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