4 @include configdoc.texi
5 @c (configdoc.texi is generated by the Makefile)
12 * Ld: (ld). The GNU linker.
18 This file documents the GNU linker LD.
20 Copyright (C) 1991, 92, 93, 94, 1995 Free Software Foundation, Inc.
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.
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.
31 Permission is granted to copy and distribute translations of this manual
32 into another language, under the above conditions for modified versions.
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).
44 @setchapternewpage odd
45 @settitle Using LD, the GNU linker
48 @subtitle The GNU linker
50 @subtitle @code{ld} version 2
51 @subtitle January 1994
52 @author Steve Chamberlain and Roland Pesch
53 @author Cygnus Support
58 \hfill Cygnus Support\par
59 \hfill steve\@cygnus.com, pesch\@cygnus.com\par
60 \hfill {\it Using LD, the GNU linker}\par
61 \hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
62 \hfill and Roland Pesch (pesch\@cygnus.com)\par
64 \global\parindent=0pt % Steve likes it this way.
67 @vskip 0pt plus 1filll
68 Copyright @copyright{} 1991, 92, 93, 94, 1995 Free Software Foundation, Inc.
70 Permission is granted to make and distribute verbatim copies of
71 this manual provided the copyright notice and this permission notice
72 are preserved on all copies.
74 Permission is granted to copy and distribute modified versions of this
75 manual under the conditions for verbatim copying, provided also that
76 the entire resulting derived work is distributed under the terms of a
77 permission notice identical to this one.
79 Permission is granted to copy and distribute translations of this manual
80 into another language, under the above conditions for modified versions.
83 @c FIXME: Talk about importance of *order* of args, cmds to linker!
88 This file documents the GNU linker ld.
92 * Invocation:: Invocation
93 * Commands:: Command Language
95 * Machine Dependent:: Machine Dependent Features
99 * H8/300:: ld and the H8/300
102 * Hitachi:: ld and other Hitachi micros
105 * i960:: ld and the Intel 960 family
108 @ifclear SingleFormat
111 @c Following blank line required for remaining bug in makeinfo conds/menus
113 * MRI:: MRI Compatible Script Files
122 @cindex what is this?
123 @code{ld} combines a number of object and archive files, relocates
124 their data and ties up symbol references. Usually the last step in
125 compiling a program is to run @code{ld}.
127 @code{ld} accepts Linker Command Language files written in
128 a superset of AT&T's Link Editor Command Language syntax,
129 to provide explicit and total control over the linking process.
131 @ifclear SingleFormat
132 This version of @code{ld} uses the general purpose BFD libraries
133 to operate on object files. This allows @code{ld} to read, combine, and
134 write object files in many different formats---for example, COFF or
135 @code{a.out}. Different formats may be linked together to produce any
136 available kind of object file. @xref{BFD}, for more information.
139 Aside from its flexibility, the GNU linker is more helpful than other
140 linkers in providing diagnostic information. Many linkers abandon
141 execution immediately upon encountering an error; whenever possible,
142 @code{ld} continues executing, allowing you to identify other errors
143 (or, in some cases, to get an output file in spite of the error).
148 The GNU linker @code{ld} is meant to cover a broad range of situations,
149 and to be as compatible as possible with other linkers. As a result,
150 you have many choices to control its behavior.
154 * Options:: Command Line Options
155 * Environment:: Environment Variables
159 @section Command Line Options
164 Here is a summary of the options you can use on the @code{ld} command
167 @c FIXME! -relax only avail h8/300, i960. Conditionals screwed in examples.
169 ld [ -o @var{output} ] @var{objfile}@dots{}
170 [ -A@var{architecture} ] [ -b @var{input-format} ]
171 [ -Bstatic ] [ -Bdynamic ] [ -Bsymbolic ]
172 [ -c @var{MRI-commandfile} ] [ -d | -dc | -dp ]
173 [ -defsym @var{symbol}=@var{expression} ]
174 [ -dynamic-linker @var{file} ] [ -embedded-relocs ]
175 [ -e @var{entry} ] [ -F ] [ -F @var{format} ]
176 [ -format @var{input-format} ] [ -g ] [ -G @var{size} ] [ -help ]
177 [ -i ] [ -l@var{archive} ] [ -L@var{searchdir} ] [ -M ]
178 [ -Map @var{mapfile} ] [ -m @var{emulation} ] [ -N | -n ]
179 [ -noinhibit-exec ] [ -no-keep-memory ] [ -oformat @var{output-format} ]
180 [ -R @var{filename} ] [ -relax ] [ -retain-symbols-file @var{filename} ]
181 [ -r | -Ur ] [ -rpath @var{dir} ] [ -S ] [ -s ] [ -soname @var{name} ]
182 [ -shared ] [ -sort-common ] [ -stats ] [ -T @var{commandfile} ]
183 [ -Ttext @var{org} ] [ -Tdata @var{org} ]
184 [ -Tbss @var{org} ] [ -t ] [ -traditional-format ]
185 [ -u @var{symbol}] [-V] [-v] [ -verbose] [ -version ]
186 [ -warn-common ] [ -warn-constructors] [ -warn-once ]
187 [ -y @var{symbol} ] [ -X ] [-x ]
188 [ -( [ archives ] -) ] [ --start-group [ archives ] --end-group ]
189 [ -split-by-reloc @var{count} ] [ -split-by-file ] [ --whole-archive ]
192 This plethora of command-line options may seem intimidating, but in
193 actual practice few of them are used in any particular context.
194 @cindex standard Unix system
195 For instance, a frequent use of @code{ld} is to link standard Unix
196 object files on a standard, supported Unix system. On such a system, to
197 link a file @code{hello.o}:
200 ld -o @var{output} /lib/crt0.o hello.o -lc
203 This tells @code{ld} to produce a file called @var{output} as the
204 result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
205 the library @code{libc.a}, which will come from the standard search
206 directories. (See the discussion of the @samp{-l} option below.)
208 The command-line options to @code{ld} may be specified in any order, and
209 may be repeated at will. Repeating most options with a
210 different argument will either have no further effect, or override prior
211 occurrences (those further to the left on the command line) of that
214 @ifclear SingleFormat
215 The exceptions---which may meaningfully be used more than once---are
216 @samp{-A}, @samp{-b} (or its synonym @samp{-format}), @samp{-defsym},
217 @samp{-L}, @samp{-l}, @samp{-R}, @samp{-u}, and @samp{-(} (or its
218 synonym @samp{--start-group})..
221 The exceptions---which may meaningfully be used more than once---are
222 @samp{-A}, @samp{-defsym}, @samp{-L}, @samp{-l}, @samp{-R}, @samp{-u},
223 and @samp{-(} (or its synonym @samp{--start-group}).
227 The list of object files to be linked together, shown as @var{objfile}@dots{},
228 may follow, precede, or be mixed in with command-line options, except that
229 an @var{objfile} argument may not be placed between an option and
232 Usually the linker is invoked with at least one object file, but you can
233 specify other forms of binary input files using @samp{-l}, @samp{-R},
234 and the script command language. If @emph{no} binary input files at all
235 are specified, the linker does not produce any output, and issues the
236 message @samp{No input files}.
238 If the linker can not recognize the format of an object file, it will
239 assume that it is a linker script. A script specified in this way
240 augments the main linker script used for the link (either the default
241 linker script or the one specified by using @samp{-T}). This feature
242 permits the linker to link against a file which appears to be an object
243 or an archive, but actually merely defines some symbol values, or uses
244 @code{INPUT} or @code{GROUP} to load other objects. @xref{Commands}.
246 For options whose names are a single letter,
247 option arguments must either follow the option letter without intervening
248 whitespace, or be given as separate arguments immediately following the
249 option that requires them.
251 For options whose names are multiple letters, either one dash or two can
252 precede the option name; for example, @samp{--oformat} and
253 @samp{-oformat} are equivalent. Arguments to multiple-letter options
254 must either be separated from the option name by an equals sign, or be
255 given as separate arguments immediately following the option that
256 requires them. For example, @samp{--oformat srec} and
257 @samp{--oformat=srec} are equivalent. Unique abbreviations of the names
258 of multiple-letter options are accepted.
262 @cindex architectures
264 @item -A@var{architecture}
265 In the current release of @code{ld}, this option is useful only for the
266 Intel 960 family of architectures. In that @code{ld} configuration, the
267 @var{architecture} argument identifies the particular architecture in
268 the 960 family, enabling some safeguards and modifying the
269 archive-library search path. @xref{i960,,@code{ld} and the Intel 960
270 family}, for details.
272 Future releases of @code{ld} may support similar functionality for
273 other architecture families.
276 @ifclear SingleFormat
277 @cindex binary input format
278 @kindex -b @var{format}
280 @item -b @var{input-format}
282 @code{ld} may be configured to support more than one kind of object
283 file. If your @code{ld} is configured this way, you can use the
284 @samp{-b} option to specify the binary format for input object files
285 that follow this option on the command line. Even when @code{ld} is
286 configured to support alternative object formats, you don't usually need
287 to specify this, as @code{ld} should be configured to expect as a
288 default input format the most usual format on each machine.
289 @var{input-format} is a text string, the name of a particular format
290 supported by the BFD libraries. (You can list the available binary
291 formats with @samp{objdump -i}.) @w{@samp{-format @var{input-format}}}
292 has the same effect, as does the script command @code{TARGET}.
295 You may want to use this option if you are linking files with an unusual
296 binary format. You can also use @samp{-b} to switch formats explicitly (when
297 linking object files of different formats), by including
298 @samp{-b @var{input-format}} before each group of object files in a
301 The default format is taken from the environment variable
306 You can also define the input
307 format from a script, using the command @code{TARGET}; see @ref{Option
313 Do not link against shared libraries. This is only meaningful on
314 platforms for which shared libraries are supported.
318 Link against dynamic libraries. This is only meaningful on platforms
319 for which shared libraries are supported. This option is normally the
320 default on such platforms.
324 When creating a shared library, bind references to global symbols to the
325 definition within the shared library, if any. Normally, it is possible
326 for a program linked against a shared library to override the definition
327 within the shared library. This option is only meaningful on ELF
328 platforms which support shared libraries.
330 @kindex -c @var{MRI-cmdfile}
331 @cindex compatibility, MRI
332 @item -c @var{MRI-commandfile}
333 For compatibility with linkers produced by MRI, @code{ld} accepts script
334 files written in an alternate, restricted command language, described in
335 @ref{MRI,,MRI Compatible Script Files}. Introduce MRI script files with
336 the option @samp{-c}; use the @samp{-T} option to run linker
337 scripts written in the general-purpose @code{ld} scripting language.
338 If @var{MRI-cmdfile} does not exist, @code{ld} looks for it in the directories
339 specified by any @samp{-L} options.
341 @cindex common allocation
348 These three options are equivalent; multiple forms are supported for
349 compatibility with other linkers. They
350 assign space to common symbols even if a relocatable output file is
351 specified (with @samp{-r}). The script command
352 @code{FORCE_COMMON_ALLOCATION} has the same effect. @xref{Option
355 @cindex symbols, from command line
356 @kindex -defsym @var{symbol}=@var{exp}
357 @item -defsym @var{symbol}=@var{expression}
358 Create a global symbol in the output file, containing the absolute
359 address given by @var{expression}. You may use this option as many
360 times as necessary to define multiple symbols in the command line. A
361 limited form of arithmetic is supported for the @var{expression} in this
362 context: you may give a hexadecimal constant or the name of an existing
363 symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
364 constants or symbols. If you need more elaborate expressions, consider
365 using the linker command language from a script (@pxref{Assignment, ,
366 Assignment: Symbol Definitions}). @emph{Note:} there should be no
367 white space between @var{symbol}, the equals sign (``@key{=}''), and
371 @cindex dynamic linker, from command line
372 @kindex -dynamic-linker @var{file}
373 @item -dynamic-linker @var{file}
374 Set the name of the dynamic linker. This is only meaningful when
375 generating dynamically linked ELF executables. The default dynamic
376 linker is normally correct; don't use this unless you know what you are
380 @cindex MIPS embedded PIC code
381 @kindex -embedded-relocs
382 @item -embedded-relocs
383 This option is only meaningful when linking MIPS embedded PIC code,
384 generated by the -membedded-pic option to the GNU compiler and
385 assembler. It causes the linker to create a table which may be used at
386 runtime to relocate any data which was statically initialized to pointer
387 values. See the code in testsuite/ld-empic for details.
389 @cindex entry point, from command line
390 @kindex -e @var{entry}
392 Use @var{entry} as the explicit symbol for beginning execution of your
393 program, rather than the default entry point. @xref{Entry Point}, for a
394 discussion of defaults and other ways of specifying the
397 @ifclear SingleFormat
400 @itemx -F@var{format}
401 Ignored. Some older linkers used this option throughout a compilation
402 toolchain for specifying object-file format for both input and output
403 object files. The mechanisms @code{ld} uses for this purpose (the
404 @samp{-b} or @samp{-format} options for input files, @samp{-oformat}
405 option or the @code{TARGET} command in linker scripts for output files,
406 the @code{GNUTARGET} environment variable) are more flexible, but
407 @code{ld} accepts the @samp{-F} option for compatibility with scripts
408 written to call the old linker.
411 @item -format @var{input-format}
412 Synonym for @samp{-b @var{input-format}}.
417 Ignored. Provided for compatibility with other tools.
422 @itemx -G @var{value}
423 Set the maximum size of objects to be optimized using the GP register to
424 @var{size} under MIPS ECOFF. Ignored for other object file formats.
430 Print a summary of the command-line options on the standard output and exit.
433 @cindex incremental link
435 Perform an incremental link (same as option @samp{-r}).
437 @cindex archive files, from cmd line
438 @kindex -l@var{archive}
440 Add archive file @var{archive} to the list of files to link. This
441 option may be used any number of times. @code{ld} will search its
442 path-list for occurrences of @code{lib@var{ar}.a} for every @var{archive}
445 @cindex search directory, from cmd line
447 @item -L@var{searchdir}
448 @itemx -L @var{searchdir}
449 Add path @var{searchdir} to the list of paths that @code{ld} will search
450 for archive libraries and @code{ld} control scripts. You may use this
451 option any number of times. The directories are searched in the order
452 in which they are specified on the command line. Directories specified
453 on the command line are searched before the default directories. All
454 @code{-L} options apply to all @code{-l} options, regardless of the
455 order in which the options appear.
458 The default set of paths searched (without being specified with
459 @samp{-L}) depends on which emulation mode @code{ld} is using, and in
460 some cases also on how it was configured. @xref{Environment}.
463 The paths can also be specified in a link script with the
464 @code{SEARCH_DIR} command. Directories specified this way are searched
465 at the point in which the linker script appears in the command line.
470 Print (to the standard output) a link map---diagnostic information
471 about where symbols are mapped by @code{ld}, and information on global
472 common storage allocation.
476 @item -Map @var{mapfile}
477 Print to the file @var{mapfile} a link map---diagnostic information
478 about where symbols are mapped by @code{ld}, and information on global
479 common storage allocation.
482 @kindex -m @var{emulation}
483 @item -m@var{emulation}
484 @itemx -m @var{emulation}
485 Emulate the @var{emulation} linker. You can list the available
486 emulations with the @samp{--verbose} or @samp{-V} options. The default
487 depends on how your @code{ld} was configured.
490 @cindex read/write from cmd line
493 Set the text and data sections to be readable and writable. Also, do
494 not page-align the data segment. If the output format supports Unix
495 style magic numbers, mark the output as @code{OMAGIC}.
498 @cindex read-only text
501 Set the text segment to be read only, and mark the output as
502 @code{NMAGIC} if possible.
504 @item -noinhibit-exec
505 @cindex output file after errors
506 @kindex -noinhibit-exec
507 Retain the executable output file whenever it is still usable.
508 Normally, the linker will not produce an output file if it encounters
509 errors during the link process; it exits without writing an output file
510 when it issues any error whatsoever.
512 @item -no-keep-memory
514 @kindex -no-keep-memory
515 @code{ld} normally optimizes for speed over memory usage by caching the
516 symbol tables of input files in memory. This option tells @code{ld} to
517 instead optimize for memory usage, by rereading the symbol tables as
518 necessary. This may be required if @code{ld} runs out of memory space
519 while linking a large executable.
521 @item -o @var{output}
522 @kindex -o @var{output}
523 @cindex naming the output file
524 Use @var{output} as the name for the program produced by @code{ld}; if this
525 option is not specified, the name @file{a.out} is used by default. The
526 script command @code{OUTPUT} can also specify the output file name.
528 @ifclear SingleFormat
530 @item -oformat @var{output-format}
531 @code{ld} may be configured to support more than one kind of object
532 file. If your @code{ld} is configured this way, you can use the
533 @samp{-oformat} option to specify the binary format for the output
534 object file. Even when @code{ld} is configured to support alternative
535 object formats, you don't usually need to specify this, as @code{ld}
536 should be configured to produce as a default output format the most
537 usual format on each machine. @var{output-format} is a text string, the
538 name of a particular format supported by the BFD libraries. (You can
539 list the available binary formats with @samp{objdump -i}.) The script
540 command @code{OUTPUT_FORMAT} can also specify the output format, but
541 this option overrides it. @xref{BFD}.
544 @item -R @var{filename}
545 @kindex -R @var{file}
546 @cindex symbol-only input
547 Read symbol names and their addresses from @var{filename}, but do not
548 relocate it or include it in the output. This allows your output file
549 to refer symbolically to absolute locations of memory defined in other
553 @cindex synthesizing linker
554 @cindex relaxing addressing modes
556 An option with machine dependent effects.
558 Currently this option is only supported on the H8/300 and the Intel 960.
561 @xref{H8/300,,@code{ld} and the H8/300}.
564 @xref{i960,, @code{ld} and the Intel 960 family}.
567 On some platforms, the @samp{-relax} option performs global optimizations that
568 become possible when the linker resolves addressing in the program, such
569 as relaxing address modes and synthesizing new instructions in the
573 On platforms where this is not supported, @samp{-relax} is accepted, but
577 @item -retain-symbols-file @var{filename}
578 @cindex retaining specified symbols
579 @cindex stripping all but some symbols
580 @cindex symbols, retaining selectively
581 Retain @emph{only} the symbols listed in the file @var{filename},
582 discarding all others. @var{filename} is simply a flat file, with one
583 symbol name per line. This option is especially useful in environments
587 where a large global symbol table is accumulated gradually, to conserve
590 @samp{-retain-symbols-file} does @emph{not} discard undefined symbols,
591 or symbols needed for relocations.
593 You may only specify @samp{-retain-symbols-file} once in the command
594 line. It overrides @samp{-s} and @samp{-S}.
597 @item -rpath @var{dir}
598 @cindex runtime library search path
600 Add a directory to the runtime library search path. This is used when
601 linking an ELF executable with shared objects. All @code{-rpath}
602 arguments are concatenated and passed to the runtime linker, which uses
603 them to locate shared objects at runtime.
605 The @code{-rpath} option may also be used on SunOS. By default, on
606 SunOS, the linker will form a runtime search patch out of all the
607 @code{-L} options it is given. If a @code{rpath} option is used, the
608 runtime search path will be formed exclusively using the @code{-rpath}
609 options, ignoring the @code{-L} options. This can be useful when using
610 gcc, which adds many @code{-L} options which may be on NFS mounted
615 @cindex relocatable output
618 Generate relocatable output---i.e., generate an output file that can in
619 turn serve as input to @code{ld}. This is often called @dfn{partial
620 linking}. As a side effect, in environments that support standard Unix
621 magic numbers, this option also sets the output file's magic number to
624 If this option is not specified, an absolute file is produced. When
625 linking C++ programs, this option @emph{will not} resolve references to
626 constructors; to do that, use @samp{-Ur}.
628 This option does the same thing as @samp{-i}.
631 @cindex strip debugger symbols
633 Omit debugger symbol information (but not all symbols) from the output file.
636 @cindex strip all symbols
638 Omit all symbol information from the output file.
641 @item -soname @var{name}
642 @cindex runtime library name
644 When creating an ELF shared object, set the internal DT_SONAME field to
645 the specified name. When an executable is linked with a shared object
646 which has a DT_SONAME field, then when the executable is run the dynamic
647 linker will attempt to load the shared object specified by the DT_SONAME
648 field rather than the using the file name given to the linker.
652 @cindex shared libraries
654 Create a shared library. This is currently only supported on ELF
659 Normally, when @code{ld} places the global common symbols in the
660 appropriate output sections, it sorts them by size. First come all the
661 one byte symbols, then all the two bytes, then all the four bytes, and
662 then everything else. This is to prevent gaps between symbols due to
663 alignment constraints. This option disables that sorting.
665 @item -split-by-reloc @var{count}
667 Trys to creates extra sections in the output file so that no single output section
668 in the file contains more than @var{count} relocations. This
669 is useful when generating huge relocatable for downloading into
670 certain real time kernels with the COFF object file format; since
671 COFF cannot represent more than 65535 relocations in a single section.
672 Note that this will fail to work with object file formats which do not
673 support arbitrary sections. The linker will not split up individual input
674 sections for redistribution, so if a single input section contains
675 more than @var{count} relocations one output section will contain that
680 Similar to -split-by-reloc but creates a new output section for each
684 Compute and display statistics about the operation of the linker,
685 such as execution time and memory usage.
687 @item -Tbss @var{org}
688 @kindex -Tbss @var{org}
689 @itemx -Tdata @var{org}
690 @kindex -Tdata @var{org}
691 @itemx -Ttext @var{org}
692 @kindex -Ttext @var{org}
693 @cindex segment origins, cmd line
694 Use @var{org} as the starting address for---respectively---the
695 @code{bss}, @code{data}, or the @code{text} segment of the output file.
696 @var{org} must be a single hexadecimal integer;
697 for compatibility with other linkers, you may omit the leading
698 @samp{0x} usually associated with hexadecimal values.
700 @item -T @var{commandfile}
701 @itemx -T@var{commandfile}
702 @kindex -T @var{script}
704 Read link commands from the file @var{commandfile}. These commands
705 replace @code{ld}'s default link script (rather than adding
706 to it), so @var{commandfile} must specify everything necessary to describe
707 the target format. @xref{Commands}. If @var{commandfile} does not
708 exist, @code{ld} looks for it in the directories specified by any
709 preceding @samp{-L} options. Multiple @samp{-T} options accumulate.
713 @cindex input files, displaying
715 Print the names of the input files as @code{ld} processes them.
717 @kindex -traditional-format
718 @cindex traditional format
719 @item -traditional-format
720 For some targets, the output of @code{ld} is different in some ways from
721 the output of some existing linker. This switch requests @code{ld} to
722 use the traditional format instead.
725 For example, on SunOS, @code{ld} combines duplicate entries in the
726 symbol string table. This can reduce the size of an output file with
727 full debugging information by over 30 percent. Unfortunately, the SunOS
728 @code{dbx} program can not read the resulting program (@code{gdb} has no
729 trouble). The @samp{-traditional-format} switch tells @code{ld} to not
730 combine duplicate entries.
732 @item -u @var{symbol}
733 @kindex -u @var{symbol}
734 @cindex undefined symbol
735 Force @var{symbol} to be entered in the output file as an undefined symbol.
736 Doing this may, for example, trigger linking of additional modules from
737 standard libraries. @samp{-u} may be repeated with different option
738 arguments to enter additional undefined symbols.
739 @c Nice idea, but no such command: This option is equivalent
740 @c to the @code{EXTERN} linker command.
745 For anything other than C++ programs, this option is equivalent to
746 @samp{-r}: it generates relocatable output---i.e., an output file that can in
747 turn serve as input to @code{ld}. When linking C++ programs, @samp{-Ur}
748 @emph{does} resolve references to constructors, unlike @samp{-r}.
749 It does not work to use @samp{-Ur} on files that were themselves linked
750 with @samp{-Ur}; once the constructor table has been built, it cannot
751 be added to. Use @samp{-Ur} only for the last partial link, and
752 @samp{-r} for the others.
757 Display the version number for @code{ld} and list the linker emulations
758 supported. Display which input files can and cannot be opened.
765 Display the version number for @code{ld}. The @code{-V} option also
766 lists the supported emulations.
770 Display the version number for @code{ld} and exit.
774 @cindex warnings, on combining symbols
775 @cindex combining symbols, warnings on
776 Warn when a common symbol is combined with another common symbol or with
777 a symbol definition. Unix linkers allow this somewhat sloppy practice,
778 but linkers on some other operating systems do not. This option allows
779 you to find potential problems from combining global symbols.
780 Unfortunately, some C libraries use this practice, so you may get some
781 warnings about symbols in the libraries as well as in your programs.
783 There are three kinds of global symbols, illustrated here by C examples:
787 A definition, which goes in the initialized data section of the output
791 An undefined reference, which does not allocate space.
792 There must be either a definition or a common symbol for the
796 A common symbol. If there are only (one or more) common symbols for a
797 variable, it goes in the uninitialized data area of the output file.
798 The linker merges multiple common symbols for the same variable into a
799 single symbol. If they are of different sizes, it picks the largest
800 size. The linker turns a common symbol into a declaration, if there is
801 a definition of the same variable.
804 The @samp{-warn-common} option can produce five kinds of warnings. Each
805 warning consists of a pair of lines: the first describes the symbol just
806 encountered, and the second describes the previous symbol encountered
807 with the same name. One or both of the two symbols will be a common
812 Turning a common symbol into a reference, because there is already a
813 definition for the symbol.
815 @var{file}(@var{section}): warning: common of `@var{symbol}'
816 overridden by definition
817 @var{file}(@var{section}): warning: defined here
821 Turning a common symbol into a reference, because a later definition for
822 the symbol is encountered. This is the same as the previous case,
823 except that the symbols are encountered in a different order.
825 @var{file}(@var{section}): warning: definition of `@var{symbol}'
827 @var{file}(@var{section}): warning: common is here
831 Merging a common symbol with a previous same-sized common symbol.
833 @var{file}(@var{section}): warning: multiple common
835 @var{file}(@var{section}): warning: previous common is here
839 Merging a common symbol with a previous larger common symbol.
841 @var{file}(@var{section}): warning: common of `@var{symbol}'
842 overridden by larger common
843 @var{file}(@var{section}): warning: larger common is here
847 Merging a common symbol with a previous smaller common symbol. This is
848 the same as the previous case, except that the symbols are
849 encountered in a different order.
851 @var{file}(@var{section}): warning: common of `@var{symbol}'
852 overriding smaller common
853 @var{file}(@var{section}): warning: smaller common is here
857 @kindex -warn-constructors
858 @item -warn-constructors
859 Warn if any global constructors are used. This is only useful for a few
860 object file formats. For formats like COFF or ELF, the linker can not
861 detect the use of global constructors.
864 @cindex warnings, on undefined symbols
865 @cindex undefined symbols, warnings on
867 Only warn once for each undefined symbol, rather than once per module
870 @kindex --whole-archive
871 @cindex including an entire archive
872 For each archive mentioned on the command line, include every object
873 file in the archive in the link, rather than searching the archive for
874 the required object files. This is normally used to turn an archive
875 file into a shared library, forcing every object to be included in the
876 resulting shared library.
879 @cindex local symbols, deleting
880 @cindex L, deleting symbols beginning
882 Delete all temporary local symbols. For most targets, this is all local
883 symbols whose names begin with @samp{L}.
886 @cindex deleting local symbols
888 Delete all local symbols.
890 @item -y @var{symbol}
891 @kindex -y @var{symbol}
892 @cindex symbol tracing
893 Print the name of each linked file in which @var{symbol} appears. This
894 option may be given any number of times. On many systems it is necessary
895 to prepend an underscore.
897 This option is useful when you have an undefined symbol in your link but
898 don't know where the reference is coming from.
900 @item -( @var{archives} -)
901 @itemx --start-group @var{archives} --end-group
903 @cindex groups of archives
904 The @var{archives} should be a list of archive files. They may be
905 either explicit file names, or @samp{-l} options.
907 The specified archives are searched repeatedly until no new undefined
908 references are created. Normally, an archive is searched only once in
909 the order that it is specified on the command line. If a symbol in that
910 archive is needed to resolve an undefined symbol referred to by an
911 object in an archive that appears later on the command line, the linker
912 would not be able to resolve that reference. By grouping the archives,
913 they all be searched repeatedly until all possible references are
916 Using this option has a significant performance cost. It is best to use
917 it only when there are unavoidable circular references between two or
923 @section Environment Variables
925 You can change the behavior of @code{ld} with the environment
926 variable @code{GNUTARGET}.
929 @cindex default input format
930 @code{GNUTARGET} determines the input-file object format if you don't
931 use @samp{-b} (or its synonym @samp{-format}). Its value should be one
932 of the BFD names for an input format (@pxref{BFD}). If there is no
933 @code{GNUTARGET} in the environment, @code{ld} uses the natural format
934 of the target. If @code{GNUTARGET} is set to @code{default} then BFD attempts to discover the
935 input format by examining binary input files; this method often
936 succeeds, but there are potential ambiguities, since there is no method
937 of ensuring that the magic number used to specify object-file formats is
938 unique. However, the configuration procedure for BFD on each system
939 places the conventional format for that system first in the search-list,
940 so ambiguities are resolved in favor of convention.
944 @chapter Command Language
946 @cindex command files
947 The command language provides explicit control over the link process,
948 allowing complete specification of the mapping between the linker's
949 input files and its output. It controls:
958 addresses of sections
960 placement of common blocks
963 You may supply a command file (also known as a link script) to the
964 linker either explicitly through the @samp{-T} option, or implicitly as
965 an ordinary file. If the linker opens a file which it cannot recognize
966 as a supported object or archive format, it reports an error.
969 * Scripts:: Linker Scripts
970 * Expressions:: Expressions
971 * MEMORY:: MEMORY Command
972 * SECTIONS:: SECTIONS Command
973 * Entry Point:: The Entry Point
974 * Option Commands:: Option Commands
978 @section Linker Scripts
979 The @code{ld} command language is a collection of statements; some are
980 simple keywords setting a particular option, some are used to select and
981 group input files or name output files; and two statement
982 types have a fundamental and pervasive impact on the linking process.
984 @cindex fundamental script commands
985 @cindex commands, fundamental
986 @cindex output file layout
987 @cindex layout of output file
988 The most fundamental command of the @code{ld} command language is the
989 @code{SECTIONS} command (@pxref{SECTIONS}). Every meaningful command
990 script must have a @code{SECTIONS} command: it specifies a
991 ``picture'' of the output file's layout, in varying degrees of detail.
992 No other command is required in all cases.
994 The @code{MEMORY} command complements @code{SECTIONS} by describing the
995 available memory in the target architecture. This command is optional;
996 if you don't use a @code{MEMORY} command, @code{ld} assumes sufficient
997 memory is available in a contiguous block for all output.
1001 You may include comments in linker scripts just as in C: delimited
1002 by @samp{/*} and @samp{*/}. As in C, comments are syntactically
1003 equivalent to whitespace.
1006 @section Expressions
1007 @cindex expression syntax
1009 Many useful commands involve arithmetic expressions. The syntax for
1010 expressions in the command language is identical to that of C
1011 expressions, with the following features:
1014 All expressions evaluated as integers and
1015 are of ``long'' or ``unsigned long'' type.
1017 All constants are integers.
1019 All of the C arithmetic operators are provided.
1021 You may reference, define, and create global variables.
1023 You may call special purpose built-in functions.
1027 * Integers:: Integers
1028 * Symbols:: Symbol Names
1029 * Location Counter:: The Location Counter
1030 * Operators:: Operators
1031 * Evaluation:: Evaluation
1032 * Assignment:: Assignment: Defining Symbols
1033 * Arithmetic Functions:: Built-In Functions
1037 @subsection Integers
1038 @cindex integer notation
1039 @cindex octal integers
1040 An octal integer is @samp{0} followed by zero or more of the octal
1041 digits (@samp{01234567}).
1043 _as_octal = 0157255;
1046 @cindex decimal integers
1047 A decimal integer starts with a non-zero digit followed by zero or
1048 more digits (@samp{0123456789}).
1050 _as_decimal = 57005;
1053 @cindex hexadecimal integers
1055 A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
1056 more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
1061 @cindex negative integers
1062 To write a negative integer, use
1063 the prefix operator @samp{-}; @pxref{Operators}.
1068 @cindex scaled integers
1069 @cindex K and M integer suffixes
1070 @cindex M and K integer suffixes
1071 @cindex suffixes for integers
1072 @cindex integer suffixes
1073 Additionally the suffixes @code{K} and @code{M} may be used to scale a
1077 @c END TEXI2ROFF-KILL
1078 @code{1024} or @code{1024*1024}
1082 ${\rm 1024}$ or ${\rm 1024}^2$
1084 @c END TEXI2ROFF-KILL
1085 respectively. For example, the following all refer to the same quantity:
1094 @subsection Symbol Names
1095 @cindex symbol names
1097 @cindex quoted symbol names
1099 Unless quoted, symbol names start with a letter, underscore, or point
1100 and may include any letters, underscores, digits, points,
1101 and hyphens. Unquoted symbol names must not conflict with any
1102 keywords. You can specify a symbol which contains odd characters or has
1103 the same name as a keyword, by surrounding the symbol name in double quotes:
1106 "with a space" = "also with a space" + 10;
1109 Since symbols can contain many non-alphabetic characters, it is safest
1110 to delimit symbols with spaces. For example, @samp{A-B} is one symbol,
1111 whereas @samp{A - B} is an expression involving subtraction.
1113 @node Location Counter
1114 @subsection The Location Counter
1117 @cindex location counter
1118 @cindex current output location
1119 The special linker variable @dfn{dot} @samp{.} always contains the
1120 current output location counter. Since the @code{.} always refers to
1121 a location in an output section, it must always appear in an
1122 expression within a @code{SECTIONS} command. The @code{.} symbol
1123 may appear anywhere that an ordinary symbol is allowed in an
1124 expression, but its assignments have a side effect. Assigning a value
1125 to the @code{.} symbol will cause the location counter to be moved.
1127 This may be used to create holes in the output section. The location
1128 counter may never be moved backwards.
1143 In the previous example, @code{file1} is located at the beginning of the
1144 output section, then there is a 1000 byte gap. Then @code{file2}
1145 appears, also with a 1000 byte gap following before @code{file3} is
1146 loaded. The notation @samp{= 0x1234} specifies what data to write in
1147 the gaps (@pxref{Section Options}).
1155 @subsection Operators
1156 @cindex Operators for arithmetic
1157 @cindex arithmetic operators
1158 @cindex precedence in expressions
1159 The linker recognizes the standard C set of arithmetic operators, with
1160 the standard bindings and precedence levels:
1163 @c END TEXI2ROFF-KILL
1165 precedence associativity Operators Notes
1171 5 left == != > < <= >=
1177 11 right &= += -= *= /= (2)
1181 (1) Prefix operators
1182 (2) @xref{Assignment}
1186 \vskip \baselineskip
1187 %"lispnarrowing" is the extra indent used generally for @example
1188 \hskip\lispnarrowing\vbox{\offinterlineskip
1191 {\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr
1192 height2pt&\omit&&\omit&&\omit&\cr
1193 &Precedence&& Associativity &&{\rm Operators}&\cr
1194 height2pt&\omit&&\omit&&\omit&\cr
1196 height2pt&\omit&&\omit&&\omit&\cr
1198 % '176 is tilde, '~' in tt font
1199 &1&&left&&\qquad- \char'176\ !\qquad\dag&\cr
1200 &2&&left&&* / \%&\cr
1203 &5&&left&&== != > < <= >=&\cr
1206 &8&&left&&{\&\&}&\cr
1209 &11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr
1211 height2pt&\omit&&\omit&&\omit&\cr}
1216 @obeylines@parskip=0pt@parindent=0pt
1217 @dag@quad Prefix operators.
1218 @ddag@quad @xref{Assignment}.
1221 @c END TEXI2ROFF-KILL
1224 @subsection Evaluation
1226 @cindex lazy evaluation
1227 @cindex expression evaluation order
1228 The linker uses ``lazy evaluation'' for expressions; it only calculates
1229 an expression when absolutely necessary. The linker needs the value of
1230 the start address, and the lengths of memory regions, in order to do any
1231 linking at all; these values are computed as soon as possible when the
1232 linker reads in the command file. However, other values (such as symbol
1233 values) are not known or needed until after storage allocation. Such
1234 values are evaluated later, when other information (such as the sizes of
1235 output sections) is available for use in the symbol assignment
1239 @subsection Assignment: Defining Symbols
1240 @cindex assignment in scripts
1241 @cindex symbol definition, scripts
1242 @cindex variables, defining
1243 You may create global symbols, and assign values (addresses) to global
1244 symbols, using any of the C assignment operators:
1247 @item @var{symbol} = @var{expression} ;
1248 @itemx @var{symbol} &= @var{expression} ;
1249 @itemx @var{symbol} += @var{expression} ;
1250 @itemx @var{symbol} -= @var{expression} ;
1251 @itemx @var{symbol} *= @var{expression} ;
1252 @itemx @var{symbol} /= @var{expression} ;
1255 Two things distinguish assignment from other operators in @code{ld}
1259 Assignment may only be used at the root of an expression;
1260 @samp{a=b+3;} is allowed, but @samp{a+b=3;} is an error.
1265 You must place a trailing semicolon (``@key{;}'') at the end of an
1266 assignment statement.
1269 Assignment statements may appear:
1272 as commands in their own right in an @code{ld} script; or
1274 as independent statements within a @code{SECTIONS} command; or
1276 as part of the contents of a section definition in a
1277 @code{SECTIONS} command.
1280 The first two cases are equivalent in effect---both define a symbol with
1281 an absolute address. The last case defines a symbol whose address is
1282 relative to a particular section (@pxref{SECTIONS}).
1284 @cindex absolute and relocatable symbols
1285 @cindex relocatable and absolute symbols
1286 @cindex symbols, relocatable and absolute
1287 When a linker expression is evaluated and assigned to a variable, it is
1288 given either an absolute or a relocatable type. An absolute expression
1289 type is one in which the symbol contains the value that it will have in
1290 the output file; a relocatable expression type is one in which the
1291 value is expressed as a fixed offset from the base of a section.
1293 The type of the expression is controlled by its position in the script
1294 file. A symbol assigned within a section definition is created relative
1295 to the base of the section; a symbol assigned in any other place is
1296 created as an absolute symbol. Since a symbol created within a
1297 section definition is relative to the base of the section, it
1298 will remain relocatable if relocatable output is requested. A symbol
1299 may be created with an absolute value even when assigned to within a
1300 section definition by using the absolute assignment function
1301 @code{ABSOLUTE}. For example, to create an absolute symbol whose address
1302 is the last byte of an output section named @code{.data}:
1308 _edata = ABSOLUTE(.) ;
1313 The linker tries to put off the evaluation of an assignment until all
1314 the terms in the source expression are known (@pxref{Evaluation}). For
1315 instance, the sizes of sections cannot be known until after allocation,
1316 so assignments dependent upon these are not performed until after
1317 allocation. Some expressions, such as those depending upon the location
1318 counter @dfn{dot}, @samp{.} must be evaluated during allocation. If the
1319 result of an expression is required, but the value is not available,
1320 then an error results. For example, a script like the following
1323 text 9+this_isnt_constant :
1328 @kindex Non constant expression
1330 will cause the error message ``@code{Non constant expression for initial
1334 In some cases, it is desirable for a linker script to define a symbol
1335 only if it is referenced, and only if it is not defined by any object
1336 included in the link. For example, traditional linkers defined the
1337 symbol @samp{etext}. However, ANSI C requires that the user be able to
1338 use @samp{etext} as a function name without encountering an error.
1339 The @code{PROVIDE} keyword may be used to define a symbol, such as
1340 @samp{etext}, only if it is referenced but not defined. The syntax is
1341 @code{PROVIDE(@var{symbol} = @var{expression})}.
1343 @node Arithmetic Functions
1344 @subsection Arithmetic Functions
1345 @cindex functions in expression language
1346 The command language includes a number of built-in
1347 functions for use in link script expressions.
1349 @item ABSOLUTE(@var{exp})
1350 @kindex ABSOLUTE(@var{exp})
1351 @cindex expression, absolute
1352 Return the absolute (non-relocatable, as opposed to non-negative) value
1353 of the expression @var{exp}. Primarily useful to assign an absolute
1354 value to a symbol within a section definition, where symbol values are
1355 normally section-relative.
1357 @item ADDR(@var{section})
1358 @kindex ADDR(@var{section})
1359 @cindex section address
1360 Return the absolute address of the named @var{section}. Your script must
1361 previously have defined the location of that section. In the following
1362 example, @code{symbol_1} and @code{symbol_2} are assigned identical
1368 start_of_output_1 = ABSOLUTE(.);
1373 symbol_1 = ADDR(.output1);
1374 symbol_2 = start_of_output_1;
1379 @item ALIGN(@var{exp})
1380 @kindex ALIGN(@var{exp})
1381 @cindex rounding up location counter
1382 Return the result of the current location counter (@code{.}) aligned to
1383 the next @var{exp} boundary. @var{exp} must be an expression whose
1384 value is a power of two. This is equivalent to
1386 (. + @var{exp} - 1) & ~(@var{exp} - 1)
1389 @code{ALIGN} doesn't change the value of the location counter---it just
1390 does arithmetic on it. As an example, to align the output @code{.data}
1391 section to the next @code{0x2000} byte boundary after the preceding
1392 section and to set a variable within the section to the next
1393 @code{0x8000} boundary after the input sections:
1396 .data ALIGN(0x2000): @{
1398 variable = ALIGN(0x8000);
1403 The first use of @code{ALIGN} in this example specifies the location of
1404 a section because it is used as the optional @var{start} attribute of a
1405 section definition (@pxref{Section Options}). The second use simply
1406 defines the value of a variable.
1408 The built-in @code{NEXT} is closely related to @code{ALIGN}.
1410 @item DEFINED(@var{symbol})
1411 @kindex DEFINED(@var{symbol})
1412 @cindex symbol defaults
1413 Return 1 if @var{symbol} is in the linker global symbol table and is
1414 defined, otherwise return 0. You can use this function to provide default
1415 values for symbols. For example, the following command-file fragment shows how
1416 to set a global symbol @code{begin} to the first location in the
1417 @code{.text} section---but if a symbol called @code{begin} already
1418 existed, its value is preserved:
1423 begin = DEFINED(begin) ? begin : . ;
1429 @item NEXT(@var{exp})
1430 @kindex NEXT(@var{exp})
1431 @cindex unallocated address, next
1432 Return the next unallocated address that is a multiple of @var{exp}.
1433 This function is closely related to @code{ALIGN(@var{exp})}; unless you
1434 use the @code{MEMORY} command to define discontinuous memory for the
1435 output file, the two functions are equivalent.
1437 @item SIZEOF(@var{section})
1438 @kindex SIZEOF(@var{section})
1439 @cindex section size
1440 Return the size in bytes of the named @var{section}, if that section has
1441 been allocated. In the following example, @code{symbol_1} and
1442 @code{symbol_2} are assigned identical values:
1443 @c What does it return if the section hasn't been allocated? 0?
1451 symbol_1 = .end - .start ;
1452 symbol_2 = SIZEOF(.output);
1457 @item SIZEOF_HEADERS
1458 @kindex SIZEOF_HEADERS
1460 @itemx sizeof_headers
1461 @kindex sizeof_headers
1462 Return the size in bytes of the output file's headers. You can use this number
1463 as the start address of the first section, if you choose, to facilitate
1469 @section Memory Layout
1471 @cindex regions of memory
1472 @cindex discontinuous memory
1473 @cindex allocating memory
1474 The linker's default configuration permits allocation of all available memory.
1475 You can override this configuration by using the @code{MEMORY} command. The
1476 @code{MEMORY} command describes the location and size of blocks of
1477 memory in the target. By using it carefully, you can describe which
1478 memory regions may be used by the linker, and which memory regions it
1479 must avoid. The linker does not shuffle sections to fit into the
1480 available regions, but does move the requested sections into the correct
1481 regions and issue errors when the regions become too full.
1483 A command file may contain at most one use of the @code{MEMORY}
1484 command; however, you can define as many blocks of memory within it as
1485 you wish. The syntax is:
1490 @var{name} (@var{attr}) : ORIGIN = @var{origin}, LENGTH = @var{len}
1495 @cindex naming memory regions
1497 is a name used internally by the linker to refer to the region. Any
1498 symbol name may be used. The region names are stored in a separate
1499 name space, and will not conflict with symbols, file names or section
1500 names. Use distinct names to specify multiple regions.
1502 @cindex memory region attributes
1504 is an optional list of attributes, permitted for compatibility with the
1505 AT&T linker but not used by @code{ld} beyond checking that the
1506 attribute list is valid. Valid attribute lists must be made up of the
1507 characters ``@code{LIRWX}''. If you omit the attribute list, you may
1508 omit the parentheses around it as well.
1514 is the start address of the region in physical memory. It is
1515 an expression that must evaluate to a constant before
1516 memory allocation is performed. The keyword @code{ORIGIN} may be
1517 abbreviated to @code{org} or @code{o} (but not, for example, @samp{ORG}).
1523 is the size in bytes of the region (an expression).
1524 The keyword @code{LENGTH} may be abbreviated to @code{len} or @code{l}.
1527 For example, to specify that memory has two regions available for
1528 allocation---one starting at 0 for 256 kilobytes, and the other
1529 starting at @code{0x40000000} for four megabytes:
1534 rom : ORIGIN = 0, LENGTH = 256K
1535 ram : org = 0x40000000, l = 4M
1539 Once you have defined a region of memory named @var{mem}, you can direct
1540 specific output sections there by using a command ending in
1541 @samp{>@var{mem}} within the @code{SECTIONS} command (@pxref{Section
1542 Options}). If the combined output sections directed to a region are too
1543 big for the region, the linker will issue an error message.
1546 @section Specifying Output Sections
1549 The @code{SECTIONS} command controls exactly where input sections are
1550 placed into output sections, their order in the output file, and to
1551 which output sections they are allocated.
1553 You may use at most one @code{SECTIONS} command in a script file,
1554 but you can have as many statements within it as you wish. Statements
1555 within the @code{SECTIONS} command can do one of three things:
1559 define the entry point;
1562 assign a value to a symbol;
1565 describe the placement of a named output section, and which input
1566 sections go into it.
1569 You can also use the first two operations---defining the entry point and
1570 defining symbols---outside the @code{SECTIONS} command: @pxref{Entry
1571 Point}, and @pxref{Assignment}. They are permitted here as well for
1572 your convenience in reading the script, so that symbols and the entry
1573 point can be defined at meaningful points in your output-file layout.
1575 If you do not use a @code{SECTIONS} command, the linker places each input
1576 section into an identically named output section in the order that the
1577 sections are first encountered in the input files. If all input sections
1578 are present in the first file, for example, the order of sections in the
1579 output file will match the order in the first input file.
1582 * Section Definition:: Section Definitions
1583 * Section Placement:: Section Placement
1584 * Section Data Expressions:: Section Data Expressions
1585 * Section Options:: Optional Section Attributes
1588 @node Section Definition
1589 @subsection Section Definitions
1590 @cindex section definition
1591 The most frequently used statement in the @code{SECTIONS} command is
1592 the @dfn{section definition}, which specifies the
1593 properties of an output section: its location, alignment, contents,
1594 fill pattern, and target memory region. Most of
1595 these specifications are optional; the simplest form of a section
1604 @cindex naming output sections
1606 @var{secname} is the name of the output section, and @var{contents} a
1607 specification of what goes there---for example, a list of input files or
1608 sections of input files (@pxref{Section Placement}). As you might
1609 assume, the whitespace shown is optional. You do need the colon
1610 @samp{:} and the braces @samp{@{@}}, however.
1612 @var{secname} must meet the constraints of your output format. In
1613 formats which only support a limited number of sections, such as
1614 @code{a.out}, the name must be one of the names supported by the format
1615 (@code{a.out}, for example, allows only @code{.text}, @code{.data} or
1616 @code{.bss}). If the output format supports any number of sections, but
1617 with numbers and not names (as is the case for Oasys), the name should be
1618 supplied as a quoted numeric string. A section name may consist of any
1619 sequence of characters, but any name which does not conform to the standard
1620 @code{ld} symbol name syntax must be quoted.
1621 @xref{Symbols, , Symbol Names}.
1623 The linker will not create output sections which do not have any
1624 contents. This is for convenience when referring to input sections that
1625 may or may not exist. For example,
1629 will only create a @samp{.foo} section in the output file if there is a
1630 @samp{.foo} section in at least one input file.
1632 @node Section Placement
1633 @subsection Section Placement
1635 @cindex contents of a section
1636 In a section definition, you can specify the contents of an output
1637 section by listing particular input files, by listing particular
1638 input-file sections, or by a combination of the two. You can also place
1639 arbitrary data in the section, and define symbols relative to the
1640 beginning of the section.
1642 The @var{contents} of a section definition may include any of the
1643 following kinds of statement. You can include as many of these as you
1644 like in a single section definition, separated from one another by
1648 @kindex @var{filename}
1649 @cindex input files, section defn
1650 @cindex files, including in output sections
1651 @item @var{filename}
1652 You may simply name a particular input file to be placed in the current
1653 output section; @emph{all} sections from that file are placed in the
1654 current section definition. If the file name has already been mentioned
1655 in another section definition, with an explicit section name list, then
1656 only those sections which have not yet been allocated are used.
1658 To specify a list of particular files by name:
1660 .data : @{ afile.o bfile.o cfile.o @}
1663 The example also illustrates that multiple statements can be included in
1664 the contents of a section definition, since each file name is a separate
1667 @kindex @var{filename}(@var{section})
1668 @cindex files and sections, section defn
1669 @item @var{filename}( @var{section} )
1670 @itemx @var{filename}( @var{section}, @var{section}, @dots{} )
1671 @itemx @var{filename}( @var{section} @var{section} @dots{} )
1672 You can name one or more sections from your input files, for
1673 insertion in the current output section. If you wish to specify a list
1674 of input-file sections inside the parentheses, you may separate the
1675 section names by either commas or whitespace.
1677 @cindex input sections to output section
1678 @kindex *(@var{section})
1679 @item * (@var{section})
1680 @itemx * (@var{section}, @var{section}, @dots{})
1681 @itemx * (@var{section} @var{section} @dots{})
1682 Instead of explicitly naming particular input files in a link control
1683 script, you can refer to @emph{all} files from the @code{ld} command
1684 line: use @samp{*} instead of a particular file name before the
1685 parenthesized input-file section list.
1687 If you have already explicitly included some files by name, @samp{*}
1688 refers to all @emph{remaining} files---those whose places in the output
1689 file have not yet been defined.
1691 For example, to copy sections @code{1} through @code{4} from an Oasys file
1692 into the @code{.text} section of an @code{a.out} file, and sections @code{13}
1693 and @code{14} into the @code{.data} section:
1706 @cindex @code{[@var{section}@dots{}]}, not supported
1707 @samp{[ @var{section} @dots{} ]} used to be accepted as an alternate way
1708 to specify named sections from all unallocated input files. Because
1709 some operating systems (VMS) allow brackets in file names, that notation
1710 is no longer supported.
1712 @cindex uninitialized data
1713 @cindex commons in output
1715 @item @var{filename}@code{( COMMON )}
1717 Specify where in your output file to place uninitialized data
1718 with this notation. @code{*(COMMON)} by itself refers to all
1719 uninitialized data from all input files (so far as it is not yet
1720 allocated); @var{filename}@code{(COMMON)} refers to uninitialized data
1721 from a particular file. Both are special cases of the general
1722 mechanisms for specifying where to place input-file sections:
1723 @code{ld} permits you to refer to uninitialized data as if it
1724 were in an input-file section named @code{COMMON}, regardless of the
1725 input file's format.
1728 For example, the following command script arranges the output file into
1729 three consecutive sections, named @code{.text}, @code{.data}, and
1730 @code{.bss}, taking the input for each from the correspondingly named
1731 sections of all the input files:
1735 .text : @{ *(.text) @}
1736 .data : @{ *(.data) @}
1737 .bss : @{ *(.bss) *(COMMON) @}
1741 The following example reads all of the sections from file @code{all.o}
1742 and places them at the start of output section @code{outputa} which
1743 starts at location @code{0x10000}. All of section @code{.input1} from
1744 file @code{foo.o} follows immediately, in the same output section. All
1745 of section @code{.input2} from @code{foo.o} goes into output section
1746 @code{outputb}, followed by section @code{.input1} from @code{foo1.o}.
1747 All of the remaining @code{.input1} and @code{.input2} sections from any
1748 files are written to output section @code{outputc}.
1770 @node Section Data Expressions
1771 @subsection Section Data Expressions
1773 @cindex expressions in a section
1774 The foregoing statements arrange, in your output file, data originating
1775 from your input files. You can also place data directly in an output
1776 section from the link command script. Most of these additional
1777 statements involve expressions; @pxref{Expressions}. Although these
1778 statements are shown separately here for ease of presentation, no such
1779 segregation is needed within a section definition in the @code{SECTIONS}
1780 command; you can intermix them freely with any of the statements we've
1784 @cindex input filename symbols
1785 @cindex filename symbols
1786 @kindex CREATE_OBJECT_SYMBOLS
1787 @item CREATE_OBJECT_SYMBOLS
1788 Create a symbol for each input file
1789 in the current section, set to the address of the first byte of
1790 data written from that input file. For instance, with @code{a.out}
1791 files it is conventional to have a symbol for each input file. You can
1792 accomplish this by defining the output @code{.text} section as follows:
1797 CREATE_OBJECT_SYMBOLS
1799 _etext = ALIGN(0x2000);
1805 If @code{sample.ld} is a file containing this script, and @code{a.o},
1806 @code{b.o}, @code{c.o}, and @code{d.o} are four input files with
1807 contents like the following---
1817 @samp{ld -M -T sample.ld a.o b.o c.o d.o} would create a map like this,
1818 containing symbols matching the object file names:
1820 00000000 A __DYNAMIC
1823 00002020 T _afunction
1826 00002038 T _bfunction
1829 00002050 T _cfunction
1832 00002068 T _dfunction
1842 @kindex @var{symbol} = @var{expression} ;
1843 @kindex @var{symbol} @var{f}= @var{expression} ;
1844 @item @var{symbol} = @var{expression} ;
1845 @itemx @var{symbol} @var{f}= @var{expression} ;
1846 @var{symbol} is any symbol name (@pxref{Symbols}). ``@var{f}=''
1847 refers to any of the operators @code{&= += -= *= /=} which combine
1848 arithmetic and assignment.
1850 @cindex assignment, in section defn
1851 When you assign a value to a symbol within a particular section
1852 definition, the value is relative to the beginning of the section
1853 (@pxref{Assignment}). If you write
1859 .data : @{ @dots{} rel = 14 ; @dots{} @}
1860 abs2 = 14 + ADDR(.data);
1865 @c FIXME: Try above example!
1867 @code{abs} and @code{rel} do not have the same value; @code{rel} has the
1868 same value as @code{abs2}.
1870 @kindex BYTE(@var{expression})
1871 @kindex SHORT(@var{expression})
1872 @kindex LONG(@var{expression})
1873 @kindex QUAD(@var{expression})
1874 @cindex direct output
1875 @item BYTE(@var{expression})
1876 @itemx SHORT(@var{expression})
1877 @itemx LONG(@var{expression})
1878 @itemx QUAD(@var{expression})
1879 By including one of these four statements in a section definition, you
1880 can explicitly place one, two, four, or eight bytes (respectively) at
1881 the current address of that section. @code{QUAD} is only supported when
1882 using a 64 bit host or target.
1884 @ifclear SingleFormat
1885 Multiple-byte quantities are represented in whatever byte order is
1886 appropriate for the output file format (@pxref{BFD}).
1889 @item FILL(@var{expression})
1890 @kindex FILL(@var{expression})
1891 @cindex holes, filling
1892 @cindex unspecified memory
1893 Specify the ``fill pattern'' for the current section. Any otherwise
1894 unspecified regions of memory within the section (for example, regions
1895 you skip over by assigning a new value to the location counter @samp{.})
1896 are filled with the two least significant bytes from the
1897 @var{expression} argument. A @code{FILL} statement covers memory
1898 locations @emph{after} the point it occurs in the section definition; by
1899 including more than one @code{FILL} statement, you can have different
1900 fill patterns in different parts of an output section.
1903 @node Section Options
1904 @subsection Optional Section Attributes
1905 @cindex section defn, full syntax
1906 Here is the full syntax of a section definition, including all the
1912 @var{secname} @var{start} BLOCK(@var{align}) (NOLOAD) : AT ( @var{ldadr} )
1913 @{ @var{contents} @} >@var{region} =@var{fill}
1918 @var{secname} and @var{contents} are required. @xref{Section
1919 Definition}, and @pxref{Section Placement} for details on
1920 @var{contents}. The remaining elements---@var{start},
1921 @code{BLOCK(@var{align)}}, @code{(NOLOAD)}, @code{AT ( @var{ldadr} )},
1922 @code{>@var{region}}, and @code{=@var{fill}}---are all optional.
1925 @cindex start address, section
1926 @cindex section start
1927 @cindex section address
1929 You can force the output section to be loaded at a specified address by
1930 specifying @var{start} immediately following the section name.
1931 @var{start} can be represented as any expression. The following
1932 example generates section @var{output} at location
1938 output 0x40000000: @{
1945 @kindex BLOCK(@var{align})
1946 @cindex section alignment
1947 @cindex aligning sections
1948 @item BLOCK(@var{align})
1949 You can include @code{BLOCK()} specification to advance
1950 the location counter @code{.} prior to the beginning of the section, so
1951 that the section will begin at the specified alignment. @var{align} is
1955 @cindex prevent unnecessary loading
1956 @cindex loading, preventing
1958 Use @samp{(NOLOAD)} to prevent a section from being loaded into memory
1959 each time it is accessed. For example, in the script sample below, the
1960 @code{ROM} segment is addressed at memory location @samp{0} and does not
1961 need to be loaded into each object file:
1965 ROM 0 (NOLOAD) : @{ @dots{} @}
1970 @kindex AT ( @var{ldadr} )
1971 @cindex specify load address
1972 @cindex load address, specifying
1973 @item AT ( @var{ldadr} )
1974 The expression @var{ldadr} that follows the @code{AT} keyword specifies
1975 the load address of the section. The default (if you do not use the
1976 @code{AT} keyword) is to make the load address the same as the
1977 relocation address. This feature is designed to make it easy to build a
1978 ROM image. For example, this @code{SECTIONS} definition creates two
1979 output sections: one called @samp{.text}, which starts at @code{0x1000},
1980 and one called @samp{.mdata}, which is loaded at the end of the
1981 @samp{.text} section even though its relocation address is
1982 @code{0x2000}. The symbol @code{_data} is defined with the value
1988 .text 0x1000 : @{ *(.text) _etext = . ; @}
1990 AT ( ADDR(.text) + SIZEOF ( .text ) )
1991 @{ _data = . ; *(.data); _edata = . ; @}
1993 @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@}
1997 The run-time initialization code (for C programs, usually @code{crt0})
1998 for use with a ROM generated this way has to include something like
1999 the following, to copy the initialized data from the ROM image to its runtime
2006 /* ROM has data at end of text; copy it. */
2007 while (dst < _edata) @{
2012 for (dst = _bstart; dst< _bend; dst++)
2016 @kindex >@var{region}
2017 @cindex section, assigning to memory region
2018 @cindex memory regions and sections
2020 Assign this section to a previously defined region of memory.
2024 @cindex section fill pattern
2025 @cindex fill pattern, entire section
2027 Including @code{=@var{fill}} in a section definition specifies the
2028 initial fill value for that section. You may use any expression to
2029 specify @var{fill}. Any unallocated holes in the current output section
2030 when written to the output file will be filled with the two least
2031 significant bytes of the value, repeated as necessary. You can also
2032 change the fill value with a @code{FILL} statement in the @var{contents}
2033 of a section definition.
2038 @section The Entry Point
2039 @kindex ENTRY(@var{symbol})
2040 @cindex start of execution
2041 @cindex first instruction
2042 The linker command language includes a command specifically for
2043 defining the first executable instruction in an output file (its
2044 @dfn{entry point}). Its argument is a symbol name:
2049 Like symbol assignments, the @code{ENTRY} command may be placed either
2050 as an independent command in the command file, or among the section
2051 definitions within the @code{SECTIONS} command---whatever makes the most
2052 sense for your layout.
2054 @cindex entry point, defaults
2055 @code{ENTRY} is only one of several ways of choosing the entry point.
2056 You may indicate it in any of the following ways (shown in descending
2057 order of priority: methods higher in the list override methods lower down).
2060 the @samp{-e} @var{entry} command-line option;
2062 the @code{ENTRY(@var{symbol})} command in a linker control script;
2064 the value of the symbol @code{start}, if present;
2066 the value of the symbol @code{_main}, if present;
2068 the address of the first byte of the @code{.text} section, if present;
2070 The address @code{0}.
2073 For example, you can use these rules to generate an entry point with an
2074 assignment statement: if no symbol @code{start} is defined within your
2075 input files, you can simply define it, assigning it an appropriate
2083 The example shows an absolute address, but you can use any expression.
2084 For example, if your input object files use some other symbol-name
2085 convention for the entry point, you can just assign the value of
2086 whatever symbol contains the start address to @code{start}:
2089 start = other_symbol ;
2092 @node Option Commands
2093 @section Option Commands
2094 The command language includes a number of other commands that you can
2095 use for specialized purposes. They are similar in purpose to
2096 command-line options.
2099 @kindex CONSTRUCTORS
2100 @cindex C++ constructors, arranging in link
2101 @cindex constructors, arranging in link
2103 This command ties up C++ style constructor and destructor records. The
2104 details of the constructor representation vary from one object format to
2105 another, but usually lists of constructors and destructors appear as
2106 special sections. The @code{CONSTRUCTORS} command specifies where the
2107 linker is to place the data from these sections, relative to the rest of
2108 the linked output. Constructor data is marked by the symbol
2109 @w{@code{__CTOR_LIST__}} at the start, and @w{@code{__CTOR_LIST_END}} at
2110 the end; destructor data is bracketed similarly, between
2111 @w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_LIST_END}}. (The compiler
2112 must arrange to actually run this code; GNU C++ calls constructors from
2113 a subroutine @code{__main}, which it inserts automatically into the
2114 startup code for @code{main}, and destructors from @code{_exit}.)
2121 These keywords were used in some older linkers to request a particular
2122 math subroutine library. @code{ld} doesn't use the keywords, assuming
2123 instead that any necessary subroutines are in libraries specified using
2124 the general mechanisms for linking to archives; but to permit the use of
2125 scripts that were written for the older linkers, the keywords
2126 @code{FLOAT} and @code{NOFLOAT} are accepted and ignored.
2128 @kindex FORCE_COMMON_ALLOCATION
2129 @cindex common allocation
2130 @item FORCE_COMMON_ALLOCATION
2131 This command has the same effect as the @samp{-d} command-line option:
2132 to make @code{ld} assign space to common symbols even if a relocatable
2133 output file is specified (@samp{-r}).
2135 @kindex INPUT ( @var{files} )
2136 @cindex binary input files
2137 @item INPUT ( @var{file}, @var{file}, @dots{} )
2138 @itemx INPUT ( @var{file} @var{file} @dots{} )
2139 Use this command to include binary input files in the link, without
2140 including them in a particular section definition.
2141 Specify the full name for each @var{file}, including @samp{.a} if
2144 @code{ld} searches for each @var{file} through the archive-library
2145 search path, just as for files you specify on the command line.
2146 See the description of @samp{-L} in @ref{Options,,Command Line
2149 If you use @samp{-l@var{file}}, @code{ld} will transform the name to
2150 @code{lib@var{file}.a} as with the command line argument @samp{-l}.
2152 @kindex GROUP ( @var{files} )
2153 @cindex grouping input files
2154 @item GROUP ( @var{file}, @var{file}, @dots{} )
2155 @itemx GROUP ( @var{file} @var{file} @dots{} )
2156 This command is like @code{INPUT}, except that the named files should
2157 all be archives, and they are searched repeatedly until no new undefined
2158 references are created. See the description of @samp{-(} in
2159 @ref{Options,,Command Line Options}.
2162 @item MAP ( @var{name} )
2163 @kindex MAP ( @var{name} )
2164 @c MAP(...) appears to look for an F in the arg, ignoring all other
2165 @c chars; if it finds one, it sets "map_option_f" to true. But nothing
2166 @c checks map_option_f. Apparently a stub for the future...
2169 @item OUTPUT ( @var{filename} )
2170 @kindex OUTPUT ( @var{filename} )
2171 @cindex naming the output file
2172 Use this command to name the link output file @var{filename}. The
2173 effect of @code{OUTPUT(@var{filename})} is identical to the effect of
2174 @w{@samp{-o @var{filename}}}, which overrides it. You can use this
2175 command to supply a default output-file name other than @code{a.out}.
2177 @ifclear SingleFormat
2178 @item OUTPUT_ARCH ( @var{bfdname} )
2179 @kindex OUTPUT_ARCH ( @var{bfdname} )
2180 @cindex machine architecture, output
2181 Specify a particular output machine architecture, with one of the names
2182 used by the BFD back-end routines (@pxref{BFD}). This command is often
2183 unnecessary; the architecture is most often set implicitly by either the
2184 system BFD configuration or as a side effect of the @code{OUTPUT_FORMAT}
2187 @item OUTPUT_FORMAT ( @var{bfdname} )
2188 @kindex OUTPUT_FORMAT ( @var{bfdname} )
2189 @cindex format, output file
2190 When @code{ld} is configured to support multiple object code formats,
2191 you can use this command to specify a particular output format.
2192 @var{bfdname} is one of the names used by the BFD back-end routines
2193 (@pxref{BFD}). The effect is identical to the effect of the
2194 @samp{-oformat} command-line option. This selection affects only
2195 the output file; the related command @code{TARGET} affects primarily
2199 @item SEARCH_DIR ( @var{path} )
2200 @kindex SEARCH_DIR ( @var{path} )
2201 @cindex path for libraries
2202 @cindex search path, libraries
2203 Add @var{path} to the list of paths where @code{ld} looks for
2204 archive libraries. @code{SEARCH_DIR(@var{path})} has the same
2205 effect as @samp{-L@var{path}} on the command line.
2207 @item STARTUP ( @var{filename} )
2208 @kindex STARTUP ( @var{filename} )
2209 @cindex first input file
2210 Ensure that @var{filename} is the first input file used in the link
2213 @ifclear SingleFormat
2214 @item TARGET ( @var{format} )
2215 @cindex input file format
2216 @kindex TARGET ( @var{format} )
2217 When @code{ld} is configured to support multiple object code formats,
2218 you can use this command to change the input-file object code format
2219 (like the command-line option @samp{-b} or its synonym @samp{-format}).
2220 The argument @var{format} is one of the strings used by BFD to name
2221 binary formats. If @code{TARGET} is specified but @code{OUTPUT_FORMAT}
2222 is not, the last @code{TARGET} argument is also used as the default
2223 format for the @code{ld} output file. @xref{BFD}.
2226 If you don't use the @code{TARGET} command, @code{ld} uses the value of
2227 the environment variable @code{GNUTARGET}, if available, to select the
2228 output file format. If that variable is also absent, @code{ld} uses
2229 the default format configured for your machine in the BFD libraries.
2234 @node Machine Dependent
2235 @chapter Machine Dependent Features
2237 @cindex machine dependencies
2238 @code{ld} has additional features on some platforms; the following
2239 sections describe them. Machines where @code{ld} has no additional
2240 functionality are not listed.
2243 * H8/300:: @code{ld} and the H8/300
2244 * i960:: @code{ld} and the Intel 960 family
2248 @c FIXME! This could use @raisesections/@lowersections, but there seems to be a conflict
2249 @c between those and node-defaulting.
2255 @section @code{ld} and the H8/300
2257 @cindex H8/300 support
2258 For the H8/300, @code{ld} can perform these global optimizations when
2259 you specify the @samp{-relax} command-line option.
2262 @item relaxing address modes
2263 @cindex relaxing on H8/300
2264 @code{ld} finds all @code{jsr} and @code{jmp} instructions whose
2265 targets are within eight bits, and turns them into eight-bit
2266 program-counter relative @code{bsr} and @code{bra} instructions,
2269 @item synthesizing instructions
2270 @cindex synthesizing on H8/300
2271 @c FIXME: specifically mov.b, or any mov instructions really?
2272 @code{ld} finds all @code{mov.b} instructions which use the
2273 sixteen-bit absolute address form, but refer to the top
2274 page of memory, and changes them to use the eight-bit address form.
2275 (That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into
2276 @samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the
2277 top page of memory).
2286 @c This stuff is pointless to say unless you're especially concerned
2287 @c with Hitachi chips; don't enable it for generic case, please.
2289 @chapter @code{ld} and other Hitachi chips
2291 @code{ld} also supports the H8/300H, the H8/500, and the Hitachi SH. No
2292 special features, commands, or command-line options are required for
2302 @section @code{ld} and the Intel 960 family
2304 @cindex i960 support
2306 You can use the @samp{-A@var{architecture}} command line option to
2307 specify one of the two-letter names identifying members of the 960
2308 family; the option specifies the desired output target, and warns of any
2309 incompatible instructions in the input files. It also modifies the
2310 linker's search strategy for archive libraries, to support the use of
2311 libraries specific to each particular architecture, by including in the
2312 search loop names suffixed with the string identifying the architecture.
2314 For example, if your @code{ld} command line included @w{@samp{-ACA}} as
2315 well as @w{@samp{-ltry}}, the linker would look (in its built-in search
2316 paths, and in any paths you specify with @samp{-L}) for a library with
2327 The first two possibilities would be considered in any event; the last
2328 two are due to the use of @w{@samp{-ACA}}.
2330 You can meaningfully use @samp{-A} more than once on a command line, since
2331 the 960 architecture family allows combination of target architectures; each
2332 use will add another pair of name variants to search for when @w{@samp{-l}}
2333 specifies a library.
2335 @cindex @code{-relax} on i960
2336 @cindex relaxing on i960
2337 @code{ld} supports the @samp{-relax} option for the i960 family. If you
2338 specify @samp{-relax}, @code{ld} finds all @code{balx} and @code{calx}
2339 instructions whose targets are within 24 bits, and turns them into
2340 24-bit program-counter relative @code{bal} and @code{cal}
2341 instructions, respectively. @code{ld} also turns @code{cal}
2342 instructions into @code{bal} instructions when it determines that the
2343 target subroutine is a leaf routine (that is, the target subroutine does
2344 not itself call any subroutines).
2351 @ifclear SingleFormat
2356 @cindex object file management
2357 @cindex object formats available
2359 The linker accesses object and archive files using the BFD libraries.
2360 These libraries allow the linker to use the same routines to operate on
2361 object files whatever the object file format. A different object file
2362 format can be supported simply by creating a new BFD back end and adding
2363 it to the library. To conserve runtime memory, however, the linker and
2364 associated tools are usually configured to support only a subset of the
2365 object file formats available. You can use @code{objdump -i}
2366 (@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to
2367 list all the formats available for your configuration.
2369 @cindex BFD requirements
2370 @cindex requirements for BFD
2371 As with most implementations, BFD is a compromise between
2372 several conflicting requirements. The major factor influencing
2373 BFD design was efficiency: any time used converting between
2374 formats is time which would not have been spent had BFD not
2375 been involved. This is partly offset by abstraction payback; since
2376 BFD simplifies applications and back ends, more time and care
2377 may be spent optimizing algorithms for a greater speed.
2379 One minor artifact of the BFD solution which you should bear in
2380 mind is the potential for information loss. There are two places where
2381 useful information can be lost using the BFD mechanism: during
2382 conversion and during output. @xref{BFD information loss}.
2385 * BFD outline:: How it works: an outline of BFD
2389 @section How it works: an outline of BFD
2390 @cindex opening object files
2391 @include bfdsumm.texi
2395 @appendix MRI Compatible Script Files
2396 @cindex MRI compatibility
2397 To aid users making the transition to @sc{gnu} @code{ld} from the MRI
2398 linker, @code{ld} can use MRI compatible linker scripts as an
2399 alternative to the more general-purpose linker scripting language
2400 described in @ref{Commands,,Command Language}. MRI compatible linker
2401 scripts have a much simpler command set than the scripting language
2402 otherwise used with @code{ld}. @sc{gnu} @code{ld} supports the most
2403 commonly used MRI linker commands; these commands are described here.
2405 In general, MRI scripts aren't of much use with the @code{a.out} object
2406 file format, since it only has three sections and MRI scripts lack some
2407 features to make use of them.
2409 You can specify a file containing an MRI-compatible script using the
2410 @samp{-c} command-line option.
2412 Each command in an MRI-compatible script occupies its own line; each
2413 command line starts with the keyword that identifies the command (though
2414 blank lines are also allowed for punctuation). If a line of an
2415 MRI-compatible script begins with an unrecognized keyword, @code{ld}
2416 issues a warning message, but continues processing the script.
2418 Lines beginning with @samp{*} are comments.
2420 You can write these commands using all upper-case letters, or all
2421 lower case; for example, @samp{chip} is the same as @samp{CHIP}.
2422 The following list shows only the upper-case form of each command.
2425 @cindex @code{ABSOLUTE} (MRI)
2426 @item ABSOLUTE @var{secname}
2427 @item ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
2428 Normally, @code{ld} includes in the output file all sections from all
2429 the input files. However, in an MRI-compatible script, you can use the
2430 @code{ABSOLUTE} command to restrict the sections that will be present in
2431 your output program. If the @code{ABSOLUTE} command is used at all in a
2432 script, then only the sections named explicitly in @code{ABSOLUTE}
2433 commands will appear in the linker output. You can still use other
2434 input sections (whatever you select on the command line, or using
2435 @code{LOAD}) to resolve addresses in the output file.
2437 @cindex @code{ALIAS} (MRI)
2438 @item ALIAS @var{out-secname}, @var{in-secname}
2439 Use this command to place the data from input section @var{in-secname}
2440 in a section called @var{out-secname} in the linker output file.
2442 @var{in-secname} may be an integer.
2444 @cindex @code{BASE} (MRI)
2445 @item BASE @var{expression}
2446 Use the value of @var{expression} as the lowest address (other than
2447 absolute addresses) in the output file.
2449 @cindex @code{CHIP} (MRI)
2450 @item CHIP @var{expression}
2451 @itemx CHIP @var{expression}, @var{expression}
2452 This command does nothing; it is accepted only for compatibility.
2454 @cindex @code{END} (MRI)
2456 This command does nothing whatever; it's only accepted for compatibility.
2458 @cindex @code{FORMAT} (MRI)
2459 @item FORMAT @var{output-format}
2460 Similar to the @code{OUTPUT_FORMAT} command in the more general linker
2461 language, but restricted to one of these output formats:
2465 S-records, if @var{output-format} is @samp{S}
2468 IEEE, if @var{output-format} is @samp{IEEE}
2471 COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is
2475 @cindex @code{LIST} (MRI)
2476 @item LIST @var{anything}@dots{}
2477 Print (to the standard output file) a link map, as produced by the
2478 @code{ld} command-line option @samp{-M}.
2480 The keyword @code{LIST} may be followed by anything on the
2481 same line, with no change in its effect.
2483 @cindex @code{LOAD} (MRI)
2484 @item LOAD @var{filename}
2485 @item LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
2486 Include one or more object file @var{filename} in the link; this has the
2487 same effect as specifying @var{filename} directly on the @code{ld}
2490 @cindex @code{NAME} (MRI)
2491 @item NAME @var{output-name}
2492 @var{output-name} is the name for the program produced by @code{ld}; the
2493 MRI-compatible command @code{NAME} is equivalent to the command-line
2494 option @samp{-o} or the general script language command @code{OUTPUT}.
2496 @cindex @code{ORDER} (MRI)
2497 @item ORDER @var{secname}, @var{secname}, @dots{} @var{secname}
2498 @itemx ORDER @var{secname} @var{secname} @var{secname}
2499 Normally, @code{ld} orders the sections in its output file in the
2500 order in which they first appear in the input files. In an MRI-compatible
2501 script, you can override this ordering with the @code{ORDER} command. The
2502 sections you list with @code{ORDER} will appear first in your output
2503 file, in the order specified.
2505 @cindex @code{PUBLIC} (MRI)
2506 @item PUBLIC @var{name}=@var{expression}
2507 @itemx PUBLIC @var{name},@var{expression}
2508 @itemx PUBLIC @var{name} @var{expression}
2509 Supply a value (@var{expression}) for external symbol
2510 @var{name} used in the linker input files.
2512 @cindex @code{SECT} (MRI)
2513 @item SECT @var{secname}, @var{expression}
2514 @itemx SECT @var{secname}=@var{expression}
2515 @itemx SECT @var{secname} @var{expression}
2516 You can use any of these three forms of the @code{SECT} command to
2517 specify the start address (@var{expression}) for section @var{secname}.
2518 If you have more than one @code{SECT} statement for the same
2519 @var{secname}, only the @emph{first} sets the start address.
2529 % I think something like @colophon should be in texinfo. In the
2531 \long\def\colophon{\hbox to0pt{}\vfill
2532 \centerline{The body of this manual is set in}
2533 \centerline{\fontname\tenrm,}
2534 \centerline{with headings in {\bf\fontname\tenbf}}
2535 \centerline{and examples in {\tt\fontname\tentt}.}
2536 \centerline{{\it\fontname\tenit\/} and}
2537 \centerline{{\sl\fontname\tensl\/}}
2538 \centerline{are used for emphasis.}\vfill}
2540 % Blame: pesch@cygnus.com, 28mar91.