Commit | Line | Data |
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f22eee08 | 1 | \input texinfo |
c8072296 | 2 | @setfilename ld.info |
b4d4e8e3 | 3 | @syncodeindex ky cp |
7f9ae73e | 4 | @include configdoc.texi |
8de26d62 | 5 | @c (configdoc.texi is generated by the Makefile) |
ec40bbb8 DM |
6 | |
7 | @c @smallbook | |
c8072296 | 8 | @c @cropmarks |
1c48127e RP |
9 | |
10 | @ifinfo | |
11 | @format | |
12 | START-INFO-DIR-ENTRY | |
8ddef552 | 13 | * Ld:: The GNU linker. |
1c48127e RP |
14 | END-INFO-DIR-ENTRY |
15 | @end format | |
16 | @end ifinfo | |
17 | ||
b4d4e8e3 | 18 | @ifinfo |
246504a5 | 19 | This file documents the GNU linker LD. |
b4d4e8e3 | 20 | |
d76ae847 | 21 | Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc. |
b4d4e8e3 RP |
22 | |
23 | Permission is granted to make and distribute verbatim copies of | |
24 | this manual provided the copyright notice and this permission notice | |
25 | are preserved on all copies. | |
26 | ||
d76ae847 RP |
27 | Permission is granted to copy and distribute modified versions of this |
28 | manual under the conditions for verbatim copying, provided also that | |
29 | the entire resulting derived work is distributed under the terms of a | |
30 | permission notice identical to this one. | |
31 | ||
32 | Permission is granted to copy and distribute translations of this manual | |
33 | into another language, under the above conditions for modified versions. | |
34 | ||
b4d4e8e3 RP |
35 | @ignore |
36 | Permission is granted to process this file through Tex and print the | |
37 | results, provided the printed document carries copying permission | |
38 | notice identical to this one except for the removal of this paragraph | |
39 | (this paragraph not being relevant to the printed manual). | |
40 | ||
41 | @end ignore | |
b4d4e8e3 | 42 | @end ifinfo |
2c5c0674 RP |
43 | @iftex |
44 | @finalout | |
b4d4e8e3 | 45 | @setchapternewpage odd |
246504a5 | 46 | @settitle Using LD, the GNU linker |
f22eee08 | 47 | @titlepage |
246504a5 | 48 | @title Using ld |
c8072296 | 49 | @subtitle The GNU linker |
f22eee08 | 50 | @sp 1 |
cb70c872 | 51 | @subtitle @code{ld} version 2 |
d76ae847 | 52 | @subtitle March 1993 |
c8072296 RP |
53 | @author Steve Chamberlain and Roland Pesch |
54 | @author Cygnus Support | |
b4d4e8e3 RP |
55 | @page |
56 | ||
57 | @tex | |
b4d4e8e3 RP |
58 | {\parskip=0pt |
59 | \hfill Cygnus Support\par | |
2c5c0674 | 60 | \hfill steve\@cygnus.com, pesch\@cygnus.com\par |
ec40bbb8 DM |
61 | \hfill {\it Using LD, the GNU linker}\par |
62 | \hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com), March 1993.\par | |
b4d4e8e3 RP |
63 | } |
64 | \global\parindent=0pt % Steve likes it this way. | |
65 | @end tex | |
66 | ||
f22eee08 | 67 | @vskip 0pt plus 1filll |
d76ae847 | 68 | Copyright @copyright{} 1991, 1992, 1993 Free Software Foundation, Inc. |
f22eee08 RP |
69 | |
70 | Permission is granted to make and distribute verbatim copies of | |
71 | this manual provided the copyright notice and this permission notice | |
72 | are preserved on all copies. | |
73 | ||
74 | Permission is granted to copy and distribute modified versions of this | |
75 | manual under the conditions for verbatim copying, provided also that | |
76 | the entire resulting derived work is distributed under the terms of a | |
77 | permission notice identical to this one. | |
78 | ||
79 | Permission is granted to copy and distribute translations of this manual | |
80 | into another language, under the above conditions for modified versions. | |
f22eee08 | 81 | @end titlepage |
2c5c0674 | 82 | @end iftex |
b4d4e8e3 | 83 | @c FIXME: Talk about importance of *order* of args, cmds to linker! |
f22eee08 | 84 | |
f22eee08 | 85 | @ifinfo |
ec40bbb8 DM |
86 | @node Top |
87 | @top Using ld | |
246504a5 | 88 | This file documents the GNU linker ld. |
f22eee08 | 89 | |
2c5c0674 | 90 | @menu |
2d59b2c3 RP |
91 | * Overview:: Overview |
92 | * Invocation:: Invocation | |
93 | * Commands:: Command Language | |
ec40bbb8 | 94 | @ifset GENERIC |
2d59b2c3 | 95 | * Machine Dependent:: Machine Dependent Features |
ec40bbb8 DM |
96 | @end ifset |
97 | @ifclear GENERIC | |
98 | @ifset H8300 | |
99 | * H8/300:: ld and the H8/300 | |
100 | @end ifset | |
101 | @ifset I960 | |
102 | * i960:: ld and the Intel 960 family | |
103 | @end ifset | |
104 | @end ifclear | |
105 | @ifclear SingleFormat | |
2d59b2c3 | 106 | * BFD:: BFD |
ec40bbb8 DM |
107 | @end ifclear |
108 | @c Following blank line required for remaining bug in makeinfo conds/menus | |
109 | ||
2d59b2c3 RP |
110 | * MRI:: MRI Compatible Script Files |
111 | * Index:: Index | |
2c5c0674 | 112 | @end menu |
ec40bbb8 | 113 | @end ifinfo |
2c5c0674 | 114 | |
ec40bbb8 | 115 | @node Overview |
f22eee08 RP |
116 | @chapter Overview |
117 | ||
2c5c0674 RP |
118 | @cindex GNU linker |
119 | @cindex what is this? | |
246504a5 | 120 | @code{ld} combines a number of object and archive files, relocates |
ec40bbb8 DM |
121 | their data and ties up symbol references. Usually the last step in |
122 | compiling a program is to run @code{ld}. | |
f22eee08 | 123 | |
246504a5 | 124 | @code{ld} accepts Linker Command Language files written in |
2c5c0674 | 125 | a superset of AT&T's Link Editor Command Language syntax, |
b4d4e8e3 | 126 | to provide explicit and total control over the linking process. |
f22eee08 | 127 | |
ec40bbb8 | 128 | @ifclear SingleFormat |
246504a5 RP |
129 | This version of @code{ld} uses the general purpose BFD libraries |
130 | to operate on object files. This allows @code{ld} to read, combine, and | |
b4d4e8e3 RP |
131 | write object files in many different formats---for example, COFF or |
132 | @code{a.out}. Different formats may be linked together to produce any | |
133 | available kind of object file. @xref{BFD} for a list of formats | |
134 | supported on various architectures. | |
ec40bbb8 | 135 | @end ifclear |
f22eee08 | 136 | |
2c5c0674 RP |
137 | Aside from its flexibility, the GNU linker is more helpful than other |
138 | linkers in providing diagnostic information. Many linkers abandon | |
139 | execution immediately upon encountering an error; whenever possible, | |
246504a5 | 140 | @code{ld} continues executing, allowing you to identify other errors |
2c5c0674 RP |
141 | (or, in some cases, to get an output file in spite of the error). |
142 | ||
ec40bbb8 | 143 | @node Invocation |
2c5c0674 RP |
144 | @chapter Invocation |
145 | ||
246504a5 | 146 | The GNU linker @code{ld} is meant to cover a broad range of situations, |
2c5c0674 | 147 | and to be as compatible as possible with other linkers. As a result, |
ec40bbb8 | 148 | you have many choices to control its behavior. |
2c5c0674 | 149 | |
ec40bbb8 | 150 | @ifset UsesEnvVars |
2c5c0674 | 151 | @menu |
2d59b2c3 RP |
152 | * Options:: Command Line Options |
153 | * Environment:: Environment Variables | |
2c5c0674 | 154 | @end menu |
f22eee08 | 155 | |
ec40bbb8 | 156 | @node Options |
2c5c0674 | 157 | @section Command Line Options |
ec40bbb8 | 158 | @end ifset |
2c5c0674 RP |
159 | |
160 | @cindex command line | |
161 | @cindex options | |
ec40bbb8 | 162 | Here is a summary of the options you can use on the @code{ld} command |
2c5c0674 | 163 | line: |
f22eee08 | 164 | |
ec40bbb8 | 165 | @c FIXME! -relax only avail h8/300, i960. Conditionals screwed in examples. |
c8072296 | 166 | @smallexample |
de87cdb4 | 167 | ld [ -o @var{output} ] @var{objfile}@dots{} |
cb70c872 RP |
168 | [ -A@var{architecture} ] [ -b @var{input-format} ] [ -Bstatic ] |
169 | [ -c @var{MRI-commandfile} ] [ -d | -dc | -dp ] | |
d76ae847 | 170 | [ -defsym @var{symbol}=@var{expression} ] |
cb70c872 | 171 | [ -e @var{entry} ] [ -F ] [ -F @var{format} ] |
de87cdb4 DM |
172 | [ -format @var{input-format} ] [ -g ] [ -G @var{size} ] [ --help ] [ -i ] |
173 | [ -l@var{archive} ] [ -L@var{searchdir} ] [ -M ] [ -Map @var{mapfile} ] | |
d18a4527 | 174 | [ -m @var{emulation} ] [ -N | -n ] [ -noinhibit-exec ] |
346535cc | 175 | [ -oformat @var{output-format} ] [ -R @var{filename} ] [ -relax ] |
8594f568 SS |
176 | [ -r | -Ur ] [ -S ] [ -s ] [ -sort-common ] [ -stats ] |
177 | [ -T @var{commandfile} ] | |
867a1b8a DM |
178 | [ -Ttext @var{org} ] [ -Tdata @var{org} ] |
179 | [ -Tbss @var{org} ] [ -t ] [ -u @var{symbol}] [-V] [-v] [ --version ] | |
2a28d8b0 | 180 | [ -warn-common ] [ -y@var{symbol} ] [ -X ] [-x ] |
c8072296 | 181 | @end smallexample |
b4d4e8e3 RP |
182 | |
183 | This plethora of command-line options may seem intimidating, but in | |
184 | actual practice few of them are used in any particular context. | |
2c5c0674 | 185 | @cindex standard Unix system |
246504a5 | 186 | For instance, a frequent use of @code{ld} is to link standard Unix |
b4d4e8e3 RP |
187 | object files on a standard, supported Unix system. On such a system, to |
188 | link a file @code{hello.o}: | |
ec40bbb8 | 189 | |
f22eee08 | 190 | @example |
ec40bbb8 | 191 | ld -o @var{output} /lib/crt0.o hello.o -lc |
f22eee08 | 192 | @end example |
ec40bbb8 | 193 | |
d76ae847 | 194 | This tells @code{ld} to produce a file called @var{output} as the |
b4d4e8e3 | 195 | result of linking the file @code{/lib/crt0.o} with @code{hello.o} and |
ec40bbb8 DM |
196 | the library @code{libc.a}, which will come from the standard search |
197 | directories. (See the discussion of the @samp{-l} option below.) | |
f22eee08 | 198 | |
246504a5 | 199 | The command-line options to @code{ld} may be specified in any order, and |
ec40bbb8 | 200 | may be repeated at will. Repeating most options with a |
f22eee08 | 201 | different argument will either have no further effect, or override prior |
ec40bbb8 | 202 | occurrences (those further to the left on the command line) of that |
f22eee08 RP |
203 | option. |
204 | ||
ec40bbb8 | 205 | @ifclear SingleFormat |
2c5c0674 | 206 | The exceptions---which may meaningfully be used more than once---are |
ec40bbb8 DM |
207 | @samp{-A}, @samp{-b} (or its synonym @samp{-format}), @samp{-defsym}, |
208 | @samp{-L}, @samp{-l}, @samp{-R}, and @samp{-u}. | |
209 | @end ifclear | |
210 | @ifset SingleFormat | |
211 | The exceptions---which may meaningfully be used more than once---are | |
212 | @samp{-A}, @samp{-defsym}, @samp{-L}, @samp{-l}, @samp{-R}, and @samp{-u}. | |
213 | @end ifset | |
f22eee08 | 214 | |
2c5c0674 | 215 | @cindex object files |
8ddef552 | 216 | The list of object files to be linked together, shown as @var{objfile}@dots{}, |
ec40bbb8 DM |
217 | may follow, precede, or be mixed in with command-line options, except that |
218 | an @var{objfile} argument may not be placed between an option and | |
b4d4e8e3 | 219 | its argument. |
f22eee08 | 220 | |
7f9ae73e RP |
221 | Usually the linker is invoked with at least one object file, but you can |
222 | specify other forms of binary input files using @samp{-l}, @samp{-R}, | |
223 | and the script command language. If @emph{no} binary input files at all | |
224 | are specified, the linker does not produce any output, and issues the | |
225 | message @samp{No input files}. | |
2c5c0674 RP |
226 | |
227 | Option arguments must either follow the option letter without intervening | |
f22eee08 RP |
228 | whitespace, or be given as separate arguments immediately following the |
229 | option that requires them. | |
230 | ||
231 | @table @code | |
ec40bbb8 | 232 | @ifset I960 |
2c5c0674 RP |
233 | @cindex architectures |
234 | @kindex -A@var{arch} | |
b4d4e8e3 | 235 | @item -A@var{architecture} |
246504a5 RP |
236 | In the current release of @code{ld}, this option is useful only for the |
237 | Intel 960 family of architectures. In that @code{ld} configuration, the | |
1c48127e RP |
238 | @var{architecture} argument identifies the particular architecture in |
239 | the 960 family, enabling some safeguards and modifying the | |
d76ae847 RP |
240 | archive-library search path. @xref{i960,,@code{ld} and the Intel 960 |
241 | family}, for details. | |
b4d4e8e3 | 242 | |
246504a5 | 243 | Future releases of @code{ld} may support similar functionality for |
b4d4e8e3 | 244 | other architecture families. |
ec40bbb8 | 245 | @end ifset |
b4d4e8e3 | 246 | |
ec40bbb8 | 247 | @ifclear SingleFormat |
2c5c0674 RP |
248 | @cindex binary input format |
249 | @kindex -b @var{format} | |
250 | @cindex input format | |
251 | @item -b @var{input-format} | |
252 | @cindex input format | |
253 | Specify the binary format for input object files that follow this option | |
254 | on the command line. You don't usually need to specify this, as | |
246504a5 | 255 | @code{ld} is configured to expect as a default input format the most |
2c5c0674 | 256 | usual format on each machine. @var{input-format} is a text string, the |
d76ae847 | 257 | name of a particular format supported by the BFD libraries. |
346535cc DM |
258 | (You can list the available binary formats with @samp{objdump -i}.) |
259 | @w{@samp{-format @var{input-format}}} has the same effect, as does the | |
260 | script command @code{TARGET}. @xref{BFD}. | |
2c5c0674 RP |
261 | |
262 | You may want to use this option if you are linking files with an unusual | |
ec40bbb8 | 263 | binary format. You can also use @samp{-b} to switch formats explicitly (when |
2c5c0674 | 264 | linking object files of different formats), by including |
ec40bbb8 | 265 | @samp{-b @var{input-format}} before each group of object files in a |
2c5c0674 RP |
266 | particular format. |
267 | ||
268 | The default format is taken from the environment variable | |
ec40bbb8 DM |
269 | @code{GNUTARGET}. |
270 | @ifset UsesEnvVars | |
271 | @xref{Environment}. | |
272 | @end ifset | |
273 | You can also define the input | |
867a1b8a | 274 | format from a script, using the command @code{TARGET}; see @ref{Option |
d76ae847 | 275 | Commands}. |
ec40bbb8 | 276 | @end ifclear |
2c5c0674 RP |
277 | |
278 | @kindex -Bstatic | |
f22eee08 | 279 | @item -Bstatic |
ec40bbb8 DM |
280 | Ignored. This option is accepted for command-line compatibility with |
281 | the SunOS linker. | |
f22eee08 | 282 | |
2d59b2c3 RP |
283 | @kindex -c @var{MRI-cmdfile} |
284 | @cindex compatibility, MRI | |
285 | @item -c @var{MRI-commandfile} | |
286 | For compatibility with linkers produced by MRI, @code{ld} accepts script | |
287 | files written in an alternate, restricted command language, described in | |
d76ae847 | 288 | @ref{MRI,,MRI Compatible Script Files}. Introduce MRI script files with |
ec40bbb8 | 289 | the option @samp{-c}; use the @samp{-T} option to run linker |
d76ae847 | 290 | scripts written in the general-purpose @code{ld} scripting language. |
8ddef552 DM |
291 | If @var{MRI-cmdfile} does not exist, @code{ld} looks for it in the directories |
292 | specified by any @samp{-L} options. | |
b4d4e8e3 | 293 | |
2c5c0674 RP |
294 | @cindex common allocation |
295 | @kindex -d | |
b4d4e8e3 | 296 | @item -d |
2c5c0674 | 297 | @kindex -dc |
b4d4e8e3 | 298 | @itemx -dc |
2c5c0674 | 299 | @kindex -dp |
b4d4e8e3 RP |
300 | @itemx -dp |
301 | These three options are equivalent; multiple forms are supported for | |
ec40bbb8 | 302 | compatibility with other linkers. They |
2c5c0674 | 303 | assign space to common symbols even if a relocatable output file is |
ec40bbb8 | 304 | specified (with @samp{-r}). The script command |
867a1b8a | 305 | @code{FORCE_COMMON_ALLOCATION} has the same effect. @xref{Option |
d76ae847 | 306 | Commands}. |
b4d4e8e3 | 307 | |
2c5c0674 | 308 | @cindex symbols, from command line |
d76ae847 RP |
309 | @kindex -defsym @var{symbol}=@var{exp} |
310 | @item -defsym @var{symbol}=@var{expression} | |
2c5c0674 RP |
311 | Create a global symbol in the output file, containing the absolute |
312 | address given by @var{expression}. You may use this option as many | |
313 | times as necessary to define multiple symbols in the command line. A | |
314 | limited form of arithmetic is supported for the @var{expression} in this | |
315 | context: you may give a hexadecimal constant or the name of an existing | |
316 | symbol, or use @code{+} and @code{-} to add or subtract hexadecimal | |
317 | constants or symbols. If you need more elaborate expressions, consider | |
d76ae847 RP |
318 | using the linker command language from a script (@pxref{Assignment, , |
319 | Assignment: Symbol Definitions}). @emph{Note:} there should be no | |
320 | white space between @var{symbol}, the equals sign (``@key{=}''), and | |
321 | @var{expression}. | |
2c5c0674 RP |
322 | |
323 | @cindex entry point, from command line | |
324 | @kindex -e @var{entry} | |
f22eee08 RP |
325 | @item -e @var{entry} |
326 | Use @var{entry} as the explicit symbol for beginning execution of your | |
b4d4e8e3 RP |
327 | program, rather than the default entry point. @xref{Entry Point}, for a |
328 | discussion of defaults and other ways of specifying the | |
329 | entry point. | |
f22eee08 | 330 | |
ec40bbb8 | 331 | @ifclear SingleFormat |
2c5c0674 | 332 | @kindex -F |
b4d4e8e3 | 333 | @item -F |
2c5c0674 | 334 | @itemx -F@var{format} |
ec40bbb8 DM |
335 | Ignored. Some older linkers used this option throughout a compilation |
336 | toolchain for specifying object-file format for both input and output | |
337 | object files. The mechanisms @code{ld} uses for this purpose (the | |
867a1b8a DM |
338 | @samp{-b} or @samp{-format} options for input files, @samp{-oformat} |
339 | option or the @code{TARGET} command in linker scripts for output files, | |
340 | the @code{GNUTARGET} environment variable) are more flexible, but | |
341 | @code{ld} accepts the @samp{-F} option for compatibility with scripts | |
342 | written to call the old linker. | |
2c5c0674 RP |
343 | |
344 | @kindex -format | |
345 | @item -format @var{input-format} | |
ec40bbb8 DM |
346 | Synonym for @samp{-b @var{input-format}}. |
347 | @end ifclear | |
2c5c0674 RP |
348 | |
349 | @kindex -g | |
b4d4e8e3 | 350 | @item -g |
ec40bbb8 | 351 | Ignored. Provided for compatibility with other tools. |
b4d4e8e3 | 352 | |
8ddef552 DM |
353 | @kindex -G |
354 | @cindex object size | |
355 | @item -G@var{value} | |
356 | @itemx -G @var{value} | |
357 | Set the maximum size of objects to be optimized using the GP register to | |
358 | @var{size} under MIPS ECOFF. Ignored for other object file formats. | |
359 | ||
de87cdb4 DM |
360 | @item --help |
361 | @kindex --help | |
362 | @cindex help | |
363 | @cindex usage | |
364 | Print a summary of the command-line options on the standard output and exit. | |
365 | This option and @samp{--version} begin with two dashes instead of one | |
366 | for compatibility with other GNU programs. The other options start with | |
367 | only one dash for compatibility with other linkers. | |
368 | ||
2c5c0674 RP |
369 | @kindex -i |
370 | @cindex incremental link | |
f22eee08 | 371 | @item -i |
ec40bbb8 | 372 | Perform an incremental link (same as option @samp{-r}). |
f22eee08 | 373 | |
2c5c0674 | 374 | @cindex archive files, from cmd line |
de87cdb4 | 375 | @kindex -l@var{archive} |
b4d4e8e3 | 376 | @item -l@var{ar} |
de87cdb4 | 377 | Add archive file @var{archive} to the list of files to link. This |
f22eee08 | 378 | option may be used any number of times. @code{ld} will search its |
de87cdb4 | 379 | path-list for occurrences of @code{lib@var{ar}.a} for every @var{archive} |
f22eee08 RP |
380 | specified. |
381 | ||
2c5c0674 RP |
382 | @cindex search directory, from cmd line |
383 | @kindex -L@var{dir} | |
b4d4e8e3 | 384 | @item -L@var{searchdir} |
836a5ee4 | 385 | @itemx -L @var{searchdir} |
ec40bbb8 | 386 | Add path @var{searchdir} to the list of paths that @code{ld} will search |
8ddef552 DM |
387 | for archive libraries and @code{ld} control scripts. You may use this |
388 | option any number of times. | |
f22eee08 | 389 | |
ec40bbb8 | 390 | @ifset UsesEnvVars |
2c5c0674 | 391 | The default set of paths searched (without being specified with |
ec40bbb8 DM |
392 | @samp{-L}) depends on which emulation mode @code{ld} is using, and in |
393 | some cases also on how it was configured. @xref{Environment}. | |
394 | @end ifset | |
395 | ||
396 | The paths can also be specified in a link script with the | |
397 | @code{SEARCH_DIR} command. | |
f22eee08 | 398 | |
2c5c0674 RP |
399 | @cindex link map |
400 | @kindex -M | |
f22eee08 | 401 | @item -M |
ec40bbb8 | 402 | Print (to the standard output) a link map---diagnostic information |
f22eee08 RP |
403 | about where symbols are mapped by @code{ld}, and information on global |
404 | common storage allocation. | |
405 | ||
d18a4527 DM |
406 | @cindex link map |
407 | @kindex -Map | |
408 | @item -Map @var{mapfile} | |
409 | Print to the file @var{mapfile} a link map---diagnostic information | |
410 | about where symbols are mapped by @code{ld}, and information on global | |
411 | common storage allocation. | |
412 | ||
8ddef552 DM |
413 | @cindex emulation |
414 | @kindex -m @var{emulation} | |
415 | @item -m@var{emulation} | |
416 | @itemx -m @var{emulation} | |
417 | Emulate the @var{emulation} linker. You can list the available | |
418 | emulations with the @samp{-V} option. The | |
419 | default is the system for which you configured @code{ld}. | |
420 | ||
2c5c0674 RP |
421 | @kindex -N |
422 | @cindex read/write from cmd line | |
423 | @kindex OMAGIC | |
f22eee08 | 424 | @item -N |
ec40bbb8 DM |
425 | Set the text and data sections to be readable and writable. Also, do |
426 | not page-align the data segment. If the output format supports Unix | |
427 | style magic numbers, mark the output as @code{OMAGIC}. | |
f22eee08 RP |
428 | |
429 | @item -n | |
2c5c0674 RP |
430 | @kindex -n |
431 | @cindex read-only text | |
432 | @kindex NMAGIC | |
ec40bbb8 DM |
433 | Set the text segment to be read only, and mark the output as |
434 | @code{NMAGIC} if possible. | |
f22eee08 | 435 | |
b4d4e8e3 | 436 | @item -noinhibit-exec |
2c5c0674 RP |
437 | @cindex output file after errors |
438 | @kindex -noinhibit-exec | |
ec40bbb8 | 439 | Retain the executable output file whenever it is still usable. |
b4d4e8e3 | 440 | Normally, the linker will not produce an output file if it encounters |
ec40bbb8 DM |
441 | errors during the link process; it exits without writing an output file |
442 | when it issues any error whatsoever. | |
b4d4e8e3 | 443 | |
f22eee08 | 444 | @item -o @var{output} |
2c5c0674 RP |
445 | @kindex -o @var{output} |
446 | @cindex naming the output file | |
ec40bbb8 DM |
447 | Use @var{output} as the name for the program produced by @code{ld}; if this |
448 | option is not specified, the name @file{a.out} is used by default. The | |
2c5c0674 | 449 | script command @code{OUTPUT} can also specify the output file name. |
f22eee08 | 450 | |
7f9ae73e | 451 | @ifclear SingleFormat |
346535cc DM |
452 | @kindex -oformat |
453 | @item -oformat @var{output-format} | |
454 | Specify the binary format for the output object file. You don't usually | |
455 | need to specify this, as @code{ld} is configured to produce as a default | |
456 | output format the most usual format on each machine. | |
457 | @var{output-format} is a text string, the name of a particular format | |
458 | supported by the BFD libraries. (You can list the available binary | |
459 | formats with @samp{objdump -i}.) The script command | |
460 | @code{OUTPUT_FORMAT} can also specify the output format, but this option | |
461 | overrides it. @xref{BFD}. | |
7f9ae73e | 462 | @end ifclear |
346535cc | 463 | |
b4d4e8e3 | 464 | @item -R @var{filename} |
2c5c0674 RP |
465 | @kindex -R @var{file} |
466 | @cindex symbol-only input | |
867a1b8a DM |
467 | Read symbol names and their addresses from @var{filename}, but do not |
468 | relocate it or include it in the output. This allows your output file | |
469 | to refer symbolically to absolute locations of memory defined in other | |
470 | programs. | |
ec40bbb8 | 471 | |
1c48127e RP |
472 | @item -relax |
473 | @kindex -relax | |
474 | @cindex synthesizing linker | |
475 | @cindex relaxing addressing modes | |
476 | An option with machine dependent effects. Currently this option is only | |
ec40bbb8 DM |
477 | supported on the H8/300. |
478 | @ifset H8300 | |
479 | @xref{H8/300,,@code{ld} and the H8/300}. | |
480 | @end ifset | |
1c48127e | 481 | |
ec40bbb8 DM |
482 | On some platforms, use option performs global optimizations that |
483 | become possible when the linker resolves addressing in the program, such | |
1c48127e RP |
484 | as relaxing address modes and synthesizing new instructions in the |
485 | output object file. | |
486 | ||
487 | On platforms where this is not supported, @samp{-relax} is accepted, but | |
ec40bbb8 | 488 | ignored. |
1c48127e | 489 | |
f22eee08 | 490 | @item -r |
b4d4e8e3 | 491 | @cindex partial link |
2c5c0674 RP |
492 | @cindex relocatable output |
493 | @kindex -r | |
ec40bbb8 | 494 | Generate relocatable output---i.e., generate an output file that can in |
246504a5 | 495 | turn serve as input to @code{ld}. This is often called @dfn{partial |
2c5c0674 RP |
496 | linking}. As a side effect, in environments that support standard Unix |
497 | magic numbers, this option also sets the output file's magic number to | |
498 | @code{OMAGIC}. | |
499 | @c ; see @code{-N}. | |
500 | If this option is not specified, an absolute file is produced. When | |
501 | linking C++ programs, this option @emph{will not} resolve references to | |
ec40bbb8 | 502 | constructors; to do that, use @samp{-Ur}. |
2c5c0674 | 503 | |
867a1b8a | 504 | This option does the same thing as @samp{-i}. |
f22eee08 RP |
505 | |
506 | @item -S | |
2c5c0674 RP |
507 | @kindex -S |
508 | @cindex strip debugger symbols | |
ec40bbb8 | 509 | Omit debugger symbol information (but not all symbols) from the output file. |
f22eee08 RP |
510 | |
511 | @item -s | |
2c5c0674 RP |
512 | @kindex -s |
513 | @cindex strip all symbols | |
ec40bbb8 | 514 | Omit all symbol information from the output file. |
f22eee08 | 515 | |
2a28d8b0 DM |
516 | @item -sort-common |
517 | Normally, when @code{ld} places the global common symbols in the | |
518 | appropriate output sections, it sorts them by size. First come all the | |
519 | one byte symbols, then all the two bytes, then all the four bytes, and | |
836a5ee4 DM |
520 | then everything else. This is to prevent gaps between symbols due to |
521 | alignment constraints. This option disables that sorting. | |
2a28d8b0 | 522 | |
8594f568 SS |
523 | @item -stats |
524 | Compute and display statistics about the operation of the linker, | |
525 | such as execution time and memory usage. | |
526 | ||
867a1b8a DM |
527 | @item -Tbss @var{org} |
528 | @kindex -Tbss @var{org} | |
529 | @itemx -Tdata @var{org} | |
530 | @kindex -Tdata @var{org} | |
531 | @itemx -Ttext @var{org} | |
532 | @kindex -Ttext @var{org} | |
2c5c0674 RP |
533 | @cindex segment origins, cmd line |
534 | Use @var{org} as the starting address for---respectively---the | |
b4d4e8e3 | 535 | @code{bss}, @code{data}, or the @code{text} segment of the output file. |
ec40bbb8 DM |
536 | @var{org} must be a single hexadecimal integer; |
537 | for compatibility with other linkers, you may omit the leading | |
d76ae847 | 538 | @samp{0x} usually associated with hexadecimal values. |
f22eee08 | 539 | |
b4d4e8e3 RP |
540 | @item -T @var{commandfile} |
541 | @itemx -T@var{commandfile} | |
2c5c0674 | 542 | @kindex -T @var{script} |
2d59b2c3 | 543 | @cindex script files |
de87cdb4 | 544 | Read link commands from the file @var{commandfile}. These commands |
8de26d62 DM |
545 | replace @code{ld}'s default link script (rather than adding |
546 | to it), so @var{commandfile} must specify everything necessary to describe | |
de87cdb4 DM |
547 | the target format. @xref{Commands}. If @var{commandfile} does not |
548 | exist, @code{ld} looks for it in the directories specified by any | |
549 | preceding @samp{-L} options. Multiple @samp{-T} options accumulate. | |
f22eee08 RP |
550 | |
551 | @item -t | |
2c5c0674 RP |
552 | @kindex -t |
553 | @cindex verbose | |
554 | @cindex input files, displaying | |
ec40bbb8 | 555 | Print the names of the input files as @code{ld} processes them. |
f22eee08 | 556 | |
de87cdb4 DM |
557 | @item -u @var{symbol} |
558 | @kindex -u @var{symbol} | |
2c5c0674 | 559 | @cindex undefined symbol |
de87cdb4 | 560 | Force @var{symbol} to be entered in the output file as an undefined symbol. |
ec40bbb8 DM |
561 | Doing this may, for example, trigger linking of additional modules from |
562 | standard libraries. @samp{-u} may be repeated with different option | |
2c5c0674 RP |
563 | arguments to enter additional undefined symbols. |
564 | @c Nice idea, but no such command: This option is equivalent | |
565 | @c to the @code{EXTERN} linker command. | |
f22eee08 | 566 | |
b4d4e8e3 | 567 | @item -Ur |
2c5c0674 | 568 | @kindex -Ur |
b4d4e8e3 RP |
569 | @cindex constructors |
570 | For anything other than C++ programs, this option is equivalent to | |
ec40bbb8 DM |
571 | @samp{-r}: it generates relocatable output---i.e., an output file that can in |
572 | turn serve as input to @code{ld}. When linking C++ programs, @samp{-Ur} | |
573 | @emph{will} resolve references to constructors, unlike @samp{-r}. | |
3e27cc11 DM |
574 | It does not work to use @samp{-Ur} on files that were themselves linked |
575 | with @samp{-Ur}; once the constructor table has been built, it can not | |
576 | be added to. Use @samp{-Ur} only for the last partial link, and | |
577 | @samp{-r} for the others. | |
b4d4e8e3 | 578 | |
8ddef552 DM |
579 | @item -V |
580 | @kindex -V | |
581 | @cindex version | |
582 | Display the version number for @code{ld} and list the supported emulations. | |
de87cdb4 | 583 | Display which input files can and can not be opened. |
8ddef552 | 584 | |
b4d4e8e3 | 585 | @item -v |
2c5c0674 | 586 | @kindex -v |
b4d4e8e3 | 587 | @cindex version |
246504a5 | 588 | Display the version number for @code{ld}. |
de87cdb4 DM |
589 | |
590 | @item --version | |
591 | @kindex --version | |
592 | Display the version number for @code{ld} and exit. | |
b4d4e8e3 | 593 | |
2a28d8b0 | 594 | @item -warn-common |
7f9ae73e RP |
595 | @kindex -warn-comon |
596 | @cindex warnings, on combining symbols | |
597 | @cindex combining symbols, warnings on | |
2a28d8b0 DM |
598 | Warn when a common symbol is combined with another common symbol or with |
599 | a symbol definition. Unix linkers allow this somewhat sloppy practice, | |
600 | but linkers on some other operating systems do not. This option allows | |
601 | you to find potential problems from combining global symbols. | |
1cd4cca9 DM |
602 | Unfortunately, some C libraries use this practice, so you may get some |
603 | warnings about symbols in the libraries as well as in your programs. | |
2a28d8b0 DM |
604 | |
605 | There are three kinds of global symbols, illustrated here by C examples: | |
606 | ||
607 | @table @samp | |
608 | @item int i = 1; | |
609 | A definition, which goes in the initialized data section of the output | |
610 | file. | |
611 | ||
612 | @item extern int i; | |
613 | An undefined reference, which does not allocate space. | |
614 | There must be either a definition or a common symbol for the | |
615 | variable somewhere. | |
616 | ||
617 | @item int i; | |
618 | A common symbol. If there are only (one or more) common symbols for a | |
619 | variable, it goes in the uninitialized data area of the output file. | |
620 | The linker merges multiple common symbols for the same variable into a | |
621 | single symbol. If they are of different sizes, it picks the largest | |
622 | size. The linker turns a common symbol into a declaration, if there is | |
623 | a definition of the same variable. | |
624 | @end table | |
625 | ||
626 | The @samp{-warn-common} option can produce five kinds of warnings. Each | |
627 | warning consists of a pair of lines: the first describes the symbol just | |
628 | encountered, and the second describes the previous symbol encountered | |
629 | with the same name. One or both of the two symbols will be a common | |
630 | symbol. | |
631 | ||
632 | @enumerate | |
633 | @item | |
634 | Turning a common symbol into a reference, because there is already a | |
635 | definition for the symbol. | |
636 | @smallexample | |
8920addc RP |
637 | @var{file}(@var{section}): warning: common of `@var{symbol}' |
638 | overridden by definition | |
2a28d8b0 DM |
639 | @var{file}(@var{section}): warning: defined here |
640 | @end smallexample | |
641 | ||
642 | @item | |
643 | Turning a common symbol into a reference, because a later definition for | |
644 | the symbol is encountered. This is the same as the previous case, | |
645 | except that the symbols are encountered in a different order. | |
646 | @smallexample | |
8920addc RP |
647 | @var{file}(@var{section}): warning: definition of `@var{symbol}' |
648 | overriding common | |
2a28d8b0 DM |
649 | @var{file}(@var{section}): warning: common is here |
650 | @end smallexample | |
651 | ||
652 | @item | |
653 | Merging a common symbol with a previous same-sized common symbol. | |
654 | @smallexample | |
8920addc RP |
655 | @var{file}(@var{section}): warning: multiple common |
656 | of `@var{symbol}' | |
2a28d8b0 DM |
657 | @var{file}(@var{section}): warning: previous common is here |
658 | @end smallexample | |
659 | ||
660 | @item | |
661 | Merging a common symbol with a previous larger common symbol. | |
662 | @smallexample | |
8920addc RP |
663 | @var{file}(@var{section}): warning: common of `@var{symbol}' |
664 | overridden by larger common | |
2a28d8b0 DM |
665 | @var{file}(@var{section}): warning: larger common is here |
666 | @end smallexample | |
667 | ||
668 | @item | |
669 | Merging a common symbol with a previous smaller common symbol. This is | |
670 | the same as the previous case, except that the symbols are | |
671 | encountered in a different order. | |
672 | @smallexample | |
8920addc RP |
673 | @var{file}(@var{section}): warning: common of `@var{symbol}' |
674 | overriding smaller common | |
2a28d8b0 DM |
675 | @var{file}(@var{section}): warning: smaller common is here |
676 | @end smallexample | |
677 | @end enumerate | |
678 | ||
f22eee08 | 679 | @item -X |
2c5c0674 RP |
680 | @kindex -X |
681 | @cindex local symbols, deleting | |
682 | @cindex L, deleting symbols beginning | |
ec40bbb8 | 683 | If @samp{-s} or @samp{-S} is also specified, delete only local symbols |
f22eee08 RP |
684 | beginning with @samp{L}. |
685 | ||
b4d4e8e3 | 686 | @item -x |
2c5c0674 RP |
687 | @kindex -x |
688 | @cindex deleting local symbols | |
ec40bbb8 | 689 | If @samp{-s} or @samp{-S} is also specified, delete all local symbols, |
b4d4e8e3 RP |
690 | not just those beginning with @samp{L}. |
691 | ||
ec40bbb8 | 692 | @item -y@var{symbol} |
d76ae847 RP |
693 | @kindex -y@var{symbol} |
694 | @cindex symbol tracing | |
ec40bbb8 | 695 | Print the name of each linked file in which @var{symbol} appears. This |
d76ae847 RP |
696 | option may be given any number of times. On many systems it is necessary |
697 | to prepend an underscore. | |
698 | ||
699 | This option is useful when you have an undefined symbol in your link but | |
700 | don't know where the reference is coming from. | |
f22eee08 | 701 | @end table |
b4d4e8e3 | 702 | |
ec40bbb8 DM |
703 | @ifset UsesEnvVars |
704 | @node Environment | |
2c5c0674 RP |
705 | @section Environment Variables |
706 | ||
d76ae847 RP |
707 | You can change the behavior of @code{ld} with the environment |
708 | variable @code{GNUTARGET}. | |
2c5c0674 RP |
709 | |
710 | @kindex GNUTARGET | |
711 | @cindex default input format | |
712 | @code{GNUTARGET} determines the input-file object format if you don't | |
ec40bbb8 | 713 | use @samp{-b} (or its synonym @samp{-format}). Its value should be one |
2c5c0674 | 714 | of the BFD names for an input format (@pxref{BFD}). If there is no |
246504a5 | 715 | @code{GNUTARGET} in the environment, @code{ld} uses the natural format |
8920addc | 716 | of the target. If @code{GNUTARGET} is set to @code{default} then BFD attempts to discover the |
2c5c0674 RP |
717 | input format by examining binary input files; this method often |
718 | succeeds, but there are potential ambiguities, since there is no method | |
ec40bbb8 | 719 | of ensuring that the magic number used to specify object-file formats is |
2c5c0674 RP |
720 | unique. However, the configuration procedure for BFD on each system |
721 | places the conventional format for that system first in the search-list, | |
722 | so ambiguities are resolved in favor of convention. | |
ec40bbb8 | 723 | @end ifset |
2c5c0674 | 724 | |
ec40bbb8 | 725 | @node Commands |
2c5c0674 | 726 | @chapter Command Language |
f22eee08 | 727 | |
2c5c0674 | 728 | @cindex command files |
ec40bbb8 | 729 | The command language provides explicit control over the link process, |
b4d4e8e3 | 730 | allowing complete specification of the mapping between the linker's |
ec40bbb8 | 731 | input files and its output. It controls: |
b4d4e8e3 | 732 | @itemize @bullet |
2c5c0674 RP |
733 | @item |
734 | input files | |
735 | @item | |
736 | file formats | |
737 | @item | |
867a1b8a | 738 | output file layout |
2c5c0674 RP |
739 | @item |
740 | addresses of sections | |
741 | @item | |
742 | placement of common blocks | |
b4d4e8e3 | 743 | @end itemize |
f22eee08 | 744 | |
2c5c0674 | 745 | You may supply a command file (also known as a link script) to the |
ec40bbb8 | 746 | linker either explicitly through the @samp{-T} option, or implicitly as |
2c5c0674 | 747 | an ordinary file. If the linker opens a file which it cannot recognize |
867a1b8a | 748 | as a supported object or archive format, it reports an error. |
2c5c0674 | 749 | |
2c5c0674 | 750 | @menu |
2d59b2c3 RP |
751 | * Scripts:: Linker Scripts |
752 | * Expressions:: Expressions | |
753 | * MEMORY:: MEMORY Command | |
754 | * SECTIONS:: SECTIONS Command | |
755 | * Entry Point:: The Entry Point | |
867a1b8a | 756 | * Option Commands:: Option Commands |
2c5c0674 RP |
757 | @end menu |
758 | ||
ec40bbb8 | 759 | @node Scripts |
b4d4e8e3 | 760 | @section Linker Scripts |
246504a5 | 761 | The @code{ld} command language is a collection of statements; some are |
ec40bbb8 DM |
762 | simple keywords setting a particular option, some are used to select and |
763 | group input files or name output files; and two statement | |
b4d4e8e3 RP |
764 | types have a fundamental and pervasive impact on the linking process. |
765 | ||
2c5c0674 RP |
766 | @cindex fundamental script commands |
767 | @cindex commands, fundamental | |
768 | @cindex output file layout | |
769 | @cindex layout of output file | |
246504a5 | 770 | The most fundamental command of the @code{ld} command language is the |
b4d4e8e3 RP |
771 | @code{SECTIONS} command (@pxref{SECTIONS}). Every meaningful command |
772 | script must have a @code{SECTIONS} command: it specifies a | |
773 | ``picture'' of the output file's layout, in varying degrees of detail. | |
774 | No other command is required in all cases. | |
775 | ||
776 | The @code{MEMORY} command complements @code{SECTIONS} by describing the | |
2c5c0674 | 777 | available memory in the target architecture. This command is optional; |
246504a5 | 778 | if you don't use a @code{MEMORY} command, @code{ld} assumes sufficient |
2c5c0674 RP |
779 | memory is available in a contiguous block for all output. |
780 | @xref{MEMORY}. | |
b4d4e8e3 | 781 | |
2c5c0674 RP |
782 | @cindex comments |
783 | You may include comments in linker scripts just as in C: delimited | |
784 | by @samp{/*} and @samp{*/}. As in C, comments are syntactically | |
785 | equivalent to whitespace. | |
786 | ||
ec40bbb8 | 787 | @node Expressions |
f22eee08 | 788 | @section Expressions |
2c5c0674 RP |
789 | @cindex expression syntax |
790 | @cindex arithmetic | |
b4d4e8e3 RP |
791 | Many useful commands involve arithmetic expressions. The syntax for |
792 | expressions in the command language is identical to that of C | |
793 | expressions, with the following features: | |
794 | @itemize @bullet | |
2c5c0674 RP |
795 | @item |
796 | All expressions evaluated as integers and | |
f22eee08 | 797 | are of ``long'' or ``unsigned long'' type. |
2c5c0674 RP |
798 | @item |
799 | All constants are integers. | |
800 | @item | |
801 | All of the C arithmetic operators are provided. | |
802 | @item | |
803 | You may reference, define, and create global variables. | |
804 | @item | |
805 | You may call special purpose built-in functions. | |
b4d4e8e3 | 806 | @end itemize |
f22eee08 | 807 | |
2c5c0674 | 808 | @menu |
2d59b2c3 RP |
809 | * Integers:: Integers |
810 | * Symbols:: Symbol Names | |
811 | * Location Counter:: The Location Counter | |
812 | * Operators:: Operators | |
813 | * Evaluation:: Evaluation | |
814 | * Assignment:: Assignment: Defining Symbols | |
867a1b8a | 815 | * Arithmetic Functions:: Built-In Functions |
2c5c0674 RP |
816 | @end menu |
817 | ||
ec40bbb8 | 818 | @node Integers |
f22eee08 | 819 | @subsection Integers |
2c5c0674 RP |
820 | @cindex integer notation |
821 | @cindex octal integers | |
f22eee08 RP |
822 | An octal integer is @samp{0} followed by zero or more of the octal |
823 | digits (@samp{01234567}). | |
b4d4e8e3 | 824 | @example |
2c5c0674 | 825 | _as_octal = 0157255; |
b4d4e8e3 | 826 | @end example |
f22eee08 | 827 | |
2c5c0674 | 828 | @cindex decimal integers |
f22eee08 RP |
829 | A decimal integer starts with a non-zero digit followed by zero or |
830 | more digits (@samp{0123456789}). | |
b4d4e8e3 | 831 | @example |
2c5c0674 | 832 | _as_decimal = 57005; |
b4d4e8e3 | 833 | @end example |
f22eee08 | 834 | |
2c5c0674 RP |
835 | @cindex hexadecimal integers |
836 | @kindex 0x | |
f22eee08 RP |
837 | A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or |
838 | more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}. | |
b4d4e8e3 RP |
839 | @example |
840 | _as_hex = 0xdead; | |
841 | @end example | |
f22eee08 | 842 | |
2c5c0674 | 843 | @cindex negative integers |
ec40bbb8 | 844 | To write a negative integer, use |
b4d4e8e3 RP |
845 | the prefix operator @samp{-}; @pxref{Operators}. |
846 | @example | |
b4d4e8e3 RP |
847 | _as_neg = -57005; |
848 | @end example | |
f22eee08 | 849 | |
2c5c0674 RP |
850 | @cindex scaled integers |
851 | @cindex K and M integer suffixes | |
852 | @cindex M and K integer suffixes | |
853 | @cindex suffixes for integers | |
854 | @cindex integer suffixes | |
b4d4e8e3 RP |
855 | Additionally the suffixes @code{K} and @code{M} may be used to scale a |
856 | constant by | |
c8072296 RP |
857 | @c TEXI2ROFF-KILL |
858 | @ifinfo | |
859 | @c END TEXI2ROFF-KILL | |
860 | @code{1024} or @code{1024*1024} | |
861 | @c TEXI2ROFF-KILL | |
862 | @end ifinfo | |
f22eee08 | 863 | @tex |
b4d4e8e3 | 864 | ${\rm 1024}$ or ${\rm 1024}^2$ |
f22eee08 | 865 | @end tex |
c8072296 | 866 | @c END TEXI2ROFF-KILL |
ec40bbb8 | 867 | respectively. For example, the following all refer to the same quantity: |
f22eee08 RP |
868 | |
869 | @example | |
2c5c0674 RP |
870 | _fourk_1 = 4K; |
871 | _fourk_2 = 4096; | |
872 | _fourk_3 = 0x1000; | |
f22eee08 | 873 | @end example |
b4d4e8e3 | 874 | |
ec40bbb8 | 875 | @node Symbols |
b4d4e8e3 | 876 | @subsection Symbol Names |
2c5c0674 RP |
877 | @cindex symbol names |
878 | @cindex names | |
879 | @cindex quoted symbol names | |
880 | @kindex " | |
b4d4e8e3 | 881 | Unless quoted, symbol names start with a letter, underscore, point or |
2c5c0674 | 882 | hyphen and may include any letters, underscores, digits, points, |
b4d4e8e3 RP |
883 | and minus signs. Unquoted symbol names must not conflict with any |
884 | keywords. You can specify a symbol which contains odd characters or has | |
885 | the same name as a keyword, by surrounding the symbol name in double quotes: | |
886 | @example | |
887 | "SECTION" = 9; | |
888 | "with a space" = "also with a space" + 10; | |
889 | @end example | |
890 | ||
ec40bbb8 | 891 | @node Location Counter |
b4d4e8e3 | 892 | @subsection The Location Counter |
2c5c0674 RP |
893 | @kindex . |
894 | @cindex dot | |
895 | @cindex location counter | |
896 | @cindex current output location | |
b4d4e8e3 RP |
897 | The special linker variable @dfn{dot} @samp{.} always contains the |
898 | current output location counter. Since the @code{.} always refers to | |
899 | a location in an output section, it must always appear in an | |
900 | expression within a @code{SECTIONS} command. The @code{.} symbol | |
901 | may appear anywhere that an ordinary symbol is allowed in an | |
902 | expression, but its assignments have a side effect. Assigning a value | |
903 | to the @code{.} symbol will cause the location counter to be moved. | |
2c5c0674 | 904 | @cindex holes |
b4d4e8e3 RP |
905 | This may be used to create holes in the output section. The location |
906 | counter may never be moved backwards. | |
907 | @example | |
2c5c0674 RP |
908 | SECTIONS |
909 | @{ | |
910 | output : | |
b4d4e8e3 | 911 | @{ |
2c5c0674 RP |
912 | file1(.text) |
913 | . = . + 1000; | |
914 | file2(.text) | |
915 | . += 1000; | |
916 | file3(.text) | |
917 | @} = 0x1234; | |
918 | @} | |
b4d4e8e3 | 919 | @end example |
2c5c0674 RP |
920 | @noindent |
921 | In the previous example, @code{file1} is located at the beginning of the | |
922 | output section, then there is a 1000 byte gap. Then @code{file2} | |
923 | appears, also with a 1000 byte gap following before @code{file3} is | |
924 | loaded. The notation @samp{= 0x1234} specifies what data to write in | |
925 | the gaps (@pxref{Section Options}). | |
b4d4e8e3 | 926 | |
ec40bbb8 | 927 | @node Operators |
f22eee08 | 928 | @subsection Operators |
2c5c0674 RP |
929 | @cindex Operators for arithmetic |
930 | @cindex arithmetic operators | |
931 | @cindex precedence in expressions | |
b4d4e8e3 | 932 | The linker recognizes the standard C set of arithmetic operators, with |
f22eee08 | 933 | the standard bindings and precedence levels: |
c8072296 | 934 | @c TEXI2ROFF-KILL |
b4d4e8e3 | 935 | @ifinfo |
c8072296 | 936 | @c END TEXI2ROFF-KILL |
f22eee08 | 937 | @example |
c8072296 | 938 | precedence associativity Operators Notes |
b4d4e8e3 | 939 | (highest) |
c8072296 RP |
940 | 1 left ! - ~ (1) |
941 | 2 left * / % | |
942 | 3 left + - | |
943 | 4 left >> << | |
944 | 5 left == != > < <= >= | |
945 | 6 left & | |
946 | 7 left | | |
947 | 8 left && | |
948 | 9 left || | |
949 | 10 right ? : | |
950 | 11 right &= += -= *= /= (2) | |
b4d4e8e3 | 951 | (lowest) |
f22eee08 | 952 | @end example |
2c5c0674 RP |
953 | Notes: |
954 | (1) Prefix operators | |
955 | (2) @xref{Assignment} | |
c8072296 | 956 | @c TEXI2ROFF-KILL |
b4d4e8e3 | 957 | @end ifinfo |
f22eee08 | 958 | @tex |
2c5c0674 RP |
959 | \vskip \baselineskip |
960 | %"lispnarrowing" is the extra indent used generally for @example | |
961 | \hskip\lispnarrowing\vbox{\offinterlineskip | |
f22eee08 RP |
962 | \hrule |
963 | \halign | |
2c5c0674 RP |
964 | {\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr |
965 | height2pt&\omit&&\omit&&\omit&\cr | |
966 | &Precedence&& Associativity &&{\rm Operators}&\cr | |
967 | height2pt&\omit&&\omit&&\omit&\cr | |
f22eee08 | 968 | \noalign{\hrule} |
2c5c0674 | 969 | height2pt&\omit&&\omit&&\omit&\cr |
b4d4e8e3 | 970 | &highest&&&&&\cr |
2c5c0674 RP |
971 | % '176 is tilde, '~' in tt font |
972 | &1&&left&&\qquad- \char'176\ !\qquad\dag&\cr | |
973 | &2&&left&&* / \%&\cr | |
974 | &3&&left&&+ -&\cr | |
975 | &4&&left&&>> <<&\cr | |
976 | &5&&left&&== != > < <= >=&\cr | |
f22eee08 | 977 | &6&&left&&\&&\cr |
f22eee08 | 978 | &7&&left&&|&\cr |
f22eee08 | 979 | &8&&left&&{\&\&}&\cr |
f22eee08 | 980 | &9&&left&&||&\cr |
2c5c0674 RP |
981 | &10&&right&&? :&\cr |
982 | &11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr | |
b4d4e8e3 | 983 | &lowest&&&&&\cr |
2c5c0674 | 984 | height2pt&\omit&&\omit&&\omit&\cr} |
f22eee08 RP |
985 | \hrule} |
986 | @end tex | |
2c5c0674 RP |
987 | @iftex |
988 | { | |
989 | @obeylines@parskip=0pt@parindent=0pt | |
990 | @dag@quad Prefix operators. | |
991 | @ddag@quad @xref{Assignment}. | |
992 | } | |
993 | @end iftex | |
c8072296 | 994 | @c END TEXI2ROFF-KILL |
f22eee08 | 995 | |
ec40bbb8 | 996 | @node Evaluation |
b4d4e8e3 RP |
997 | @subsection Evaluation |
998 | ||
2c5c0674 RP |
999 | @cindex lazy evaluation |
1000 | @cindex expression evaluation order | |
b4d4e8e3 RP |
1001 | The linker uses ``lazy evaluation'' for expressions; it only calculates |
1002 | an expression when absolutely necessary. The linker needs the value of | |
1003 | the start address, and the lengths of memory regions, in order to do any | |
1004 | linking at all; these values are computed as soon as possible when the | |
1005 | linker reads in the command file. However, other values (such as symbol | |
1006 | values) are not known or needed until after storage allocation. Such | |
1007 | values are evaluated later, when other information (such as the sizes of | |
1008 | output sections) is available for use in the symbol assignment | |
1009 | expression. | |
1010 | ||
ec40bbb8 | 1011 | @node Assignment |
b4d4e8e3 | 1012 | @subsection Assignment: Defining Symbols |
2c5c0674 RP |
1013 | @cindex assignment in scripts |
1014 | @cindex symbol definition, scripts | |
1015 | @cindex variables, defining | |
b4d4e8e3 RP |
1016 | You may create global symbols, and assign values (addresses) to global |
1017 | symbols, using any of the C assignment operators: | |
1018 | ||
1019 | @table @code | |
1020 | @item @var{symbol} = @var{expression} ; | |
2c5c0674 | 1021 | @itemx @var{symbol} &= @var{expression} ; |
b4d4e8e3 RP |
1022 | @itemx @var{symbol} += @var{expression} ; |
1023 | @itemx @var{symbol} -= @var{expression} ; | |
1024 | @itemx @var{symbol} *= @var{expression} ; | |
1025 | @itemx @var{symbol} /= @var{expression} ; | |
1026 | @end table | |
1027 | ||
246504a5 | 1028 | Two things distinguish assignment from other operators in @code{ld} |
b4d4e8e3 RP |
1029 | expressions. |
1030 | @itemize @bullet | |
2c5c0674 RP |
1031 | @item |
1032 | Assignment may only be used at the root of an expression; | |
b4d4e8e3 | 1033 | @samp{a=b+3;} is allowed, but @samp{a+b=3;} is an error. |
2c5c0674 RP |
1034 | |
1035 | @kindex ; | |
1036 | @cindex semicolon | |
1037 | @item | |
d76ae847 RP |
1038 | You must place a trailing semicolon (``@key{;}'') at the end of an |
1039 | assignment statement. | |
b4d4e8e3 RP |
1040 | @end itemize |
1041 | ||
1042 | Assignment statements may appear: | |
1043 | @itemize @bullet | |
2c5c0674 | 1044 | @item |
246504a5 | 1045 | as commands in their own right in an @code{ld} script; or |
2c5c0674 RP |
1046 | @item |
1047 | as independent statements within a @code{SECTIONS} command; or | |
1048 | @item | |
1049 | as part of the contents of a section definition in a | |
b4d4e8e3 RP |
1050 | @code{SECTIONS} command. |
1051 | @end itemize | |
1052 | ||
1053 | The first two cases are equivalent in effect---both define a symbol with | |
ec40bbb8 | 1054 | an absolute address. The last case defines a symbol whose address is |
b4d4e8e3 RP |
1055 | relative to a particular section (@pxref{SECTIONS}). |
1056 | ||
2c5c0674 RP |
1057 | @cindex absolute and relocatable symbols |
1058 | @cindex relocatable and absolute symbols | |
1059 | @cindex symbols, relocatable and absolute | |
1060 | When a linker expression is evaluated and assigned to a variable, it is | |
1061 | given either an absolute or a relocatable type. An absolute expression | |
1062 | type is one in which the symbol contains the value that it will have in | |
867a1b8a | 1063 | the output file; a relocatable expression type is one in which the |
2c5c0674 | 1064 | value is expressed as a fixed offset from the base of a section. |
b4d4e8e3 RP |
1065 | |
1066 | The type of the expression is controlled by its position in the script | |
2c5c0674 RP |
1067 | file. A symbol assigned within a section definition is created relative |
1068 | to the base of the section; a symbol assigned in any other place is | |
1069 | created as an absolute symbol. Since a symbol created within a | |
1070 | section definition is relative to the base of the section, it | |
1071 | will remain relocatable if relocatable output is requested. A symbol | |
1072 | may be created with an absolute value even when assigned to within a | |
1073 | section definition by using the absolute assignment function | |
1074 | @code{ABSOLUTE}. For example, to create an absolute symbol whose address | |
1075 | is the last byte of an output section named @code{.data}: | |
b4d4e8e3 | 1076 | @example |
2c5c0674 | 1077 | SECTIONS@{ @dots{} |
b4d4e8e3 RP |
1078 | .data : |
1079 | @{ | |
1080 | *(.data) | |
1081 | _edata = ABSOLUTE(.) ; | |
1082 | @} | |
2c5c0674 | 1083 | @dots{} @} |
b4d4e8e3 RP |
1084 | @end example |
1085 | ||
2c5c0674 RP |
1086 | The linker tries to put off the evaluation of an assignment until all |
1087 | the terms in the source expression are known (@pxref{Evaluation}). For | |
ec40bbb8 | 1088 | instance, the sizes of sections cannot be known until after allocation, |
2c5c0674 RP |
1089 | so assignments dependent upon these are not performed until after |
1090 | allocation. Some expressions, such as those depending upon the location | |
1091 | counter @dfn{dot}, @samp{.} must be evaluated during allocation. If the | |
1092 | result of an expression is required, but the value is not available, | |
1093 | then an error results. For example, a script like the following | |
b4d4e8e3 | 1094 | @example |
2c5c0674 | 1095 | SECTIONS @{ @dots{} |
cb70c872 | 1096 | text 9+this_isnt_constant : |
b4d4e8e3 RP |
1097 | @{ @dots{} |
1098 | @} | |
2c5c0674 | 1099 | @dots{} @} |
b4d4e8e3 | 1100 | @end example |
2c5c0674 RP |
1101 | @kindex Non constant expression |
1102 | @noindent | |
1103 | will cause the error message ``@code{Non constant expression for initial | |
b4d4e8e3 RP |
1104 | address}''. |
1105 | ||
867a1b8a DM |
1106 | @node Arithmetic Functions |
1107 | @subsection Arithmetic Functions | |
2c5c0674 | 1108 | @cindex functions in expression language |
ec40bbb8 | 1109 | The command language includes a number of built-in |
2c5c0674 RP |
1110 | functions for use in link script expressions. |
1111 | @table @code | |
1112 | @item ABSOLUTE(@var{exp}) | |
1113 | @kindex ABSOLUTE(@var{exp}) | |
1114 | @cindex expression, absolute | |
ec40bbb8 DM |
1115 | Return the absolute (non-relocatable, as opposed to non-negative) value |
1116 | of the expression @var{exp}. Primarily useful to assign an absolute | |
1117 | value to a symbol within a section definition, where symbol values are | |
1118 | normally section-relative. | |
2c5c0674 RP |
1119 | |
1120 | @item ADDR(@var{section}) | |
1121 | @kindex ADDR(@var{section}) | |
1122 | @cindex section address | |
ec40bbb8 | 1123 | Return the absolute address of the named @var{section}. Your script must |
b4d4e8e3 | 1124 | previously have defined the location of that section. In the following |
ec40bbb8 | 1125 | example, @code{symbol_1} and @code{symbol_2} are assigned identical |
b4d4e8e3 | 1126 | values: |
f22eee08 | 1127 | @example |
2c5c0674 | 1128 | SECTIONS@{ @dots{} |
cb70c872 | 1129 | .output1 : |
f22eee08 | 1130 | @{ |
2c5c0674 RP |
1131 | start_of_output_1 = ABSOLUTE(.); |
1132 | @dots{} | |
f22eee08 | 1133 | @} |
cb70c872 | 1134 | .output : |
f22eee08 RP |
1135 | @{ |
1136 | symbol_1 = ADDR(.output1); | |
1137 | symbol_2 = start_of_output_1; | |
1138 | @} | |
2c5c0674 RP |
1139 | @dots{} @} |
1140 | @end example | |
1141 | ||
1142 | @item ALIGN(@var{exp}) | |
1143 | @kindex ALIGN(@var{exp}) | |
1144 | @cindex rounding up location counter | |
ec40bbb8 | 1145 | Return the result of the current location counter (@code{.}) aligned to |
2c5c0674 RP |
1146 | the next @var{exp} boundary. @var{exp} must be an expression whose |
1147 | value is a power of two. This is equivalent to | |
1148 | @example | |
cb70c872 | 1149 | (. + @var{exp} - 1) & ~(@var{exp} - 1) |
2c5c0674 RP |
1150 | @end example |
1151 | ||
1152 | @code{ALIGN} doesn't change the value of the location counter---it just | |
1153 | does arithmetic on it. As an example, to align the output @code{.data} | |
1154 | section to the next @code{0x2000} byte boundary after the preceding | |
1155 | section and to set a variable within the section to the next | |
1156 | @code{0x8000} boundary after the input sections: | |
1157 | @example | |
1158 | SECTIONS@{ @dots{} | |
1159 | .data ALIGN(0x2000): @{ | |
1160 | *(.data) | |
1161 | variable = ALIGN(0x8000); | |
1162 | @} | |
1163 | @dots{} @} | |
1164 | @end example | |
1165 | @noindent | |
1166 | The first use of @code{ALIGN} in this example specifies the location of | |
1167 | a section because it is used as the optional @var{start} attribute of a | |
1168 | section definition (@pxref{Section Options}). The second use simply | |
1169 | defines the value of a variable. | |
1170 | ||
1171 | The built-in @code{NEXT} is closely related to @code{ALIGN}. | |
1172 | ||
1173 | @item DEFINED(@var{symbol}) | |
1174 | @kindex DEFINED(@var{symbol}) | |
1175 | @cindex symbol defaults | |
ec40bbb8 DM |
1176 | Return 1 if @var{symbol} is in the linker global symbol table and is |
1177 | defined, otherwise return 0. You can use this function to provide default | |
1178 | values for symbols. For example, the following command-file fragment shows how | |
2c5c0674 RP |
1179 | to set a global symbol @code{begin} to the first location in the |
1180 | @code{.text} section---but if a symbol called @code{begin} already | |
1181 | existed, its value is preserved: | |
c8072296 | 1182 | @smallexample |
2c5c0674 | 1183 | SECTIONS@{ @dots{} |
cb70c872 | 1184 | .text : @{ |
2c5c0674 RP |
1185 | begin = DEFINED(begin) ? begin : . ; |
1186 | @dots{} | |
1187 | @} | |
1188 | @dots{} @} | |
c8072296 | 1189 | @end smallexample |
f22eee08 | 1190 | |
2c5c0674 RP |
1191 | @item NEXT(@var{exp}) |
1192 | @kindex NEXT(@var{exp}) | |
1193 | @cindex unallocated address, next | |
ec40bbb8 DM |
1194 | Return the next unallocated address that is a multiple of @var{exp}. |
1195 | This function is closely related to @code{ALIGN(@var{exp})}; unless you | |
2c5c0674 | 1196 | use the @code{MEMORY} command to define discontinuous memory for the |
ec40bbb8 | 1197 | output file, the two functions are equivalent. |
2c5c0674 RP |
1198 | |
1199 | @item SIZEOF(@var{section}) | |
1200 | @kindex SIZEOF(@var{section}) | |
1201 | @cindex section size | |
ec40bbb8 DM |
1202 | Return the size in bytes of the named @var{section}, if that section has |
1203 | been allocated. In the following example, @code{symbol_1} and | |
f22eee08 | 1204 | @code{symbol_2} are assigned identical values: |
ec40bbb8 | 1205 | @c What does it return if the section hasn't been allocated? 0? |
f22eee08 | 1206 | @example |
2c5c0674 | 1207 | SECTIONS@{ @dots{} |
f22eee08 RP |
1208 | .output @{ |
1209 | .start = . ; | |
2c5c0674 | 1210 | @dots{} |
cb70c872 | 1211 | .end = . ; |
f22eee08 | 1212 | @} |
cb70c872 | 1213 | symbol_1 = .end - .start ; |
f22eee08 | 1214 | symbol_2 = SIZEOF(.output); |
2c5c0674 | 1215 | @dots{} @} |
f22eee08 | 1216 | |
f22eee08 | 1217 | @end example |
b4d4e8e3 | 1218 | |
2c5c0674 RP |
1219 | @item SIZEOF_HEADERS |
1220 | @kindex SIZEOF_HEADERS | |
1221 | @cindex header size | |
1222 | @itemx sizeof_headers | |
1223 | @kindex sizeof_headers | |
ec40bbb8 | 1224 | Return the size in bytes of the output file's headers. You can use this number |
2c5c0674 RP |
1225 | as the start address of the first section, if you choose, to facilitate |
1226 | paging. | |
1227 | ||
1228 | @end table | |
1229 | ||
ec40bbb8 | 1230 | @node MEMORY |
867a1b8a | 1231 | @section Memory Layout |
2c5c0674 RP |
1232 | @kindex MEMORY |
1233 | @cindex regions of memory | |
1234 | @cindex discontinuous memory | |
1235 | @cindex allocating memory | |
ec40bbb8 DM |
1236 | The linker's default configuration permits allocation of all available memory. |
1237 | You can override this configuration by using the @code{MEMORY} command. The | |
b4d4e8e3 RP |
1238 | @code{MEMORY} command describes the location and size of blocks of |
1239 | memory in the target. By using it carefully, you can describe which | |
1240 | memory regions may be used by the linker, and which memory regions it | |
1241 | must avoid. The linker does not shuffle sections to fit into the | |
1242 | available regions, but does move the requested sections into the correct | |
1243 | regions and issue errors when the regions become too full. | |
1244 | ||
867a1b8a | 1245 | A command file may contain at most one use of the @code{MEMORY} |
b4d4e8e3 RP |
1246 | command; however, you can define as many blocks of memory within it as |
1247 | you wish. The syntax is: | |
c8072296 | 1248 | |
f22eee08 | 1249 | @example |
b4d4e8e3 RP |
1250 | MEMORY |
1251 | @{ | |
cb70c872 | 1252 | @var{name} (@var{attr}) : ORIGIN = @var{origin}, LENGTH = @var{len} |
2c5c0674 | 1253 | @dots{} |
b4d4e8e3 | 1254 | @} |
f22eee08 RP |
1255 | @end example |
1256 | @table @code | |
1257 | @item @var{name} | |
2c5c0674 | 1258 | @cindex naming memory regions |
f22eee08 RP |
1259 | is a name used internally by the linker to refer to the region. Any |
1260 | symbol name may be used. The region names are stored in a separate | |
ec40bbb8 | 1261 | name space, and will not conflict with symbols, file names or section |
b4d4e8e3 RP |
1262 | names. Use distinct names to specify multiple regions. |
1263 | @item (@var{attr}) | |
2c5c0674 RP |
1264 | @cindex memory region attributes |
1265 | is an optional list of attributes, permitted for compatibility with the | |
246504a5 | 1266 | AT&T linker but not used by @code{ld} beyond checking that the |
2c5c0674 RP |
1267 | attribute list is valid. Valid attribute lists must be made up of the |
1268 | characters ``@code{LIRWX}''. If you omit the attribute list, you may | |
1269 | omit the parentheses around it as well. | |
f22eee08 | 1270 | @item @var{origin} |
cb70c872 RP |
1271 | @kindex ORIGIN = |
1272 | @kindex o = | |
1273 | @kindex org = | |
ec40bbb8 DM |
1274 | is the start address of the region in physical memory. It is |
1275 | an expression that must evaluate to a constant before | |
f22eee08 | 1276 | memory allocation is performed. The keyword @code{ORIGIN} may be |
867a1b8a | 1277 | abbreviated to @code{org} or @code{o} (but not, for example, @samp{ORG}). |
f22eee08 | 1278 | @item @var{len} |
cb70c872 RP |
1279 | @kindex LENGTH = |
1280 | @kindex len = | |
1281 | @kindex l = | |
b4d4e8e3 | 1282 | is the size in bytes of the region (an expression). |
2c5c0674 | 1283 | The keyword @code{LENGTH} may be abbreviated to @code{len} or @code{l}. |
f22eee08 RP |
1284 | @end table |
1285 | ||
1286 | For example, to specify that memory has two regions available for | |
ec40bbb8 | 1287 | allocation---one starting at 0 for 256 kilobytes, and the other |
2c5c0674 | 1288 | starting at @code{0x40000000} for four megabytes: |
f22eee08 RP |
1289 | |
1290 | @example | |
b4d4e8e3 RP |
1291 | MEMORY |
1292 | @{ | |
cb70c872 RP |
1293 | rom : ORIGIN = 0, LENGTH = 256K |
1294 | ram : org = 0x40000000, l = 4M | |
b4d4e8e3 | 1295 | @} |
f22eee08 RP |
1296 | @end example |
1297 | ||
b4d4e8e3 | 1298 | Once you have defined a region of memory named @var{mem}, you can direct |
2c5c0674 RP |
1299 | specific output sections there by using a command ending in |
1300 | @samp{>@var{mem}} within the @code{SECTIONS} command (@pxref{Section | |
1301 | Options}). If the combined output sections directed to a region are too | |
1302 | big for the region, the linker will issue an error message. | |
b4d4e8e3 | 1303 | |
ec40bbb8 | 1304 | @node SECTIONS |
867a1b8a | 1305 | @section Specifying Output Sections |
2c5c0674 | 1306 | @kindex SECTIONS |
b4d4e8e3 | 1307 | The @code{SECTIONS} command controls exactly where input sections are |
867a1b8a DM |
1308 | placed into output sections, their order in the output file, and to |
1309 | which output sections they are allocated. | |
b4d4e8e3 | 1310 | |
867a1b8a | 1311 | You may use at most one @code{SECTIONS} command in a script file, |
b4d4e8e3 RP |
1312 | but you can have as many statements within it as you wish. Statements |
1313 | within the @code{SECTIONS} command can do one of three things: | |
1314 | @itemize @bullet | |
1315 | @item | |
1316 | define the entry point; | |
1317 | @item | |
1318 | assign a value to a symbol; | |
1319 | @item | |
867a1b8a DM |
1320 | describe the placement of a named output section, and which input |
1321 | sections go into it. | |
b4d4e8e3 RP |
1322 | @end itemize |
1323 | ||
8920addc RP |
1324 | You can also use the first two operations---defining the entry point and |
1325 | defining symbols---outside the @code{SECTIONS} command: @pxref{Entry | |
1326 | Point}, and @pxref{Assignment}. They are permitted here as well for | |
1327 | your convenience in reading the script, so that symbols and the entry | |
1328 | point can be defined at meaningful points in your output-file layout. | |
f22eee08 | 1329 | |
867a1b8a DM |
1330 | When no @code{SECTIONS} command is given, the linker places each input |
1331 | section into an identically named output section in the order that the | |
1332 | sections are first encountered in the input files. If all input sections | |
1333 | are present in the first file, for example, the order of sections in the | |
1334 | output file will match the order in the first input file. | |
b4d4e8e3 | 1335 | |
2c5c0674 | 1336 | @menu |
2d59b2c3 | 1337 | * Section Definition:: Section Definitions |
867a1b8a DM |
1338 | * Section Placement:: Section Placement |
1339 | * Section Data Expressions:: Section Data Expressions | |
2d59b2c3 | 1340 | * Section Options:: Optional Section Attributes |
2c5c0674 RP |
1341 | @end menu |
1342 | ||
ec40bbb8 | 1343 | @node Section Definition |
b4d4e8e3 | 1344 | @subsection Section Definitions |
2c5c0674 | 1345 | @cindex section definition |
b4d4e8e3 | 1346 | The most frequently used statement in the @code{SECTIONS} command is |
867a1b8a | 1347 | the @dfn{section definition}, which specifies the |
b4d4e8e3 | 1348 | properties of an output section: its location, alignment, contents, |
ec40bbb8 | 1349 | fill pattern, and target memory region. Most of |
b4d4e8e3 RP |
1350 | these specifications are optional; the simplest form of a section |
1351 | definition is | |
1352 | @example | |
2c5c0674 | 1353 | SECTIONS @{ @dots{} |
b4d4e8e3 RP |
1354 | @var{secname} : @{ |
1355 | @var{contents} | |
1356 | @} | |
2c5c0674 | 1357 | @dots{} @} |
b4d4e8e3 | 1358 | @end example |
2c5c0674 | 1359 | @cindex naming output sections |
b4d4e8e3 RP |
1360 | @noindent |
1361 | @var{secname} is the name of the output section, and @var{contents} a | |
ec40bbb8 | 1362 | specification of what goes there---for example, a list of input files or |
867a1b8a DM |
1363 | sections of input files (@pxref{Section Placement}). As you might |
1364 | assume, the whitespace shown is optional. You do need the colon | |
1365 | @samp{:} and the braces @samp{@{@}}, however. | |
b4d4e8e3 RP |
1366 | |
1367 | @var{secname} must meet the constraints of your output format. In | |
1368 | formats which only support a limited number of sections, such as | |
1369 | @code{a.out}, the name must be one of the names supported by the format | |
2c5c0674 RP |
1370 | (@code{a.out}, for example, allows only @code{.text}, @code{.data} or |
1371 | @code{.bss}). If the output format supports any number of sections, but | |
1372 | with numbers and not names (as is the case for Oasys), the name should be | |
1373 | supplied as a quoted numeric string. A section name may consist of any | |
867a1b8a | 1374 | sequence of characters, but any name which does not conform to the standard |
246504a5 | 1375 | @code{ld} symbol name syntax must be quoted. |
ec40bbb8 | 1376 | @xref{Symbols, , Symbol Names}. |
2c5c0674 | 1377 | |
867a1b8a DM |
1378 | @node Section Placement |
1379 | @subsection Section Placement | |
2c5c0674 | 1380 | @cindex contents of a section |
b4d4e8e3 | 1381 | In a section definition, you can specify the contents of an output section by |
867a1b8a | 1382 | listing particular input files, by listing particular input-file |
ec40bbb8 | 1383 | sections, or by a combination of the two. You can also place arbitrary |
b4d4e8e3 RP |
1384 | data in the section, and define symbols relative to the beginning of the |
1385 | section. | |
1386 | ||
1387 | The @var{contents} of a section definition may include any of the | |
1388 | following kinds of statement. You can include as many of these as you | |
1389 | like in a single section definition, separated from one another by | |
1390 | whitespace. | |
f22eee08 | 1391 | |
b4d4e8e3 | 1392 | @table @code |
b4d4e8e3 | 1393 | @item @var{filename} |
2c5c0674 RP |
1394 | @kindex @var{filename} |
1395 | @cindex input files, section defn | |
1396 | @cindex files, including in output sections | |
b4d4e8e3 | 1397 | You may simply name a particular input file to be placed in the current |
2c5c0674 | 1398 | output section; @emph{all} sections from that file are placed in the |
867a1b8a DM |
1399 | current section definition. If the file name has already been mentioned |
1400 | in another section definition, with an explicit section name list, then | |
1401 | only those sections which have not yet been allocated are used. | |
1402 | ||
1403 | To specify a list of particular files by name: | |
f22eee08 | 1404 | @example |
cb70c872 | 1405 | .data : @{ afile.o bfile.o cfile.o @} |
f22eee08 | 1406 | @end example |
2c5c0674 RP |
1407 | @noindent |
1408 | The example also illustrates that multiple statements can be included in | |
ec40bbb8 | 1409 | the contents of a section definition, since each file name is a separate |
2c5c0674 | 1410 | statement. |
f22eee08 | 1411 | |
2c5c0674 RP |
1412 | @item @var{filename}( @var{section} ) |
1413 | @itemx @var{filename}( @var{section}, @var{section}, @dots{} ) | |
1414 | @itemx @var{filename}( @var{section} @var{section} @dots{} ) | |
1415 | @kindex @var{filename}(@var{section}) | |
1416 | @cindex files and sections, section defn | |
1417 | You can name one or more sections from your input files, for | |
1418 | insertion in the current output section. If you wish to specify a list | |
1419 | of input-file sections inside the parentheses, you may separate the | |
1420 | section names by either commas or whitespace. | |
1421 | ||
b4d4e8e3 RP |
1422 | @item * (@var{section}) |
1423 | @itemx * (@var{section}, @var{section}, @dots{}) | |
836a5ee4 | 1424 | @itemx * (@var{section} @var{section} @dots{}) |
2c5c0674 RP |
1425 | @cindex input sections to output section |
1426 | @kindex *(@var{section}) | |
b4d4e8e3 | 1427 | Instead of explicitly naming particular input files in a link control |
246504a5 | 1428 | script, you can refer to @emph{all} files from the @code{ld} command |
ec40bbb8 | 1429 | line: use @samp{*} instead of a particular file name before the |
b4d4e8e3 RP |
1430 | parenthesized input-file section list. |
1431 | ||
867a1b8a DM |
1432 | If you have already explicitly included some files by name, @samp{*} |
1433 | refers to all @emph{remaining} files---those whose places in the output | |
1434 | file have not yet been defined. | |
1435 | ||
ec40bbb8 | 1436 | For example, to copy sections @code{1} through @code{4} from an Oasys file |
b4d4e8e3 RP |
1437 | into the @code{.text} section of an @code{a.out} file, and sections @code{13} |
1438 | and @code{14} into the @code{.data} section: | |
1439 | @example | |
2c5c0674 | 1440 | SECTIONS @{ |
b4d4e8e3 RP |
1441 | .text :@{ |
1442 | *("1" "2" "3" "4") | |
1443 | @} | |
f22eee08 | 1444 | |
b4d4e8e3 RP |
1445 | .data :@{ |
1446 | *("13" "14") | |
f22eee08 | 1447 | @} |
b4d4e8e3 | 1448 | @} |
f22eee08 RP |
1449 | @end example |
1450 | ||
836a5ee4 DM |
1451 | @samp{[ @var{section} @dots{} ]} used to be accepted as an alternate way |
1452 | to specify named sections from all unallocated input files. Because | |
1453 | some operating systems (VMS) allow brackets in file names, that notation | |
1454 | is no longer supported. | |
1455 | ||
b4d4e8e3 | 1456 | @item @var{filename}@code{( COMMON )} |
836a5ee4 DM |
1457 | @itemx *( COMMON ) |
1458 | @kindex *( COMMON ) | |
2c5c0674 RP |
1459 | @cindex uninitialized data |
1460 | @cindex commons in output | |
b4d4e8e3 | 1461 | Specify where in your output file to place uninitialized data |
d76ae847 | 1462 | with this notation. @code{*(COMMON)} by itself refers to all |
b4d4e8e3 RP |
1463 | uninitialized data from all input files (so far as it is not yet |
1464 | allocated); @var{filename}@code{(COMMON)} refers to uninitialized data | |
1465 | from a particular file. Both are special cases of the general | |
1466 | mechanisms for specifying where to place input-file sections: | |
246504a5 | 1467 | @code{ld} permits you to refer to uninitialized data as if it |
b4d4e8e3 RP |
1468 | were in an input-file section named @code{COMMON}, regardless of the |
1469 | input file's format. | |
1470 | @end table | |
1471 | ||
2c5c0674 | 1472 | For example, the following command script arranges the output file into |
b4d4e8e3 RP |
1473 | three consecutive sections, named @code{.text}, @code{.data}, and |
1474 | @code{.bss}, taking the input for each from the correspondingly named | |
1475 | sections of all the input files: | |
f22eee08 | 1476 | @example |
2c5c0674 | 1477 | SECTIONS @{ |
d76ae847 RP |
1478 | .text : @{ *(.text) @} |
1479 | .data : @{ *(.data) @} | |
1480 | .bss : @{ *(.bss) *(COMMON) @} | |
2c5c0674 | 1481 | @} |
f22eee08 | 1482 | @end example |
b4d4e8e3 RP |
1483 | |
1484 | The following example reads all of the sections from file @code{all.o} | |
1485 | and places them at the start of output section @code{outputa} which | |
1486 | starts at location @code{0x10000}. All of section @code{.input1} from | |
1487 | file @code{foo.o} follows immediately, in the same output section. All | |
1488 | of section @code{.input2} from @code{foo.o} goes into output section | |
1489 | @code{outputb}, followed by section @code{.input1} from @code{foo1.o}. | |
1490 | All of the remaining @code{.input1} and @code{.input2} sections from any | |
1491 | files are written to output section @code{outputc}. | |
1492 | ||
1493 | @example | |
2c5c0674 | 1494 | SECTIONS @{ |
b4d4e8e3 RP |
1495 | outputa 0x10000 : |
1496 | @{ | |
1497 | all.o | |
1498 | foo.o (.input1) | |
f22eee08 | 1499 | @} |
b4d4e8e3 RP |
1500 | outputb : |
1501 | @{ | |
1502 | foo.o (.input2) | |
1503 | foo1.o (.input1) | |
f22eee08 | 1504 | @} |
b4d4e8e3 RP |
1505 | outputc : |
1506 | @{ | |
1507 | *(.input1) | |
1508 | *(.input2) | |
f22eee08 | 1509 | @} |
2c5c0674 | 1510 | @} |
b4d4e8e3 RP |
1511 | @end example |
1512 | ||
867a1b8a DM |
1513 | @node Section Data Expressions |
1514 | @subsection Section Data Expressions | |
1515 | @cindex expressions in a section | |
1516 | The foregoing statements | |
b4d4e8e3 RP |
1517 | arrange, in your output file, data originating from your input files. |
1518 | You can also place data directly in an output section from the link | |
1519 | command script. Most of these additional statements involve | |
1520 | expressions; @pxref{Expressions}. Although these statements are shown | |
1521 | separately here for ease of presentation, no such segregation is needed | |
1522 | within a section definition in the @code{SECTIONS} command; you can | |
1523 | intermix them freely with any of the statements we've just described. | |
f22eee08 | 1524 | |
b4d4e8e3 RP |
1525 | @table @code |
1526 | @item CREATE_OBJECT_SYMBOLS | |
2c5c0674 RP |
1527 | @kindex CREATE_OBJECT_SYMBOLS |
1528 | @cindex input filename symbols | |
1529 | @cindex filename symbols | |
ec40bbb8 DM |
1530 | Create a symbol for each input file |
1531 | in the current section, set to the address of the first byte of | |
867a1b8a | 1532 | data written from that input file. For instance, with @code{a.out} |
b4d4e8e3 RP |
1533 | files it is conventional to have a symbol for each input file. You can |
1534 | accomplish this by defining the output @code{.text} section as follows: | |
1535 | @example | |
1536 | SECTIONS @{ | |
1537 | .text 0x2020 : | |
1538 | @{ | |
1539 | CREATE_OBJECT_SYMBOLS | |
1540 | *(.text) | |
1541 | _etext = ALIGN(0x2000); | |
f22eee08 | 1542 | @} |
2c5c0674 RP |
1543 | @dots{} |
1544 | @} | |
f22eee08 | 1545 | @end example |
b4d4e8e3 | 1546 | |
867a1b8a | 1547 | If @code{sample.ld} is a file containing this script, and @code{a.o}, |
b4d4e8e3 RP |
1548 | @code{b.o}, @code{c.o}, and @code{d.o} are four input files with |
1549 | contents like the following--- | |
f22eee08 | 1550 | @example |
b4d4e8e3 RP |
1551 | /* a.c */ |
1552 | ||
2c5c0674 | 1553 | afunction() @{ @} |
b4d4e8e3 RP |
1554 | int adata=1; |
1555 | int abss; | |
1556 | @end example | |
f22eee08 | 1557 | |
b4d4e8e3 | 1558 | @noindent |
867a1b8a | 1559 | @samp{ld -M -T sample.ld a.o b.o c.o d.o} would create a map like this, |
b4d4e8e3 RP |
1560 | containing symbols matching the object file names: |
1561 | @example | |
f22eee08 RP |
1562 | 00000000 A __DYNAMIC |
1563 | 00004020 B _abss | |
1564 | 00004000 D _adata | |
1565 | 00002020 T _afunction | |
1566 | 00004024 B _bbss | |
1567 | 00004008 D _bdata | |
1568 | 00002038 T _bfunction | |
1569 | 00004028 B _cbss | |
1570 | 00004010 D _cdata | |
1571 | 00002050 T _cfunction | |
1572 | 0000402c B _dbss | |
1573 | 00004018 D _ddata | |
1574 | 00002068 T _dfunction | |
1575 | 00004020 D _edata | |
1576 | 00004030 B _end | |
1577 | 00004000 T _etext | |
1578 | 00002020 t a.o | |
1579 | 00002038 t b.o | |
1580 | 00002050 t c.o | |
1581 | 00002068 t d.o | |
f22eee08 RP |
1582 | @end example |
1583 | ||
b4d4e8e3 | 1584 | @item @var{symbol} = @var{expression} ; |
2c5c0674 | 1585 | @kindex @var{symbol} = @var{expression} ; |
b4d4e8e3 | 1586 | @itemx @var{symbol} @var{f}= @var{expression} ; |
2c5c0674 RP |
1587 | @kindex @var{symbol} @var{f}= @var{expression} ; |
1588 | @var{symbol} is any symbol name (@pxref{Symbols}). ``@var{f}='' | |
1589 | refers to any of the operators @code{&= += -= *= /=} which combine | |
1590 | arithmetic and assignment. | |
1591 | ||
1592 | @cindex assignment, in section defn | |
1593 | When you assign a value to a symbol within a particular section | |
1594 | definition, the value is relative to the beginning of the section | |
1595 | (@pxref{Assignment}). If you write | |
b4d4e8e3 | 1596 | @example |
2c5c0674 | 1597 | SECTIONS @{ |
b4d4e8e3 | 1598 | abs = 14 ; |
2c5c0674 | 1599 | @dots{} |
cb70c872 | 1600 | .data : @{ @dots{} rel = 14 ; @dots{} @} |
b4d4e8e3 | 1601 | abs2 = 14 + ADDR(.data); |
2c5c0674 RP |
1602 | @dots{} |
1603 | @} | |
f22eee08 | 1604 | @end example |
2c5c0674 | 1605 | @c FIXME: Try above example! |
b4d4e8e3 | 1606 | @noindent |
ec40bbb8 | 1607 | @code{abs} and @code{rel} do not have the same value; @code{rel} has the |
b4d4e8e3 RP |
1608 | same value as @code{abs2}. |
1609 | ||
b4d4e8e3 | 1610 | @item BYTE(@var{expression}) |
2c5c0674 | 1611 | @kindex BYTE(@var{expression}) |
b4d4e8e3 | 1612 | @itemx SHORT(@var{expression}) |
2c5c0674 | 1613 | @kindex SHORT(@var{expression}) |
b4d4e8e3 | 1614 | @itemx LONG(@var{expression}) |
2c5c0674 | 1615 | @kindex LONG(@var{expression}) |
c477527c ILT |
1616 | @itemx QUAD(@var{expression}) |
1617 | @kindex QUAD(@var{expression}) | |
2c5c0674 | 1618 | @cindex direct output |
c477527c ILT |
1619 | By including one of these four statements in a section definition, you |
1620 | can explicitly place one, two, four, or eight bytes (respectively) at | |
1621 | the current address of that section. @code{QUAD} is only supported when | |
1622 | using a 64 bit host or target. | |
ec40bbb8 DM |
1623 | |
1624 | @ifclear SingleFormat | |
1625 | Multiple-byte quantities are represented in whatever byte order is | |
1626 | appropriate for the output file format (@pxref{BFD}). | |
1627 | @end ifclear | |
b4d4e8e3 RP |
1628 | |
1629 | @item FILL(@var{expression}) | |
2c5c0674 RP |
1630 | @kindex FILL(@var{expression}) |
1631 | @cindex holes, filling | |
1632 | @cindex unspecified memory | |
867a1b8a | 1633 | Specify the ``fill pattern'' for the current section. Any otherwise |
b4d4e8e3 RP |
1634 | unspecified regions of memory within the section (for example, regions |
1635 | you skip over by assigning a new value to the location counter @samp{.}) | |
1636 | are filled with the two least significant bytes from the | |
1637 | @var{expression} argument. A @code{FILL} statement covers memory | |
1638 | locations @emph{after} the point it occurs in the section definition; by | |
1639 | including more than one @code{FILL} statement, you can have different | |
1640 | fill patterns in different parts of an output section. | |
1641 | @end table | |
1642 | ||
ec40bbb8 | 1643 | @node Section Options |
b4d4e8e3 | 1644 | @subsection Optional Section Attributes |
2c5c0674 | 1645 | @cindex section defn, full syntax |
b4d4e8e3 RP |
1646 | Here is the full syntax of a section definition, including all the |
1647 | optional portions: | |
1648 | ||
d76ae847 | 1649 | @smallexample |
2c5c0674 RP |
1650 | SECTIONS @{ |
1651 | @dots{} | |
d76ae847 | 1652 | @var{secname} @var{start} BLOCK(@var{align}) (NOLOAD) : @{ @var{contents} @} =@var{fill} >@var{region} |
2c5c0674 | 1653 | @dots{} |
b4d4e8e3 | 1654 | @} |
d76ae847 | 1655 | @end smallexample |
b4d4e8e3 RP |
1656 | |
1657 | @var{secname} and @var{contents} are required. @xref{Section | |
867a1b8a | 1658 | Definition}, and @pxref{Section Placement} for details on @var{contents}. |
2c5c0674 | 1659 | The remaining elements---@var{start}, @code{BLOCK(@var{align)}}, |
d76ae847 RP |
1660 | @code{(NOLOAD)} @code{=@var{fill}}, and @code{>@var{region}}---are all |
1661 | optional. | |
f22eee08 | 1662 | |
b4d4e8e3 RP |
1663 | @table @code |
1664 | @item @var{start} | |
2c5c0674 RP |
1665 | @cindex start address, section |
1666 | @cindex section start | |
1667 | @cindex section address | |
b4d4e8e3 RP |
1668 | You can force the output section to be loaded at a specified address by |
1669 | specifying @var{start} immediately following the section name. | |
1670 | @var{start} can be represented as any expression. The following | |
1671 | example generates section @var{output} at location | |
1672 | @code{0x40000000}: | |
1673 | @example | |
1674 | SECTIONS @{ | |
2c5c0674 | 1675 | @dots{} |
b4d4e8e3 RP |
1676 | output 0x40000000: @{ |
1677 | @dots{} | |
1678 | @} | |
2c5c0674 | 1679 | @dots{} |
b4d4e8e3 | 1680 | @} |
f22eee08 | 1681 | @end example |
f22eee08 | 1682 | |
b4d4e8e3 | 1683 | @item BLOCK(@var{align}) |
2c5c0674 RP |
1684 | @kindex BLOCK(@var{align}) |
1685 | @cindex section alignment | |
1686 | @cindex aligning sections | |
ec40bbb8 | 1687 | You can include @code{BLOCK()} specification to advance |
2c5c0674 RP |
1688 | the location counter @code{.} prior to the beginning of the section, so |
1689 | that the section will begin at the specified alignment. @var{align} is | |
1690 | an expression. | |
f22eee08 | 1691 | |
d76ae847 RP |
1692 | @item (NOLOAD) |
1693 | @kindex NOLOAD | |
1694 | @cindex prevent unnecessary loading | |
1695 | Use @samp{(NOLOAD)} to prevent a section from being loaded into memory | |
1696 | each time it is accessed. For example, in the script sample below, the | |
1697 | @code{ROM} segment is addressed at memory location @samp{0} and does not | |
1698 | need to be loaded into each object file: | |
1699 | @example | |
1700 | SECTIONS @{ | |
1701 | ROM 0 (NOLOAD) : @{ @dots{} @} | |
1702 | @dots{} | |
1703 | @} | |
1704 | @end example | |
1705 | ||
b4d4e8e3 | 1706 | @item =@var{fill} |
2c5c0674 RP |
1707 | @kindex =@var{fill} |
1708 | @cindex section fill pattern | |
1709 | @cindex fill pattern, entire section | |
ec40bbb8 | 1710 | Including |
b4d4e8e3 | 1711 | @code{=@var{fill}} in a section definition specifies the initial fill |
ec40bbb8 DM |
1712 | value for that section. |
1713 | You may use any expression to specify @var{fill}. | |
1714 | Any unallocated holes in the current output | |
b4d4e8e3 RP |
1715 | section when written to the output file will be filled with the two |
1716 | least significant bytes of the value, repeated as necessary. You can | |
1717 | also change the fill value with a @code{FILL} statement in the | |
1718 | @var{contents} of a section definition. | |
f22eee08 | 1719 | |
b4d4e8e3 | 1720 | @item >@var{region} |
2c5c0674 RP |
1721 | @kindex >@var{region} |
1722 | @cindex section, assigning to memory region | |
1723 | @cindex memory regions and sections | |
1724 | Assign this section to a previously defined region of memory. | |
1725 | @xref{MEMORY}. | |
f22eee08 | 1726 | |
f22eee08 | 1727 | @end table |
b4d4e8e3 | 1728 | |
ec40bbb8 | 1729 | @node Entry Point |
b4d4e8e3 | 1730 | @section The Entry Point |
2c5c0674 RP |
1731 | @kindex ENTRY(@var{symbol}) |
1732 | @cindex start of execution | |
1733 | @cindex first instruction | |
b4d4e8e3 RP |
1734 | The linker command language includes a command specifically for |
1735 | defining the first executable instruction in an output file (its | |
1736 | @dfn{entry point}). Its argument is a symbol name: | |
f22eee08 | 1737 | @example |
b4d4e8e3 | 1738 | ENTRY(@var{symbol}) |
f22eee08 | 1739 | @end example |
b4d4e8e3 RP |
1740 | |
1741 | Like symbol assignments, the @code{ENTRY} command may be placed either | |
1742 | as an independent command in the command file, or among the section | |
1743 | definitions within the @code{SECTIONS} command---whatever makes the most | |
1744 | sense for your layout. | |
1745 | ||
2c5c0674 | 1746 | @cindex entry point, defaults |
b4d4e8e3 RP |
1747 | @code{ENTRY} is only one of several ways of choosing the entry point. |
1748 | You may indicate it in any of the following ways (shown in descending | |
1749 | order of priority: methods higher in the list override methods lower down). | |
f22eee08 RP |
1750 | @itemize @bullet |
1751 | @item | |
ec40bbb8 | 1752 | the @samp{-e} @var{entry} command-line option; |
f22eee08 | 1753 | @item |
8de26d62 | 1754 | the @code{ENTRY(@var{symbol})} command in a linker control script; |
f22eee08 | 1755 | @item |
b4d4e8e3 | 1756 | the value of the symbol @code{start}, if present; |
f22eee08 | 1757 | @item |
b4d4e8e3 | 1758 | the value of the symbol @code{_main}, if present; |
f22eee08 | 1759 | @item |
b4d4e8e3 | 1760 | the address of the first byte of the @code{.text} section, if present; |
f22eee08 | 1761 | @item |
b4d4e8e3 | 1762 | The address @code{0}. |
f22eee08 | 1763 | @end itemize |
b4d4e8e3 | 1764 | |
2c5c0674 RP |
1765 | For example, you can use these rules to generate an entry point with an |
1766 | assignment statement: if no symbol @code{start} is defined within your | |
1767 | input files, you can simply define it, assigning it an appropriate | |
1768 | value--- | |
f22eee08 | 1769 | @example |
b4d4e8e3 | 1770 | start = 0x2020; |
f22eee08 | 1771 | @end example |
b4d4e8e3 RP |
1772 | |
1773 | @noindent | |
1774 | The example shows an absolute address, but you can use any expression. | |
1775 | For example, if your input object files use some other symbol-name | |
1776 | convention for the entry point, you can just assign the value of | |
1777 | whatever symbol contains the start address to @code{start}: | |
f22eee08 | 1778 | @example |
cb70c872 | 1779 | start = other_symbol ; |
f22eee08 | 1780 | @end example |
f22eee08 | 1781 | |
867a1b8a DM |
1782 | @node Option Commands |
1783 | @section Option Commands | |
b4d4e8e3 RP |
1784 | The command language includes a number of other commands that you can |
1785 | use for specialized purposes. They are similar in purpose to | |
1786 | command-line options. | |
1787 | ||
1788 | @table @code | |
1789 | @item FLOAT | |
2c5c0674 | 1790 | @kindex FLOAT |
b4d4e8e3 | 1791 | @itemx NOFLOAT |
2c5c0674 RP |
1792 | @kindex NOFLOAT |
1793 | These keywords were used in some older linkers to request a particular | |
246504a5 | 1794 | math subroutine library. @code{ld} doesn't use the keywords, assuming |
2c5c0674 RP |
1795 | instead that any necessary subroutines are in libraries specified using |
1796 | the general mechanisms for linking to archives; but to permit the use of | |
1797 | scripts that were written for the older linkers, the keywords | |
1798 | @code{FLOAT} and @code{NOFLOAT} are accepted and ignored. | |
1799 | ||
1800 | @item FORCE_COMMON_ALLOCATION | |
1801 | @kindex FORCE_COMMON_ALLOCATION | |
1802 | @cindex common allocation | |
ec40bbb8 | 1803 | This command has the same effect as the @samp{-d} command-line option: |
2c5c0674 | 1804 | to make @code{ld} assign space to common symbols even if a relocatable |
ec40bbb8 | 1805 | output file is specified (@samp{-r}). |
b4d4e8e3 | 1806 | |
b4d4e8e3 | 1807 | @item INPUT ( @var{file}, @var{file}, @dots{} ) |
2c5c0674 | 1808 | @kindex INPUT ( @var{files} ) |
b4d4e8e3 | 1809 | @itemx INPUT ( @var{file} @var{file} @dots{} ) |
2c5c0674 RP |
1810 | @cindex binary input files |
1811 | Use this command to include binary input files in the link, without | |
7f9ae73e RP |
1812 | including them in a particular section definition. |
1813 | Specify the full name for each @var{file}, including @samp{.a} if | |
1814 | required. | |
1815 | ||
1816 | @code{ld} searches for each @var{file} through the archive-library | |
1817 | search path, just as for files you specify on the command line. | |
1818 | See the description of @samp{-L} in @ref{Options,,Command Line | |
1819 | Options}. | |
b4d4e8e3 | 1820 | |
2c5c0674 | 1821 | @ignore |
b4d4e8e3 | 1822 | @item MAP ( @var{name} ) |
2c5c0674 RP |
1823 | @kindex MAP ( @var{name} ) |
1824 | @c MAP(...) appears to look for an F in the arg, ignoring all other | |
1825 | @c chars; if it finds one, it sets "map_option_f" to true. But nothing | |
1826 | @c checks map_option_f. Apparently a stub for the future... | |
1827 | @end ignore | |
b4d4e8e3 RP |
1828 | |
1829 | @item OUTPUT ( @var{filename} ) | |
2c5c0674 RP |
1830 | @kindex OUTPUT ( @var{filename} ) |
1831 | @cindex naming the output file | |
d76ae847 RP |
1832 | Use this command to name the link output file @var{filename}. The |
1833 | effect of @code{OUTPUT(@var{filename})} is identical to the effect of | |
c477527c ILT |
1834 | @w{@samp{-o @var{filename}}}, which overrides it. You can use this |
1835 | command to supply a default output-file name other than @code{a.out}. | |
2c5c0674 | 1836 | |
ec40bbb8 | 1837 | @ifclear SingleFormat |
2c5c0674 RP |
1838 | @item OUTPUT_ARCH ( @var{bfdname} ) |
1839 | @kindex OUTPUT_ARCH ( @var{bfdname} ) | |
1840 | @cindex machine architecture, output | |
1841 | Specify a particular output machine architecture, with one of the names | |
1842 | used by the BFD back-end routines (@pxref{BFD}). This command is often | |
1843 | unnecessary; the architecture is most often set implicitly by either the | |
1844 | system BFD configuration or as a side effect of the @code{OUTPUT_FORMAT} | |
ec40bbb8 | 1845 | command. |
2c5c0674 RP |
1846 | |
1847 | @item OUTPUT_FORMAT ( @var{bfdname} ) | |
1848 | @kindex OUTPUT_FORMAT ( @var{bfdname} ) | |
1849 | @cindex format, output file | |
1850 | Specify a particular output format, with one of the names used by the | |
867a1b8a DM |
1851 | BFD back-end routines (@pxref{BFD}). The effect is identical to the |
1852 | effect of the @samp{-oformat} command-line option. | |
1853 | This selection will only affect | |
2c5c0674 | 1854 | the output file; the related command @code{TARGET} affects primarily |
ec40bbb8 DM |
1855 | input files. |
1856 | @end ifclear | |
2c5c0674 RP |
1857 | |
1858 | @item SEARCH_DIR ( @var{path} ) | |
1859 | @kindex SEARCH_DIR ( @var{path} ) | |
1860 | @cindex path for libraries | |
1861 | @cindex search path, libraries | |
246504a5 | 1862 | Add @var{path} to the list of paths where @code{ld} looks for |
2c5c0674 | 1863 | archive libraries. @code{SEARCH_DIR(@var{path})} has the same |
ec40bbb8 | 1864 | effect as @samp{-L@var{path}} on the command line. |
2c5c0674 RP |
1865 | |
1866 | @item STARTUP ( @var{filename} ) | |
1867 | @kindex STARTUP ( @var{filename} ) | |
1868 | @cindex first input file | |
1869 | Ensure that @var{filename} is the first input file used in the link | |
1870 | process. | |
b4d4e8e3 | 1871 | |
ec40bbb8 | 1872 | @ifclear SingleFormat |
b4d4e8e3 | 1873 | @item TARGET ( @var{format} ) |
2c5c0674 RP |
1874 | @cindex input file format |
1875 | @kindex TARGET ( @var{format} ) | |
1876 | Change the input-file object code format (like the command-line option | |
ec40bbb8 | 1877 | @samp{-b} or its synonym @samp{-format}). The argument @var{format} is |
867a1b8a DM |
1878 | one of the strings used by BFD to name binary formats. If @code{TARGET} |
1879 | is specified but @code{OUTPUT_FORMAT} is not, the last @code{TARGET} | |
1880 | argument is also used as the default format for the @code{ld} output | |
1881 | file. @xref{BFD}. | |
2c5c0674 RP |
1882 | |
1883 | @kindex GNUTARGET | |
246504a5 | 1884 | If you don't use the @code{TARGET} command, @code{ld} uses the value of |
2c5c0674 | 1885 | the environment variable @code{GNUTARGET}, if available, to select the |
246504a5 | 1886 | output file format. If that variable is also absent, @code{ld} uses |
2c5c0674 | 1887 | the default format configured for your machine in the BFD libraries. |
ec40bbb8 | 1888 | @end ifclear |
b4d4e8e3 RP |
1889 | @end table |
1890 | ||
ec40bbb8 DM |
1891 | @ifset GENERIC |
1892 | @node Machine Dependent | |
1c48127e RP |
1893 | @chapter Machine Dependent Features |
1894 | ||
1895 | @cindex machine dependencies | |
246504a5 RP |
1896 | @code{ld} has additional features on some platforms; the following |
1897 | sections describe them. Machines where @code{ld} has no additional | |
1c48127e RP |
1898 | functionality are not listed. |
1899 | ||
1900 | @menu | |
246504a5 RP |
1901 | * H8/300:: @code{ld} and the H8/300 |
1902 | * i960:: @code{ld} and the Intel 960 family | |
1c48127e | 1903 | @end menu |
ec40bbb8 DM |
1904 | @end ifset |
1905 | ||
7f9ae73e | 1906 | @c FIXME! This could use @raisesections/@lowersections, but there seems to be a conflict |
ec40bbb8 DM |
1907 | @c between those and node-defaulting. |
1908 | @ifset H8300 | |
1909 | @ifclear GENERIC | |
7f9ae73e | 1910 | @raisesections |
ec40bbb8 DM |
1911 | @end ifclear |
1912 | @node H8/300 | |
246504a5 | 1913 | @section @code{ld} and the H8/300 |
1c48127e RP |
1914 | |
1915 | @cindex H8/300 support | |
246504a5 | 1916 | For the H8/300, @code{ld} can perform these global optimizations when |
1c48127e RP |
1917 | you specify the @samp{-relax} command-line option. |
1918 | ||
1919 | @table @emph | |
1920 | @item relaxing address modes | |
d76ae847 | 1921 | @cindex relaxing on H8/300 |
246504a5 | 1922 | @code{ld} finds all @code{jsr} and @code{jmp} instructions whose |
1c48127e RP |
1923 | targets are within eight bits, and turns them into eight-bit |
1924 | program-counter relative @code{bsr} and @code{bra} instructions, | |
1925 | respectively. | |
1926 | ||
1927 | @item synthesizing instructions | |
d76ae847 | 1928 | @cindex synthesizing on H8/300 |
1c48127e | 1929 | @c FIXME: specifically mov.b, or any mov instructions really? |
246504a5 | 1930 | @code{ld} finds all @code{mov.b} instructions which use the |
1c48127e RP |
1931 | sixteen-bit absolute address form, but refer to the top |
1932 | page of memory, and changes them to use the eight-bit address form. | |
1933 | (That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into | |
1934 | @samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the | |
1935 | top page of memory). | |
1936 | @end table | |
ec40bbb8 | 1937 | @ifclear GENERIC |
7f9ae73e | 1938 | @lowersections |
ec40bbb8 DM |
1939 | @end ifclear |
1940 | @end ifset | |
1941 | ||
1942 | @ifset I960 | |
1943 | @ifclear GENERIC | |
7f9ae73e | 1944 | @raisesections |
ec40bbb8 DM |
1945 | @end ifclear |
1946 | @node i960 | |
246504a5 | 1947 | @section @code{ld} and the Intel 960 family |
1c48127e RP |
1948 | |
1949 | @cindex i960 support | |
d76ae847 | 1950 | |
1c48127e RP |
1951 | You can use the @samp{-A@var{architecture}} command line option to |
1952 | specify one of the two-letter names identifying members of the 960 | |
1953 | family; the option specifies the desired output target, and warns of any | |
1954 | incompatible instructions in the input files. It also modifies the | |
1955 | linker's search strategy for archive libraries, to support the use of | |
1956 | libraries specific to each particular architecture, by including in the | |
1957 | search loop names suffixed with the string identifying the architecture. | |
1958 | ||
246504a5 | 1959 | For example, if your @code{ld} command line included @w{@samp{-ACA}} as |
1c48127e | 1960 | well as @w{@samp{-ltry}}, the linker would look (in its built-in search |
ec40bbb8 | 1961 | paths, and in any paths you specify with @samp{-L}) for a library with |
1c48127e | 1962 | the names |
ec40bbb8 | 1963 | |
1c48127e RP |
1964 | @example |
1965 | try | |
1966 | libtry.a | |
1967 | tryca | |
1968 | libtryca.a | |
1969 | @end example | |
ec40bbb8 | 1970 | |
1c48127e RP |
1971 | @noindent |
1972 | The first two possibilities would be considered in any event; the last | |
1973 | two are due to the use of @w{@samp{-ACA}}. | |
1974 | ||
ec40bbb8 | 1975 | You can meaningfully use @samp{-A} more than once on a command line, since |
1c48127e | 1976 | the 960 architecture family allows combination of target architectures; each |
ec40bbb8 | 1977 | use will add another pair of name variants to search for when @w{@samp{-l}} |
1c48127e | 1978 | specifies a library. |
ec40bbb8 | 1979 | @ifclear GENERIC |
7f9ae73e | 1980 | @lowersections |
ec40bbb8 DM |
1981 | @end ifclear |
1982 | @end ifset | |
1c48127e | 1983 | |
ec40bbb8 DM |
1984 | @ifclear SingleFormat |
1985 | @node BFD | |
f22eee08 RP |
1986 | @chapter BFD |
1987 | ||
2c5c0674 RP |
1988 | @cindex back end |
1989 | @cindex object file management | |
1990 | The linker accesses object and archive files using the BFD libraries. | |
1991 | These libraries allow the linker to use the same routines to operate on | |
1992 | object files whatever the object file format. A different object file | |
1993 | format can be supported simply by creating a new BFD back end and adding | |
1c48127e RP |
1994 | it to the library. You can use @code{objdump -i} |
1995 | (@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to | |
1996 | list all the formats available for each architecture under BFD. This | |
1997 | was the list of formats, and of architectures supported for each format, | |
1998 | as of the time this manual was prepared: | |
2c5c0674 RP |
1999 | @cindex formats available |
2000 | @cindex architectures available | |
2c5c0674 | 2001 | @example |
1c48127e RP |
2002 | BFD header file version 0.18 |
2003 | a.out-i386 | |
2004 | (header big endian, data big endian) | |
2005 | m68k:68020 | |
2006 | a29k | |
2007 | sparc | |
2008 | i386 | |
2009 | a.out-sunos-big | |
2010 | (header big endian, data big endian) | |
2011 | m68k:68020 | |
2012 | a29k | |
2013 | sparc | |
2014 | i386 | |
2015 | b.out.big | |
2016 | (header big endian, data little endian) | |
2017 | i960:core | |
2018 | b.out.little | |
2019 | (header little endian, data little endian) | |
2020 | i960:core | |
2021 | coff-a29k-big | |
2022 | (header big endian, data big endian) | |
2023 | a29k | |
2024 | coff-h8300 | |
2025 | (header big endian, data big endian) | |
2026 | H8/300 | |
2027 | coff-i386 | |
2028 | (header little endian, data little endian) | |
2029 | i386 | |
2030 | coff-Intel-big | |
2031 | (header big endian, data little endian) | |
2032 | i960:core | |
2033 | coff-Intel-little | |
2034 | (header little endian, data little endian) | |
2035 | i960:core | |
2036 | coff-m68k | |
2037 | (header big endian, data big endian) | |
2038 | m68k:68020 | |
2039 | coff-m88kbcs | |
2040 | (header big endian, data big endian) | |
2041 | m88k:88100 | |
2042 | ecoff-bigmips | |
2043 | (header big endian, data big endian) | |
2044 | mips | |
2045 | ecoff-littlemips | |
2046 | (header little endian, data little endian) | |
2047 | mips | |
2048 | elf-big | |
2049 | (header big endian, data big endian) | |
2050 | m68k:68020 | |
2051 | vax | |
2052 | i960:core | |
2053 | a29k | |
2054 | sparc | |
2055 | mips | |
2056 | i386 | |
2057 | m88k:88100 | |
2058 | H8/300 | |
2059 | rs6000:6000 | |
2060 | elf-little | |
2061 | (header little endian, data little endian) | |
2062 | m68k:68020 | |
2063 | vax | |
2064 | i960:core | |
2065 | a29k | |
2066 | sparc | |
2067 | mips | |
2068 | i386 | |
2069 | m88k:88100 | |
2070 | H8/300 | |
2071 | rs6000:6000 | |
2072 | ieee | |
2073 | (header big endian, data big endian) | |
2074 | m68k:68020 | |
2075 | vax | |
2076 | i960:core | |
2077 | a29k | |
2078 | sparc | |
2079 | mips | |
2080 | i386 | |
2081 | m88k:88100 | |
2082 | H8/300 | |
2083 | rs6000:6000 | |
2084 | srec | |
2085 | (header big endian, data big endian) | |
2086 | m68k:68020 | |
2087 | vax | |
2088 | i960:core | |
2089 | a29k | |
2090 | sparc | |
2091 | mips | |
2092 | i386 | |
2093 | m88k:88100 | |
2094 | H8/300 | |
2095 | rs6000:6000 | |
2c5c0674 | 2096 | @end example |
f22eee08 | 2097 | |
2c5c0674 RP |
2098 | @cindex BFD requirements |
2099 | @cindex requirements for BFD | |
2100 | As with most implementations, BFD is a compromise between | |
f22eee08 | 2101 | several conflicting requirements. The major factor influencing |
2c5c0674 RP |
2102 | BFD design was efficiency: any time used converting between |
2103 | formats is time which would not have been spent had BFD not | |
f22eee08 | 2104 | been involved. This is partly offset by abstraction payback; since |
2c5c0674 | 2105 | BFD simplifies applications and back ends, more time and care |
f22eee08 RP |
2106 | may be spent optimizing algorithms for a greater speed. |
2107 | ||
2c5c0674 RP |
2108 | One minor artifact of the BFD solution which you should bear in |
2109 | mind is the potential for information loss. There are two places where | |
ec40bbb8 | 2110 | useful information can be lost using the BFD mechanism: during |
2c5c0674 RP |
2111 | conversion and during output. @xref{BFD information loss}. |
2112 | ||
2113 | @menu | |
2d59b2c3 | 2114 | * BFD outline:: How it works: an outline of BFD |
2c5c0674 | 2115 | @end menu |
f22eee08 | 2116 | |
ec40bbb8 | 2117 | @node BFD outline |
b4d4e8e3 | 2118 | @section How it works: an outline of BFD |
2c5c0674 | 2119 | @cindex opening object files |
3e27cc11 | 2120 | @include bfdsumm.texi |
ec40bbb8 | 2121 | @end ifclear |
f22eee08 | 2122 | |
ec40bbb8 | 2123 | @node MRI |
2d59b2c3 RP |
2124 | @appendix MRI Compatible Script Files |
2125 | @cindex MRI compatibility | |
2126 | To aid users making the transition to @sc{gnu} @code{ld} from the MRI | |
2127 | linker, @code{ld} can use MRI compatible linker scripts as an | |
2128 | alternative to the more general-purpose linker scripting language | |
2129 | described in @ref{Commands,,Command Language}. MRI compatible linker | |
2130 | scripts have a much simpler command set than the scripting language | |
2131 | otherwise used with @code{ld}. @sc{gnu} @code{ld} supports the most | |
2132 | commonly used MRI linker commands; these commands are described here. | |
2133 | ||
867a1b8a DM |
2134 | In general, MRI scripts aren't of much use with the @code{a.out} object |
2135 | file format, since it only has three sections and MRI scripts lack some | |
2136 | features to make use of them. | |
2137 | ||
2d59b2c3 RP |
2138 | You can specify a file containing an MRI-compatible script using the |
2139 | @samp{-c} command-line option. | |
2140 | ||
2141 | Each command in an MRI-compatible script occupies its own line; each | |
2142 | command line starts with the keyword that identifies the command (though | |
2143 | blank lines are also allowed for punctuation). If a line of an | |
2144 | MRI-compatible script begins with an unrecognized keyword, @code{ld} | |
2145 | issues a warning message, but continues processing the script. | |
2146 | ||
2147 | Lines beginning with @samp{*} are comments. | |
2148 | ||
2149 | You can write these commands using all upper-case letters, or all | |
2150 | lower case; for example, @samp{chip} is the same as @samp{CHIP}. | |
2151 | The following list shows only the upper-case form of each command. | |
2152 | ||
2153 | @table @code | |
2154 | @item ABSOLUTE @var{secname} | |
2155 | @item ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname} | |
2156 | @cindex @code{ABSOLUTE} (MRI) | |
2157 | Normally, @code{ld} includes in the output file all sections from all | |
2158 | the input files. However, in an MRI-compatible script, you can use the | |
2159 | @code{ABSOLUTE} command to restrict the sections that will be present in | |
2160 | your output program. If the @code{ABSOLUTE} command is used at all in a | |
2161 | script, then only the sections named explicitly in @code{ABSOLUTE} | |
2162 | commands will appear in the linker output. You can still use other | |
2163 | input sections (whatever you select on the command line, or using | |
7b015547 | 2164 | @code{LOAD}) to resolve addresses in the output file. |
2d59b2c3 RP |
2165 | |
2166 | @item ALIAS @var{out-secname}, @var{in-secname} | |
2167 | @cindex @code{ALIAS} (MRI) | |
2168 | Use this command to place the data from input section @var{in-secname} | |
2169 | in a section called @var{out-secname} in the linker output file. | |
2170 | ||
2171 | @var{in-secname} may be an integer. | |
2172 | ||
2173 | @item BASE @var{expression} | |
2174 | @cindex @code{BASE} (MRI) | |
2175 | Use the value of @var{expression} as the lowest address (other than | |
2176 | absolute addresses) in the output file. | |
2177 | ||
2178 | @item CHIP @var{expression} | |
2179 | @itemx CHIP @var{expression}, @var{expression} | |
2180 | @cindex @code{CHIP} (MRI) | |
ec40bbb8 | 2181 | This command does nothing; it is accepted only for compatibility. |
2d59b2c3 RP |
2182 | |
2183 | @item END | |
2184 | @cindex @code{END} (MRI) | |
2185 | This command does nothing whatever; it's only accepted for compatibility. | |
2186 | ||
2187 | @item FORMAT @var{output-format} | |
2188 | @cindex @code{FORMAT} (MRI) | |
2189 | Similar to the @code{OUTPUT_FORMAT} command in the more general linker | |
2190 | language, but restricted to one of these output formats: | |
2191 | @enumerate | |
2192 | @item | |
2193 | S-records, if @var{output-format} is @samp{S} | |
2194 | ||
2195 | @item | |
2196 | IEEE, if @var{output-format} is @samp{IEEE} | |
2197 | ||
2198 | @item | |
2199 | COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is | |
2200 | @samp{COFF} | |
2201 | @end enumerate | |
2202 | ||
8ddef552 | 2203 | @item LIST @var{anything}@dots{} |
2d59b2c3 RP |
2204 | @cindex @code{LIST} (MRI) |
2205 | Print (to the standard output file) a link map, as produced by the | |
2206 | @code{ld} command-line option @samp{-M}. | |
2207 | ||
ec40bbb8 DM |
2208 | The keyword @code{LIST} may be followed by anything on the |
2209 | same line, with no change in its effect. | |
2d59b2c3 RP |
2210 | |
2211 | @item LOAD @var{filename} | |
2212 | @item LOAD @var{filename}, @var{filename}, @dots{} @var{filename} | |
2213 | @cindex @code{LOAD} (MRI) | |
2214 | Include one or more object file @var{filename} in the link; this has the | |
2215 | same effect as specifying @var{filename} directly on the @code{ld} | |
2216 | command line. | |
2217 | ||
2218 | @item NAME @var{output-name} | |
2219 | @cindex @code{NAME} (MRI) | |
2220 | @var{output-name} is the name for the program produced by @code{ld}; the | |
2221 | MRI-compatible command @code{NAME} is equivalent to the command-line | |
2222 | option @samp{-o} or the general script language command @code{OUTPUT}. | |
2223 | ||
2224 | @item ORDER @var{secname}, @var{secname}, @dots{} @var{secname} | |
2225 | @itemx ORDER @var{secname} @var{secname} @var{secname} | |
2226 | @cindex @code{ORDER} (MRI) | |
ec40bbb8 DM |
2227 | Normally, @code{ld} orders the sections in its output file in the |
2228 | order in which they first appear in the input files. In an MRI-compatible | |
2229 | script, you can override this ordering with the @code{ORDER} command. The | |
2d59b2c3 RP |
2230 | sections you list with @code{ORDER} will appear first in your output |
2231 | file, in the order specified. | |
2232 | ||
2233 | @item PUBLIC @var{name}=@var{expression} | |
2234 | @itemx PUBLIC @var{name},@var{expression} | |
2235 | @itemx PUBLIC @var{name} @var{expression} | |
2236 | @cindex @code{PUBLIC} (MRI) | |
ec40bbb8 | 2237 | Supply a value (@var{expression}) for external symbol |
2d59b2c3 RP |
2238 | @var{name} used in the linker input files. |
2239 | ||
2240 | @item SECT @var{secname}, @var{expression} | |
2241 | @itemx SECT @var{secname}=@var{expression} | |
2242 | @itemx SECT @var{secname} @var{expression} | |
2243 | @cindex @code{SECT} (MRI) | |
2244 | You can use any of these three forms of the @code{SECT} command to | |
2245 | specify the start address (@var{expression}) for section @var{secname}. | |
2246 | If you have more than one @code{SECT} statement for the same | |
2247 | @var{secname}, only the @emph{first} sets the start address. | |
2248 | @end table | |
2249 | ||
2250 | ||
ec40bbb8 | 2251 | @node Index |
2c5c0674 RP |
2252 | @unnumbered Index |
2253 | ||
2254 | @printindex cp | |
2255 | ||
2256 | @tex | |
2257 | % I think something like @colophon should be in texinfo. In the | |
2258 | % meantime: | |
2259 | \long\def\colophon{\hbox to0pt{}\vfill | |
2260 | \centerline{The body of this manual is set in} | |
2261 | \centerline{\fontname\tenrm,} | |
2262 | \centerline{with headings in {\bf\fontname\tenbf}} | |
2263 | \centerline{and examples in {\tt\fontname\tentt}.} | |
2264 | \centerline{{\it\fontname\tenit\/} and} | |
2265 | \centerline{{\sl\fontname\tensl\/}} | |
2266 | \centerline{are used for emphasis.}\vfill} | |
2267 | \page\colophon | |
2268 | % Blame: pesch@cygnus.com, 28mar91. | |
2269 | @end tex | |
2270 | ||
2271 | ||
b4d4e8e3 | 2272 | @contents |
f22eee08 RP |
2273 | @bye |
2274 | ||
2275 |