1LD(1) GNU Development Tools LD(1)
2
6 ld - Using LD, the GNU linker
7
9 ld [options] objfile ...
10
12 ld combines a number of object and archive files, relocates their data
13 and ties up symbol references. Usually the last step in compiling a
14 program is to run ld.
15 ld accepts Linker Command Language files written in a superset of
17 AT&T's Link Editor Command Language syntax, to provide explicit and
18 total control over the linking process.
19 This man page does not describe the command language; see the ld entry
21 in "info", or the manual ld: the GNU linker, for full details on the
22 command language and on other aspects of the GNU linker.
23 This version of ld uses the general purpose BFD libraries to operate on
25 object files. This allows ld to read, combine, and write object files
26 in many different formats---for example, COFF or "a.out". Different
27 formats may be linked together to produce any available kind of object
28 file.
29 Aside from its flexibility, the GNU linker is more helpful than other
31 linkers in providing diagnostic information. Many linkers abandon exe‐
32 cution immediately upon encountering an error; whenever possible, ld
33 continues executing, allowing you to identify other errors (or, in some
34 cases, to get an output file in spite of the error).
35 The GNU linker ld is meant to cover a broad range of situations, and to
37 be as compatible as possible with other linkers. As a result, you have
38 many choices to control its behavior.
39
41 The linker supports a plethora of command-line options, but in actual
42 practice few of them are used in any particular context. For instance,
43 a frequent use of ld is to link standard Unix object files on a stan‐
44 dard, supported Unix system. On such a system, to link a file
45 "hello.o":
46 ld -o <output> /lib/crt0.o hello.o -lc
48 This tells ld to produce a file called output as the result of linking
50 the file "/lib/crt0.o" with "hello.o" and the library "libc.a", which
51 will come from the standard search directories. (See the discussion of
52 the -l option below.)
53 Some of the command-line options to ld may be specified at any point in
55 the command line. However, options which refer to files, such as -l or
56 -T, cause the file to be read at the point at which the option appears
57 in the command line, relative to the object files and other file
58 options. Repeating non-file options with a different argument will
59 either have no further effect, or override prior occurrences (those
60 further to the left on the command line) of that option. Options which
61 may be meaningfully specified more than once are noted in the descrip‐
62 tions below.
63 Non-option arguments are object files or archives which are to be
65 linked together. They may follow, precede, or be mixed in with com‐
66 mand-line options, except that an object file argument may not be
67 placed between an option and its argument.
68 Usually the linker is invoked with at least one object file, but you
70 can specify other forms of binary input files using -l, -R, and the
71 script command language. If no binary input files at all are speci‐
72 fied, the linker does not produce any output, and issues the message No
73 input files.
74 If the linker cannot recognize the format of an object file, it will
76 assume that it is a linker script. A script specified in this way aug‐
77 ments the main linker script used for the link (either the default
78 linker script or the one specified by using -T). This feature permits
79 the linker to link against a file which appears to be an object or an
80 archive, but actually merely defines some symbol values, or uses
81 "INPUT" or "GROUP" to load other objects. Note that specifying a
82 script in this way merely augments the main linker script; use the -T
83 option to replace the default linker script entirely.
84 For options whose names are a single letter, option arguments must
86 either follow the option letter without intervening whitespace, or be
87 given as separate arguments immediately following the option that
88 requires them.
89 For options whose names are multiple letters, either one dash or two
91 can precede the option name; for example, -trace-symbol and
92 --trace-symbol are equivalent. Note---there is one exception to this
93 rule. Multiple letter options that start with a lower case 'o' can
94 only be preceeded by two dashes. This is to reduce confusion with the
95 -o option. So for example -omagic sets the output file name to magic
96 whereas --omagic sets the NMAGIC flag on the output.
97 Arguments to multiple-letter options must either be separated from the
99 option name by an equals sign, or be given as separate arguments imme‐
100 diately following the option that requires them. For example,
101 --trace-symbol foo and --trace-symbol=foo are equivalent. Unique
102 abbreviations of the names of multiple-letter options are accepted.
103 Note---if the linker is being invoked indirectly, via a compiler driver
105 (e.g. gcc) then all the linker command line options should be prefixed
106 by -Wl, (or whatever is appropriate for the particular compiler driver)
107 like this:
108 gcc -Wl,--startgroup foo.o bar.o -Wl,--endgroup
110 This is important, because otherwise the compiler driver program may
112 silently drop the linker options, resulting in a bad link.
113 Here is a table of the generic command line switches accepted by the
115 GNU linker:
116 @file
118 Read command-line options from file. The options read are inserted
119 in place of the original @file option. If file does not exist, or
120 cannot be read, then the option will be treated literally, and not
121 removed.
122 Options in file are separated by whitespace. A whitespace charac‐
124 ter may be included in an option by surrounding the entire option
125 in either single or double quotes. Any character (including a
126 backslash) may be included by prefixing the character to be
127 included with a backslash. The file may itself contain additional
128 @file options; any such options will be processed recursively.
129 -akeyword
131 This option is supported for HP/UX compatibility. The keyword
132 argument must be one of the strings archive, shared, or default.
133 -aarchive is functionally equivalent to -Bstatic, and the other two
134 keywords are functionally equivalent to -Bdynamic. This option may
135 be used any number of times.
136 -Aarchitecture
138 --architecture=architecture
139 In the current release of ld, this option is useful only for the
140 Intel 960 family of architectures. In that ld configuration, the
141 architecture argument identifies the particular architecture in the
142 960 family, enabling some safeguards and modifying the archive-
143 library search path.
144 Future releases of ld may support similar functionality for other
146 architecture families.
147 -b input-format
149 --format=input-format
150 ld may be configured to support more than one kind of object file.
151 If your ld is configured this way, you can use the -b option to
152 specify the binary format for input object files that follow this
153 option on the command line. Even when ld is configured to support
154 alternative object formats, you don't usually need to specify this,
155 as ld should be configured to expect as a default input format the
156 most usual format on each machine. input-format is a text string,
157 the name of a particular format supported by the BFD libraries.
158 (You can list the available binary formats with objdump -i.)
159 You may want to use this option if you are linking files with an
161 unusual binary format. You can also use -b to switch formats
162 explicitly (when linking object files of different formats), by
163 including -b input-format before each group of object files in a
164 particular format.
165 The default format is taken from the environment variable "GNUTAR‐
167 GET".
168 You can also define the input format from a script, using the com‐
170 mand "TARGET";
171 -c MRI-commandfile
173 --mri-script=MRI-commandfile
174 For compatibility with linkers produced by MRI, ld accepts script
175 files written in an alternate, restricted command language,
176 described in the MRI Compatible Script Files section of GNU ld doc‐
177 umentation. Introduce MRI script files with the option -c; use the
178 -T option to run linker scripts written in the general-purpose ld
179 scripting language. If MRI-cmdfile does not exist, ld looks for it
180 in the directories specified by any -L options.
181 -d
183 -dc
184 -dp These three options are equivalent; multiple forms are supported
185 for compatibility with other linkers. They assign space to common
186 symbols even if a relocatable output file is specified (with -r).
187 The script command "FORCE_COMMON_ALLOCATION" has the same effect.
188 -e entry
190 --entry=entry
191 Use entry as the explicit symbol for beginning execution of your
192 program, rather than the default entry point. If there is no sym‐
193 bol named entry, the linker will try to parse entry as a number,
194 and use that as the entry address (the number will be interpreted
195 in base 10; you may use a leading 0x for base 16, or a leading 0
196 for base 8).
197 --exclude-libs lib,lib,...
199 Specifies a list of archive libraries from which symbols should not
200 be automatically exported. The library names may be delimited by
201 commas or colons. Specifying "--exclude-libs ALL" excludes symbols
202 in all archive libraries from automatic export. This option is
203 available only for the i386 PE targeted port of the linker and for
204 ELF targeted ports. For i386 PE, symbols explicitly listed in a
205 .def file are still exported, regardless of this option. For ELF
206 targeted ports, symbols affected by this option will be treated as
207 hidden.
208 -E
210 --export-dynamic
211 When creating a dynamically linked executable, add all symbols to
212 the dynamic symbol table. The dynamic symbol table is the set of
213 symbols which are visible from dynamic objects at run time.
214 If you do not use this option, the dynamic symbol table will nor‐
216 mally contain only those symbols which are referenced by some
217 dynamic object mentioned in the link.
218 If you use "dlopen" to load a dynamic object which needs to refer
220 back to the symbols defined by the program, rather than some other
221 dynamic object, then you will probably need to use this option when
222 linking the program itself.
223 You can also use the version script to control what symbols should
225 be added to the dynamic symbol table if the output format supports
226 it. See the description of --version-script in VERSION.
227 -EB Link big-endian objects. This affects the default output format.
229 -EL Link little-endian objects. This affects the default output for‐
231 mat.
232 -f
234 --auxiliary name
235 When creating an ELF shared object, set the internal DT_AUXILIARY
236 field to the specified name. This tells the dynamic linker that
237 the symbol table of the shared object should be used as an auxil‐
238 iary filter on the symbol table of the shared object name.
239 If you later link a program against this filter object, then, when
241 you run the program, the dynamic linker will see the DT_AUXILIARY
242 field. If the dynamic linker resolves any symbols from the filter
243 object, it will first check whether there is a definition in the
244 shared object name. If there is one, it will be used instead of
245 the definition in the filter object. The shared object name need
246 not exist. Thus the shared object name may be used to provide an
247 alternative implementation of certain functions, perhaps for debug‐
248 ging or for machine specific performance.
249 This option may be specified more than once. The DT_AUXILIARY
251 entries will be created in the order in which they appear on the
252 command line.
253 -F name
255 --filter name
256 When creating an ELF shared object, set the internal DT_FILTER
257 field to the specified name. This tells the dynamic linker that
258 the symbol table of the shared object which is being created should
259 be used as a filter on the symbol table of the shared object name.
260 If you later link a program against this filter object, then, when
262 you run the program, the dynamic linker will see the DT_FILTER
263 field. The dynamic linker will resolve symbols according to the
264 symbol table of the filter object as usual, but it will actually
265 link to the definitions found in the shared object name. Thus the
266 filter object can be used to select a subset of the symbols pro‐
267 vided by the object name.
268 Some older linkers used the -F option throughout a compilation
270 toolchain for specifying object-file format for both input and out‐
271 put object files. The GNU linker uses other mechanisms for this
272 purpose: the -b, --format, --oformat options, the "TARGET" command
273 in linker scripts, and the "GNUTARGET" environment variable. The
274 GNU linker will ignore the -F option when not creating an ELF
275 shared object.
276 -fini name
278 When creating an ELF executable or shared object, call NAME when
279 the executable or shared object is unloaded, by setting DT_FINI to
280 the address of the function. By default, the linker uses "_fini"
281 as the function to call.
282 -g Ignored. Provided for compatibility with other tools.
284 -Gvalue
286 --gpsize=value
287 Set the maximum size of objects to be optimized using the GP regis‐
288 ter to size. This is only meaningful for object file formats such
289 as MIPS ECOFF which supports putting large and small objects into
290 different sections. This is ignored for other object file formats.
291 -hname
293 -soname=name
294 When creating an ELF shared object, set the internal DT_SONAME
295 field to the specified name. When an executable is linked with a
296 shared object which has a DT_SONAME field, then when the executable
297 is run the dynamic linker will attempt to load the shared object
298 specified by the DT_SONAME field rather than the using the file
299 name given to the linker.
300 -i Perform an incremental link (same as option -r).
302 -init name
304 When creating an ELF executable or shared object, call NAME when
305 the executable or shared object is loaded, by setting DT_INIT to
306 the address of the function. By default, the linker uses "_init"
307 as the function to call.
308 -larchive
310 --library=archive
311 Add archive file archive to the list of files to link. This option
312 may be used any number of times. ld will search its path-list for
313 occurrences of "libarchive.a" for every archive specified.
314 On systems which support shared libraries, ld may also search for
316 libraries with extensions other than ".a". Specifically, on ELF
317 and SunOS systems, ld will search a directory for a library with an
318 extension of ".so" before searching for one with an extension of
319 ".a". By convention, a ".so" extension indicates a shared library.
320 The linker will search an archive only once, at the location where
322 it is specified on the command line. If the archive defines a sym‐
323 bol which was undefined in some object which appeared before the
324 archive on the command line, the linker will include the appropri‐
325 ate file(s) from the archive. However, an undefined symbol in an
326 object appearing later on the command line will not cause the
327 linker to search the archive again.
328 See the -( option for a way to force the linker to search archives
330 multiple times.
331 You may list the same archive multiple times on the command line.
333 This type of archive searching is standard for Unix linkers. How‐
335 ever, if you are using ld on AIX, note that it is different from
336 the behaviour of the AIX linker.
337 -Lsearchdir
339 --library-path=searchdir
340 Add path searchdir to the list of paths that ld will search for ar‐
341 chive libraries and ld control scripts. You may use this option
342 any number of times. The directories are searched in the order in
343 which they are specified on the command line. Directories speci‐
344 fied on the command line are searched before the default directo‐
345 ries. All -L options apply to all -l options, regardless of the
346 order in which the options appear.
347 If searchdir begins with "=", then the "=" will be replaced by the
349 sysroot prefix, a path specified when the linker is configured.
350 The default set of paths searched (without being specified with -L)
352 depends on which emulation mode ld is using, and in some cases also
353 on how it was configured.
354 The paths can also be specified in a link script with the
356 "SEARCH_DIR" command. Directories specified this way are searched
357 at the point in which the linker script appears in the command
358 line.
359 -memulation
361 Emulate the emulation linker. You can list the available emula‐
362 tions with the --verbose or -V options.
363 If the -m option is not used, the emulation is taken from the
365 "LDEMULATION" environment variable, if that is defined.
366 Otherwise, the default emulation depends upon how the linker was
368 configured.
369 -M
371 --print-map
372 Print a link map to the standard output. A link map provides
373 information about the link, including the following:
374 * Where object files are mapped into memory.
376 * How common symbols are allocated.
378 * All archive members included in the link, with a mention of the
380 symbol which caused the archive member to be brought in.
381 * The values assigned to symbols.
383 Note - symbols whose values are computed by an expression which
385 involves a reference to a previous value of the same symbol may
386 not have correct result displayed in the link map. This is
387 because the linker discards intermediate results and only
388 retains the final value of an expression. Under such circum‐
389 stances the linker will display the final value enclosed by
390 square brackets. Thus for example a linker script containing:
391 foo = 1
393 foo = foo * 4
394 foo = foo + 8
395 will produce the following output in the link map if the -M
397 option is used:
398 0x00000001 foo = 0x1
400 [0x0000000c] foo = (foo * 0x4)
401 [0x0000000c] foo = (foo + 0x8)
402 See Expressions for more information about expressions in
404 linker scripts.
405 -n
407 --nmagic
408 Turn off page alignment of sections, and mark the output as
409 "NMAGIC" if possible.
410 -N
412 --omagic
413 Set the text and data sections to be readable and writable. Also,
414 do not page-align the data segment, and disable linking against
415 shared libraries. If the output format supports Unix style magic
416 numbers, mark the output as "OMAGIC". Note: Although a writable
417 text section is allowed for PE-COFF targets, it does not conform to
418 the format specification published by Microsoft.
419 --no-omagic
421 This option negates most of the effects of the -N option. It sets
422 the text section to be read-only, and forces the data segment to be
423 page-aligned. Note - this option does not enable linking against
424 shared libraries. Use -Bdynamic for this.
425 -o output
427 --output=output
428 Use output as the name for the program produced by ld; if this
429 option is not specified, the name a.out is used by default. The
430 script command "OUTPUT" can also specify the output file name.
431 -O level
433 If level is a numeric values greater than zero ld optimizes the
434 output. This might take significantly longer and therefore proba‐
435 bly should only be enabled for the final binary.
436 -q
438 --emit-relocs
439 Leave relocation sections and contents in fully linked exececuta‐
440 bles. Post link analysis and optimization tools may need this
441 information in order to perform correct modifications of executa‐
442 bles. This results in larger executables.
443 This option is currently only supported on ELF platforms.
445 --force-dynamic
447 Force the output file to have dynamic sections. This option is
448 specific to VxWorks targets.
449 -r
451 --relocatable
452 Generate relocatable output---i.e., generate an output file that
453 can in turn serve as input to ld. This is often called partial
454 linking. As a side effect, in environments that support standard
455 Unix magic numbers, this option also sets the output file's magic
456 number to "OMAGIC". If this option is not specified, an absolute
457 file is produced. When linking C++ programs, this option will not
458 resolve references to constructors; to do that, use -Ur.
459 When an input file does not have the same format as the output
461 file, partial linking is only supported if that input file does not
462 contain any relocations. Different output formats can have further
463 restrictions; for example some "a.out"-based formats do not support
464 partial linking with input files in other formats at all.
465 This option does the same thing as -i.
467 -R filename
469 --just-symbols=filename
470 Read symbol names and their addresses from filename, but do not
471 relocate it or include it in the output. This allows your output
472 file to refer symbolically to absolute locations of memory defined
473 in other programs. You may use this option more than once.
474 For compatibility with other ELF linkers, if the -R option is fol‐
476 lowed by a directory name, rather than a file name, it is treated
477 as the -rpath option.
478 -s
480 --strip-all
481 Omit all symbol information from the output file.
482 -S
484 --strip-debug
485 Omit debugger symbol information (but not all symbols) from the
486 output file.
487 -t
489 --trace
490 Print the names of the input files as ld processes them.
491 -T scriptfile
493 --script=scriptfile
494 Use scriptfile as the linker script. This script replaces ld's
495 default linker script (rather than adding to it), so commandfile
496 must specify everything necessary to describe the output file.
497 If scriptfile does not exist in the current directory, "ld" looks
498 for it in the directories specified by any preceding -L options.
499 Multiple -T options accumulate.
500 -u symbol
502 --undefined=symbol
503 Force symbol to be entered in the output file as an undefined sym‐
504 bol. Doing this may, for example, trigger linking of additional
505 modules from standard libraries. -u may be repeated with different
506 option arguments to enter additional undefined symbols. This
507 option is equivalent to the "EXTERN" linker script command.
508 -Ur For anything other than C++ programs, this option is equivalent to
510 -r: it generates relocatable output---i.e., an output file that can
511 in turn serve as input to ld. When linking C++ programs, -Ur does
512 resolve references to constructors, unlike -r. It does not work to
513 use -Ur on files that were themselves linked with -Ur; once the
514 constructor table has been built, it cannot be added to. Use -Ur
515 only for the last partial link, and -r for the others.
516 --unique[=SECTION]
518 Creates a separate output section for every input section matching
519 SECTION, or if the optional wildcard SECTION argument is missing,
520 for every orphan input section. An orphan section is one not
521 specifically mentioned in a linker script. You may use this option
522 multiple times on the command line; It prevents the normal merging
523 of input sections with the same name, overriding output section
524 assignments in a linker script.
525 -v
527 --version
528 -V Display the version number for ld. The -V option also lists the
529 supported emulations.
530 -x
532 --discard-all
533 Delete all local symbols.
534 -X
536 --discard-locals
537 Delete all temporary local symbols. For most targets, this is all
538 local symbols whose names begin with L.
539 -y symbol
541 --trace-symbol=symbol
542 Print the name of each linked file in which symbol appears. This
543 option may be given any number of times. On many systems it is
544 necessary to prepend an underscore.
545 This option is useful when you have an undefined symbol in your
547 link but don't know where the reference is coming from.
548 -Y path
550 Add path to the default library search path. This option exists
551 for Solaris compatibility.
552 -z keyword
554 The recognized keywords are:
555 combreloc
557 Combines multiple reloc sections and sorts them to make dynamic
558 symbol lookup caching possible.
559 defs
561 Disallows undefined symbols in object files. Undefined symbols
562 in shared libraries are still allowed.
563 execstack
565 Marks the object as requiring executable stack.
566 initfirst
568 This option is only meaningful when building a shared object.
569 It marks the object so that its runtime initialization will
570 occur before the runtime initialization of any other objects
571 brought into the process at the same time. Similarly the run‐
572 time finalization of the object will occur after the runtime
573 finalization of any other objects.
574 interpose
576 Marks the object that its symbol table interposes before all
577 symbols but the primary executable.
578 loadfltr
580 Marks the object that its filters be processed immediately at
581 runtime.
582 muldefs
584 Allows multiple definitions.
585 nocombreloc
587 Disables multiple reloc sections combining.
588 nocopyreloc
590 Disables production of copy relocs.
591 nodefaultlib
593 Marks the object that the search for dependencies of this
594 object will ignore any default library search paths.
595 nodelete
597 Marks the object shouldn't be unloaded at runtime.
598 nodlopen
600 Marks the object not available to "dlopen".
601 nodump
603 Marks the object can not be dumped by "dldump".
604 noexecstack
606 Marks the object as not requiring executable stack.
607 norelro
609 Don't create an ELF "PT_GNU_RELRO" segment header in the
610 object.
611 now When generating an executable or shared library, mark it to
613 tell the dynamic linker to resolve all symbols when the program
614 is started, or when the shared library is linked to using
615 dlopen, instead of deferring function call resolution to the
616 point when the function is first called.
617 origin
619 Marks the object may contain $ORIGIN.
620 relro
622 Create an ELF "PT_GNU_RELRO" segment header in the object.
623 Other keywords are ignored for Solaris compatibility.
625 -( archives -)
627 --start-group archives --end-group
628 The archives should be a list of archive files. They may be either
629 explicit file names, or -l options.
630 The specified archives are searched repeatedly until no new unde‐
632 fined references are created. Normally, an archive is searched
633 only once in the order that it is specified on the command line.
634 If a symbol in that archive is needed to resolve an undefined sym‐
635 bol referred to by an object in an archive that appears later on
636 the command line, the linker would not be able to resolve that ref‐
637 erence. By grouping the archives, they all be searched repeatedly
638 until all possible references are resolved.
639 Using this option has a significant performance cost. It is best
641 to use it only when there are unavoidable circular references
642 between two or more archives.
643 --accept-unknown-input-arch
645 --no-accept-unknown-input-arch
646 Tells the linker to accept input files whose architecture cannot be
647 recognised. The assumption is that the user knows what they are
648 doing and deliberately wants to link in these unknown input files.
649 This was the default behaviour of the linker, before release 2.14.
650 The default behaviour from release 2.14 onwards is to reject such
651 input files, and so the --accept-unknown-input-arch option has been
652 added to restore the old behaviour.
653 --as-needed
655 --no-as-needed
656 This option affects ELF DT_NEEDED tags for dynamic libraries men‐
657 tioned on the command line after the --as-needed option. Normally,
658 the linker will add a DT_NEEDED tag for each dynamic library men‐
659 tioned on the command line, regardless of whether the library is
660 actually needed. --as-needed causes DT_NEEDED tags to only be
661 emitted for libraries that satisfy some symbol reference from regu‐
662 lar objects which is undefined at the point that the library was
663 linked. --no-as-needed restores the default behaviour.
664 --add-needed
666 --no-add-needed
667 This option affects the treatment of dynamic libraries from ELF
668 DT_NEEDED tags in dynamic libraries mentioned on the command line
669 after the --no-add-needed option. Normally, the linker will add a
670 DT_NEEDED tag for each dynamic library from DT_NEEDED tags.
671 --no-add-needed causes DT_NEEDED tags will never be emitted for
672 those libraries from DT_NEEDED tags. --add-needed restores the
673 default behaviour.
674 -assert keyword
676 This option is ignored for SunOS compatibility.
677 -Bdynamic
679 -dy
680 -call_shared
681 Link against dynamic libraries. This is only meaningful on plat‐
682 forms for which shared libraries are supported. This option is
683 normally the default on such platforms. The different variants of
684 this option are for compatibility with various systems. You may
685 use this option multiple times on the command line: it affects
686 library searching for -l options which follow it.
687 -Bgroup
689 Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the dynamic
690 section. This causes the runtime linker to handle lookups in this
691 object and its dependencies to be performed only inside the group.
692 --unresolved-symbols=report-all is implied. This option is only
693 meaningful on ELF platforms which support shared libraries.
694 -Bstatic
696 -dn
697 -non_shared
698 -static
699 Do not link against shared libraries. This is only meaningful on
700 platforms for which shared libraries are supported. The different
701 variants of this option are for compatibility with various systems.
702 You may use this option multiple times on the command line: it
703 affects library searching for -l options which follow it. This
704 option also implies --unresolved-symbols=report-all. This option
705 can be used with -shared. Doing so means that a shared library is
706 being created but that all of the library's external references
707 must be resolved by pulling in entries from static libraries.
708 -Bsymbolic
710 When creating a shared library, bind references to global symbols
711 to the definition within the shared library, if any. Normally, it
712 is possible for a program linked against a shared library to over‐
713 ride the definition within the shared library. This option is only
714 meaningful on ELF platforms which support shared libraries.
715 --check-sections
717 --no-check-sections
718 Asks the linker not to check section addresses after they have been
719 assigned to see if there are any overlaps. Normally the linker
720 will perform this check, and if it finds any overlaps it will pro‐
721 duce suitable error messages. The linker does know about, and does
722 make allowances for sections in overlays. The default behaviour
723 can be restored by using the command line switch --check-sections.
724 --cref
726 Output a cross reference table. If a linker map file is being gen‐
727 erated, the cross reference table is printed to the map file. Oth‐
728 erwise, it is printed on the standard output.
729 The format of the table is intentionally simple, so that it may be
731 easily processed by a script if necessary. The symbols are printed
732 out, sorted by name. For each symbol, a list of file names is
733 given. If the symbol is defined, the first file listed is the
734 location of the definition. The remaining files contain references
735 to the symbol.
736 --no-define-common
738 This option inhibits the assignment of addresses to common symbols.
739 The script command "INHIBIT_COMMON_ALLOCATION" has the same effect.
740 The --no-define-common option allows decoupling the decision to
742 assign addresses to Common symbols from the choice of the output
743 file type; otherwise a non-Relocatable output type forces assigning
744 addresses to Common symbols. Using --no-define-common allows Com‐
745 mon symbols that are referenced from a shared library to be
746 assigned addresses only in the main program. This eliminates the
747 unused duplicate space in the shared library, and also prevents any
748 possible confusion over resolving to the wrong duplicate when there
749 are many dynamic modules with specialized search paths for runtime
750 symbol resolution.
751 --defsym symbol=expression
753 Create a global symbol in the output file, containing the absolute
754 address given by expression. You may use this option as many times
755 as necessary to define multiple symbols in the command line. A
756 limited form of arithmetic is supported for the expression in this
757 context: you may give a hexadecimal constant or the name of an
758 existing symbol, or use "+" and "-" to add or subtract hexadecimal
759 constants or symbols. If you need more elaborate expressions, con‐
760 sider using the linker command language from a script. Note: there
761 should be no white space between symbol, the equals sign ("="), and
762 expression.
763 --demangle[=style]
765 --no-demangle
766 These options control whether to demangle symbol names in error
767 messages and other output. When the linker is told to demangle, it
768 tries to present symbol names in a readable fashion: it strips
769 leading underscores if they are used by the object file format, and
770 converts C++ mangled symbol names into user readable names. Dif‐
771 ferent compilers have different mangling styles. The optional
772 demangling style argument can be used to choose an appropriate
773 demangling style for your compiler. The linker will demangle by
774 default unless the environment variable COLLECT_NO_DEMANGLE is set.
775 These options may be used to override the default.
776 --dynamic-linker file
778 Set the name of the dynamic linker. This is only meaningful when
779 generating dynamically linked ELF executables. The default dynamic
780 linker is normally correct; don't use this unless you know what you
781 are doing.
782 --fatal-warnings
784 Treat all warnings as errors.
785 --force-exe-suffix
787 Make sure that an output file has a .exe suffix.
788 If a successfully built fully linked output file does not have a
790 ".exe" or ".dll" suffix, this option forces the linker to copy the
791 output file to one of the same name with a ".exe" suffix. This
792 option is useful when using unmodified Unix makefiles on a Micro‐
793 soft Windows host, since some versions of Windows won't run an
794 image unless it ends in a ".exe" suffix.
795 --no-gc-sections
797 --gc-sections
798 Enable garbage collection of unused input sections. It is ignored
799 on targets that do not support this option. This option is not
800 compatible with -r. The default behaviour (of not performing this
801 garbage collection) can be restored by specifying --no-gc-sections
802 on the command line.
803 --help
805 Print a summary of the command-line options on the standard output
806 and exit.
807 --target-help
809 Print a summary of all target specific options on the standard out‐
810 put and exit.
811 -Map mapfile
813 Print a link map to the file mapfile. See the description of the
814 -M option, above.
815 --no-keep-memory
817 ld normally optimizes for speed over memory usage by caching the
818 symbol tables of input files in memory. This option tells ld to
819 instead optimize for memory usage, by rereading the symbol tables
820 as necessary. This may be required if ld runs out of memory space
821 while linking a large executable.
822 --no-undefined
824 -z defs
825 Report unresolved symbol references from regular object files.
826 This is done even if the linker is creating a non-symbolic shared
827 library. The switch --[no-]allow-shlib-undefined controls the be‐
828 haviour for reporting unresolved references found in shared
829 libraries being linked in.
830 --allow-multiple-definition
832 -z muldefs
833 Normally when a symbol is defined multiple times, the linker will
834 report a fatal error. These options allow multiple definitions and
835 the first definition will be used.
836 --allow-shlib-undefined
838 --no-allow-shlib-undefined
839 Allows (the default) or disallows undefined symbols in shared
840 libraries. This switch is similar to --no-undefined except that it
841 determines the behaviour when the undefined symbols are in a shared
842 library rather than a regular object file. It does not affect how
843 undefined symbols in regular object files are handled.
844 The reason that --allow-shlib-undefined is the default is that the
846 shared library being specified at link time may not be the same as
847 the one that is available at load time, so the symbols might actu‐
848 ally be resolvable at load time. Plus there are some systems, (eg
849 BeOS) where undefined symbols in shared libraries is normal. (The
850 kernel patches them at load time to select which function is most
851 appropriate for the current architecture. This is used for example
852 to dynamically select an appropriate memset function). Apparently
853 it is also normal for HPPA shared libraries to have undefined sym‐
854 bols.
855 --no-undefined-version
857 Normally when a symbol has an undefined version, the linker will
858 ignore it. This option disallows symbols with undefined version and
859 a fatal error will be issued instead.
860 --default-symver
862 Create and use a default symbol version (the soname) for unver‐
863 sioned exported symbols.
864 --default-imported-symver
866 Create and use a default symbol version (the soname) for unver‐
867 sioned imported symbols.
868 --no-warn-mismatch
870 Normally ld will give an error if you try to link together input
871 files that are mismatched for some reason, perhaps because they
872 have been compiled for different processors or for different endi‐
873 annesses. This option tells ld that it should silently permit such
874 possible errors. This option should only be used with care, in
875 cases when you have taken some special action that ensures that the
876 linker errors are inappropriate.
877 --no-whole-archive
879 Turn off the effect of the --whole-archive option for subsequent
880 archive files.
881 --noinhibit-exec
883 Retain the executable output file whenever it is still usable.
884 Normally, the linker will not produce an output file if it encoun‐
885 ters errors during the link process; it exits without writing an
886 output file when it issues any error whatsoever.
887 -nostdlib
889 Only search library directories explicitly specified on the command
890 line. Library directories specified in linker scripts (including
891 linker scripts specified on the command line) are ignored.
892 --oformat output-format
894 ld may be configured to support more than one kind of object file.
895 If your ld is configured this way, you can use the --oformat option
896 to specify the binary format for the output object file. Even when
897 ld is configured to support alternative object formats, you don't
898 usually need to specify this, as ld should be configured to produce
899 as a default output format the most usual format on each machine.
900 output-format is a text string, the name of a particular format
901 supported by the BFD libraries. (You can list the available binary
902 formats with objdump -i.) The script command "OUTPUT_FORMAT" can
903 also specify the output format, but this option overrides it.
904 -pie
906 --pic-executable
907 Create a position independent executable. This is currently only
908 supported on ELF platforms. Position independent executables are
909 similar to shared libraries in that they are relocated by the
910 dynamic linker to the virtual address the OS chooses for them
911 (which can vary between invocations). Like normal dynamically
912 linked executables they can be executed and symbols defined in the
913 executable cannot be overridden by shared libraries.
914 -qmagic
916 This option is ignored for Linux compatibility.
917 -Qy This option is ignored for SVR4 compatibility.
919 --relax
921 An option with machine dependent effects. This option is only sup‐
922 ported on a few targets.
923 On some platforms, the --relax option performs global optimizations
925 that become possible when the linker resolves addressing in the
926 program, such as relaxing address modes and synthesizing new
927 instructions in the output object file.
928 On some platforms these link time global optimizations may make
930 symbolic debugging of the resulting executable impossible. This is
931 known to be the case for the Matsushita MN10200 and MN10300 family
932 of processors.
933 On platforms where this is not supported, --relax is accepted, but
935 ignored.
936 --retain-symbols-file filename
938 Retain only the symbols listed in the file filename, discarding all
939 others. filename is simply a flat file, with one symbol name per
940 line. This option is especially useful in environments (such as
941 VxWorks) where a large global symbol table is accumulated gradu‐
942 ally, to conserve run-time memory.
943 --retain-symbols-file does not discard undefined symbols, or sym‐
945 bols needed for relocations.
946 You may only specify --retain-symbols-file once in the command
948 line. It overrides -s and -S.
949 -rpath dir
951 Add a directory to the runtime library search path. This is used
952 when linking an ELF executable with shared objects. All -rpath
953 arguments are concatenated and passed to the runtime linker, which
954 uses them to locate shared objects at runtime. The -rpath option
955 is also used when locating shared objects which are needed by
956 shared objects explicitly included in the link; see the description
957 of the -rpath-link option. If -rpath is not used when linking an
958 ELF executable, the contents of the environment variable
959 "LD_RUN_PATH" will be used if it is defined.
960 The -rpath option may also be used on SunOS. By default, on SunOS,
962 the linker will form a runtime search patch out of all the -L
963 options it is given. If a -rpath option is used, the runtime
964 search path will be formed exclusively using the -rpath options,
965 ignoring the -L options. This can be useful when using gcc, which
966 adds many -L options which may be on NFS mounted filesystems.
967 For compatibility with other ELF linkers, if the -R option is fol‐
969 lowed by a directory name, rather than a file name, it is treated
970 as the -rpath option.
971 -rpath-link DIR
973 When using ELF or SunOS, one shared library may require another.
974 This happens when an "ld -shared" link includes a shared library as
975 one of the input files.
976 When the linker encounters such a dependency when doing a
978 non-shared, non-relocatable link, it will automatically try to
979 locate the required shared library and include it in the link, if
980 it is not included explicitly. In such a case, the -rpath-link
981 option specifies the first set of directories to search. The
982 -rpath-link option may specify a sequence of directory names either
983 by specifying a list of names separated by colons, or by appearing
984 multiple times.
985 This option should be used with caution as it overrides the search
987 path that may have been hard compiled into a shared library. In
988 such a case it is possible to use unintentionally a different
989 search path than the runtime linker would do.
990 The linker uses the following search paths to locate required
992 shared libraries.
993 1. Any directories specified by -rpath-link options.
995 2. Any directories specified by -rpath options. The difference
997 between -rpath and -rpath-link is that directories specified by
998 -rpath options are included in the executable and used at run‐
999 time, whereas the -rpath-link option is only effective at link
1000 time. It is for the native linker only.
1001 3. On an ELF system, if the -rpath and "rpath-link" options were
1003 not used, search the contents of the environment variable
1004 "LD_RUN_PATH". It is for the native linker only.
1005 4. On SunOS, if the -rpath option was not used, search any direc‐
1007 tories specified using -L options.
1008 5. For a native linker, the contents of the environment variable
1010 "LD_LIBRARY_PATH".
1011 6. For a native ELF linker, the directories in "DT_RUNPATH" or
1013 "DT_RPATH" of a shared library are searched for shared
1014 libraries needed by it. The "DT_RPATH" entries are ignored if
1015 "DT_RUNPATH" entries exist.
1016 7. The default directories, normally /lib and /usr/lib.
1018 8. For a native linker on an ELF system, if the file
1020 /etc/ld.so.conf exists, the list of directories found in that
1021 file.
1022 If the required shared library is not found, the linker will issue
1024 a warning and continue with the link.
1025 -shared
1027 -Bshareable
1028 Create a shared library. This is currently only supported on ELF,
1029 XCOFF and SunOS platforms. On SunOS, the linker will automatically
1030 create a shared library if the -e option is not used and there are
1031 undefined symbols in the link.
1032 --sort-common
1034 This option tells ld to sort the common symbols by size when it
1035 places them in the appropriate output sections. First come all the
1036 one byte symbols, then all the two byte, then all the four byte,
1037 and then everything else. This is to prevent gaps between symbols
1038 due to alignment constraints.
1039 --sort-section name
1041 This option will apply "SORT_BY_NAME" to all wildcard section pat‐
1042 terns in the linker script.
1043 --sort-section alignment
1045 This option will apply "SORT_BY_ALIGNMENT" to all wildcard section
1046 patterns in the linker script.
1047 --split-by-file [size]
1049 Similar to --split-by-reloc but creates a new output section for
1050 each input file when size is reached. size defaults to a size of 1
1051 if not given.
1052 --split-by-reloc [count]
1054 Tries to creates extra sections in the output file so that no sin‐
1055 gle output section in the file contains more than count reloca‐
1056 tions. This is useful when generating huge relocatable files for
1057 downloading into certain real time kernels with the COFF object
1058 file format; since COFF cannot represent more than 65535 reloca‐
1059 tions in a single section. Note that this will fail to work with
1060 object file formats which do not support arbitrary sections. The
1061 linker will not split up individual input sections for redistribu‐
1062 tion, so if a single input section contains more than count reloca‐
1063 tions one output section will contain that many relocations. count
1064 defaults to a value of 32768.
1065 --stats
1067 Compute and display statistics about the operation of the linker,
1068 such as execution time and memory usage.
1069 --sysroot=directory
1071 Use directory as the location of the sysroot, overriding the con‐
1072 figure-time default. This option is only supported by linkers that
1073 were configured using --with-sysroot.
1074 --traditional-format
1076 For some targets, the output of ld is different in some ways from
1077 the output of some existing linker. This switch requests ld to use
1078 the traditional format instead.
1079 For example, on SunOS, ld combines duplicate entries in the symbol
1081 string table. This can reduce the size of an output file with full
1082 debugging information by over 30 percent. Unfortunately, the SunOS
1083 "dbx" program can not read the resulting program ("gdb" has no
1084 trouble). The --traditional-format switch tells ld to not combine
1085 duplicate entries.
1086 --section-start sectionname=org
1088 Locate a section in the output file at the absolute address given
1089 by org. You may use this option as many times as necessary to
1090 locate multiple sections in the command line. org must be a single
1091 hexadecimal integer; for compatibility with other linkers, you may
1092 omit the leading 0x usually associated with hexadecimal values.
1093 Note: there should be no white space between sectionname, the
1094 equals sign ("="), and org.
1095 -Tbss org
1097 -Tdata org
1098 -Ttext org
1099 Same as --section-start, with ".bss", ".data" or ".text" as the
1100 sectionname.
1101 --unresolved-symbols=method
1103 Determine how to handle unresolved symbols. There are four possi‐
1104 ble values for method:
1105 ignore-all
1107 Do not report any unresolved symbols.
1108 report-all
1110 Report all unresolved symbols. This is the default.
1111 ignore-in-object-files
1113 Report unresolved symbols that are contained in shared
1114 libraries, but ignore them if they come from regular object
1115 files.
1116 ignore-in-shared-libs
1118 Report unresolved symbols that come from regular object files,
1119 but ignore them if they come from shared libraries. This can
1120 be useful when creating a dynamic binary and it is known that
1121 all the shared libraries that it should be referencing are
1122 included on the linker's command line.
1123 The behaviour for shared libraries on their own can also be con‐
1125 trolled by the --[no-]allow-shlib-undefined option.
1126 Normally the linker will generate an error message for each
1128 reported unresolved symbol but the option --warn-unresolved-symbols
1129 can change this to a warning.
1130 --dll-verbose
1132 --verbose
1133 Display the version number for ld and list the linker emulations
1134 supported. Display which input files can and cannot be opened.
1135 Display the linker script being used by the linker.
1136 --version-script=version-scriptfile
1138 Specify the name of a version script to the linker. This is typi‐
1139 cally used when creating shared libraries to specify additional
1140 information about the version hierarchy for the library being cre‐
1141 ated. This option is only meaningful on ELF platforms which sup‐
1142 port shared libraries.
1143 --warn-common
1145 Warn when a common symbol is combined with another common symbol or
1146 with a symbol definition. Unix linkers allow this somewhat sloppy
1147 practise, but linkers on some other operating systems do not. This
1148 option allows you to find potential problems from combining global
1149 symbols. Unfortunately, some C libraries use this practise, so you
1150 may get some warnings about symbols in the libraries as well as in
1151 your programs.
1152 There are three kinds of global symbols, illustrated here by C
1154 examples:
1155 int i = 1;
1157 A definition, which goes in the initialized data section of the
1158 output file.
1159 extern int i;
1161 An undefined reference, which does not allocate space. There
1162 must be either a definition or a common symbol for the variable
1163 somewhere.
1164 int i;
1166 A common symbol. If there are only (one or more) common sym‐
1167 bols for a variable, it goes in the uninitialized data area of
1168 the output file. The linker merges multiple common symbols for
1169 the same variable into a single symbol. If they are of differ‐
1170 ent sizes, it picks the largest size. The linker turns a com‐
1171 mon symbol into a declaration, if there is a definition of the
1172 same variable.
1173 The --warn-common option can produce five kinds of warnings. Each
1175 warning consists of a pair of lines: the first describes the symbol
1176 just encountered, and the second describes the previous symbol
1177 encountered with the same name. One or both of the two symbols
1178 will be a common symbol.
1179 1. Turning a common symbol into a reference, because there is
1181 already a definition for the symbol.
1182 <file>(<section>): warning: common of `<symbol>'
1184 overridden by definition
1185 <file>(<section>): warning: defined here
1186 2. Turning a common symbol into a reference, because a later defi‐
1188 nition for the symbol is encountered. This is the same as the
1189 previous case, except that the symbols are encountered in a
1190 different order.
1191 <file>(<section>): warning: definition of `<symbol>'
1193 overriding common
1194 <file>(<section>): warning: common is here
1195 3. Merging a common symbol with a previous same-sized common sym‐
1197 bol.
1198 <file>(<section>): warning: multiple common
1200 of `<symbol>'
1201 <file>(<section>): warning: previous common is here
1202 4. Merging a common symbol with a previous larger common symbol.
1204 <file>(<section>): warning: common of `<symbol>'
1206 overridden by larger common
1207 <file>(<section>): warning: larger common is here
1208 5. Merging a common symbol with a previous smaller common symbol.
1210 This is the same as the previous case, except that the symbols
1211 are encountered in a different order.
1212 <file>(<section>): warning: common of `<symbol>'
1214 overriding smaller common
1215 <file>(<section>): warning: smaller common is here
1216 --warn-constructors
1218 Warn if any global constructors are used. This is only useful for
1219 a few object file formats. For formats like COFF or ELF, the
1220 linker can not detect the use of global constructors.
1221 --warn-multiple-gp
1223 Warn if multiple global pointer values are required in the output
1224 file. This is only meaningful for certain processors, such as the
1225 Alpha. Specifically, some processors put large-valued constants in
1226 a special section. A special register (the global pointer) points
1227 into the middle of this section, so that constants can be loaded
1228 efficiently via a base-register relative addressing mode. Since
1229 the offset in base-register relative mode is fixed and relatively
1230 small (e.g., 16 bits), this limits the maximum size of the constant
1231 pool. Thus, in large programs, it is often necessary to use multi‐
1232 ple global pointer values in order to be able to address all possi‐
1233 ble constants. This option causes a warning to be issued whenever
1234 this case occurs.
1235 --warn-once
1237 Only warn once for each undefined symbol, rather than once per mod‐
1238 ule which refers to it.
1239 --warn-section-align
1241 Warn if the address of an output section is changed because of
1242 alignment. Typically, the alignment will be set by an input sec‐
1243 tion. The address will only be changed if it not explicitly speci‐
1244 fied; that is, if the "SECTIONS" command does not specify a start
1245 address for the section.
1246 --warn-shared-textrel
1248 Warn if the linker adds a DT_TEXTREL to a shared object.
1249 --warn-unresolved-symbols
1251 If the linker is going to report an unresolved symbol (see the
1252 option --unresolved-symbols) it will normally generate an error.
1253 This option makes it generate a warning instead.
1254 --error-unresolved-symbols
1256 This restores the linker's default behaviour of generating errors
1257 when it is reporting unresolved symbols.
1258 --whole-archive
1260 For each archive mentioned on the command line after the
1261 --whole-archive option, include every object file in the archive in
1262 the link, rather than searching the archive for the required object
1263 files. This is normally used to turn an archive file into a shared
1264 library, forcing every object to be included in the resulting
1265 shared library. This option may be used more than once.
1266 Two notes when using this option from gcc: First, gcc doesn't know
1268 about this option, so you have to use -Wl,-whole-archive. Second,
1269 don't forget to use -Wl,-no-whole-archive after your list of ar‐
1270 chives, because gcc will add its own list of archives to your link
1271 and you may not want this flag to affect those as well.
1272 --wrap symbol
1274 Use a wrapper function for symbol. Any undefined reference to sym‐
1275 bol will be resolved to "__wrap_symbol". Any undefined reference
1276 to "__real_symbol" will be resolved to symbol.
1277 This can be used to provide a wrapper for a system function. The
1279 wrapper function should be called "__wrap_symbol". If it wishes to
1280 call the system function, it should call "__real_symbol".
1281 Here is a trivial example:
1283 void *
1285 __wrap_malloc (size_t c)
1286 {
1287 printf ("malloc called with %zu\n", c);
1288 return __real_malloc (c);
1289 }
1290 If you link other code with this file using --wrap malloc, then all
1292 calls to "malloc" will call the function "__wrap_malloc" instead.
1293 The call to "__real_malloc" in "__wrap_malloc" will call the real
1294 "malloc" function.
1295 You may wish to provide a "__real_malloc" function as well, so that
1297 links without the --wrap option will succeed. If you do this, you
1298 should not put the definition of "__real_malloc" in the same file
1299 as "__wrap_malloc"; if you do, the assembler may resolve the call
1300 before the linker has a chance to wrap it to "malloc".
1301 --eh-frame-hdr
1303 Request creation of ".eh_frame_hdr" section and ELF
1304 "PT_GNU_EH_FRAME" segment header.
1305 --enable-new-dtags
1307 --disable-new-dtags
1308 This linker can create the new dynamic tags in ELF. But the older
1309 ELF systems may not understand them. If you specify
1310 --enable-new-dtags, the dynamic tags will be created as needed. If
1311 you specify --disable-new-dtags, no new dynamic tags will be cre‐
1312 ated. By default, the new dynamic tags are not created. Note that
1313 those options are only available for ELF systems.
1314 --hash-size=number
1316 Set the default size of the linker's hash tables to a prime number
1317 close to number. Increasing this value can reduce the length of
1318 time it takes the linker to perform its tasks, at the expense of
1319 increasing the linker's memory requirements. Similarly reducing
1320 this value can reduce the memory requirements at the expense of
1321 speed.
1322 --reduce-memory-overheads
1324 This option reduces memory requirements at ld runtime, at the
1325 expense of linking speed. This was introduced to select the old
1326 O(n^2) algorithm for link map file generation, rather than the new
1327 O(n) algorithm which uses about 40% more memory for symbol storage.
1328 Another effect of the switch is to set the default hash table size
1330 to 1021, which again saves memory at the cost of lengthening the
1331 linker's run time. This is not done however if the --hash-size
1332 switch has been used.
1333 The --reduce-memory-overheads switch may be also be used to enable
1335 other tradeoffs in future versions of the linker.
1336 The i386 PE linker supports the -shared option, which causes the output
1338 to be a dynamically linked library (DLL) instead of a normal exe‐
1339 cutable. You should name the output "*.dll" when you use this option.
1340 In addition, the linker fully supports the standard "*.def" files,
1341 which may be specified on the linker command line like an object file
1342 (in fact, it should precede archives it exports symbols from, to ensure
1343 that they get linked in, just like a normal object file).
1344 In addition to the options common to all targets, the i386 PE linker
1346 support additional command line options that are specific to the i386
1347 PE target. Options that take values may be separated from their values
1348 by either a space or an equals sign.
1349 --add-stdcall-alias
1351 If given, symbols with a stdcall suffix (@nn) will be exported as-
1352 is and also with the suffix stripped. [This option is specific to
1353 the i386 PE targeted port of the linker]
1354 --base-file file
1356 Use file as the name of a file in which to save the base addresses
1357 of all the relocations needed for generating DLLs with dlltool.
1358 [This is an i386 PE specific option]
1359 --dll
1361 Create a DLL instead of a regular executable. You may also use
1362 -shared or specify a "LIBRARY" in a given ".def" file. [This
1363 option is specific to the i386 PE targeted port of the linker]
1364 --enable-stdcall-fixup
1366 --disable-stdcall-fixup
1367 If the link finds a symbol that it cannot resolve, it will attempt
1368 to do "fuzzy linking" by looking for another defined symbol that
1369 differs only in the format of the symbol name (cdecl vs stdcall)
1370 and will resolve that symbol by linking to the match. For example,
1371 the undefined symbol "_foo" might be linked to the function
1372 "_foo@12", or the undefined symbol "_bar@16" might be linked to the
1373 function "_bar". When the linker does this, it prints a warning,
1374 since it normally should have failed to link, but sometimes import
1375 libraries generated from third-party dlls may need this feature to
1376 be usable. If you specify --enable-stdcall-fixup, this feature is
1377 fully enabled and warnings are not printed. If you specify --dis‐
1378 able-stdcall-fixup, this feature is disabled and such mismatches
1379 are considered to be errors. [This option is specific to the i386
1380 PE targeted port of the linker]
1381 --export-all-symbols
1383 If given, all global symbols in the objects used to build a DLL
1384 will be exported by the DLL. Note that this is the default if
1385 there otherwise wouldn't be any exported symbols. When symbols are
1386 explicitly exported via DEF files or implicitly exported via func‐
1387 tion attributes, the default is to not export anything else unless
1388 this option is given. Note that the symbols "DllMain@12", "DllEn‐
1389 tryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will not be
1390 automatically exported. Also, symbols imported from other DLLs
1391 will not be re-exported, nor will symbols specifying the DLL's
1392 internal layout such as those beginning with "_head_" or ending
1393 with "_iname". In addition, no symbols from "libgcc", "libstd++",
1394 "libmingw32", or "crtX.o" will be exported. Symbols whose names
1395 begin with "__rtti_" or "__builtin_" will not be exported, to help
1396 with C++ DLLs. Finally, there is an extensive list of cygwin-pri‐
1397 vate symbols that are not exported (obviously, this applies on when
1398 building DLLs for cygwin targets). These cygwin-excludes are:
1399 "_cygwin_dll_entry@12", "_cygwin_crt0_common@8", "_cygwin_noncyg‐
1400 win_dll_entry@12", "_fmode", "_impure_ptr", "cygwin_attach_dll",
1401 "cygwin_premain0", "cygwin_premain1", "cygwin_premain2", "cyg‐
1402 win_premain3", and "environ". [This option is specific to the i386
1403 PE targeted port of the linker]
1404 --exclude-symbols symbol,symbol,...
1406 Specifies a list of symbols which should not be automatically
1407 exported. The symbol names may be delimited by commas or colons.
1408 [This option is specific to the i386 PE targeted port of the
1409 linker]
1410 --file-alignment
1412 Specify the file alignment. Sections in the file will always begin
1413 at file offsets which are multiples of this number. This defaults
1414 to 512. [This option is specific to the i386 PE targeted port of
1415 the linker]
1416 --heap reserve
1418 --heap reserve,commit
1419 Specify the amount of memory to reserve (and optionally commit) to
1420 be used as heap for this program. The default is 1Mb reserved, 4K
1421 committed. [This option is specific to the i386 PE targeted port
1422 of the linker]
1423 --image-base value
1425 Use value as the base address of your program or dll. This is the
1426 lowest memory location that will be used when your program or dll
1427 is loaded. To reduce the need to relocate and improve performance
1428 of your dlls, each should have a unique base address and not over‐
1429 lap any other dlls. The default is 0x400000 for executables, and
1430 0x10000000 for dlls. [This option is specific to the i386 PE tar‐
1431 geted port of the linker]
1432 --kill-at
1434 If given, the stdcall suffixes (@nn) will be stripped from symbols
1435 before they are exported. [This option is specific to the i386 PE
1436 targeted port of the linker]
1437 --large-address-aware
1439 If given, the appropriate bit in the "Charateristics" field of the
1440 COFF header is set to indicate that this executable supports vir‐
1441 tual addresses greater than 2 gigabytes. This should be used in
1442 conjuction with the /3GB or /USERVA=value megabytes switch in the
1443 "[operating systems]" section of the BOOT.INI. Otherwise, this bit
1444 has no effect. [This option is specific to PE targeted ports of
1445 the linker]
1446 --major-image-version value
1448 Sets the major number of the "image version". Defaults to 1.
1449 [This option is specific to the i386 PE targeted port of the
1450 linker]
1451 --major-os-version value
1453 Sets the major number of the "os version". Defaults to 4. [This
1454 option is specific to the i386 PE targeted port of the linker]
1455 --major-subsystem-version value
1457 Sets the major number of the "subsystem version". Defaults to 4.
1458 [This option is specific to the i386 PE targeted port of the
1459 linker]
1460 --minor-image-version value
1462 Sets the minor number of the "image version". Defaults to 0.
1463 [This option is specific to the i386 PE targeted port of the
1464 linker]
1465 --minor-os-version value
1467 Sets the minor number of the "os version". Defaults to 0. [This
1468 option is specific to the i386 PE targeted port of the linker]
1469 --minor-subsystem-version value
1471 Sets the minor number of the "subsystem version". Defaults to 0.
1472 [This option is specific to the i386 PE targeted port of the
1473 linker]
1474 --output-def file
1476 The linker will create the file file which will contain a DEF file
1477 corresponding to the DLL the linker is generating. This DEF file
1478 (which should be called "*.def") may be used to create an import
1479 library with "dlltool" or may be used as a reference to automati‐
1480 cally or implicitly exported symbols. [This option is specific to
1481 the i386 PE targeted port of the linker]
1482 --out-implib file
1484 The linker will create the file file which will contain an import
1485 lib corresponding to the DLL the linker is generating. This import
1486 lib (which should be called "*.dll.a" or "*.a" may be used to link
1487 clients against the generated DLL; this behaviour makes it possible
1488 to skip a separate "dlltool" import library creation step. [This
1489 option is specific to the i386 PE targeted port of the linker]
1490 --enable-auto-image-base
1492 Automatically choose the image base for DLLs, unless one is speci‐
1493 fied using the "--image-base" argument. By using a hash generated
1494 from the dllname to create unique image bases for each DLL, in-mem‐
1495 ory collisions and relocations which can delay program execution
1496 are avoided. [This option is specific to the i386 PE targeted port
1497 of the linker]
1498 --disable-auto-image-base
1500 Do not automatically generate a unique image base. If there is no
1501 user-specified image base ("--image-base") then use the platform
1502 default. [This option is specific to the i386 PE targeted port of
1503 the linker]
1504 --dll-search-prefix string
1506 When linking dynamically to a dll without an import library, search
1507 for "<string><basename>.dll" in preference to "lib<basename>.dll".
1508 This behaviour allows easy distinction between DLLs built for the
1509 various "subplatforms": native, cygwin, uwin, pw, etc. For
1510 instance, cygwin DLLs typically use "--dll-search-prefix=cyg".
1511 [This option is specific to the i386 PE targeted port of the
1512 linker]
1513 --enable-auto-import
1515 Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA
1516 imports from DLLs, and create the necessary thunking symbols when
1517 building the import libraries with those DATA exports. Note: Use of
1518 the 'auto-import' extension will cause the text section of the
1519 image file to be made writable. This does not conform to the PE-
1520 COFF format specification published by Microsoft.
1521 Using 'auto-import' generally will 'just work' -- but sometimes you
1523 may see this message:
1524 "variable '<var>' can't be auto-imported. Please read the documen‐
1526 tation for ld's "--enable-auto-import" for details."
1527 This message occurs when some (sub)expression accesses an address
1529 ultimately given by the sum of two constants (Win32 import tables
1530 only allow one). Instances where this may occur include accesses
1531 to member fields of struct variables imported from a DLL, as well
1532 as using a constant index into an array variable imported from a
1533 DLL. Any multiword variable (arrays, structs, long long, etc) may
1534 trigger this error condition. However, regardless of the exact
1535 data type of the offending exported variable, ld will always detect
1536 it, issue the warning, and exit.
1537 There are several ways to address this difficulty, regardless of
1539 the data type of the exported variable:
1540 One way is to use --enable-runtime-pseudo-reloc switch. This leaves
1542 the task of adjusting references in your client code for runtime
1543 environment, so this method works only when runtime environment
1544 supports this feature.
1545 A second solution is to force one of the 'constants' to be a vari‐
1547 able -- that is, unknown and un-optimizable at compile time. For
1548 arrays, there are two possibilities: a) make the indexee (the
1549 array's address) a variable, or b) make the 'constant' index a
1550 variable. Thus:
1551 extern type extern_array[];
1553 extern_array[1] -->
1554 { volatile type *t=extern_array; t[1] }
1555 or
1557 extern type extern_array[];
1559 extern_array[1] -->
1560 { volatile int t=1; extern_array[t] }
1561 For structs (and most other multiword data types) the only option
1563 is to make the struct itself (or the long long, or the ...) vari‐
1564 able:
1565 extern struct s extern_struct;
1567 extern_struct.field -->
1568 { volatile struct s *t=&extern_struct; t->field }
1569 or
1571 extern long long extern_ll;
1573 extern_ll -->
1574 { volatile long long * local_ll=&extern_ll; *local_ll }
1575 A third method of dealing with this difficulty is to abandon
1577 'auto-import' for the offending symbol and mark it with
1578 "__declspec(dllimport)". However, in practise that requires using
1579 compile-time #defines to indicate whether you are building a DLL,
1580 building client code that will link to the DLL, or merely build‐
1581 ing/linking to a static library. In making the choice between the
1582 various methods of resolving the 'direct address with constant off‐
1583 set' problem, you should consider typical real-world usage:
1584 Original:
1586 --foo.h
1588 extern int arr[];
1589 --foo.c
1590 #include "foo.h"
1591 void main(int argc, char **argv){
1592 printf("%d\n",arr[1]);
1593 }
1594 Solution 1:
1596 --foo.h
1598 extern int arr[];
1599 --foo.c
1600 #include "foo.h"
1601 void main(int argc, char **argv){
1602 /* This workaround is for win32 and cygwin; do not "optimize" */
1603 volatile int *parr = arr;
1604 printf("%d\n",parr[1]);
1605 }
1606 Solution 2:
1608 --foo.h
1610 /* Note: auto-export is assumed (no __declspec(dllexport)) */
1611 #if (defined(_WIN32) || defined(__CYGWIN__)) && \
1612 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
1613 #define FOO_IMPORT __declspec(dllimport)
1614 #else
1615 #define FOO_IMPORT
1616 #endif
1617 extern FOO_IMPORT int arr[];
1618 --foo.c
1619 #include "foo.h"
1620 void main(int argc, char **argv){
1621 printf("%d\n",arr[1]);
1622 }
1623 A fourth way to avoid this problem is to re-code your library to
1625 use a functional interface rather than a data interface for the
1626 offending variables (e.g. set_foo() and get_foo() accessor func‐
1627 tions). [This option is specific to the i386 PE targeted port of
1628 the linker]
1629 --disable-auto-import
1631 Do not attempt to do sophisticated linking of "_symbol" to
1632 "__imp__symbol" for DATA imports from DLLs. [This option is spe‐
1633 cific to the i386 PE targeted port of the linker]
1634 --enable-runtime-pseudo-reloc
1636 If your code contains expressions described in --enable-auto-import
1637 section, that is, DATA imports from DLL with non-zero offset, this
1638 switch will create a vector of 'runtime pseudo relocations' which
1639 can be used by runtime environment to adjust references to such
1640 data in your client code. [This option is specific to the i386 PE
1641 targeted port of the linker]
1642 --disable-runtime-pseudo-reloc
1644 Do not create pseudo relocations for non-zero offset DATA imports
1645 from DLLs. This is the default. [This option is specific to the
1646 i386 PE targeted port of the linker]
1647 --enable-extra-pe-debug
1649 Show additional debug info related to auto-import symbol thunking.
1650 [This option is specific to the i386 PE targeted port of the
1651 linker]
1652 --section-alignment
1654 Sets the section alignment. Sections in memory will always begin
1655 at addresses which are a multiple of this number. Defaults to
1656 0x1000. [This option is specific to the i386 PE targeted port of
1657 the linker]
1658 --stack reserve
1660 --stack reserve,commit
1661 Specify the amount of memory to reserve (and optionally commit) to
1662 be used as stack for this program. The default is 2Mb reserved, 4K
1663 committed. [This option is specific to the i386 PE targeted port
1664 of the linker]
1665 --subsystem which
1667 --subsystem which:major
1668 --subsystem which:major.minor
1669 Specifies the subsystem under which your program will execute. The
1670 legal values for which are "native", "windows", "console", "posix",
1671 and "xbox". You may optionally set the subsystem version also.
1672 Numeric values are also accepted for which. [This option is spe‐
1673 cific to the i386 PE targeted port of the linker]
1674 The 68HC11 and 68HC12 linkers support specific options to control the
1676 memory bank switching mapping and trampoline code generation.
1677 --no-trampoline
1679 This option disables the generation of trampoline. By default a
1680 trampoline is generated for each far function which is called using
1681 a "jsr" instruction (this happens when a pointer to a far function
1682 is taken).
1683 --bank-window name
1685 This option indicates to the linker the name of the memory region
1686 in the MEMORY specification that describes the memory bank window.
1687 The definition of such region is then used by the linker to compute
1688 paging and addresses within the memory window.
1689
1691 You can change the behaviour of ld with the environment variables "GNU‐
1692 TARGET", "LDEMULATION" and "COLLECT_NO_DEMANGLE".
1693 "GNUTARGET" determines the input-file object format if you don't use -b
1695 (or its synonym --format). Its value should be one of the BFD names
1696 for an input format. If there is no "GNUTARGET" in the environment, ld
1697 uses the natural format of the target. If "GNUTARGET" is set to
1698 "default" then BFD attempts to discover the input format by examining
1699 binary input files; this method often succeeds, but there are potential
1700 ambiguities, since there is no method of ensuring that the magic number
1701 used to specify object-file formats is unique. However, the configura‐
1702 tion procedure for BFD on each system places the conventional format
1703 for that system first in the search-list, so ambiguities are resolved
1704 in favor of convention.
1705 "LDEMULATION" determines the default emulation if you don't use the -m
1707 option. The emulation can affect various aspects of linker behaviour,
1708 particularly the default linker script. You can list the available
1709 emulations with the --verbose or -V options. If the -m option is not
1710 used, and the "LDEMULATION" environment variable is not defined, the
1711 default emulation depends upon how the linker was configured.
1712 Normally, the linker will default to demangling symbols. However, if
1714 "COLLECT_NO_DEMANGLE" is set in the environment, then it will default
1715 to not demangling symbols. This environment variable is used in a sim‐
1716 ilar fashion by the "gcc" linker wrapper program. The default may be
1717 overridden by the --demangle and --no-demangle options.
1718
1720 ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries
1721 for binutils and ld.
1722
1724 Copyright (c) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
1725 2003, 2004 Free Software Foundation, Inc.
1726 Permission is granted to copy, distribute and/or modify this document
1728 under the terms of the GNU Free Documentation License, Version 1.1 or
1729 any later version published by the Free Software Foundation; with no
1730 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
1731 Texts. A copy of the license is included in the section entitled "GNU
1732 Free Documentation License".
1733binutils-2.17 2006-06-23 LD(1)