |
6442 | instruction. The original instruction is then replaced with a branch to | |
6443 | the veneer. The extra cycles required to call and return from the veneer | |
6444 | are sufficient to avoid the erratum in both the scalar and vector cases. | |
6445 | ||
2de70689 MGD |
6446 | @cindex ARM1176 erratum workaround |
6447 | @kindex --fix-arm1176 | |
6448 | @kindex --no-fix-arm1176 | |
9d5777a3 RM |
6449 | The @samp{--fix-arm1176} switch enables a link-time workaround for an erratum |
6450 | in certain ARM1176 processors. The workaround is enabled by default if you | |
6451 | are targeting ARM v6 (excluding ARM v6T2) or earlier. It can be disabled | |
2de70689 MGD |
6452 | unconditionally by specifying @samp{--no-fix-arm1176}. |
6453 | ||
9d5777a3 | 6454 | Further information is available in the ``ARM1176JZ-S and ARM1176JZF-S |
11e7fd74 | 6455 | Programmer Advice Notice'' available on the ARM documentation website at: |
2de70689 MGD |
6456 | http://infocenter.arm.com/. |
6457 | ||
bf21ed78 MS |
6458 | @cindex NO_ENUM_SIZE_WARNING |
6459 | @kindex --no-enum-size-warning | |
726150b7 | 6460 | The @option{--no-enum-size-warning} switch prevents the linker from |
bf21ed78 MS |
6461 | warning when linking object files that specify incompatible EABI |
6462 | enumeration size attributes. For example, with this switch enabled, | |
6463 | linking of an object file using 32-bit enumeration values with another | |
6464 | using enumeration values fitted into the smallest possible space will | |
6465 | not be diagnosed. | |
a9dc9481 JM |
6466 | |
6467 | @cindex NO_WCHAR_SIZE_WARNING | |
6468 | @kindex --no-wchar-size-warning | |
6469 | The @option{--no-wchar-size-warning} switch prevents the linker from | |
6470 | warning when linking object files that specify incompatible EABI | |
6471 | @code{wchar_t} size attributes. For example, with this switch enabled, | |
6472 | linking of an object file using 32-bit @code{wchar_t} values with another | |
6473 | using 16-bit @code{wchar_t} values will not be diagnosed. | |
bf21ed78 | 6474 | |
726150b7 NC |
6475 | @cindex PIC_VENEER |
6476 | @kindex --pic-veneer | |
6477 | The @samp{--pic-veneer} switch makes the linker use PIC sequences for | |
6478 | ARM/Thumb interworking veneers, even if the rest of the binary | |
6479 | is not PIC. This avoids problems on uClinux targets where | |
6480 | @samp{--emit-relocs} is used to generate relocatable binaries. | |
6481 | ||
6482 | @cindex STUB_GROUP_SIZE | |
6483 | @kindex --stub-group-size=@var{N} | |
6484 | The linker will automatically generate and insert small sequences of | |
6485 | code into a linked ARM ELF executable whenever an attempt is made to | |
6486 | perform a function call to a symbol that is too far away. The | |
6487 | placement of these sequences of instructions - called stubs - is | |
6488 | controlled by the command line option @option{--stub-group-size=N}. | |
6489 | The placement is important because a poor choice can create a need for | |
11e7fd74 | 6490 | duplicate stubs, increasing the code size. The linker will try to |
726150b7 NC |
6491 | group stubs together in order to reduce interruptions to the flow of |
6492 | code, but it needs guidance as to how big these groups should be and | |
6493 | where they should be placed. | |
6494 | ||
6495 | The value of @samp{N}, the parameter to the | |
6496 | @option{--stub-group-size=} option controls where the stub groups are | |
07d72278 | 6497 | placed. If it is negative then all stubs are placed after the first |
726150b7 NC |
6498 | branch that needs them. If it is positive then the stubs can be |
6499 | placed either before or after the branches that need them. If the | |
6500 | value of @samp{N} is 1 (either +1 or -1) then the linker will choose | |
6501 | exactly where to place groups of stubs, using its built in heuristics. | |
6502 | A value of @samp{N} greater than 1 (or smaller than -1) tells the | |
6503 | linker that a single group of stubs can service at most @samp{N} bytes | |
6504 | from the input sections. | |
6505 | ||
6506 | The default, if @option{--stub-group-size=} is not specified, is | |
6507 | @samp{N = +1}. | |
6508 | ||
1a51c1a4 NC |
6509 | Farcalls stubs insertion is fully supported for the ARM-EABI target |
6510 | only, because it relies on object files properties not present | |
6511 | otherwise. | |
6512 | ||
36f63dca NC |
6513 | @ifclear GENERIC |
6514 | @lowersections | |
6515 | @end ifclear | |
6516 | @end ifset | |
6517 | ||
6518 | @ifset HPPA | |
6519 | @ifclear GENERIC | |
6520 | @raisesections | |
6521 | @end ifclear | |
6522 | ||
6523 | @node HPPA ELF32 | |
6524 | @section @command{ld} and HPPA 32-bit ELF Support | |
6525 | @cindex HPPA multiple sub-space stubs | |
6526 | @kindex --multi-subspace | |
6527 | When generating a shared library, @command{ld} will by default generate | |
6528 | import stubs suitable for use with a single sub-space application. | |
6529 | The @samp{--multi-subspace} switch causes @command{ld} to generate export | |
6530 | stubs, and different (larger) import stubs suitable for use with | |
6531 | multiple sub-spaces. | |
6532 | ||
6533 | @cindex HPPA stub grouping | |
6534 | @kindex --stub-group-size=@var{N} | |
6535 | Long branch stubs and import/export stubs are placed by @command{ld} in | |
6536 | stub sections located between groups of input sections. | |
6537 | @samp{--stub-group-size} specifies the maximum size of a group of input | |
6538 | sections handled by one stub section. Since branch offsets are signed, | |
6539 | a stub section may serve two groups of input sections, one group before | |
6540 | the stub section, and one group after it. However, when using | |
6541 | conditional branches that require stubs, it may be better (for branch | |
6542 | prediction) that stub sections only serve one group of input sections. | |
6543 | A negative value for @samp{N} chooses this scheme, ensuring that | |
6544 | branches to stubs always use a negative offset. Two special values of | |
6545 | @samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct | |
6546 | @command{ld} to automatically size input section groups for the branch types | |
6547 | detected, with the same behaviour regarding stub placement as other | |
6548 | positive or negative values of @samp{N} respectively. | |
6549 | ||
6550 | Note that @samp{--stub-group-size} does not split input sections. A | |
6551 | single input section larger than the group size specified will of course | |
6552 | create a larger group (of one section). If input sections are too | |
6553 | large, it may not be possible for a branch to reach its stub. | |
6554 | ||
6555 | @ifclear GENERIC | |
6556 | @lowersections | |
6557 | @end ifclear | |
6558 | @end ifset | |
6559 | ||
7fb9f789 NC |
6560 | @ifset M68K |
6561 | @ifclear GENERIC | |
6562 | @raisesections | |
6563 | @end ifclear | |
6564 | ||
6565 | @node M68K | |
6566 | @section @command{ld} and the Motorola 68K family | |
6567 | ||
6568 | @cindex Motorola 68K GOT generation | |
6569 | @kindex --got=@var{type} | |
6570 | The @samp{--got=@var{type}} option lets you choose the GOT generation scheme. | |
6571 | The choices are @samp{single}, @samp{negative}, @samp{multigot} and | |
6572 | @samp{target}. When @samp{target} is selected the linker chooses | |
6573 | the default GOT generation scheme for the current target. | |
6574 | @samp{single} tells the linker to generate a single GOT with | |
6575 | entries only at non-negative offsets. | |
6576 | @samp{negative} instructs the linker to generate a single GOT with | |
6577 | entries at both negative and positive offsets. Not all environments | |
6578 | support such GOTs. | |
6579 | @samp{multigot} allows the linker to generate several GOTs in the | |
6580 | output file. All GOT references from a single input object | |
6581 | file access the same GOT, but references from different input object | |
6582 | files might access different GOTs. Not all environments support such GOTs. | |
6583 | ||
6584 | @ifclear GENERIC | |
6585 | @lowersections | |
6586 | @end ifclear | |
6587 | @end ifset | |
6588 | ||
833794fc MR |
6589 | @ifset MIPS |
6590 | @ifclear GENERIC | |
6591 | @raisesections | |
6592 | @end ifclear | |
6593 | ||
6594 | @node MIPS | |
6595 | @section @command{ld} and the MIPS family | |
6596 | ||
6597 | @cindex MIPS microMIPS instruction choice selection | |
6598 | @kindex --insn32 | |
6599 | @kindex --no-insn32 | |
6600 | The @samp{--insn32} and @samp{--no-insn32} options control the choice of | |
6601 | microMIPS instructions used in code generated by the linker, such as that | |
6602 | in the PLT or lazy binding stubs, or in relaxation. If @samp{--insn32} is | |
6603 | used, then the linker only uses 32-bit instruction encodings. By default | |
6604 | or if @samp{--no-insn32} is used, all instruction encodings are used, | |
6605 | including 16-bit ones where possible. | |
6606 | ||
6607 | @ifclear GENERIC | |
6608 | @lowersections | |
6609 | @end ifclear | |
6610 | @end ifset | |
6611 | ||
36f63dca NC |
6612 | @ifset MMIX |
6613 | @ifclear GENERIC | |
6614 | @raisesections | |
6615 | @end ifclear | |
6616 | ||
6617 | @node MMIX | |
6618 | @section @code{ld} and MMIX | |
6619 | For MMIX, there is a choice of generating @code{ELF} object files or | |
6620 | @code{mmo} object files when linking. The simulator @code{mmix} | |
6621 | understands the @code{mmo} format. The binutils @code{objcopy} utility | |
6622 | can translate between the two formats. | |
6623 | ||
6624 | There is one special section, the @samp{.MMIX.reg_contents} section. | |
6625 | Contents in this section is assumed to correspond to that of global | |
6626 | registers, and symbols referring to it are translated to special symbols, | |
6627 | equal to registers. In a final link, the start address of the | |
6628 | @samp{.MMIX.reg_contents} section corresponds to the first allocated | |
6629 | global register multiplied by 8. Register @code{$255} is not included in | |
6630 | this section; it is always set to the program entry, which is at the | |
6631 | symbol @code{Main} for @code{mmo} files. | |
6632 | ||
7a2de473 HPN |
6633 | Global symbols with the prefix @code{__.MMIX.start.}, for example |
6634 | @code{__.MMIX.start..text} and @code{__.MMIX.start..data} are special. | |
6635 | The default linker script uses these to set the default start address | |
6636 | of a section. | |
36f63dca NC |
6637 | |
6638 | Initial and trailing multiples of zero-valued 32-bit words in a section, | |
6639 | are left out from an mmo file. | |
6640 | ||
6641 | @ifclear GENERIC | |
6642 | @lowersections | |
6643 | @end ifclear | |
6644 | @end ifset | |
6645 | ||
6646 | @ifset MSP430 | |
6647 | @ifclear GENERIC | |
6648 | @raisesections | |
6649 | @end ifclear | |
6650 | ||
6651 | @node MSP430 | |
6652 | @section @code{ld} and MSP430 | |
6653 | For the MSP430 it is possible to select the MPU architecture. The flag @samp{-m [mpu type]} | |
6654 | will select an appropriate linker script for selected MPU type. (To get a list of known MPUs | |
6655 | just pass @samp{-m help} option to the linker). | |
6656 | ||
6657 | @cindex MSP430 extra sections | |
6658 | The linker will recognize some extra sections which are MSP430 specific: | |
6659 | ||
6660 | @table @code | |
6661 | @item @samp{.vectors} | |
6662 | Defines a portion of ROM where interrupt vectors located. | |
6663 | ||
6664 | @item @samp{.bootloader} | |
6665 | Defines the bootloader portion of the ROM (if applicable). Any code | |
6666 | in this section will be uploaded to the MPU. | |
6667 | ||
6668 | @item @samp{.infomem} | |
6669 | Defines an information memory section (if applicable). Any code in | |
6670 | this section will be uploaded to the MPU. | |
6671 | ||
c0065db7 | 6672 | @item @samp{.infomemnobits} |
36f63dca NC |
6673 | This is the same as the @samp{.infomem} section except that any code |
6674 | in this section will not be uploaded to the MPU. | |
6675 | ||
6676 | @item @samp{.noinit} | |
6677 | Denotes a portion of RAM located above @samp{.bss} section. | |
6678 | ||
c0065db7 | 6679 | The last two sections are used by gcc. |
36f63dca NC |
6680 | @end table |
6681 | ||
6682 | @ifclear GENERIC | |
6683 | @lowersections | |
6684 | @end ifclear | |
6685 | @end ifset | |
6686 | ||
2a60a7a8 AM |
6687 | @ifset POWERPC |
6688 | @ifclear GENERIC | |
6689 | @raisesections | |
6690 | @end ifclear | |
6691 | ||
6692 | @node PowerPC ELF32 | |
6693 | @section @command{ld} and PowerPC 32-bit ELF Support | |
6694 | @cindex PowerPC long branches | |
6695 | @kindex --relax on PowerPC | |
6696 | Branches on PowerPC processors are limited to a signed 26-bit | |
6697 | displacement, which may result in @command{ld} giving | |
6698 | @samp{relocation truncated to fit} errors with very large programs. | |
6699 | @samp{--relax} enables the generation of trampolines that can access | |
6700 | the entire 32-bit address space. These trampolines are inserted at | |
6701 | section boundaries, so may not themselves be reachable if an input | |
c8a1f254 NS |
6702 | section exceeds 33M in size. You may combine @samp{-r} and |
6703 | @samp{--relax} to add trampolines in a partial link. In that case | |
6704 | both branches to undefined symbols and inter-section branches are also | |
6705 | considered potentially out of range, and trampolines inserted. | |
2a60a7a8 AM |
6706 | |
6707 | @cindex PowerPC ELF32 options | |
6708 | @table @option | |
6709 | @cindex PowerPC PLT | |
6710 | @kindex --bss-plt | |
6711 | @item --bss-plt | |
6712 | Current PowerPC GCC accepts a @samp{-msecure-plt} option that | |
6713 | generates code capable of using a newer PLT and GOT layout that has | |
6714 | the security advantage of no executable section ever needing to be | |
6715 | writable and no writable section ever being executable. PowerPC | |
6716 | @command{ld} will generate this layout, including stubs to access the | |
6717 | PLT, if all input files (including startup and static libraries) were | |
6718 | compiled with @samp{-msecure-plt}. @samp{--bss-plt} forces the old | |
6719 | BSS PLT (and GOT layout) which can give slightly better performance. | |
6720 | ||
016687f8 AM |
6721 | @kindex --secure-plt |
6722 | @item --secure-plt | |
6723 | @command{ld} will use the new PLT and GOT layout if it is linking new | |
6724 | @samp{-fpic} or @samp{-fPIC} code, but does not do so automatically | |
6725 | when linking non-PIC code. This option requests the new PLT and GOT | |
6726 | layout. A warning will be given if some object file requires the old | |
6727 | style BSS PLT. | |
6728 | ||
2a60a7a8 AM |
6729 | @cindex PowerPC GOT |
6730 | @kindex --sdata-got | |
6731 | @item --sdata-got | |
6732 | The new secure PLT and GOT are placed differently relative to other | |
6733 | sections compared to older BSS PLT and GOT placement. The location of | |
6734 | @code{.plt} must change because the new secure PLT is an initialized | |
6735 | section while the old PLT is uninitialized. The reason for the | |
6736 | @code{.got} change is more subtle: The new placement allows | |
6737 | @code{.got} to be read-only in applications linked with | |
6738 | @samp{-z relro -z now}. However, this placement means that | |
6739 | @code{.sdata} cannot always be used in shared libraries, because the | |
6740 | PowerPC ABI accesses @code{.sdata} in shared libraries from the GOT | |
6741 | pointer. @samp{--sdata-got} forces the old GOT placement. PowerPC | |
6742 | GCC doesn't use @code{.sdata} in shared libraries, so this option is | |
6743 | really only useful for other compilers that may do so. | |
6744 | ||
6745 | @cindex PowerPC stub symbols | |
6746 | @kindex --emit-stub-syms | |
6747 | @item --emit-stub-syms | |
6748 | This option causes @command{ld} to label linker stubs with a local | |
6749 | symbol that encodes the stub type and destination. | |
6750 | ||
6751 | @cindex PowerPC TLS optimization | |
6752 | @kindex --no-tls-optimize | |
6753 | @item --no-tls-optimize | |
6754 | PowerPC @command{ld} normally performs some optimization of code | |
6755 | sequences used to access Thread-Local Storage. Use this option to | |
6756 | disable the optimization. | |
6757 | @end table | |
6758 | ||
6759 | @ifclear GENERIC | |
6760 | @lowersections | |
6761 | @end ifclear | |
6762 | @end ifset | |
6763 | ||
6764 | @ifset POWERPC64 | |
6765 | @ifclear GENERIC | |
6766 | @raisesections | |
6767 | @end ifclear | |
6768 | ||
6769 | @node PowerPC64 ELF64 | |
6770 | @section @command{ld} and PowerPC64 64-bit ELF Support | |
6771 | ||
6772 | @cindex PowerPC64 ELF64 options | |
6773 | @table @option | |
6774 | @cindex PowerPC64 stub grouping | |
6775 | @kindex --stub-group-size | |
6776 | @item --stub-group-size | |
6777 | Long branch stubs, PLT call stubs and TOC adjusting stubs are placed | |
6778 | by @command{ld} in stub sections located between groups of input sections. | |
6779 | @samp{--stub-group-size} specifies the maximum size of a group of input | |
6780 | sections handled by one stub section. Since branch offsets are signed, | |
6781 | a stub section may serve two groups of input sections, one group before | |
6782 | the stub section, and one group after it. However, when using | |
6783 | conditional branches that require stubs, it may be better (for branch | |
6784 | prediction) that stub sections only serve one group of input sections. | |
6785 | A negative value for @samp{N} chooses this scheme, ensuring that | |
6786 | branches to stubs always use a negative offset. Two special values of | |
6787 | @samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct | |
6788 | @command{ld} to automatically size input section groups for the branch types | |
6789 | detected, with the same behaviour regarding stub placement as other | |
6790 | positive or negative values of @samp{N} respectively. | |
6791 | ||
6792 | Note that @samp{--stub-group-size} does not split input sections. A | |
6793 | single input section larger than the group size specified will of course | |
6794 | create a larger group (of one section). If input sections are too | |
6795 | large, it may not be possible for a branch to reach its stub. | |
6796 | ||
6797 | @cindex PowerPC64 stub symbols | |
6798 | @kindex --emit-stub-syms | |
6799 | @item --emit-stub-syms | |
6800 | This option causes @command{ld} to label linker stubs with a local | |
6801 | symbol that encodes the stub type and destination. | |
6802 | ||
6803 | @cindex PowerPC64 dot symbols | |
6804 | @kindex --dotsyms | |
6805 | @kindex --no-dotsyms | |
6806 | @item --dotsyms, --no-dotsyms | |
6807 | These two options control how @command{ld} interprets version patterns | |
6808 | in a version script. Older PowerPC64 compilers emitted both a | |
6809 | function descriptor symbol with the same name as the function, and a | |
6810 | code entry symbol with the name prefixed by a dot (@samp{.}). To | |
6811 | properly version a function @samp{foo}, the version script thus needs | |
6812 | to control both @samp{foo} and @samp{.foo}. The option | |
6813 | @samp{--dotsyms}, on by default, automatically adds the required | |
6814 | dot-prefixed patterns. Use @samp{--no-dotsyms} to disable this | |
6815 | feature. | |
6816 | ||
6817 | @cindex PowerPC64 TLS optimization | |
6818 | @kindex --no-tls-optimize | |
6819 | @item --no-tls-optimize | |
6820 | PowerPC64 @command{ld} normally performs some optimization of code | |
6821 | sequences used to access Thread-Local Storage. Use this option to | |
6822 | disable the optimization. | |
6823 | ||
6824 | @cindex PowerPC64 OPD optimization | |
6825 | @kindex --no-opd-optimize | |
6826 | @item --no-opd-optimize | |
6827 | PowerPC64 @command{ld} normally removes @code{.opd} section entries | |
6828 | corresponding to deleted link-once functions, or functions removed by | |
e7fc76dd | 6829 | the action of @samp{--gc-sections} or linker script @code{/DISCARD/}. |
2a60a7a8 AM |
6830 | Use this option to disable @code{.opd} optimization. |
6831 | ||
6832 | @cindex PowerPC64 OPD spacing | |
6833 | @kindex --non-overlapping-opd | |
6834 | @item --non-overlapping-opd | |
6835 | Some PowerPC64 compilers have an option to generate compressed | |
6836 | @code{.opd} entries spaced 16 bytes apart, overlapping the third word, | |
6837 | the static chain pointer (unused in C) with the first word of the next | |
6838 | entry. This option expands such entries to the full 24 bytes. | |
6839 | ||
6840 | @cindex PowerPC64 TOC optimization | |
6841 | @kindex --no-toc-optimize | |
6842 | @item --no-toc-optimize | |
6843 | PowerPC64 @command{ld} normally removes unused @code{.toc} section | |
6844 | entries. Such entries are detected by examining relocations that | |
6845 | reference the TOC in code sections. A reloc in a deleted code section | |
6846 | marks a TOC word as unneeded, while a reloc in a kept code section | |
6847 | marks a TOC word as needed. Since the TOC may reference itself, TOC | |
6848 | relocs are also examined. TOC words marked as both needed and | |
6849 | unneeded will of course be kept. TOC words without any referencing | |
6850 | reloc are assumed to be part of a multi-word entry, and are kept or | |
6851 | discarded as per the nearest marked preceding word. This works | |
6852 | reliably for compiler generated code, but may be incorrect if assembly | |
6853 | code is used to insert TOC entries. Use this option to disable the | |
6854 | optimization. | |
6855 | ||
6856 | @cindex PowerPC64 multi-TOC | |
6857 | @kindex --no-multi-toc | |
6858 | @item --no-multi-toc | |
794e51c0 AM |
6859 | If given any toc option besides @code{-mcmodel=medium} or |
6860 | @code{-mcmodel=large}, PowerPC64 GCC generates code for a TOC model | |
6861 | where TOC | |
2a60a7a8 AM |
6862 | entries are accessed with a 16-bit offset from r2. This limits the |
6863 | total TOC size to 64K. PowerPC64 @command{ld} extends this limit by | |
6864 | grouping code sections such that each group uses less than 64K for its | |
6865 | TOC entries, then inserts r2 adjusting stubs between inter-group | |
6866 | calls. @command{ld} does not split apart input sections, so cannot | |
6867 | help if a single input file has a @code{.toc} section that exceeds | |
6868 | 64K, most likely from linking multiple files with @command{ld -r}. | |
6869 | Use this option to turn off this feature. | |
794e51c0 AM |
6870 | |
6871 | @cindex PowerPC64 TOC sorting | |
6872 | @kindex --no-toc-sort | |
6873 | @item --no-toc-sort | |
6874 | By default, @command{ld} sorts TOC sections so that those whose file | |
6875 | happens to have a section called @code{.init} or @code{.fini} are | |
6876 | placed first, followed by TOC sections referenced by code generated | |
6877 | with PowerPC64 gcc's @code{-mcmodel=small}, and lastly TOC sections | |
6878 | referenced only by code generated with PowerPC64 gcc's | |
6879 | @code{-mcmodel=medium} or @code{-mcmodel=large} options. Doing this | |
6880 | results in better TOC grouping for multi-TOC. Use this option to turn | |
6881 | off this feature. | |
6882 | ||
6883 | @cindex PowerPC64 PLT stub alignment | |
6884 | @kindex --plt-align | |
6885 | @kindex --no-plt-align | |
6886 | @item --plt-align | |
6887 | @itemx --no-plt-align | |
6888 | Use these options to control whether individual PLT call stubs are | |
6889 | aligned to a 32-byte boundary, or to the specified power of two | |
6890 | boundary when using @code{--plt-align=}. By default PLT call stubs | |
6891 | are packed tightly. | |
6892 | ||
6893 | @cindex PowerPC64 PLT call stub static chain | |
6894 | @kindex --plt-static-chain | |
6895 | @kindex --no-plt-static-chain | |
6896 | @item --plt-static-chain | |
6897 | @itemx --no-plt-static-chain | |
6898 | Use these options to control whether PLT call stubs load the static | |
6899 | chain pointer (r11). @code{ld} defaults to not loading the static | |
6900 | chain since there is never any need to do so on a PLT call. | |
6901 | ||
6902 | @cindex PowerPC64 PLT call stub thread safety | |
6903 | @kindex --plt-thread-safe | |
6904 | @kindex --no-plt-thread-safe | |
6905 | @item --plt-thread-safe | |
6906 | @itemx --no-thread-safe | |
6907 | With power7's weakly ordered memory model, it is possible when using | |
6908 | lazy binding for ld.so to update a plt entry in one thread and have | |
6909 | another thread see the individual plt entry words update in the wrong | |
6910 | order, despite ld.so carefully writing in the correct order and using | |
6911 | memory write barriers. To avoid this we need some sort of read | |
6912 | barrier in the call stub, or use LD_BIND_NOW=1. By default, @code{ld} | |
6913 | looks for calls to commonly used functions that create threads, and if | |
6914 | seen, adds the necessary barriers. Use these options to change the | |
6915 | default behaviour. | |
2a60a7a8 AM |
6916 | @end table |
6917 | ||
6918 | @ifclear GENERIC | |
6919 | @lowersections | |
6920 | @end ifclear | |
6921 | @end ifset | |
6922 | ||
49fa1e15 AM |
6923 | @ifset SPU |
6924 | @ifclear GENERIC | |
6925 | @raisesections | |
6926 | @end ifclear | |
6927 | ||
6928 | @node SPU ELF | |
6929 | @section @command{ld} and SPU ELF Support | |
6930 | ||
6931 | @cindex SPU ELF options | |
6932 | @table @option | |
6933 | ||
6934 | @cindex SPU plugins | |
6935 | @kindex --plugin | |
6936 | @item --plugin | |
6937 | This option marks an executable as a PIC plugin module. | |
6938 | ||
6939 | @cindex SPU overlays | |
6940 | @kindex --no-overlays | |
6941 | @item --no-overlays | |
6942 | Normally, @command{ld} recognizes calls to functions within overlay | |
6943 | regions, and redirects such calls to an overlay manager via a stub. | |
6944 | @command{ld} also provides a built-in overlay manager. This option | |
6945 | turns off all this special overlay handling. | |
6946 | ||
6947 | @cindex SPU overlay stub symbols | |
6948 | @kindex --emit-stub-syms | |
6949 | @item --emit-stub-syms | |
6950 | This option causes @command{ld} to label overlay stubs with a local | |
6951 | symbol that encodes the stub type and destination. | |
6952 | ||
6953 | @cindex SPU extra overlay stubs | |
6954 | @kindex --extra-overlay-stubs | |
6955 | @item --extra-overlay-stubs | |
6956 | This option causes @command{ld} to add overlay call stubs on all | |
6957 | function calls out of overlay regions. Normally stubs are not added | |
6958 | on calls to non-overlay regions. | |
6959 | ||
6960 | @cindex SPU local store size | |
6961 | @kindex --local-store=lo:hi | |
6962 | @item --local-store=lo:hi | |
6963 | @command{ld} usually checks that a final executable for SPU fits in | |
6964 | the address range 0 to 256k. This option may be used to change the | |
6965 | range. Disable the check entirely with @option{--local-store=0:0}. | |
6966 | ||
c0065db7 | 6967 | @cindex SPU |
49fa1e15 AM |
6968 | @kindex --stack-analysis |
6969 | @item --stack-analysis | |
6970 | SPU local store space is limited. Over-allocation of stack space | |
6971 | unnecessarily limits space available for code and data, while | |
6972 | under-allocation results in runtime failures. If given this option, | |
6973 | @command{ld} will provide an estimate of maximum stack usage. | |
6974 | @command{ld} does this by examining symbols in code sections to | |
6975 | determine the extents of functions, and looking at function prologues | |
6976 | for stack adjusting instructions. A call-graph is created by looking | |
6977 | for relocations on branch instructions. The graph is then searched | |
6978 | for the maximum stack usage path. Note that this analysis does not | |
6979 | find calls made via function pointers, and does not handle recursion | |
6980 | and other cycles in the call graph. Stack usage may be | |
6981 | under-estimated if your code makes such calls. Also, stack usage for | |
6982 | dynamic allocation, e.g. alloca, will not be detected. If a link map | |
6983 | is requested, detailed information about each function's stack usage | |
6984 | and calls will be given. | |
6985 | ||
c0065db7 | 6986 | @cindex SPU |
49fa1e15 AM |
6987 | @kindex --emit-stack-syms |
6988 | @item --emit-stack-syms | |
6989 | This option, if given along with @option{--stack-analysis} will result | |
6990 | in @command{ld} emitting stack sizing symbols for each function. | |
6991 | These take the form @code{__stack_<function_name>} for global | |
6992 | functions, and @code{__stack_<number>_<function_name>} for static | |
6993 | functions. @code{<number>} is the section id in hex. The value of | |
6994 | such symbols is the stack requirement for the corresponding function. | |
6995 | The symbol size will be zero, type @code{STT_NOTYPE}, binding | |
c0065db7 | 6996 | @code{STB_LOCAL}, and section @code{SHN_ABS}. |
49fa1e15 AM |
6997 | @end table |
6998 | ||
6999 | @ifclear GENERIC | |
7000 | @lowersections | |
7001 | @end ifclear | |
7002 | @end ifset | |
7003 | ||
36f63dca NC |
7004 | @ifset TICOFF |
7005 | @ifclear GENERIC | |
7006 | @raisesections | |
7007 | @end ifclear | |
7008 | ||
7009 | @node TI COFF | |
7010 | @section @command{ld}'s Support for Various TI COFF Versions | |
7011 | @cindex TI COFF versions | |
7012 | @kindex --format=@var{version} | |
7013 | The @samp{--format} switch allows selection of one of the various | |
7014 | TI COFF versions. The latest of this writing is 2; versions 0 and 1 are | |
7015 | also supported. The TI COFF versions also vary in header byte-order | |
7016 | format; @command{ld} will read any version or byte order, but the output | |
7017 | header format depends on the default specified by the specific target. | |
7018 | ||
7019 | @ifclear GENERIC | |
7020 | @lowersections | |
7021 | @end ifclear | |
7022 | @end ifset | |
7023 | ||
2ca22b03 NC |
7024 | @ifset WIN32 |
7025 | @ifclear GENERIC | |
7026 | @raisesections | |
7027 | @end ifclear | |
7028 | ||
7029 | @node WIN32 | |
7030 | @section @command{ld} and WIN32 (cygwin/mingw) | |
7031 | ||
c0065db7 | 7032 | This section describes some of the win32 specific @command{ld} issues. |
b45619c0 | 7033 | See @ref{Options,,Command Line Options} for detailed description of the |
dc8465bf | 7034 | command line options mentioned here. |
2ca22b03 NC |
7035 | |
7036 | @table @emph | |
c0065db7 RM |
7037 | @cindex import libraries |
7038 | @item import libraries | |
69da35b5 | 7039 | The standard Windows linker creates and uses so-called import |
2ca22b03 | 7040 | libraries, which contains information for linking to dll's. They are |
69da35b5 NC |
7041 | regular static archives and are handled as any other static |
7042 | archive. The cygwin and mingw ports of @command{ld} have specific | |
2ca22b03 NC |
7043 | support for creating such libraries provided with the |
7044 | @samp{--out-implib} command line option. | |
7045 | ||
c0065db7 RM |
7046 | @item exporting DLL symbols |
7047 | @cindex exporting DLL symbols | |
dc8465bf NC |
7048 | The cygwin/mingw @command{ld} has several ways to export symbols for dll's. |
7049 | ||
7050 | @table @emph | |
7051 | @item using auto-export functionality | |
7052 | @cindex using auto-export functionality | |
7053 | By default @command{ld} exports symbols with the auto-export functionality, | |
7054 | which is controlled by the following command line options: | |
7055 | ||
0a5d968e NC |
7056 | @itemize |
7057 | @item --export-all-symbols [This is the default] | |
7058 | @item --exclude-symbols | |
7059 | @item --exclude-libs | |
e1c37eb5 | 7060 | @item --exclude-modules-for-implib |
09e2aba4 | 7061 | @item --version-script |
0a5d968e NC |
7062 | @end itemize |
7063 | ||
09e2aba4 DK |
7064 | When auto-export is in operation, @command{ld} will export all the non-local |
7065 | (global and common) symbols it finds in a DLL, with the exception of a few | |
7066 | symbols known to belong to the system's runtime and libraries. As it will | |
7067 | often not be desirable to export all of a DLL's symbols, which may include | |
7068 | private functions that are not part of any public interface, the command-line | |
9d5777a3 | 7069 | options listed above may be used to filter symbols out from the list for |
09e2aba4 DK |
7070 | exporting. The @samp{--output-def} option can be used in order to see the |
7071 | final list of exported symbols with all exclusions taken into effect. | |
7072 | ||
7073 | If @samp{--export-all-symbols} is not given explicitly on the | |
0a5d968e NC |
7074 | command line, then the default auto-export behavior will be @emph{disabled} |
7075 | if either of the following are true: | |
7076 | ||
7077 | @itemize | |
7078 | @item A DEF file is used. | |
7079 | @item Any symbol in any object file was marked with the __declspec(dllexport) attribute. | |
7080 | @end itemize | |
dc8465bf | 7081 | |
c0065db7 RM |
7082 | @item using a DEF file |
7083 | @cindex using a DEF file | |
dc8465bf NC |
7084 | Another way of exporting symbols is using a DEF file. A DEF file is |
7085 | an ASCII file containing definitions of symbols which should be | |
7086 | exported when a dll is created. Usually it is named @samp{<dll | |
7087 | name>.def} and is added as any other object file to the linker's | |
0a5d968e | 7088 | command line. The file's name must end in @samp{.def} or @samp{.DEF}. |
dc8465bf NC |
7089 | |
7090 | @example | |
7091 | gcc -o <output> <objectfiles> <dll name>.def | |
7092 | @end example | |
7093 | ||
0a5d968e NC |
7094 | Using a DEF file turns off the normal auto-export behavior, unless the |
7095 | @samp{--export-all-symbols} option is also used. | |
7096 | ||
dc8465bf NC |
7097 | Here is an example of a DEF file for a shared library called @samp{xyz.dll}: |
7098 | ||
7099 | @example | |
4b5bd4e7 | 7100 | LIBRARY "xyz.dll" BASE=0x20000000 |
dc8465bf NC |
7101 | |
7102 | EXPORTS | |
7103 | foo | |
7104 | bar | |
7105 | _bar = bar | |
4b5bd4e7 DS |
7106 | another_foo = abc.dll.afoo |
7107 | var1 DATA | |
7fcab871 KT |
7108 | doo = foo == foo2 |
7109 | eoo DATA == var1 | |
c0065db7 | 7110 | @end example |
dc8465bf | 7111 | |
7fcab871 | 7112 | This example defines a DLL with a non-default base address and seven |
4b5bd4e7 DS |
7113 | symbols in the export table. The third exported symbol @code{_bar} is an |
7114 | alias for the second. The fourth symbol, @code{another_foo} is resolved | |
7115 | by "forwarding" to another module and treating it as an alias for | |
7116 | @code{afoo} exported from the DLL @samp{abc.dll}. The final symbol | |
7fcab871 KT |
7117 | @code{var1} is declared to be a data object. The @samp{doo} symbol in |
7118 | export library is an alias of @samp{foo}, which gets the string name | |
7119 | in export table @samp{foo2}. The @samp{eoo} symbol is an data export | |
7120 | symbol, which gets in export table the name @samp{var1}. | |
4b5bd4e7 | 7121 | |
6b31ad16 DS |
7122 | The optional @code{LIBRARY <name>} command indicates the @emph{internal} |
7123 | name of the output DLL. If @samp{<name>} does not include a suffix, | |
7124 | the default library suffix, @samp{.DLL} is appended. | |
7125 | ||
b45619c0 NC |
7126 | When the .DEF file is used to build an application, rather than a |
7127 | library, the @code{NAME <name>} command should be used instead of | |
6b31ad16 | 7128 | @code{LIBRARY}. If @samp{<name>} does not include a suffix, the default |
c0065db7 | 7129 | executable suffix, @samp{.EXE} is appended. |
6b31ad16 DS |
7130 | |
7131 | With either @code{LIBRARY <name>} or @code{NAME <name>} the optional | |
7132 | specification @code{BASE = <number>} may be used to specify a | |
c0065db7 | 7133 | non-default base address for the image. |
6b31ad16 DS |
7134 | |
7135 | If neither @code{LIBRARY <name>} nor @code{NAME <name>} is specified, | |
a2877985 DS |
7136 | or they specify an empty string, the internal name is the same as the |
7137 | filename specified on the command line. | |
6b31ad16 | 7138 | |
4b5bd4e7 DS |
7139 | The complete specification of an export symbol is: |
7140 | ||
7141 | @example | |
7142 | EXPORTS | |
7143 | ( ( ( <name1> [ = <name2> ] ) | |
7144 | | ( <name1> = <module-name> . <external-name>)) | |
7fcab871 | 7145 | [ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) * |
c0065db7 | 7146 | @end example |
4b5bd4e7 DS |
7147 | |
7148 | Declares @samp{<name1>} as an exported symbol from the DLL, or declares | |
7149 | @samp{<name1>} as an exported alias for @samp{<name2>}; or declares | |
7150 | @samp{<name1>} as a "forward" alias for the symbol | |
7151 | @samp{<external-name>} in the DLL @samp{<module-name>}. | |
7152 | Optionally, the symbol may be exported by the specified ordinal | |
7fcab871 KT |
7153 | @samp{<integer>} alias. The optional @samp{<name3>} is the to be used |
7154 | string in import/export table for the symbol. | |
4b5bd4e7 DS |
7155 | |
7156 | The optional keywords that follow the declaration indicate: | |
7157 | ||
7158 | @code{NONAME}: Do not put the symbol name in the DLL's export table. It | |
7159 | will still be exported by its ordinal alias (either the value specified | |
7160 | by the .def specification or, otherwise, the value assigned by the | |
7161 | linker). The symbol name, however, does remain visible in the import | |
7162 | library (if any), unless @code{PRIVATE} is also specified. | |
7163 | ||
7164 | @code{DATA}: The symbol is a variable or object, rather than a function. | |
7165 | The import lib will export only an indirect reference to @code{foo} as | |
7166 | the symbol @code{_imp__foo} (ie, @code{foo} must be resolved as | |
7167 | @code{*_imp__foo}). | |
7168 | ||
7169 | @code{CONSTANT}: Like @code{DATA}, but put the undecorated @code{foo} as | |
7170 | well as @code{_imp__foo} into the import library. Both refer to the | |
7171 | read-only import address table's pointer to the variable, not to the | |
7172 | variable itself. This can be dangerous. If the user code fails to add | |
7173 | the @code{dllimport} attribute and also fails to explicitly add the | |
7174 | extra indirection that the use of the attribute enforces, the | |
7175 | application will behave unexpectedly. | |
7176 | ||
7177 | @code{PRIVATE}: Put the symbol in the DLL's export table, but do not put | |
7178 | it into the static import library used to resolve imports at link time. The | |
7179 | symbol can still be imported using the @code{LoadLibrary/GetProcAddress} | |
7180 | API at runtime or by by using the GNU ld extension of linking directly to | |
7181 | the DLL without an import library. | |
c0065db7 | 7182 | |
4b5bd4e7 DS |
7183 | See ld/deffilep.y in the binutils sources for the full specification of |
7184 | other DEF file statements | |
dc8465bf NC |
7185 | |
7186 | @cindex creating a DEF file | |
7187 | While linking a shared dll, @command{ld} is able to create a DEF file | |
7188 | with the @samp{--output-def <file>} command line option. | |
0a5d968e NC |
7189 | |
7190 | @item Using decorations | |
7191 | @cindex Using decorations | |
7192 | Another way of marking symbols for export is to modify the source code | |
7193 | itself, so that when building the DLL each symbol to be exported is | |
7194 | declared as: | |
7195 | ||
7196 | @example | |
7197 | __declspec(dllexport) int a_variable | |
7198 | __declspec(dllexport) void a_function(int with_args) | |
7199 | @end example | |
7200 | ||
7201 | All such symbols will be exported from the DLL. If, however, | |
7202 | any of the object files in the DLL contain symbols decorated in | |
7203 | this way, then the normal auto-export behavior is disabled, unless | |
7204 | the @samp{--export-all-symbols} option is also used. | |
7205 | ||
7206 | Note that object files that wish to access these symbols must @emph{not} | |
c0065db7 | 7207 | decorate them with dllexport. Instead, they should use dllimport, |
0a5d968e NC |
7208 | instead: |
7209 | ||
7210 | @example | |
7211 | __declspec(dllimport) int a_variable | |
7212 | __declspec(dllimport) void a_function(int with_args) | |
7213 | @end example | |
7214 | ||
c0065db7 RM |
7215 | This complicates the structure of library header files, because |
7216 | when included by the library itself the header must declare the | |
0a5d968e NC |
7217 | variables and functions as dllexport, but when included by client |
7218 | code the header must declare them as dllimport. There are a number | |
c0065db7 | 7219 | of idioms that are typically used to do this; often client code can |
0a5d968e NC |
7220 | omit the __declspec() declaration completely. See |
7221 | @samp{--enable-auto-import} and @samp{automatic data imports} for more | |
b45619c0 | 7222 | information. |
c0065db7 | 7223 | @end table |
dc8465bf | 7224 | |
2ca22b03 NC |
7225 | @cindex automatic data imports |
7226 | @item automatic data imports | |
7227 | The standard Windows dll format supports data imports from dlls only | |
69da35b5 | 7228 | by adding special decorations (dllimport/dllexport), which let the |
2ca22b03 | 7229 | compiler produce specific assembler instructions to deal with this |
c0065db7 | 7230 | issue. This increases the effort necessary to port existing Un*x |
69da35b5 | 7231 | code to these platforms, especially for large |
2ca22b03 | 7232 | c++ libraries and applications. The auto-import feature, which was |
c0065db7 | 7233 | initially provided by Paul Sokolovsky, allows one to omit the |
b45619c0 | 7234 | decorations to achieve a behavior that conforms to that on POSIX/Un*x |
c0065db7 | 7235 | platforms. This feature is enabled with the @samp{--enable-auto-import} |
69da35b5 NC |
7236 | command-line option, although it is enabled by default on cygwin/mingw. |
7237 | The @samp{--enable-auto-import} option itself now serves mainly to | |
7238 | suppress any warnings that are ordinarily emitted when linked objects | |
7239 | trigger the feature's use. | |
7240 | ||
c0065db7 | 7241 | auto-import of variables does not always work flawlessly without |
69da35b5 NC |
7242 | additional assistance. Sometimes, you will see this message |
7243 | ||
c0065db7 | 7244 | "variable '<var>' can't be auto-imported. Please read the |
69da35b5 NC |
7245 | documentation for ld's @code{--enable-auto-import} for details." |
7246 | ||
c0065db7 RM |
7247 | The @samp{--enable-auto-import} documentation explains why this error |
7248 | occurs, and several methods that can be used to overcome this difficulty. | |
7249 | One of these methods is the @emph{runtime pseudo-relocs} feature, described | |
69da35b5 NC |
7250 | below. |
7251 | ||
7252 | @cindex runtime pseudo-relocation | |
c0065db7 RM |
7253 | For complex variables imported from DLLs (such as structs or classes), |
7254 | object files typically contain a base address for the variable and an | |
7255 | offset (@emph{addend}) within the variable--to specify a particular | |
7256 | field or public member, for instance. Unfortunately, the runtime loader used | |
7257 | in win32 environments is incapable of fixing these references at runtime | |
69da35b5 | 7258 | without the additional information supplied by dllimport/dllexport decorations. |
c0065db7 | 7259 | The standard auto-import feature described above is unable to resolve these |
69da35b5 NC |
7260 | references. |
7261 | ||
c0065db7 RM |
7262 | The @samp{--enable-runtime-pseudo-relocs} switch allows these references to |
7263 | be resolved without error, while leaving the task of adjusting the references | |
7264 | themselves (with their non-zero addends) to specialized code provided by the | |
7265 | runtime environment. Recent versions of the cygwin and mingw environments and | |
7266 | compilers provide this runtime support; older versions do not. However, the | |
7267 | support is only necessary on the developer's platform; the compiled result will | |
69da35b5 NC |
7268 | run without error on an older system. |
7269 | ||
c0065db7 RM |
7270 | @samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly |
7271 | enabled as needed. | |
2ca22b03 NC |
7272 | |
7273 | @cindex direct linking to a dll | |
7274 | @item direct linking to a dll | |
7275 | The cygwin/mingw ports of @command{ld} support the direct linking, | |
7276 | including data symbols, to a dll without the usage of any import | |
69da35b5 | 7277 | libraries. This is much faster and uses much less memory than does the |
b45619c0 | 7278 | traditional import library method, especially when linking large |
c0065db7 RM |
7279 | libraries or applications. When @command{ld} creates an import lib, each |
7280 | function or variable exported from the dll is stored in its own bfd, even | |
7281 | though a single bfd could contain many exports. The overhead involved in | |
69da35b5 | 7282 | storing, loading, and processing so many bfd's is quite large, and explains the |
c0065db7 | 7283 | tremendous time, memory, and storage needed to link against particularly |
69da35b5 NC |
7284 | large or complex libraries when using import libs. |
7285 | ||
c0065db7 | 7286 | Linking directly to a dll uses no extra command-line switches other than |
69da35b5 | 7287 | @samp{-L} and @samp{-l}, because @command{ld} already searches for a number |
c0065db7 | 7288 | of names to match each library. All that is needed from the developer's |
69da35b5 NC |
7289 | perspective is an understanding of this search, in order to force ld to |
7290 | select the dll instead of an import library. | |
7291 | ||
2ca22b03 | 7292 | |
69da35b5 NC |
7293 | For instance, when ld is called with the argument @samp{-lxxx} it will attempt |
7294 | to find, in the first directory of its search path, | |
2ca22b03 NC |
7295 | |
7296 | @example | |
45e948fe NC |
7297 | libxxx.dll.a |
7298 | xxx.dll.a | |
7299 | libxxx.a | |
7300 | xxx.lib | |
69da35b5 | 7301 | cygxxx.dll (*) |
45e948fe NC |
7302 | libxxx.dll |
7303 | xxx.dll | |
2ca22b03 NC |
7304 | @end example |
7305 | ||
69da35b5 NC |
7306 | before moving on to the next directory in the search path. |
7307 | ||
c0065db7 RM |
7308 | (*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll}, |
7309 | where @samp{<prefix>} is set by the @command{ld} option | |
7310 | @samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec | |
7311 | file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for | |
69da35b5 NC |
7312 | @samp{cygxxx.dll}. |
7313 | ||
c0065db7 RM |
7314 | Other win32-based unix environments, such as mingw or pw32, may use other |
7315 | @samp{<prefix>}es, although at present only cygwin makes use of this feature. It | |
69da35b5 NC |
7316 | was originally intended to help avoid name conflicts among dll's built for the |
7317 | various win32/un*x environments, so that (for example) two versions of a zlib dll | |
7318 | could coexist on the same machine. | |
7319 | ||
2ca22b03 NC |
7320 | The generic cygwin/mingw path layout uses a @samp{bin} directory for |
7321 | applications and dll's and a @samp{lib} directory for the import | |
69da35b5 | 7322 | libraries (using cygwin nomenclature): |
2ca22b03 NC |
7323 | |
7324 | @example | |
7325 | bin/ | |
7326 | cygxxx.dll | |
7327 | lib/ | |
7328 | libxxx.dll.a (in case of dll's) | |
c0065db7 | 7329 | libxxx.a (in case of static archive) |
2ca22b03 NC |
7330 | @end example |
7331 | ||
c0065db7 RM |
7332 | Linking directly to a dll without using the import library can be |
7333 | done two ways: | |
2ca22b03 NC |
7334 | |
7335 | 1. Use the dll directly by adding the @samp{bin} path to the link line | |
7336 | @example | |
7337 | gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx | |
c0065db7 | 7338 | @end example |
2ca22b03 | 7339 | |
69da35b5 NC |
7340 | However, as the dll's often have version numbers appended to their names |
7341 | (@samp{cygncurses-5.dll}) this will often fail, unless one specifies | |
7342 | @samp{-L../bin -lncurses-5} to include the version. Import libs are generally | |
7343 | not versioned, and do not have this difficulty. | |
7344 | ||
2ca22b03 NC |
7345 | 2. Create a symbolic link from the dll to a file in the @samp{lib} |
7346 | directory according to the above mentioned search pattern. This | |
7347 | should be used to avoid unwanted changes in the tools needed for | |
7348 | making the app/dll. | |
7349 | ||
7350 | @example | |
7351 | ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a] | |
c0065db7 | 7352 | @end example |
2ca22b03 NC |
7353 | |
7354 | Then you can link without any make environment changes. | |
7355 | ||
7356 | @example | |
7357 | gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx | |
c0065db7 | 7358 | @end example |
69da35b5 NC |
7359 | |
7360 | This technique also avoids the version number problems, because the following is | |
7361 | perfectly legal | |
7362 | ||
7363 | @example | |
7364 | bin/ | |
7365 | cygxxx-5.dll | |
7366 | lib/ | |
c0065db7 | 7367 | libxxx.dll.a -> ../bin/cygxxx-5.dll |
69da35b5 NC |
7368 | @end example |
7369 | ||
dc8465bf | 7370 | Linking directly to a dll without using an import lib will work |
69da35b5 NC |
7371 | even when auto-import features are exercised, and even when |
7372 | @samp{--enable-runtime-pseudo-relocs} is used. | |
7373 | ||
7374 | Given the improvements in speed and memory usage, one might justifiably | |
45e948fe | 7375 | wonder why import libraries are used at all. There are three reasons: |
69da35b5 NC |
7376 | |
7377 | 1. Until recently, the link-directly-to-dll functionality did @emph{not} | |
7378 | work with auto-imported data. | |
7379 | ||
dc8465bf NC |
7380 | 2. Sometimes it is necessary to include pure static objects within the |
7381 | import library (which otherwise contains only bfd's for indirection | |
7382 | symbols that point to the exports of a dll). Again, the import lib | |
7383 | for the cygwin kernel makes use of this ability, and it is not | |
7384 | possible to do this without an import lib. | |
69da35b5 | 7385 | |
45e948fe NC |
7386 | 3. Symbol aliases can only be resolved using an import lib. This is |
7387 | critical when linking against OS-supplied dll's (eg, the win32 API) | |
7388 | in which symbols are usually exported as undecorated aliases of their | |
7389 | stdcall-decorated assembly names. | |
7390 | ||
69da35b5 | 7391 | So, import libs are not going away. But the ability to replace |
c0065db7 RM |
7392 | true import libs with a simple symbolic link to (or a copy of) |
7393 | a dll, in many cases, is a useful addition to the suite of tools | |
7394 | binutils makes available to the win32 developer. Given the | |
69da35b5 NC |
7395 | massive improvements in memory requirements during linking, storage |
7396 | requirements, and linking speed, we expect that many developers | |
7397 | will soon begin to use this feature whenever possible. | |
dc8465bf | 7398 | |
c0065db7 | 7399 | @item symbol aliasing |
dc8465bf | 7400 | @table @emph |
c0065db7 RM |
7401 | @item adding additional names |
7402 | Sometimes, it is useful to export symbols with additional names. | |
dc8465bf NC |
7403 | A symbol @samp{foo} will be exported as @samp{foo}, but it can also be |
7404 | exported as @samp{_foo} by using special directives in the DEF file | |
7405 | when creating the dll. This will affect also the optional created | |
c0065db7 | 7406 | import library. Consider the following DEF file: |
dc8465bf | 7407 | |
c0065db7 | 7408 | @example |
dc8465bf NC |
7409 | LIBRARY "xyz.dll" BASE=0x61000000 |
7410 | ||
7411 | EXPORTS | |
c0065db7 | 7412 | foo |
dc8465bf | 7413 | _foo = foo |
c0065db7 | 7414 | @end example |
dc8465bf NC |
7415 | |
7416 | The line @samp{_foo = foo} maps the symbol @samp{foo} to @samp{_foo}. | |
7417 | ||
7418 | Another method for creating a symbol alias is to create it in the | |
7419 | source code using the "weak" attribute: | |
7420 | ||
c0065db7 RM |
7421 | @example |
7422 | void foo () @{ /* Do something. */; @} | |
dc8465bf | 7423 | void _foo () __attribute__ ((weak, alias ("foo"))); |
c0065db7 | 7424 | @end example |
dc8465bf NC |
7425 | |
7426 | See the gcc manual for more information about attributes and weak | |
7427 | symbols. | |
7428 | ||
7429 | @item renaming symbols | |
7430 | Sometimes it is useful to rename exports. For instance, the cygwin | |
c0065db7 | 7431 | kernel does this regularly. A symbol @samp{_foo} can be exported as |
dc8465bf NC |
7432 | @samp{foo} but not as @samp{_foo} by using special directives in the |
7433 | DEF file. (This will also affect the import library, if it is | |
c0065db7 | 7434 | created). In the following example: |
dc8465bf | 7435 | |
c0065db7 | 7436 | @example |
dc8465bf NC |
7437 | LIBRARY "xyz.dll" BASE=0x61000000 |
7438 | ||
7439 | EXPORTS | |
7440 | _foo = foo | |
c0065db7 | 7441 | @end example |
dc8465bf NC |
7442 | |
7443 | The line @samp{_foo = foo} maps the exported symbol @samp{foo} to | |
7444 | @samp{_foo}. | |
c0065db7 | 7445 | @end table |
dc8465bf | 7446 | |
0a5d968e | 7447 | Note: using a DEF file disables the default auto-export behavior, |
c0065db7 | 7448 | unless the @samp{--export-all-symbols} command line option is used. |
0a5d968e | 7449 | If, however, you are trying to rename symbols, then you should list |
c0065db7 RM |
7450 | @emph{all} desired exports in the DEF file, including the symbols |
7451 | that are not being renamed, and do @emph{not} use the | |
7452 | @samp{--export-all-symbols} option. If you list only the | |
7453 | renamed symbols in the DEF file, and use @samp{--export-all-symbols} | |
7454 | to handle the other symbols, then the both the new names @emph{and} | |
7455 | the original names for the renamed symbols will be exported. | |
7456 | In effect, you'd be aliasing those symbols, not renaming them, | |
0a5d968e | 7457 | which is probably not what you wanted. |
c87db184 CF |
7458 | |
7459 | @cindex weak externals | |
7460 | @item weak externals | |
7461 | The Windows object format, PE, specifies a form of weak symbols called | |
7462 | weak externals. When a weak symbol is linked and the symbol is not | |
7463 | defined, the weak symbol becomes an alias for some other symbol. There | |
7464 | are three variants of weak externals: | |
7465 | @itemize | |
7466 | @item Definition is searched for in objects and libraries, historically | |
7467 | called lazy externals. | |
7468 | @item Definition is searched for only in other objects, not in libraries. | |
7469 | This form is not presently implemented. | |
7470 | @item No search; the symbol is an alias. This form is not presently | |
7471 | implemented. | |
7472 | @end itemize | |
7473 | As a GNU extension, weak symbols that do not specify an alternate symbol | |
7474 | are supported. If the symbol is undefined when linking, the symbol | |
7475 | uses a default value. | |
c1711530 DK |
7476 | |
7477 | @cindex aligned common symbols | |
7478 | @item aligned common symbols | |
7479 | As a GNU extension to the PE file format, it is possible to specify the | |
7480 | desired alignment for a common symbol. This information is conveyed from | |
7481 | the assembler or compiler to the linker by means of GNU-specific commands | |
7482 | carried in the object file's @samp{.drectve} section, which are recognized | |
7483 | by @command{ld} and respected when laying out the common symbols. Native | |
7484 | tools will be able to process object files employing this GNU extension, | |
7485 | but will fail to respect the alignment instructions, and may issue noisy | |
7486 | warnings about unknown linker directives. | |
2ca22b03 NC |
7487 | @end table |
7488 | ||
7489 | @ifclear GENERIC | |
7490 | @lowersections | |
7491 | @end ifclear | |
7492 | @end ifset | |
7493 | ||
e0001a05 NC |
7494 | @ifset XTENSA |
7495 | @ifclear GENERIC | |
7496 | @raisesections | |
7497 | @end ifclear | |
7498 | ||
7499 | @node Xtensa | |
7500 | @section @code{ld} and Xtensa Processors | |
7501 | ||
7502 | @cindex Xtensa processors | |
7503 | The default @command{ld} behavior for Xtensa processors is to interpret | |
7504 | @code{SECTIONS} commands so that lists of explicitly named sections in a | |
7505 | specification with a wildcard file will be interleaved when necessary to | |
7506 | keep literal pools within the range of PC-relative load offsets. For | |
7507 | example, with the command: | |
7508 | ||
7509 | @smallexample | |
7510 | SECTIONS | |
7511 | @{ | |
7512 | .text : @{ | |
7513 | *(.literal .text) | |
7514 | @} | |
7515 | @} | |
7516 | @end smallexample | |
7517 | ||
7518 | @noindent | |
7519 | @command{ld} may interleave some of the @code{.literal} | |
7520 | and @code{.text} sections from different object files to ensure that the | |
7521 | literal pools are within the range of PC-relative load offsets. A valid | |
7522 | interleaving might place the @code{.literal} sections from an initial | |
7523 | group of files followed by the @code{.text} sections of that group of | |
7524 | files. Then, the @code{.literal} sections from the rest of the files | |
7525 | and the @code{.text} sections from the rest of the files would follow. | |
e0001a05 | 7526 | |
43cd72b9 | 7527 | @cindex @option{--relax} on Xtensa |
e0001a05 | 7528 | @cindex relaxing on Xtensa |
43cd72b9 BW |
7529 | Relaxation is enabled by default for the Xtensa version of @command{ld} and |
7530 | provides two important link-time optimizations. The first optimization | |
7531 | is to combine identical literal values to reduce code size. A redundant | |
7532 | literal will be removed and all the @code{L32R} instructions that use it | |
7533 | will be changed to reference an identical literal, as long as the | |
7534 | location of the replacement literal is within the offset range of all | |
7535 | the @code{L32R} instructions. The second optimization is to remove | |
7536 | unnecessary overhead from assembler-generated ``longcall'' sequences of | |
7537 | @code{L32R}/@code{CALLX@var{n}} when the target functions are within | |
7538 | range of direct @code{CALL@var{n}} instructions. | |
7539 | ||
7540 | For each of these cases where an indirect call sequence can be optimized | |
7541 | to a direct call, the linker will change the @code{CALLX@var{n}} | |
7542 | instruction to a @code{CALL@var{n}} instruction, remove the @code{L32R} | |
7543 | instruction, and remove the literal referenced by the @code{L32R} | |
7544 | instruction if it is not used for anything else. Removing the | |
7545 | @code{L32R} instruction always reduces code size but can potentially | |
7546 | hurt performance by changing the alignment of subsequent branch targets. | |
7547 | By default, the linker will always preserve alignments, either by | |
7548 | switching some instructions between 24-bit encodings and the equivalent | |
7549 | density instructions or by inserting a no-op in place of the @code{L32R} | |
7550 | instruction that was removed. If code size is more important than | |
7551 | performance, the @option{--size-opt} option can be used to prevent the | |
7552 | linker from widening density instructions or inserting no-ops, except in | |
7553 | a few cases where no-ops are required for correctness. | |
7554 | ||
7555 | The following Xtensa-specific command-line options can be used to | |
7556 | control the linker: | |
7557 | ||
7558 | @cindex Xtensa options | |
7559 | @table @option | |
43cd72b9 BW |
7560 | @item --size-opt |
7561 | When optimizing indirect calls to direct calls, optimize for code size | |
7562 | more than performance. With this option, the linker will not insert | |
7563 | no-ops or widen density instructions to preserve branch target | |
7564 | alignment. There may still be some cases where no-ops are required to | |
7565 | preserve the correctness of the code. | |
7566 | @end table | |
e0001a05 NC |
7567 | |
7568 | @ifclear GENERIC | |
7569 | @lowersections | |
7570 | @end ifclear | |
7571 | @end ifset | |
7572 | ||
252b5132 RH |
7573 | @ifclear SingleFormat |
7574 | @node BFD | |
7575 | @chapter BFD | |
7576 | ||
7577 | @cindex back end | |
7578 | @cindex object file management | |
7579 | @cindex object formats available | |
7580 | @kindex objdump -i | |
7581 | The linker accesses object and archive files using the BFD libraries. | |
7582 | These libraries allow the linker to use the same routines to operate on | |
7583 | object files whatever the object file format. A different object file | |
7584 | format can be supported simply by creating a new BFD back end and adding | |
7585 | it to the library. To conserve runtime memory, however, the linker and | |
7586 | associated tools are usually configured to support only a subset of the | |
7587 | object file formats available. You can use @code{objdump -i} | |
7588 | (@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to | |
7589 | list all the formats available for your configuration. | |
7590 | ||
7591 | @cindex BFD requirements | |
7592 | @cindex requirements for BFD | |
7593 | As with most implementations, BFD is a compromise between | |
7594 | several conflicting requirements. The major factor influencing | |
7595 | BFD design was efficiency: any time used converting between | |
7596 | formats is time which would not have been spent had BFD not | |
7597 | been involved. This is partly offset by abstraction payback; since | |
7598 | BFD simplifies applications and back ends, more time and care | |
7599 | may be spent optimizing algorithms for a greater speed. | |
7600 | ||
7601 | One minor artifact of the BFD solution which you should bear in | |
7602 | mind is the potential for information loss. There are two places where | |
7603 | useful information can be lost using the BFD mechanism: during | |
7604 | conversion and during output. @xref{BFD information loss}. | |
7605 | ||
7606 | @menu | |
7607 | * BFD outline:: How it works: an outline of BFD | |
7608 | @end menu | |
7609 | ||
7610 | @node BFD outline | |
36f63dca | 7611 | @section How It Works: An Outline of BFD |
252b5132 RH |
7612 | @cindex opening object files |
7613 | @include bfdsumm.texi | |
7614 | @end ifclear | |
7615 | ||
7616 | @node Reporting Bugs | |
7617 | @chapter Reporting Bugs | |
ff5dcc92 SC |
7618 | @cindex bugs in @command{ld} |
7619 | @cindex reporting bugs in @command{ld} | |
252b5132 | 7620 | |
ff5dcc92 | 7621 | Your bug reports play an essential role in making @command{ld} reliable. |
252b5132 RH |
7622 | |
7623 | Reporting a bug may help you by bringing a solution to your problem, or | |
7624 | it may not. But in any case the principal function of a bug report is | |
ff5dcc92 | 7625 | to help the entire community by making the next version of @command{ld} |
252b5132 | 7626 | work better. Bug reports are your contribution to the maintenance of |
ff5dcc92 | 7627 | @command{ld}. |
252b5132 RH |
7628 | |
7629 | In order for a bug report to serve its purpose, you must include the | |
7630 | information that enables us to fix the bug. | |
7631 | ||
7632 | @menu | |
7633 | * Bug Criteria:: Have you found a bug? | |
7634 | * Bug Reporting:: How to report bugs | |
7635 | @end menu | |
7636 | ||
7637 | @node Bug Criteria | |
36f63dca | 7638 | @section Have You Found a Bug? |
252b5132 RH |
7639 | @cindex bug criteria |
7640 | ||
7641 | If you are not sure whether you have found a bug, here are some guidelines: | |
7642 | ||
7643 | @itemize @bullet | |
7644 | @cindex fatal signal | |
7645 | @cindex linker crash | |
7646 | @cindex crash of linker | |
7647 | @item | |
7648 | If the linker gets a fatal signal, for any input whatever, that is a | |
ff5dcc92 | 7649 | @command{ld} bug. Reliable linkers never crash. |
252b5132 RH |
7650 | |
7651 | @cindex error on valid input | |
7652 | @item | |
ff5dcc92 | 7653 | If @command{ld} produces an error message for valid input, that is a bug. |
252b5132 RH |
7654 | |
7655 | @cindex invalid input | |
7656 | @item | |
ff5dcc92 | 7657 | If @command{ld} does not produce an error message for invalid input, that |
252b5132 RH |
7658 | may be a bug. In the general case, the linker can not verify that |
7659 | object files are correct. | |
7660 | ||
7661 | @item | |
7662 | If you are an experienced user of linkers, your suggestions for | |
ff5dcc92 | 7663 | improvement of @command{ld} are welcome in any case. |
252b5132 RH |
7664 | @end itemize |
7665 | ||
7666 | @node Bug Reporting | |
36f63dca | 7667 | @section How to Report Bugs |
252b5132 | 7668 | @cindex bug reports |
ff5dcc92 | 7669 | @cindex @command{ld} bugs, reporting |
252b5132 RH |
7670 | |
7671 | A number of companies and individuals offer support for @sc{gnu} | |
ff5dcc92 | 7672 | products. If you obtained @command{ld} from a support organization, we |
252b5132 RH |
7673 | recommend you contact that organization first. |
7674 | ||
7675 | You can find contact information for many support companies and | |
7676 | individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs | |
7677 | distribution. | |
7678 | ||
ad22bfe8 | 7679 | @ifset BUGURL |
ff5dcc92 | 7680 | Otherwise, send bug reports for @command{ld} to |
ad22bfe8 JM |
7681 | @value{BUGURL}. |
7682 | @end ifset | |
252b5132 RH |
7683 | |
7684 | The fundamental principle of reporting bugs usefully is this: | |
7685 | @strong{report all the facts}. If you are not sure whether to state a | |
7686 | fact or leave it out, state it! | |
7687 | ||
7688 | Often people omit facts because they think they know what causes the | |
7689 | problem and assume that some details do not matter. Thus, you might | |
b553b183 NC |
7690 | assume that the name of a symbol you use in an example does not |
7691 | matter. Well, probably it does not, but one cannot be sure. Perhaps | |
7692 | the bug is a stray memory reference which happens to fetch from the | |
7693 | location where that name is stored in memory; perhaps, if the name | |
7694 | were different, the contents of that location would fool the linker | |
7695 | into doing the right thing despite the bug. Play it safe and give a | |
7696 | specific, complete example. That is the easiest thing for you to do, | |
c0065db7 | 7697 | and the most helpful. |
b553b183 NC |
7698 | |
7699 | Keep in mind that the purpose of a bug report is to enable us to fix | |
7700 | the bug if it is new to us. Therefore, always write your bug reports | |
7701 | on the assumption that the bug has not been reported previously. | |
252b5132 RH |
7702 | |
7703 | Sometimes people give a few sketchy facts and ask, ``Does this ring a | |
36f63dca NC |
7704 | bell?'' This cannot help us fix a bug, so it is basically useless. We |
7705 | respond by asking for enough details to enable us to investigate. | |
7706 | You might as well expedite matters by sending them to begin with. | |
252b5132 RH |
7707 | |
7708 | To enable us to fix the bug, you should include all these things: | |
7709 | ||
7710 | @itemize @bullet | |
7711 | @item | |
ff5dcc92 | 7712 | The version of @command{ld}. @command{ld} announces it if you start it with |
252b5132 RH |
7713 | the @samp{--version} argument. |
7714 | ||
7715 | Without this, we will not know whether there is any point in looking for | |
ff5dcc92 | 7716 | the bug in the current version of @command{ld}. |
252b5132 RH |
7717 | |
7718 | @item | |
ff5dcc92 | 7719 | Any patches you may have applied to the @command{ld} source, including any |
252b5132 RH |
7720 | patches made to the @code{BFD} library. |
7721 | ||
7722 | @item | |
7723 | The type of machine you are using, and the operating system name and | |
7724 | version number. | |
7725 | ||
7726 | @item | |
ff5dcc92 | 7727 | What compiler (and its version) was used to compile @command{ld}---e.g. |
252b5132 RH |
7728 | ``@code{gcc-2.7}''. |
7729 | ||
7730 | @item | |
7731 | The command arguments you gave the linker to link your example and | |
7732 | observe the bug. To guarantee you will not omit something important, | |
7733 | list them all. A copy of the Makefile (or the output from make) is | |
7734 | sufficient. | |
7735 | ||
7736 | If we were to try to guess the arguments, we would probably guess wrong | |
7737 | and then we might not encounter the bug. | |
7738 | ||
7739 | @item | |
7740 | A complete input file, or set of input files, that will reproduce the | |
b553b183 NC |
7741 | bug. It is generally most helpful to send the actual object files |
7742 | provided that they are reasonably small. Say no more than 10K. For | |
7743 | bigger files you can either make them available by FTP or HTTP or else | |
7744 | state that you are willing to send the object file(s) to whomever | |
7745 | requests them. (Note - your email will be going to a mailing list, so | |
7746 | we do not want to clog it up with large attachments). But small | |
7747 | attachments are best. | |
252b5132 RH |
7748 | |
7749 | If the source files were assembled using @code{gas} or compiled using | |
7750 | @code{gcc}, then it may be OK to send the source files rather than the | |
7751 | object files. In this case, be sure to say exactly what version of | |
7752 | @code{gas} or @code{gcc} was used to produce the object files. Also say | |
7753 | how @code{gas} or @code{gcc} were configured. | |
7754 | ||
7755 | @item | |
7756 | A description of what behavior you observe that you believe is | |
7757 | incorrect. For example, ``It gets a fatal signal.'' | |
7758 | ||
ff5dcc92 | 7759 | Of course, if the bug is that @command{ld} gets a fatal signal, then we |
252b5132 RH |
7760 | will certainly notice it. But if the bug is incorrect output, we might |
7761 | not notice unless it is glaringly wrong. You might as well not give us | |
7762 | a chance to make a mistake. | |
7763 | ||
7764 | Even if the problem you experience is a fatal signal, you should still | |
7765 | say so explicitly. Suppose something strange is going on, such as, your | |
b45619c0 | 7766 | copy of @command{ld} is out of sync, or you have encountered a bug in the |
252b5132 RH |
7767 | C library on your system. (This has happened!) Your copy might crash |
7768 | and ours would not. If you told us to expect a crash, then when ours | |
7769 | fails to crash, we would know that the bug was not happening for us. If | |
7770 | you had not told us to expect a crash, then we would not be able to draw | |
7771 | any conclusion from our observations. | |
7772 | ||
7773 | @item | |
ff5dcc92 | 7774 | If you wish to suggest changes to the @command{ld} source, send us context |
252b5132 RH |
7775 | diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or |
7776 | @samp{-p} option. Always send diffs from the old file to the new file. | |
ff5dcc92 | 7777 | If you even discuss something in the @command{ld} source, refer to it by |
252b5132 RH |
7778 | context, not by line number. |
7779 | ||
7780 | The line numbers in our development sources will not match those in your | |
7781 | sources. Your line numbers would convey no useful information to us. | |
7782 | @end itemize | |
7783 | ||
7784 | Here are some things that are not necessary: | |
7785 | ||
7786 | @itemize @bullet | |
7787 | @item | |
7788 | A description of the envelope of the bug. | |
7789 | ||
7790 | Often people who encounter a bug spend a lot of time investigating | |
7791 | which changes to the input file will make the bug go away and which | |
7792 | changes will not affect it. | |
7793 | ||
7794 | This is often time consuming and not very useful, because the way we | |
7795 | will find the bug is by running a single example under the debugger | |
7796 | with breakpoints, not by pure deduction from a series of examples. | |
7797 | We recommend that you save your time for something else. | |
7798 | ||
7799 | Of course, if you can find a simpler example to report @emph{instead} | |
7800 | of the original one, that is a convenience for us. Errors in the | |
7801 | output will be easier to spot, running under the debugger will take | |
7802 | less time, and so on. | |
7803 | ||
7804 | However, simplification is not vital; if you do not want to do this, | |
7805 | report the bug anyway and send us the entire test case you used. | |
7806 | ||
7807 | @item | |
7808 | A patch for the bug. | |
7809 | ||
7810 | A patch for the bug does help us if it is a good one. But do not omit | |
7811 | the necessary information, such as the test case, on the assumption that | |
7812 | a patch is all we need. We might see problems with your patch and decide | |
7813 | to fix the problem another way, or we might not understand it at all. | |
7814 | ||
ff5dcc92 | 7815 | Sometimes with a program as complicated as @command{ld} it is very hard to |
252b5132 RH |
7816 | construct an example that will make the program follow a certain path |
7817 | through the code. If you do not send us the example, we will not be | |
7818 | able to construct one, so we will not be able to verify that the bug is | |
7819 | fixed. | |
7820 | ||
7821 | And if we cannot understand what bug you are trying to fix, or why your | |
7822 | patch should be an improvement, we will not install it. A test case will | |
7823 | help us to understand. | |
7824 | ||
7825 | @item | |
7826 | A guess about what the bug is or what it depends on. | |
7827 | ||
7828 | Such guesses are usually wrong. Even we cannot guess right about such | |
7829 | things without first using the debugger to find the facts. | |
7830 | @end itemize | |
7831 | ||
7832 | @node MRI | |
7833 | @appendix MRI Compatible Script Files | |
7834 | @cindex MRI compatibility | |
ff5dcc92 SC |
7835 | To aid users making the transition to @sc{gnu} @command{ld} from the MRI |
7836 | linker, @command{ld} can use MRI compatible linker scripts as an | |
252b5132 RH |
7837 | alternative to the more general-purpose linker scripting language |
7838 | described in @ref{Scripts}. MRI compatible linker scripts have a much | |
7839 | simpler command set than the scripting language otherwise used with | |
ff5dcc92 | 7840 | @command{ld}. @sc{gnu} @command{ld} supports the most commonly used MRI |
252b5132 RH |
7841 | linker commands; these commands are described here. |
7842 | ||
7843 | In general, MRI scripts aren't of much use with the @code{a.out} object | |
7844 | file format, since it only has three sections and MRI scripts lack some | |
7845 | features to make use of them. | |
7846 | ||
7847 | You can specify a file containing an MRI-compatible script using the | |
7848 | @samp{-c} command-line option. | |
7849 | ||
7850 | Each command in an MRI-compatible script occupies its own line; each | |
7851 | command line starts with the keyword that identifies the command (though | |
7852 | blank lines are also allowed for punctuation). If a line of an | |
ff5dcc92 | 7853 | MRI-compatible script begins with an unrecognized keyword, @command{ld} |
252b5132 RH |
7854 | issues a warning message, but continues processing the script. |
7855 | ||
7856 | Lines beginning with @samp{*} are comments. | |
7857 | ||
7858 | You can write these commands using all upper-case letters, or all | |
7859 | lower case; for example, @samp{chip} is the same as @samp{CHIP}. | |
7860 | The following list shows only the upper-case form of each command. | |
7861 | ||
7862 | @table @code | |
7863 | @cindex @code{ABSOLUTE} (MRI) | |
7864 | @item ABSOLUTE @var{secname} | |
7865 | @itemx ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname} | |
ff5dcc92 | 7866 | Normally, @command{ld} includes in the output file all sections from all |
252b5132 RH |
7867 | the input files. However, in an MRI-compatible script, you can use the |
7868 | @code{ABSOLUTE} command to restrict the sections that will be present in | |
7869 | your output program. If the @code{ABSOLUTE} command is used at all in a | |
7870 | script, then only the sections named explicitly in @code{ABSOLUTE} | |
7871 | commands will appear in the linker output. You can still use other | |
7872 | input sections (whatever you select on the command line, or using | |
7873 | @code{LOAD}) to resolve addresses in the output file. | |
7874 | ||
7875 | @cindex @code{ALIAS} (MRI) | |
7876 | @item ALIAS @var{out-secname}, @var{in-secname} | |
7877 | Use this command to place the data from input section @var{in-secname} | |
7878 | in a section called @var{out-secname} in the linker output file. | |
7879 | ||
7880 | @var{in-secname} may be an integer. | |
7881 | ||
7882 | @cindex @code{ALIGN} (MRI) | |
7883 | @item ALIGN @var{secname} = @var{expression} | |
7884 | Align the section called @var{secname} to @var{expression}. The | |
7885 | @var{expression} should be a power of two. | |
7886 | ||
7887 | @cindex @code{BASE} (MRI) | |
7888 | @item BASE @var{expression} | |
7889 | Use the value of @var{expression} as the lowest address (other than | |
7890 | absolute addresses) in the output file. | |
7891 | ||
7892 | @cindex @code{CHIP} (MRI) | |
7893 | @item CHIP @var{expression} | |
7894 | @itemx CHIP @var{expression}, @var{expression} | |
7895 | This command does nothing; it is accepted only for compatibility. | |
7896 | ||
7897 | @cindex @code{END} (MRI) | |
7898 | @item END | |
7899 | This command does nothing whatever; it's only accepted for compatibility. | |
7900 | ||
7901 | @cindex @code{FORMAT} (MRI) | |
7902 | @item FORMAT @var{output-format} | |
7903 | Similar to the @code{OUTPUT_FORMAT} command in the more general linker | |
a1ab1d2a | 7904 | language, but restricted to one of these output formats: |
252b5132 RH |
7905 | |
7906 | @enumerate | |
a1ab1d2a | 7907 | @item |
252b5132 RH |
7908 | S-records, if @var{output-format} is @samp{S} |
7909 | ||
7910 | @item | |
7911 | IEEE, if @var{output-format} is @samp{IEEE} | |
7912 | ||
7913 | @item | |
7914 | COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is | |
7915 | @samp{COFF} | |
7916 | @end enumerate | |
7917 | ||
7918 | @cindex @code{LIST} (MRI) | |
7919 | @item LIST @var{anything}@dots{} | |
7920 | Print (to the standard output file) a link map, as produced by the | |
ff5dcc92 | 7921 | @command{ld} command-line option @samp{-M}. |
252b5132 RH |
7922 | |
7923 | The keyword @code{LIST} may be followed by anything on the | |
7924 | same line, with no change in its effect. | |
7925 | ||
7926 | @cindex @code{LOAD} (MRI) | |
7927 | @item LOAD @var{filename} | |
7928 | @itemx LOAD @var{filename}, @var{filename}, @dots{} @var{filename} | |
7929 | Include one or more object file @var{filename} in the link; this has the | |
ff5dcc92 | 7930 | same effect as specifying @var{filename} directly on the @command{ld} |
252b5132 RH |
7931 | command line. |
7932 | ||
7933 | @cindex @code{NAME} (MRI) | |
7934 | @item NAME @var{output-name} | |
ff5dcc92 | 7935 | @var{output-name} is the name for the program produced by @command{ld}; the |
252b5132 RH |
7936 | MRI-compatible command @code{NAME} is equivalent to the command-line |
7937 | option @samp{-o} or the general script language command @code{OUTPUT}. | |
7938 | ||
7939 | @cindex @code{ORDER} (MRI) | |
7940 | @item ORDER @var{secname}, @var{secname}, @dots{} @var{secname} | |
7941 | @itemx ORDER @var{secname} @var{secname} @var{secname} | |
ff5dcc92 | 7942 | Normally, @command{ld} orders the sections in its output file in the |
252b5132 RH |
7943 | order in which they first appear in the input files. In an MRI-compatible |
7944 | script, you can override this ordering with the @code{ORDER} command. The | |
7945 | sections you list with @code{ORDER} will appear first in your output | |
7946 | file, in the order specified. | |
7947 | ||
7948 | @cindex @code{PUBLIC} (MRI) | |
7949 | @item PUBLIC @var{name}=@var{expression} | |
7950 | @itemx PUBLIC @var{name},@var{expression} | |
7951 | @itemx PUBLIC @var{name} @var{expression} | |
7952 | Supply a value (@var{expression}) for external symbol | |
7953 | @var{name} used in the linker input files. | |
7954 | ||
7955 | @cindex @code{SECT} (MRI) | |
7956 | @item SECT @var{secname}, @var{expression} | |
7957 | @itemx SECT @var{secname}=@var{expression} | |
7958 | @itemx SECT @var{secname} @var{expression} | |
7959 | You can use any of these three forms of the @code{SECT} command to | |
7960 | specify the start address (@var{expression}) for section @var{secname}. | |
7961 | If you have more than one @code{SECT} statement for the same | |
7962 | @var{secname}, only the @emph{first} sets the start address. | |
7963 | @end table | |
7964 | ||
793c5807 NC |
7965 | @node GNU Free Documentation License |
7966 | @appendix GNU Free Documentation License | |
36f63dca | 7967 | @include fdl.texi |
704c465c | 7968 | |
370b66a1 CD |
7969 | @node LD Index |
7970 | @unnumbered LD Index | |
252b5132 RH |
7971 | |
7972 | @printindex cp | |
7973 | ||
7974 | @tex | |
7ca01ed9 | 7975 | % I think something like @@colophon should be in texinfo. In the |
252b5132 RH |
7976 | % meantime: |
7977 | \long\def\colophon{\hbox to0pt{}\vfill | |
7978 | \centerline{The body of this manual is set in} | |
7979 | \centerline{\fontname\tenrm,} | |
7980 | \centerline{with headings in {\bf\fontname\tenbf}} | |
7981 | \centerline{and examples in {\tt\fontname\tentt}.} | |
7982 | \centerline{{\it\fontname\tenit\/} and} | |
7983 | \centerline{{\sl\fontname\tensl\/}} | |
7984 | \centerline{are used for emphasis.}\vfill} | |
7985 | \page\colophon | |
7ca01ed9 | 7986 | % Blame: doc@@cygnus.com, 28mar91. |
252b5132 RH |
7987 | @end tex |
7988 | ||
252b5132 | 7989 | @bye |