1LD(1) GNU Development Tools LD(1)
2
6 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" for full details on the command language and on other aspects
22 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
32 execution 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
44 standard, 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
62 descriptions 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
66 command-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
72 specified, the linker does not produce any output, and issues the
73 message No 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
77 augments 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. Specifying a script in this
82 way merely augments the main linker script, with the extra commands
83 placed after the main script; use the -T option to replace the default
84 linker script entirely, but note the effect of the "INSERT" command.
85 For options whose names are a single letter, option arguments must
87 either follow the option letter without intervening whitespace, or be
88 given as separate arguments immediately following the option that
89 requires them.
90 For options whose names are multiple letters, either one dash or two
92 can precede the option name; for example, -trace-symbol and
93 --trace-symbol are equivalent. Note---there is one exception to this
94 rule. Multiple letter options that start with a lower case 'o' can
95 only be preceded by two dashes. This is to reduce confusion with the
96 -o option. So for example -omagic sets the output file name to magic
97 whereas --omagic sets the NMAGIC flag on the output.
98 Arguments to multiple-letter options must either be separated from the
100 option name by an equals sign, or be given as separate arguments
101 immediately following the option that requires them. For example,
102 --trace-symbol foo and --trace-symbol=foo are equivalent. Unique
103 abbreviations of the names of multiple-letter options are accepted.
104 Note---if the linker is being invoked indirectly, via a compiler driver
106 (e.g. gcc) then all the linker command line options should be prefixed
107 by -Wl, (or whatever is appropriate for the particular compiler driver)
108 like this:
109 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
111 This is important, because otherwise the compiler driver program may
113 silently drop the linker options, resulting in a bad link. Confusion
114 may also arise when passing options that require values through a
115 driver, as the use of a space between option and argument acts as a
116 separator, and causes the driver to pass only the option to the linker
117 and the argument to the compiler. In this case, it is simplest to use
118 the joined forms of both single- and multiple-letter options, such as:
119 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
121 Here is a table of the generic command line switches accepted by the
123 GNU linker:
124 @file
126 Read command-line options from file. The options read are inserted
127 in place of the original @file option. If file does not exist, or
128 cannot be read, then the option will be treated literally, and not
129 removed.
130 Options in file are separated by whitespace. A whitespace
132 character may be included in an option by surrounding the entire
133 option in either single or double quotes. Any character (including
134 a backslash) may be included by prefixing the character to be
135 included with a backslash. The file may itself contain additional
136 @file options; any such options will be processed recursively.
137 -a keyword
139 This option is supported for HP/UX compatibility. The keyword
140 argument must be one of the strings archive, shared, or default.
141 -aarchive is functionally equivalent to -Bstatic, and the other two
142 keywords are functionally equivalent to -Bdynamic. This option may
143 be used any number of times.
144 --audit AUDITLIB
146 Adds AUDITLIB to the "DT_AUDIT" entry of the dynamic section.
147 AUDITLIB is not checked for existence, nor will it use the
148 DT_SONAME specified in the library. If specified multiple times
149 "DT_AUDIT" will contain a colon separated list of audit interfaces
150 to use. If the linker finds an object with an audit entry while
151 searching for shared libraries, it will add a corresponding
152 "DT_DEPAUDIT" entry in the output file. This option is only
153 meaningful on ELF platforms supporting the rtld-audit interface.
154 -A architecture
156 --architecture=architecture
157 In the current release of ld, this option is useful only for the
158 Intel 960 family of architectures. In that ld configuration, the
159 architecture argument identifies the particular architecture in the
160 960 family, enabling some safeguards and modifying the archive-
161 library search path.
162 Future releases of ld may support similar functionality for other
164 architecture families.
165 -b input-format
167 --format=input-format
168 ld may be configured to support more than one kind of object file.
169 If your ld is configured this way, you can use the -b option to
170 specify the binary format for input object files that follow this
171 option on the command line. Even when ld is configured to support
172 alternative object formats, you don't usually need to specify this,
173 as ld should be configured to expect as a default input format the
174 most usual format on each machine. input-format is a text string,
175 the name of a particular format supported by the BFD libraries.
176 (You can list the available binary formats with objdump -i.)
177 You may want to use this option if you are linking files with an
179 unusual binary format. You can also use -b to switch formats
180 explicitly (when linking object files of different formats), by
181 including -b input-format before each group of object files in a
182 particular format.
183 The default format is taken from the environment variable
185 "GNUTARGET".
186 You can also define the input format from a script, using the
188 command "TARGET";
189 -c MRI-commandfile
191 --mri-script=MRI-commandfile
192 For compatibility with linkers produced by MRI, ld accepts script
193 files written in an alternate, restricted command language,
194 described in the MRI Compatible Script Files section of GNU ld
195 documentation. Introduce MRI script files with the option -c; use
196 the -T option to run linker scripts written in the general-purpose
197 ld scripting language. If MRI-cmdfile does not exist, ld looks for
198 it in the directories specified by any -L options.
199 -d
201 -dc
202 -dp These three options are equivalent; multiple forms are supported
203 for compatibility with other linkers. They assign space to common
204 symbols even if a relocatable output file is specified (with -r).
205 The script command "FORCE_COMMON_ALLOCATION" has the same effect.
206 --depaudit AUDITLIB
208 -P AUDITLIB
209 Adds AUDITLIB to the "DT_DEPAUDIT" entry of the dynamic section.
210 AUDITLIB is not checked for existence, nor will it use the
211 DT_SONAME specified in the library. If specified multiple times
212 "DT_DEPAUDIT" will contain a colon separated list of audit
213 interfaces to use. This option is only meaningful on ELF platforms
214 supporting the rtld-audit interface. The -P option is provided for
215 Solaris compatibility.
216 -e entry
218 --entry=entry
219 Use entry as the explicit symbol for beginning execution of your
220 program, rather than the default entry point. If there is no
221 symbol named entry, the linker will try to parse entry as a number,
222 and use that as the entry address (the number will be interpreted
223 in base 10; you may use a leading 0x for base 16, or a leading 0
224 for base 8).
225 --exclude-libs lib,lib,...
227 Specifies a list of archive libraries from which symbols should not
228 be automatically exported. The library names may be delimited by
229 commas or colons. Specifying "--exclude-libs ALL" excludes symbols
230 in all archive libraries from automatic export. This option is
231 available only for the i386 PE targeted port of the linker and for
232 ELF targeted ports. For i386 PE, symbols explicitly listed in a
233 .def file are still exported, regardless of this option. For ELF
234 targeted ports, symbols affected by this option will be treated as
235 hidden.
236 --exclude-modules-for-implib module,module,...
238 Specifies a list of object files or archive members, from which
239 symbols should not be automatically exported, but which should be
240 copied wholesale into the import library being generated during the
241 link. The module names may be delimited by commas or colons, and
242 must match exactly the filenames used by ld to open the files; for
243 archive members, this is simply the member name, but for object
244 files the name listed must include and match precisely any path
245 used to specify the input file on the linker's command-line. This
246 option is available only for the i386 PE targeted port of the
247 linker. Symbols explicitly listed in a .def file are still
248 exported, regardless of this option.
249 -E
251 --export-dynamic
252 --no-export-dynamic
253 When creating a dynamically linked executable, using the -E option
254 or the --export-dynamic option causes the linker to add all symbols
255 to the dynamic symbol table. The dynamic symbol table is the set
256 of symbols which are visible from dynamic objects at run time.
257 If you do not use either of these options (or use the
259 --no-export-dynamic option to restore the default behavior), the
260 dynamic symbol table will normally contain only those symbols which
261 are referenced by some dynamic object mentioned in the link.
262 If you use "dlopen" to load a dynamic object which needs to refer
264 back to the symbols defined by the program, rather than some other
265 dynamic object, then you will probably need to use this option when
266 linking the program itself.
267 You can also use the dynamic list to control what symbols should be
269 added to the dynamic symbol table if the output format supports it.
270 See the description of --dynamic-list.
271 Note that this option is specific to ELF targeted ports. PE
273 targets support a similar function to export all symbols from a DLL
274 or EXE; see the description of --export-all-symbols below.
275 -EB Link big-endian objects. This affects the default output format.
277 -EL Link little-endian objects. This affects the default output
279 format.
280 -f name
282 --auxiliary=name
283 When creating an ELF shared object, set the internal DT_AUXILIARY
284 field to the specified name. This tells the dynamic linker that
285 the symbol table of the shared object should be used as an
286 auxiliary filter on the symbol table of the shared object name.
287 If you later link a program against this filter object, then, when
289 you run the program, the dynamic linker will see the DT_AUXILIARY
290 field. If the dynamic linker resolves any symbols from the filter
291 object, it will first check whether there is a definition in the
292 shared object name. If there is one, it will be used instead of
293 the definition in the filter object. The shared object name need
294 not exist. Thus the shared object name may be used to provide an
295 alternative implementation of certain functions, perhaps for
296 debugging or for machine specific performance.
297 This option may be specified more than once. The DT_AUXILIARY
299 entries will be created in the order in which they appear on the
300 command line.
301 -F name
303 --filter=name
304 When creating an ELF shared object, set the internal DT_FILTER
305 field to the specified name. This tells the dynamic linker that
306 the symbol table of the shared object which is being created should
307 be used as a filter on the symbol table of the shared object name.
308 If you later link a program against this filter object, then, when
310 you run the program, the dynamic linker will see the DT_FILTER
311 field. The dynamic linker will resolve symbols according to the
312 symbol table of the filter object as usual, but it will actually
313 link to the definitions found in the shared object name. Thus the
314 filter object can be used to select a subset of the symbols
315 provided by the object name.
316 Some older linkers used the -F option throughout a compilation
318 toolchain for specifying object-file format for both input and
319 output object files. The GNU linker uses other mechanisms for this
320 purpose: the -b, --format, --oformat options, the "TARGET" command
321 in linker scripts, and the "GNUTARGET" environment variable. The
322 GNU linker will ignore the -F option when not creating an ELF
323 shared object.
324 -fini=name
326 When creating an ELF executable or shared object, call NAME when
327 the executable or shared object is unloaded, by setting DT_FINI to
328 the address of the function. By default, the linker uses "_fini"
329 as the function to call.
330 -g Ignored. Provided for compatibility with other tools.
332 -G value
334 --gpsize=value
335 Set the maximum size of objects to be optimized using the GP
336 register to size. This is only meaningful for object file formats
337 such as MIPS ELF that support putting large and small objects into
338 different sections. This is ignored for other object file formats.
339 -h name
341 -soname=name
342 When creating an ELF shared object, set the internal DT_SONAME
343 field to the specified name. When an executable is linked with a
344 shared object which has a DT_SONAME field, then when the executable
345 is run the dynamic linker will attempt to load the shared object
346 specified by the DT_SONAME field rather than the using the file
347 name given to the linker.
348 -i Perform an incremental link (same as option -r).
350 -init=name
352 When creating an ELF executable or shared object, call NAME when
353 the executable or shared object is loaded, by setting DT_INIT to
354 the address of the function. By default, the linker uses "_init"
355 as the function to call.
356 -l namespec
358 --library=namespec
359 Add the archive or object file specified by namespec to the list of
360 files to link. This option may be used any number of times. If
361 namespec is of the form :filename, ld will search the library path
362 for a file called filename, otherwise it will search the library
363 path for a file called libnamespec.a.
364 On systems which support shared libraries, ld may also search for
366 files other than libnamespec.a. Specifically, on ELF and SunOS
367 systems, ld will search a directory for a library called
368 libnamespec.so before searching for one called libnamespec.a. (By
369 convention, a ".so" extension indicates a shared library.) Note
370 that this behavior does not apply to :filename, which always
371 specifies a file called filename.
372 The linker will search an archive only once, at the location where
374 it is specified on the command line. If the archive defines a
375 symbol which was undefined in some object which appeared before the
376 archive on the command line, the linker will include the
377 appropriate file(s) from the archive. However, an undefined symbol
378 in an object appearing later on the command line will not cause the
379 linker to search the archive again.
380 See the -( option for a way to force the linker to search archives
382 multiple times.
383 You may list the same archive multiple times on the command line.
385 This type of archive searching is standard for Unix linkers.
387 However, if you are using ld on AIX, note that it is different from
388 the behaviour of the AIX linker.
389 -L searchdir
391 --library-path=searchdir
392 Add path searchdir to the list of paths that ld will search for
393 archive libraries and ld control scripts. You may use this option
394 any number of times. The directories are searched in the order in
395 which they are specified on the command line. Directories
396 specified on the command line are searched before the default
397 directories. All -L options apply to all -l options, regardless of
398 the order in which the options appear. -L options do not affect
399 how ld searches for a linker script unless -T option is specified.
400 If searchdir begins with "=", then the "=" will be replaced by the
402 sysroot prefix, controlled by the --sysroot option, or specified
403 when the linker is configured.
404 The default set of paths searched (without being specified with -L)
406 depends on which emulation mode ld is using, and in some cases also
407 on how it was configured.
408 The paths can also be specified in a link script with the
410 "SEARCH_DIR" command. Directories specified this way are searched
411 at the point in which the linker script appears in the command
412 line.
413 -m emulation
415 Emulate the emulation linker. You can list the available
416 emulations with the --verbose or -V options.
417 If the -m option is not used, the emulation is taken from the
419 "LDEMULATION" environment variable, if that is defined.
420 Otherwise, the default emulation depends upon how the linker was
422 configured.
423 -M
425 --print-map
426 Print a link map to the standard output. A link map provides
427 information about the link, including the following:
428 · Where object files are mapped into memory.
430 · How common symbols are allocated.
432 · All archive members included in the link, with a mention of the
434 symbol which caused the archive member to be brought in.
435 · The values assigned to symbols.
437 Note - symbols whose values are computed by an expression which
439 involves a reference to a previous value of the same symbol may
440 not have correct result displayed in the link map. This is
441 because the linker discards intermediate results and only
442 retains the final value of an expression. Under such
443 circumstances the linker will display the final value enclosed
444 by square brackets. Thus for example a linker script
445 containing:
446 foo = 1
448 foo = foo * 4
449 foo = foo + 8
450 will produce the following output in the link map if the -M
452 option is used:
453 0x00000001 foo = 0x1
455 [0x0000000c] foo = (foo * 0x4)
456 [0x0000000c] foo = (foo + 0x8)
457 See Expressions for more information about expressions in
459 linker scripts.
460 -n
462 --nmagic
463 Turn off page alignment of sections, and disable linking against
464 shared libraries. If the output format supports Unix style magic
465 numbers, mark the output as "NMAGIC".
466 -N
468 --omagic
469 Set the text and data sections to be readable and writable. Also,
470 do not page-align the data segment, and disable linking against
471 shared libraries. If the output format supports Unix style magic
472 numbers, mark the output as "OMAGIC". Note: Although a writable
473 text section is allowed for PE-COFF targets, it does not conform to
474 the format specification published by Microsoft.
475 --no-omagic
477 This option negates most of the effects of the -N option. It sets
478 the text section to be read-only, and forces the data segment to be
479 page-aligned. Note - this option does not enable linking against
480 shared libraries. Use -Bdynamic for this.
481 -o output
483 --output=output
484 Use output as the name for the program produced by ld; if this
485 option is not specified, the name a.out is used by default. The
486 script command "OUTPUT" can also specify the output file name.
487 -O level
489 If level is a numeric values greater than zero ld optimizes the
490 output. This might take significantly longer and therefore
491 probably should only be enabled for the final binary. At the
492 moment this option only affects ELF shared library generation.
493 Future releases of the linker may make more use of this option.
494 Also currently there is no difference in the linker's behaviour for
495 different non-zero values of this option. Again this may change
496 with future releases.
497 --push-state
499 The --push-state allows to preserve the current state of the flags
500 which govern the input file handling so that they can all be
501 restored with one corresponding --pop-state option.
502 The option which are covered are: -Bdynamic, -Bstatic, -dn, -dy,
504 -call_shared, -non_shared, -static, -N, -n, --whole-archive,
505 --no-whole-archive, -r, -Ur, --copy-dt-needed-entries,
506 --no-copy-dt-needed-entries, --as-needed, --no-as-needed, and -a.
507 One target for this option are specifications for pkg-config. When
509 used with the --libs option all possibly needed libraries are
510 listed and then possibly linked with all the time. It is better to
511 return something as follows:
512 -Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
514 Undoes the effect of --push-state, restores the previous values of
516 the flags governing input file handling.
517 -q
519 --emit-relocs
520 Leave relocation sections and contents in fully linked executables.
521 Post link analysis and optimization tools may need this information
522 in order to perform correct modifications of executables. This
523 results in larger executables.
524 This option is currently only supported on ELF platforms.
526 --force-dynamic
528 Force the output file to have dynamic sections. This option is
529 specific to VxWorks targets.
530 -r
532 --relocatable
533 Generate relocatable output---i.e., generate an output file that
534 can in turn serve as input to ld. This is often called partial
535 linking. As a side effect, in environments that support standard
536 Unix magic numbers, this option also sets the output file's magic
537 number to "OMAGIC". If this option is not specified, an absolute
538 file is produced. When linking C++ programs, this option will not
539 resolve references to constructors; to do that, use -Ur.
540 When an input file does not have the same format as the output
542 file, partial linking is only supported if that input file does not
543 contain any relocations. Different output formats can have further
544 restrictions; for example some "a.out"-based formats do not support
545 partial linking with input files in other formats at all.
546 This option does the same thing as -i.
548 -R filename
550 --just-symbols=filename
551 Read symbol names and their addresses from filename, but do not
552 relocate it or include it in the output. This allows your output
553 file to refer symbolically to absolute locations of memory defined
554 in other programs. You may use this option more than once.
555 For compatibility with other ELF linkers, if the -R option is
557 followed by a directory name, rather than a file name, it is
558 treated as the -rpath option.
559 -s
561 --strip-all
562 Omit all symbol information from the output file.
563 -S
565 --strip-debug
566 Omit debugger symbol information (but not all symbols) from the
567 output file.
568 -t
570 --trace
571 Print the names of the input files as ld processes them.
572 -T scriptfile
574 --script=scriptfile
575 Use scriptfile as the linker script. This script replaces ld's
576 default linker script (rather than adding to it), so commandfile
577 must specify everything necessary to describe the output file.
578 If scriptfile does not exist in the current directory, "ld" looks
579 for it in the directories specified by any preceding -L options.
580 Multiple -T options accumulate.
581 -dT scriptfile
583 --default-script=scriptfile
584 Use scriptfile as the default linker script.
585 This option is similar to the --script option except that
587 processing of the script is delayed until after the rest of the
588 command line has been processed. This allows options placed after
589 the --default-script option on the command line to affect the
590 behaviour of the linker script, which can be important when the
591 linker command line cannot be directly controlled by the user. (eg
592 because the command line is being constructed by another tool, such
593 as gcc).
594 -u symbol
596 --undefined=symbol
597 Force symbol to be entered in the output file as an undefined
598 symbol. Doing this may, for example, trigger linking of additional
599 modules from standard libraries. -u may be repeated with different
600 option arguments to enter additional undefined symbols. This
601 option is equivalent to the "EXTERN" linker script command.
602 If this option is being used to force additional modules to be
604 pulled into the link, and if it is an error for the symbol to
605 remain undefined, then the option --require-defined should be used
606 instead.
607 --require-defined=symbol
609 Require that symbol is defined in the output file. This option is
610 the same as option --undefined except that if symbol is not defined
611 in the output file then the linker will issue an error and exit.
612 The same effect can be achieved in a linker script by using
613 "EXTERN", "ASSERT" and "DEFINED" together. This option can be used
614 multiple times to require additional symbols.
615 -Ur For anything other than C++ programs, this option is equivalent to
617 -r: it generates relocatable output---i.e., an output file that can
618 in turn serve as input to ld. When linking C++ programs, -Ur does
619 resolve references to constructors, unlike -r. It does not work to
620 use -Ur on files that were themselves linked with -Ur; once the
621 constructor table has been built, it cannot be added to. Use -Ur
622 only for the last partial link, and -r for the others.
623 --orphan-handling=MODE
625 Control how orphan sections are handled. An orphan section is one
626 not specifically mentioned in a linker script.
627 MODE can have any of the following values:
629 "place"
631 Orphan sections are placed into a suitable output section
632 following the strategy described in Orphan Sections. The
633 option --unique also effects how sections are placed.
634 "discard"
636 All orphan sections are discarded, by placing them in the
637 /DISCARD/ section.
638 "warn"
640 The linker will place the orphan section as for "place" and
641 also issue a warning.
642 "error"
644 The linker will exit with an error if any orphan section is
645 found.
646 The default if --orphan-handling is not given is "place".
648 --unique[=SECTION]
650 Creates a separate output section for every input section matching
651 SECTION, or if the optional wildcard SECTION argument is missing,
652 for every orphan input section. An orphan section is one not
653 specifically mentioned in a linker script. You may use this option
654 multiple times on the command line; It prevents the normal merging
655 of input sections with the same name, overriding output section
656 assignments in a linker script.
657 -v
659 --version
660 -V Display the version number for ld. The -V option also lists the
661 supported emulations.
662 -x
664 --discard-all
665 Delete all local symbols.
666 -X
668 --discard-locals
669 Delete all temporary local symbols. (These symbols start with
670 system-specific local label prefixes, typically .L for ELF systems
671 or L for traditional a.out systems.)
672 -y symbol
674 --trace-symbol=symbol
675 Print the name of each linked file in which symbol appears. This
676 option may be given any number of times. On many systems it is
677 necessary to prepend an underscore.
678 This option is useful when you have an undefined symbol in your
680 link but don't know where the reference is coming from.
681 -Y path
683 Add path to the default library search path. This option exists
684 for Solaris compatibility.
685 -z keyword
687 The recognized keywords are:
688 combreloc
690 Combines multiple reloc sections and sorts them to make dynamic
691 symbol lookup caching possible.
692 common
694 Generate common symbols with the STT_COMMON type druing a
695 relocatable link.
696 defs
698 Disallows undefined symbols in object files. Undefined symbols
699 in shared libraries are still allowed.
700 execstack
702 Marks the object as requiring executable stack.
703 global
705 This option is only meaningful when building a shared object.
706 It makes the symbols defined by this shared object available
707 for symbol resolution of subsequently loaded libraries.
708 globalaudit
710 This option is only meaningful when building a dynamic
711 executable. This option marks the executable as requiring
712 global auditing by setting the "DF_1_GLOBAUDIT" bit in the
713 "DT_FLAGS_1" dynamic tag. Global auditing requires that any
714 auditing library defined via the --depaudit or -P command line
715 options be run for all dynamic objects loaded by the
716 application.
717 initfirst
719 This option is only meaningful when building a shared object.
720 It marks the object so that its runtime initialization will
721 occur before the runtime initialization of any other objects
722 brought into the process at the same time. Similarly the
723 runtime finalization of the object will occur after the runtime
724 finalization of any other objects.
725 interpose
727 Marks the object that its symbol table interposes before all
728 symbols but the primary executable.
729 lazy
731 When generating an executable or shared library, mark it to
732 tell the dynamic linker to defer function call resolution to
733 the point when the function is called (lazy binding), rather
734 than at load time. Lazy binding is the default.
735 loadfltr
737 Marks the object that its filters be processed immediately at
738 runtime.
739 muldefs
741 Allows multiple definitions.
742 nocombreloc
744 Disables multiple reloc sections combining.
745 nocommon
747 Generate common symbols with the STT_OBJECT type druing a
748 relocatable link.
749 nocopyreloc
751 Disable linker generated .dynbss variables used in place of
752 variables defined in shared libraries. May result in dynamic
753 text relocations.
754 nodefaultlib
756 Marks the object that the search for dependencies of this
757 object will ignore any default library search paths.
758 nodelete
760 Marks the object shouldn't be unloaded at runtime.
761 nodlopen
763 Marks the object not available to "dlopen".
764 nodump
766 Marks the object can not be dumped by "dldump".
767 noexecstack
769 Marks the object as not requiring executable stack.
770 text
772 Treat DT_TEXTREL in shared object as error.
773 notext
775 Don't treat DT_TEXTREL in shared object as error.
776 textoff
778 Don't treat DT_TEXTREL in shared object as error.
779 norelro
781 Don't create an ELF "PT_GNU_RELRO" segment header in the
782 object.
783 now When generating an executable or shared library, mark it to
785 tell the dynamic linker to resolve all symbols when the program
786 is started, or when the shared library is linked to using
787 dlopen, instead of deferring function call resolution to the
788 point when the function is first called.
789 origin
791 Marks the object may contain $ORIGIN.
792 relro
794 Create an ELF "PT_GNU_RELRO" segment header in the object.
795 max-page-size=value
797 Set the emulation maximum page size to value.
798 common-page-size=value
800 Set the emulation common page size to value.
801 stack-size=value
803 Specify a stack size for in an ELF "PT_GNU_STACK" segment.
804 Specifying zero will override any default non-zero sized
805 "PT_GNU_STACK" segment creation.
806 bndplt
808 Always generate BND prefix in PLT entries. Supported for
809 Linux/x86_64.
810 noextern-protected-data
812 Don't treat protected data symbol as external when building
813 shared library. This option overrides linker backend default.
814 It can be used to workaround incorrect relocations against
815 protected data symbols generated by compiler. Updates on
816 protected data symbols by another module aren't visible to the
817 resulting shared library. Supported for i386 and x86-64.
818 nodynamic-undefined-weak
820 Don't treat undefined weak symbols as dynamic when building
821 executable. This option overrides linker backend default. It
822 can be used to avoid dynamic relocations against undefined weak
823 symbols in executable. Supported for i386 and x86-64.
824 noreloc-overflow
826 Disable relocation overflow check. This can be used to disable
827 relocation overflow check if there will be no dynamic
828 relocation overflow at run-time. Supported for x86_64.
829 call-nop=prefix-addr
831 call-nop=prefix-nop
832 call-nop=suffix-nop
833 call-nop=prefix-byte
834 call-nop=suffix-byte
835 Specify the 1-byte "NOP" padding when transforming indirect
836 call to a locally defined function, foo, via its GOT slot.
837 call-nop=prefix-addr generates "0x67 call foo".
838 call-nop=prefix-nop generates "0x90 call foo".
839 call-nop=suffix-nop generates "call foo 0x90".
840 call-nop=prefix-byte generates "byte call foo".
841 call-nop=suffix-byte generates "call foo byte". Supported for
842 i386 and x86_64.
843 Other keywords are ignored for Solaris compatibility.
845 -( archives -)
847 --start-group archives --end-group
848 The archives should be a list of archive files. They may be either
849 explicit file names, or -l options.
850 The specified archives are searched repeatedly until no new
852 undefined references are created. Normally, an archive is searched
853 only once in the order that it is specified on the command line.
854 If a symbol in that archive is needed to resolve an undefined
855 symbol referred to by an object in an archive that appears later on
856 the command line, the linker would not be able to resolve that
857 reference. By grouping the archives, they all be searched
858 repeatedly until all possible references are resolved.
859 Using this option has a significant performance cost. It is best
861 to use it only when there are unavoidable circular references
862 between two or more archives.
863 --accept-unknown-input-arch
865 --no-accept-unknown-input-arch
866 Tells the linker to accept input files whose architecture cannot be
867 recognised. The assumption is that the user knows what they are
868 doing and deliberately wants to link in these unknown input files.
869 This was the default behaviour of the linker, before release 2.14.
870 The default behaviour from release 2.14 onwards is to reject such
871 input files, and so the --accept-unknown-input-arch option has been
872 added to restore the old behaviour.
873 --as-needed
875 --no-as-needed
876 This option affects ELF DT_NEEDED tags for dynamic libraries
877 mentioned on the command line after the --as-needed option.
878 Normally the linker will add a DT_NEEDED tag for each dynamic
879 library mentioned on the command line, regardless of whether the
880 library is actually needed or not. --as-needed causes a DT_NEEDED
881 tag to only be emitted for a library that at that point in the link
882 satisfies a non-weak undefined symbol reference from a regular
883 object file or, if the library is not found in the DT_NEEDED lists
884 of other needed libraries, a non-weak undefined symbol reference
885 from another needed dynamic library. Object files or libraries
886 appearing on the command line after the library in question do not
887 affect whether the library is seen as needed. This is similar to
888 the rules for extraction of object files from archives.
889 --no-as-needed restores the default behaviour.
890 --add-needed
892 --no-add-needed
893 These two options have been deprecated because of the similarity of
894 their names to the --as-needed and --no-as-needed options. They
895 have been replaced by --copy-dt-needed-entries and
896 --no-copy-dt-needed-entries.
897 -assert keyword
899 This option is ignored for SunOS compatibility.
900 -Bdynamic
902 -dy
903 -call_shared
904 Link against dynamic libraries. This is only meaningful on
905 platforms for which shared libraries are supported. This option is
906 normally the default on such platforms. The different variants of
907 this option are for compatibility with various systems. You may
908 use this option multiple times on the command line: it affects
909 library searching for -l options which follow it.
910 -Bgroup
912 Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the dynamic
913 section. This causes the runtime linker to handle lookups in this
914 object and its dependencies to be performed only inside the group.
915 --unresolved-symbols=report-all is implied. This option is only
916 meaningful on ELF platforms which support shared libraries.
917 -Bstatic
919 -dn
920 -non_shared
921 -static
922 Do not link against shared libraries. This is only meaningful on
923 platforms for which shared libraries are supported. The different
924 variants of this option are for compatibility with various systems.
925 You may use this option multiple times on the command line: it
926 affects library searching for -l options which follow it. This
927 option also implies --unresolved-symbols=report-all. This option
928 can be used with -shared. Doing so means that a shared library is
929 being created but that all of the library's external references
930 must be resolved by pulling in entries from static libraries.
931 -Bsymbolic
933 When creating a shared library, bind references to global symbols
934 to the definition within the shared library, if any. Normally, it
935 is possible for a program linked against a shared library to
936 override the definition within the shared library. This option can
937 also be used with the --export-dynamic option, when creating a
938 position independent executable, to bind references to global
939 symbols to the definition within the executable. This option is
940 only meaningful on ELF platforms which support shared libraries and
941 position independent executables.
942 -Bsymbolic-functions
944 When creating a shared library, bind references to global function
945 symbols to the definition within the shared library, if any. This
946 option can also be used with the --export-dynamic option, when
947 creating a position independent executable, to bind references to
948 global function symbols to the definition within the executable.
949 This option is only meaningful on ELF platforms which support
950 shared libraries and position independent executables.
951 --dynamic-list=dynamic-list-file
953 Specify the name of a dynamic list file to the linker. This is
954 typically used when creating shared libraries to specify a list of
955 global symbols whose references shouldn't be bound to the
956 definition within the shared library, or creating dynamically
957 linked executables to specify a list of symbols which should be
958 added to the symbol table in the executable. This option is only
959 meaningful on ELF platforms which support shared libraries.
960 The format of the dynamic list is the same as the version node
962 without scope and node name. See VERSION for more information.
963 --dynamic-list-data
965 Include all global data symbols to the dynamic list.
966 --dynamic-list-cpp-new
968 Provide the builtin dynamic list for C++ operator new and delete.
969 It is mainly useful for building shared libstdc++.
970 --dynamic-list-cpp-typeinfo
972 Provide the builtin dynamic list for C++ runtime type
973 identification.
974 --check-sections
976 --no-check-sections
977 Asks the linker not to check section addresses after they have been
978 assigned to see if there are any overlaps. Normally the linker
979 will perform this check, and if it finds any overlaps it will
980 produce suitable error messages. The linker does know about, and
981 does make allowances for sections in overlays. The default
982 behaviour can be restored by using the command line switch
983 --check-sections. Section overlap is not usually checked for
984 relocatable links. You can force checking in that case by using
985 the --check-sections option.
986 --copy-dt-needed-entries
988 --no-copy-dt-needed-entries
989 This option affects the treatment of dynamic libraries referred to
990 by DT_NEEDED tags inside ELF dynamic libraries mentioned on the
991 command line. Normally the linker won't add a DT_NEEDED tag to the
992 output binary for each library mentioned in a DT_NEEDED tag in an
993 input dynamic library. With --copy-dt-needed-entries specified on
994 the command line however any dynamic libraries that follow it will
995 have their DT_NEEDED entries added. The default behaviour can be
996 restored with --no-copy-dt-needed-entries.
997 This option also has an effect on the resolution of symbols in
999 dynamic libraries. With --copy-dt-needed-entries dynamic libraries
1000 mentioned on the command line will be recursively searched,
1001 following their DT_NEEDED tags to other libraries, in order to
1002 resolve symbols required by the output binary. With the default
1003 setting however the searching of dynamic libraries that follow it
1004 will stop with the dynamic library itself. No DT_NEEDED links will
1005 be traversed to resolve symbols.
1006 --cref
1008 Output a cross reference table. If a linker map file is being
1009 generated, the cross reference table is printed to the map file.
1010 Otherwise, it is printed on the standard output.
1011 The format of the table is intentionally simple, so that it may be
1013 easily processed by a script if necessary. The symbols are printed
1014 out, sorted by name. For each symbol, a list of file names is
1015 given. If the symbol is defined, the first file listed is the
1016 location of the definition. If the symbol is defined as a common
1017 value then any files where this happens appear next. Finally any
1018 files that reference the symbol are listed.
1019 --no-define-common
1021 This option inhibits the assignment of addresses to common symbols.
1022 The script command "INHIBIT_COMMON_ALLOCATION" has the same effect.
1023 The --no-define-common option allows decoupling the decision to
1025 assign addresses to Common symbols from the choice of the output
1026 file type; otherwise a non-Relocatable output type forces assigning
1027 addresses to Common symbols. Using --no-define-common allows
1028 Common symbols that are referenced from a shared library to be
1029 assigned addresses only in the main program. This eliminates the
1030 unused duplicate space in the shared library, and also prevents any
1031 possible confusion over resolving to the wrong duplicate when there
1032 are many dynamic modules with specialized search paths for runtime
1033 symbol resolution.
1034 --defsym=symbol=expression
1036 Create a global symbol in the output file, containing the absolute
1037 address given by expression. You may use this option as many times
1038 as necessary to define multiple symbols in the command line. A
1039 limited form of arithmetic is supported for the expression in this
1040 context: you may give a hexadecimal constant or the name of an
1041 existing symbol, or use "+" and "-" to add or subtract hexadecimal
1042 constants or symbols. If you need more elaborate expressions,
1043 consider using the linker command language from a script. Note:
1044 there should be no white space between symbol, the equals sign
1045 ("="), and expression.
1046 --demangle[=style]
1048 --no-demangle
1049 These options control whether to demangle symbol names in error
1050 messages and other output. When the linker is told to demangle, it
1051 tries to present symbol names in a readable fashion: it strips
1052 leading underscores if they are used by the object file format, and
1053 converts C++ mangled symbol names into user readable names.
1054 Different compilers have different mangling styles. The optional
1055 demangling style argument can be used to choose an appropriate
1056 demangling style for your compiler. The linker will demangle by
1057 default unless the environment variable COLLECT_NO_DEMANGLE is set.
1058 These options may be used to override the default.
1059 -Ifile
1061 --dynamic-linker=file
1062 Set the name of the dynamic linker. This is only meaningful when
1063 generating dynamically linked ELF executables. The default dynamic
1064 linker is normally correct; don't use this unless you know what you
1065 are doing.
1066 --no-dynamic-linker
1068 When producing an executable file, omit the request for a dynamic
1069 linker to be used at load-time. This is only meaningful for ELF
1070 executables that contain dynamic relocations, and usually requires
1071 entry point code that is capable of processing these relocations.
1072 --fatal-warnings
1074 --no-fatal-warnings
1075 Treat all warnings as errors. The default behaviour can be
1076 restored with the option --no-fatal-warnings.
1077 --force-exe-suffix
1079 Make sure that an output file has a .exe suffix.
1080 If a successfully built fully linked output file does not have a
1082 ".exe" or ".dll" suffix, this option forces the linker to copy the
1083 output file to one of the same name with a ".exe" suffix. This
1084 option is useful when using unmodified Unix makefiles on a
1085 Microsoft Windows host, since some versions of Windows won't run an
1086 image unless it ends in a ".exe" suffix.
1087 --gc-sections
1089 --no-gc-sections
1090 Enable garbage collection of unused input sections. It is ignored
1091 on targets that do not support this option. The default behaviour
1092 (of not performing this garbage collection) can be restored by
1093 specifying --no-gc-sections on the command line. Note that garbage
1094 collection for COFF and PE format targets is supported, but the
1095 implementation is currently considered to be experimental.
1096 --gc-sections decides which input sections are used by examining
1098 symbols and relocations. The section containing the entry symbol
1099 and all sections containing symbols undefined on the command-line
1100 will be kept, as will sections containing symbols referenced by
1101 dynamic objects. Note that when building shared libraries, the
1102 linker must assume that any visible symbol is referenced. Once
1103 this initial set of sections has been determined, the linker
1104 recursively marks as used any section referenced by their
1105 relocations. See --entry and --undefined.
1106 This option can be set when doing a partial link (enabled with
1108 option -r). In this case the root of symbols kept must be
1109 explicitly specified either by an --entry or --undefined option or
1110 by a "ENTRY" command in the linker script.
1111 --print-gc-sections
1113 --no-print-gc-sections
1114 List all sections removed by garbage collection. The listing is
1115 printed on stderr. This option is only effective if garbage
1116 collection has been enabled via the --gc-sections) option. The
1117 default behaviour (of not listing the sections that are removed)
1118 can be restored by specifying --no-print-gc-sections on the command
1119 line.
1120 --print-output-format
1122 Print the name of the default output format (perhaps influenced by
1123 other command-line options). This is the string that would appear
1124 in an "OUTPUT_FORMAT" linker script command.
1125 --print-memory-usage
1127 Print used size, total size and used size of memory regions created
1128 with the MEMORY command. This is useful on embedded targets to
1129 have a quick view of amount of free memory. The format of the
1130 output has one headline and one line per region. It is both human
1131 readable and easily parsable by tools. Here is an example of an
1132 output:
1133 Memory region Used Size Region Size %age Used
1135 ROM: 256 KB 1 MB 25.00%
1136 RAM: 32 B 2 GB 0.00%
1137 --help
1139 Print a summary of the command-line options on the standard output
1140 and exit.
1141 --target-help
1143 Print a summary of all target specific options on the standard
1144 output and exit.
1145 -Map=mapfile
1147 Print a link map to the file mapfile. See the description of the
1148 -M option, above.
1149 --no-keep-memory
1151 ld normally optimizes for speed over memory usage by caching the
1152 symbol tables of input files in memory. This option tells ld to
1153 instead optimize for memory usage, by rereading the symbol tables
1154 as necessary. This may be required if ld runs out of memory space
1155 while linking a large executable.
1156 --no-undefined
1158 -z defs
1159 Report unresolved symbol references from regular object files.
1160 This is done even if the linker is creating a non-symbolic shared
1161 library. The switch --[no-]allow-shlib-undefined controls the
1162 behaviour for reporting unresolved references found in shared
1163 libraries being linked in.
1164 --allow-multiple-definition
1166 -z muldefs
1167 Normally when a symbol is defined multiple times, the linker will
1168 report a fatal error. These options allow multiple definitions and
1169 the first definition will be used.
1170 --allow-shlib-undefined
1172 --no-allow-shlib-undefined
1173 Allows or disallows undefined symbols in shared libraries. This
1174 switch is similar to --no-undefined except that it determines the
1175 behaviour when the undefined symbols are in a shared library rather
1176 than a regular object file. It does not affect how undefined
1177 symbols in regular object files are handled.
1178 The default behaviour is to report errors for any undefined symbols
1180 referenced in shared libraries if the linker is being used to
1181 create an executable, but to allow them if the linker is being used
1182 to create a shared library.
1183 The reasons for allowing undefined symbol references in shared
1185 libraries specified at link time are that:
1186 · A shared library specified at link time may not be the same as
1188 the one that is available at load time, so the symbol might
1189 actually be resolvable at load time.
1190 · There are some operating systems, eg BeOS and HPPA, where
1192 undefined symbols in shared libraries are normal.
1193 The BeOS kernel for example patches shared libraries at load
1195 time to select whichever function is most appropriate for the
1196 current architecture. This is used, for example, to
1197 dynamically select an appropriate memset function.
1198 --no-undefined-version
1200 Normally when a symbol has an undefined version, the linker will
1201 ignore it. This option disallows symbols with undefined version and
1202 a fatal error will be issued instead.
1203 --default-symver
1205 Create and use a default symbol version (the soname) for
1206 unversioned exported symbols.
1207 --default-imported-symver
1209 Create and use a default symbol version (the soname) for
1210 unversioned imported symbols.
1211 --no-warn-mismatch
1213 Normally ld will give an error if you try to link together input
1214 files that are mismatched for some reason, perhaps because they
1215 have been compiled for different processors or for different
1216 endiannesses. This option tells ld that it should silently permit
1217 such possible errors. This option should only be used with care,
1218 in cases when you have taken some special action that ensures that
1219 the linker errors are inappropriate.
1220 --no-warn-search-mismatch
1222 Normally ld will give a warning if it finds an incompatible library
1223 during a library search. This option silences the warning.
1224 --no-whole-archive
1226 Turn off the effect of the --whole-archive option for subsequent
1227 archive files.
1228 --noinhibit-exec
1230 Retain the executable output file whenever it is still usable.
1231 Normally, the linker will not produce an output file if it
1232 encounters errors during the link process; it exits without writing
1233 an output file when it issues any error whatsoever.
1234 -nostdlib
1236 Only search library directories explicitly specified on the command
1237 line. Library directories specified in linker scripts (including
1238 linker scripts specified on the command line) are ignored.
1239 --oformat=output-format
1241 ld may be configured to support more than one kind of object file.
1242 If your ld is configured this way, you can use the --oformat option
1243 to specify the binary format for the output object file. Even when
1244 ld is configured to support alternative object formats, you don't
1245 usually need to specify this, as ld should be configured to produce
1246 as a default output format the most usual format on each machine.
1247 output-format is a text string, the name of a particular format
1248 supported by the BFD libraries. (You can list the available binary
1249 formats with objdump -i.) The script command "OUTPUT_FORMAT" can
1250 also specify the output format, but this option overrides it.
1251 -pie
1253 --pic-executable
1254 Create a position independent executable. This is currently only
1255 supported on ELF platforms. Position independent executables are
1256 similar to shared libraries in that they are relocated by the
1257 dynamic linker to the virtual address the OS chooses for them
1258 (which can vary between invocations). Like normal dynamically
1259 linked executables they can be executed and symbols defined in the
1260 executable cannot be overridden by shared libraries.
1261 -qmagic
1263 This option is ignored for Linux compatibility.
1264 -Qy This option is ignored for SVR4 compatibility.
1266 --relax
1268 --no-relax
1269 An option with machine dependent effects. This option is only
1270 supported on a few targets.
1271 On some platforms the --relax option performs target specific,
1273 global optimizations that become possible when the linker resolves
1274 addressing in the program, such as relaxing address modes,
1275 synthesizing new instructions, selecting shorter version of current
1276 instructions, and combining constant values.
1277 On some platforms these link time global optimizations may make
1279 symbolic debugging of the resulting executable impossible. This is
1280 known to be the case for the Matsushita MN10200 and MN10300 family
1281 of processors.
1282 On platforms where this is not supported, --relax is accepted, but
1284 ignored.
1285 On platforms where --relax is accepted the option --no-relax can be
1287 used to disable the feature.
1288 --retain-symbols-file=filename
1290 Retain only the symbols listed in the file filename, discarding all
1291 others. filename is simply a flat file, with one symbol name per
1292 line. This option is especially useful in environments (such as
1293 VxWorks) where a large global symbol table is accumulated
1294 gradually, to conserve run-time memory.
1295 --retain-symbols-file does not discard undefined symbols, or
1297 symbols needed for relocations.
1298 You may only specify --retain-symbols-file once in the command
1300 line. It overrides -s and -S.
1301 -rpath=dir
1303 Add a directory to the runtime library search path. This is used
1304 when linking an ELF executable with shared objects. All -rpath
1305 arguments are concatenated and passed to the runtime linker, which
1306 uses them to locate shared objects at runtime. The -rpath option
1307 is also used when locating shared objects which are needed by
1308 shared objects explicitly included in the link; see the description
1309 of the -rpath-link option. If -rpath is not used when linking an
1310 ELF executable, the contents of the environment variable
1311 "LD_RUN_PATH" will be used if it is defined.
1312 The -rpath option may also be used on SunOS. By default, on SunOS,
1314 the linker will form a runtime search path out of all the -L
1315 options it is given. If a -rpath option is used, the runtime
1316 search path will be formed exclusively using the -rpath options,
1317 ignoring the -L options. This can be useful when using gcc, which
1318 adds many -L options which may be on NFS mounted file systems.
1319 For compatibility with other ELF linkers, if the -R option is
1321 followed by a directory name, rather than a file name, it is
1322 treated as the -rpath option.
1323 -rpath-link=dir
1325 When using ELF or SunOS, one shared library may require another.
1326 This happens when an "ld -shared" link includes a shared library as
1327 one of the input files.
1328 When the linker encounters such a dependency when doing a non-
1330 shared, non-relocatable link, it will automatically try to locate
1331 the required shared library and include it in the link, if it is
1332 not included explicitly. In such a case, the -rpath-link option
1333 specifies the first set of directories to search. The -rpath-link
1334 option may specify a sequence of directory names either by
1335 specifying a list of names separated by colons, or by appearing
1336 multiple times.
1337 This option should be used with caution as it overrides the search
1339 path that may have been hard compiled into a shared library. In
1340 such a case it is possible to use unintentionally a different
1341 search path than the runtime linker would do.
1342 The linker uses the following search paths to locate required
1344 shared libraries:
1345 1. Any directories specified by -rpath-link options.
1347 2. Any directories specified by -rpath options. The difference
1349 between -rpath and -rpath-link is that directories specified by
1350 -rpath options are included in the executable and used at
1351 runtime, whereas the -rpath-link option is only effective at
1352 link time. Searching -rpath in this way is only supported by
1353 native linkers and cross linkers which have been configured
1354 with the --with-sysroot option.
1355 3. On an ELF system, for native linkers, if the -rpath and
1357 -rpath-link options were not used, search the contents of the
1358 environment variable "LD_RUN_PATH".
1359 4. On SunOS, if the -rpath option was not used, search any
1361 directories specified using -L options.
1362 5. For a native linker, search the contents of the environment
1364 variable "LD_LIBRARY_PATH".
1365 6. For a native ELF linker, the directories in "DT_RUNPATH" or
1367 "DT_RPATH" of a shared library are searched for shared
1368 libraries needed by it. The "DT_RPATH" entries are ignored if
1369 "DT_RUNPATH" entries exist.
1370 7. The default directories, normally /lib and /usr/lib.
1372 8. For a native linker on an ELF system, if the file
1374 /etc/ld.so.conf exists, the list of directories found in that
1375 file.
1376 If the required shared library is not found, the linker will issue
1378 a warning and continue with the link.
1379 -shared
1381 -Bshareable
1382 Create a shared library. This is currently only supported on ELF,
1383 XCOFF and SunOS platforms. On SunOS, the linker will automatically
1384 create a shared library if the -e option is not used and there are
1385 undefined symbols in the link.
1386 --sort-common
1388 --sort-common=ascending
1389 --sort-common=descending
1390 This option tells ld to sort the common symbols by alignment in
1391 ascending or descending order when it places them in the
1392 appropriate output sections. The symbol alignments considered are
1393 sixteen-byte or larger, eight-byte, four-byte, two-byte, and one-
1394 byte. This is to prevent gaps between symbols due to alignment
1395 constraints. If no sorting order is specified, then descending
1396 order is assumed.
1397 --sort-section=name
1399 This option will apply "SORT_BY_NAME" to all wildcard section
1400 patterns in the linker script.
1401 --sort-section=alignment
1403 This option will apply "SORT_BY_ALIGNMENT" to all wildcard section
1404 patterns in the linker script.
1405 --split-by-file[=size]
1407 Similar to --split-by-reloc but creates a new output section for
1408 each input file when size is reached. size defaults to a size of 1
1409 if not given.
1410 --split-by-reloc[=count]
1412 Tries to creates extra sections in the output file so that no
1413 single output section in the file contains more than count
1414 relocations. This is useful when generating huge relocatable files
1415 for downloading into certain real time kernels with the COFF object
1416 file format; since COFF cannot represent more than 65535
1417 relocations in a single section. Note that this will fail to work
1418 with object file formats which do not support arbitrary sections.
1419 The linker will not split up individual input sections for
1420 redistribution, so if a single input section contains more than
1421 count relocations one output section will contain that many
1422 relocations. count defaults to a value of 32768.
1423 --stats
1425 Compute and display statistics about the operation of the linker,
1426 such as execution time and memory usage.
1427 --sysroot=directory
1429 Use directory as the location of the sysroot, overriding the
1430 configure-time default. This option is only supported by linkers
1431 that were configured using --with-sysroot.
1432 --traditional-format
1434 For some targets, the output of ld is different in some ways from
1435 the output of some existing linker. This switch requests ld to use
1436 the traditional format instead.
1437 For example, on SunOS, ld combines duplicate entries in the symbol
1439 string table. This can reduce the size of an output file with full
1440 debugging information by over 30 percent. Unfortunately, the SunOS
1441 "dbx" program can not read the resulting program ("gdb" has no
1442 trouble). The --traditional-format switch tells ld to not combine
1443 duplicate entries.
1444 --section-start=sectionname=org
1446 Locate a section in the output file at the absolute address given
1447 by org. You may use this option as many times as necessary to
1448 locate multiple sections in the command line. org must be a single
1449 hexadecimal integer; for compatibility with other linkers, you may
1450 omit the leading 0x usually associated with hexadecimal values.
1451 Note: there should be no white space between sectionname, the
1452 equals sign ("="), and org.
1453 -Tbss=org
1455 -Tdata=org
1456 -Ttext=org
1457 Same as --section-start, with ".bss", ".data" or ".text" as the
1458 sectionname.
1459 -Ttext-segment=org
1461 When creating an ELF executable, it will set the address of the
1462 first byte of the text segment.
1463 -Trodata-segment=org
1465 When creating an ELF executable or shared object for a target where
1466 the read-only data is in its own segment separate from the
1467 executable text, it will set the address of the first byte of the
1468 read-only data segment.
1469 -Tldata-segment=org
1471 When creating an ELF executable or shared object for x86-64 medium
1472 memory model, it will set the address of the first byte of the
1473 ldata segment.
1474 --unresolved-symbols=method
1476 Determine how to handle unresolved symbols. There are four
1477 possible values for method:
1478 ignore-all
1480 Do not report any unresolved symbols.
1481 report-all
1483 Report all unresolved symbols. This is the default.
1484 ignore-in-object-files
1486 Report unresolved symbols that are contained in shared
1487 libraries, but ignore them if they come from regular object
1488 files.
1489 ignore-in-shared-libs
1491 Report unresolved symbols that come from regular object files,
1492 but ignore them if they come from shared libraries. This can
1493 be useful when creating a dynamic binary and it is known that
1494 all the shared libraries that it should be referencing are
1495 included on the linker's command line.
1496 The behaviour for shared libraries on their own can also be
1498 controlled by the --[no-]allow-shlib-undefined option.
1499 Normally the linker will generate an error message for each
1501 reported unresolved symbol but the option --warn-unresolved-symbols
1502 can change this to a warning.
1503 --dll-verbose
1505 --verbose[=NUMBER]
1506 Display the version number for ld and list the linker emulations
1507 supported. Display which input files can and cannot be opened.
1508 Display the linker script being used by the linker. If the optional
1509 NUMBER argument > 1, plugin symbol status will also be displayed.
1510 --version-script=version-scriptfile
1512 Specify the name of a version script to the linker. This is
1513 typically used when creating shared libraries to specify additional
1514 information about the version hierarchy for the library being
1515 created. This option is only fully supported on ELF platforms
1516 which support shared libraries; see VERSION. It is partially
1517 supported on PE platforms, which can use version scripts to filter
1518 symbol visibility in auto-export mode: any symbols marked local in
1519 the version script will not be exported.
1520 --warn-common
1522 Warn when a common symbol is combined with another common symbol or
1523 with a symbol definition. Unix linkers allow this somewhat sloppy
1524 practice, but linkers on some other operating systems do not. This
1525 option allows you to find potential problems from combining global
1526 symbols. Unfortunately, some C libraries use this practice, so you
1527 may get some warnings about symbols in the libraries as well as in
1528 your programs.
1529 There are three kinds of global symbols, illustrated here by C
1531 examples:
1532 int i = 1;
1534 A definition, which goes in the initialized data section of the
1535 output file.
1536 extern int i;
1538 An undefined reference, which does not allocate space. There
1539 must be either a definition or a common symbol for the variable
1540 somewhere.
1541 int i;
1543 A common symbol. If there are only (one or more) common
1544 symbols for a variable, it goes in the uninitialized data area
1545 of the output file. The linker merges multiple common symbols
1546 for the same variable into a single symbol. If they are of
1547 different sizes, it picks the largest size. The linker turns a
1548 common symbol into a declaration, if there is a definition of
1549 the same variable.
1550 The --warn-common option can produce five kinds of warnings. Each
1552 warning consists of a pair of lines: the first describes the symbol
1553 just encountered, and the second describes the previous symbol
1554 encountered with the same name. One or both of the two symbols
1555 will be a common symbol.
1556 1. Turning a common symbol into a reference, because there is
1558 already a definition for the symbol.
1559 <file>(<section>): warning: common of `<symbol>'
1561 overridden by definition
1562 <file>(<section>): warning: defined here
1563 2. Turning a common symbol into a reference, because a later
1565 definition for the symbol is encountered. This is the same as
1566 the previous case, except that the symbols are encountered in a
1567 different order.
1568 <file>(<section>): warning: definition of `<symbol>'
1570 overriding common
1571 <file>(<section>): warning: common is here
1572 3. Merging a common symbol with a previous same-sized common
1574 symbol.
1575 <file>(<section>): warning: multiple common
1577 of `<symbol>'
1578 <file>(<section>): warning: previous common is here
1579 4. Merging a common symbol with a previous larger common symbol.
1581 <file>(<section>): warning: common of `<symbol>'
1583 overridden by larger common
1584 <file>(<section>): warning: larger common is here
1585 5. Merging a common symbol with a previous smaller common symbol.
1587 This is the same as the previous case, except that the symbols
1588 are encountered in a different order.
1589 <file>(<section>): warning: common of `<symbol>'
1591 overriding smaller common
1592 <file>(<section>): warning: smaller common is here
1593 --warn-constructors
1595 Warn if any global constructors are used. This is only useful for
1596 a few object file formats. For formats like COFF or ELF, the
1597 linker can not detect the use of global constructors.
1598 --warn-multiple-gp
1600 Warn if multiple global pointer values are required in the output
1601 file. This is only meaningful for certain processors, such as the
1602 Alpha. Specifically, some processors put large-valued constants in
1603 a special section. A special register (the global pointer) points
1604 into the middle of this section, so that constants can be loaded
1605 efficiently via a base-register relative addressing mode. Since
1606 the offset in base-register relative mode is fixed and relatively
1607 small (e.g., 16 bits), this limits the maximum size of the constant
1608 pool. Thus, in large programs, it is often necessary to use
1609 multiple global pointer values in order to be able to address all
1610 possible constants. This option causes a warning to be issued
1611 whenever this case occurs.
1612 --warn-once
1614 Only warn once for each undefined symbol, rather than once per
1615 module which refers to it.
1616 --warn-section-align
1618 Warn if the address of an output section is changed because of
1619 alignment. Typically, the alignment will be set by an input
1620 section. The address will only be changed if it not explicitly
1621 specified; that is, if the "SECTIONS" command does not specify a
1622 start address for the section.
1623 --warn-shared-textrel
1625 Warn if the linker adds a DT_TEXTREL to a shared object.
1626 --warn-alternate-em
1628 Warn if an object has alternate ELF machine code.
1629 --warn-unresolved-symbols
1631 If the linker is going to report an unresolved symbol (see the
1632 option --unresolved-symbols) it will normally generate an error.
1633 This option makes it generate a warning instead.
1634 --error-unresolved-symbols
1636 This restores the linker's default behaviour of generating errors
1637 when it is reporting unresolved symbols.
1638 --whole-archive
1640 For each archive mentioned on the command line after the
1641 --whole-archive option, include every object file in the archive in
1642 the link, rather than searching the archive for the required object
1643 files. This is normally used to turn an archive file into a shared
1644 library, forcing every object to be included in the resulting
1645 shared library. This option may be used more than once.
1646 Two notes when using this option from gcc: First, gcc doesn't know
1648 about this option, so you have to use -Wl,-whole-archive. Second,
1649 don't forget to use -Wl,-no-whole-archive after your list of
1650 archives, because gcc will add its own list of archives to your
1651 link and you may not want this flag to affect those as well.
1652 --wrap=symbol
1654 Use a wrapper function for symbol. Any undefined reference to
1655 symbol will be resolved to "__wrap_symbol". Any undefined
1656 reference to "__real_symbol" will be resolved to symbol.
1657 This can be used to provide a wrapper for a system function. The
1659 wrapper function should be called "__wrap_symbol". If it wishes to
1660 call the system function, it should call "__real_symbol".
1661 Here is a trivial example:
1663 void *
1665 __wrap_malloc (size_t c)
1666 {
1667 printf ("malloc called with %zu\n", c);
1668 return __real_malloc (c);
1669 }
1670 If you link other code with this file using --wrap malloc, then all
1672 calls to "malloc" will call the function "__wrap_malloc" instead.
1673 The call to "__real_malloc" in "__wrap_malloc" will call the real
1674 "malloc" function.
1675 You may wish to provide a "__real_malloc" function as well, so that
1677 links without the --wrap option will succeed. If you do this, you
1678 should not put the definition of "__real_malloc" in the same file
1679 as "__wrap_malloc"; if you do, the assembler may resolve the call
1680 before the linker has a chance to wrap it to "malloc".
1681 --eh-frame-hdr
1683 Request creation of ".eh_frame_hdr" section and ELF
1684 "PT_GNU_EH_FRAME" segment header.
1685 --no-ld-generated-unwind-info
1687 Request creation of ".eh_frame" unwind info for linker generated
1688 code sections like PLT. This option is on by default if linker
1689 generated unwind info is supported.
1690 --enable-new-dtags
1692 --disable-new-dtags
1693 This linker can create the new dynamic tags in ELF. But the older
1694 ELF systems may not understand them. If you specify
1695 --enable-new-dtags, the new dynamic tags will be created as needed
1696 and older dynamic tags will be omitted. If you specify
1697 --disable-new-dtags, no new dynamic tags will be created. By
1698 default, the new dynamic tags are not created. Note that those
1699 options are only available for ELF systems.
1700 --hash-size=number
1702 Set the default size of the linker's hash tables to a prime number
1703 close to number. Increasing this value can reduce the length of
1704 time it takes the linker to perform its tasks, at the expense of
1705 increasing the linker's memory requirements. Similarly reducing
1706 this value can reduce the memory requirements at the expense of
1707 speed.
1708 --hash-style=style
1710 Set the type of linker's hash table(s). style can be either "sysv"
1711 for classic ELF ".hash" section, "gnu" for new style GNU
1712 ".gnu.hash" section or "both" for both the classic ELF ".hash" and
1713 new style GNU ".gnu.hash" hash tables. The default is "sysv".
1714 --compress-debug-sections=none
1716 --compress-debug-sections=zlib
1717 --compress-debug-sections=zlib-gnu
1718 --compress-debug-sections=zlib-gabi
1719 On ELF platforms , these options control how DWARF debug sections
1720 are compressed using zlib. --compress-debug-sections=none doesn't
1721 compress DWARF debug sections. --compress-debug-sections=zlib-gnu
1722 compresses DWARF debug sections and rename debug section names to
1723 begin with .zdebug instead of .debug.
1724 --compress-debug-sections=zlib and
1725 --compress-debug-sections=zlib-gabi compress DWARF debug sections
1726 with SHF_COMPRESSED from the ELF ABI. The default behaviour varies
1727 depending upon the target involved and the configure options used
1728 to build the toolchain. The default can be determined by examing
1729 the output from the linker's --help option.
1730 --reduce-memory-overheads
1732 This option reduces memory requirements at ld runtime, at the
1733 expense of linking speed. This was introduced to select the old
1734 O(n^2) algorithm for link map file generation, rather than the new
1735 O(n) algorithm which uses about 40% more memory for symbol storage.
1736 Another effect of the switch is to set the default hash table size
1738 to 1021, which again saves memory at the cost of lengthening the
1739 linker's run time. This is not done however if the --hash-size
1740 switch has been used.
1741 The --reduce-memory-overheads switch may be also be used to enable
1743 other tradeoffs in future versions of the linker.
1744 --build-id
1746 --build-id=style
1747 Request the creation of a ".note.gnu.build-id" ELF note section or
1748 a ".buildid" COFF section. The contents of the note are unique
1749 bits identifying this linked file. style can be "uuid" to use 128
1750 random bits, "sha1" to use a 160-bit SHA1 hash on the normative
1751 parts of the output contents, "md5" to use a 128-bit MD5 hash on
1752 the normative parts of the output contents, or "0xhexstring" to use
1753 a chosen bit string specified as an even number of hexadecimal
1754 digits ("-" and ":" characters between digit pairs are ignored).
1755 If style is omitted, "sha1" is used.
1756 The "md5" and "sha1" styles produces an identifier that is always
1758 the same in an identical output file, but will be unique among all
1759 nonidentical output files. It is not intended to be compared as a
1760 checksum for the file's contents. A linked file may be changed
1761 later by other tools, but the build ID bit string identifying the
1762 original linked file does not change.
1763 Passing "none" for style disables the setting from any "--build-id"
1765 options earlier on the command line.
1766 The i386 PE linker supports the -shared option, which causes the output
1768 to be a dynamically linked library (DLL) instead of a normal
1769 executable. You should name the output "*.dll" when you use this
1770 option. In addition, the linker fully supports the standard "*.def"
1771 files, which may be specified on the linker command line like an object
1772 file (in fact, it should precede archives it exports symbols from, to
1773 ensure that they get linked in, just like a normal object file).
1774 In addition to the options common to all targets, the i386 PE linker
1776 support additional command line options that are specific to the i386
1777 PE target. Options that take values may be separated from their values
1778 by either a space or an equals sign.
1779 --add-stdcall-alias
1781 If given, symbols with a stdcall suffix (@nn) will be exported as-
1782 is and also with the suffix stripped. [This option is specific to
1783 the i386 PE targeted port of the linker]
1784 --base-file file
1786 Use file as the name of a file in which to save the base addresses
1787 of all the relocations needed for generating DLLs with dlltool.
1788 [This is an i386 PE specific option]
1789 --dll
1791 Create a DLL instead of a regular executable. You may also use
1792 -shared or specify a "LIBRARY" in a given ".def" file. [This
1793 option is specific to the i386 PE targeted port of the linker]
1794 --enable-long-section-names
1796 --disable-long-section-names
1797 The PE variants of the COFF object format add an extension that
1798 permits the use of section names longer than eight characters, the
1799 normal limit for COFF. By default, these names are only allowed in
1800 object files, as fully-linked executable images do not carry the
1801 COFF string table required to support the longer names. As a GNU
1802 extension, it is possible to allow their use in executable images
1803 as well, or to (probably pointlessly!) disallow it in object
1804 files, by using these two options. Executable images generated
1805 with these long section names are slightly non-standard, carrying
1806 as they do a string table, and may generate confusing output when
1807 examined with non-GNU PE-aware tools, such as file viewers and
1808 dumpers. However, GDB relies on the use of PE long section names
1809 to find Dwarf-2 debug information sections in an executable image
1810 at runtime, and so if neither option is specified on the command-
1811 line, ld will enable long section names, overriding the default and
1812 technically correct behaviour, when it finds the presence of debug
1813 information while linking an executable image and not stripping
1814 symbols. [This option is valid for all PE targeted ports of the
1815 linker]
1816 --enable-stdcall-fixup
1818 --disable-stdcall-fixup
1819 If the link finds a symbol that it cannot resolve, it will attempt
1820 to do "fuzzy linking" by looking for another defined symbol that
1821 differs only in the format of the symbol name (cdecl vs stdcall)
1822 and will resolve that symbol by linking to the match. For example,
1823 the undefined symbol "_foo" might be linked to the function
1824 "_foo@12", or the undefined symbol "_bar@16" might be linked to the
1825 function "_bar". When the linker does this, it prints a warning,
1826 since it normally should have failed to link, but sometimes import
1827 libraries generated from third-party dlls may need this feature to
1828 be usable. If you specify --enable-stdcall-fixup, this feature is
1829 fully enabled and warnings are not printed. If you specify
1830 --disable-stdcall-fixup, this feature is disabled and such
1831 mismatches are considered to be errors. [This option is specific
1832 to the i386 PE targeted port of the linker]
1833 --leading-underscore
1835 --no-leading-underscore
1836 For most targets default symbol-prefix is an underscore and is
1837 defined in target's description. By this option it is possible to
1838 disable/enable the default underscore symbol-prefix.
1839 --export-all-symbols
1841 If given, all global symbols in the objects used to build a DLL
1842 will be exported by the DLL. Note that this is the default if
1843 there otherwise wouldn't be any exported symbols. When symbols are
1844 explicitly exported via DEF files or implicitly exported via
1845 function attributes, the default is to not export anything else
1846 unless this option is given. Note that the symbols "DllMain@12",
1847 "DllEntryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will
1848 not be automatically exported. Also, symbols imported from other
1849 DLLs will not be re-exported, nor will symbols specifying the DLL's
1850 internal layout such as those beginning with "_head_" or ending
1851 with "_iname". In addition, no symbols from "libgcc", "libstd++",
1852 "libmingw32", or "crtX.o" will be exported. Symbols whose names
1853 begin with "__rtti_" or "__builtin_" will not be exported, to help
1854 with C++ DLLs. Finally, there is an extensive list of cygwin-
1855 private symbols that are not exported (obviously, this applies on
1856 when building DLLs for cygwin targets). These cygwin-excludes are:
1857 "_cygwin_dll_entry@12", "_cygwin_crt0_common@8",
1858 "_cygwin_noncygwin_dll_entry@12", "_fmode", "_impure_ptr",
1859 "cygwin_attach_dll", "cygwin_premain0", "cygwin_premain1",
1860 "cygwin_premain2", "cygwin_premain3", and "environ". [This option
1861 is specific to the i386 PE targeted port of the linker]
1862 --exclude-symbols symbol,symbol,...
1864 Specifies a list of symbols which should not be automatically
1865 exported. The symbol names may be delimited by commas or colons.
1866 [This option is specific to the i386 PE targeted port of the
1867 linker]
1868 --exclude-all-symbols
1870 Specifies no symbols should be automatically exported. [This
1871 option is specific to the i386 PE targeted port of the linker]
1872 --file-alignment
1874 Specify the file alignment. Sections in the file will always begin
1875 at file offsets which are multiples of this number. This defaults
1876 to 512. [This option is specific to the i386 PE targeted port of
1877 the linker]
1878 --heap reserve
1880 --heap reserve,commit
1881 Specify the number of bytes of memory to reserve (and optionally
1882 commit) to be used as heap for this program. The default is 1MB
1883 reserved, 4K committed. [This option is specific to the i386 PE
1884 targeted port of the linker]
1885 --image-base value
1887 Use value as the base address of your program or dll. This is the
1888 lowest memory location that will be used when your program or dll
1889 is loaded. To reduce the need to relocate and improve performance
1890 of your dlls, each should have a unique base address and not
1891 overlap any other dlls. The default is 0x400000 for executables,
1892 and 0x10000000 for dlls. [This option is specific to the i386 PE
1893 targeted port of the linker]
1894 --kill-at
1896 If given, the stdcall suffixes (@nn) will be stripped from symbols
1897 before they are exported. [This option is specific to the i386 PE
1898 targeted port of the linker]
1899 --large-address-aware
1901 If given, the appropriate bit in the "Characteristics" field of the
1902 COFF header is set to indicate that this executable supports
1903 virtual addresses greater than 2 gigabytes. This should be used in
1904 conjunction with the /3GB or /USERVA=value megabytes switch in the
1905 "[operating systems]" section of the BOOT.INI. Otherwise, this bit
1906 has no effect. [This option is specific to PE targeted ports of
1907 the linker]
1908 --disable-large-address-aware
1910 Reverts the effect of a previous --large-address-aware option.
1911 This is useful if --large-address-aware is always set by the
1912 compiler driver (e.g. Cygwin gcc) and the executable does not
1913 support virtual addresses greater than 2 gigabytes. [This option
1914 is specific to PE targeted ports of the linker]
1915 --major-image-version value
1917 Sets the major number of the "image version". Defaults to 1.
1918 [This option is specific to the i386 PE targeted port of the
1919 linker]
1920 --major-os-version value
1922 Sets the major number of the "os version". Defaults to 4. [This
1923 option is specific to the i386 PE targeted port of the linker]
1924 --major-subsystem-version value
1926 Sets the major number of the "subsystem version". Defaults to 4.
1927 [This option is specific to the i386 PE targeted port of the
1928 linker]
1929 --minor-image-version value
1931 Sets the minor number of the "image version". Defaults to 0.
1932 [This option is specific to the i386 PE targeted port of the
1933 linker]
1934 --minor-os-version value
1936 Sets the minor number of the "os version". Defaults to 0. [This
1937 option is specific to the i386 PE targeted port of the linker]
1938 --minor-subsystem-version value
1940 Sets the minor number of the "subsystem version". Defaults to 0.
1941 [This option is specific to the i386 PE targeted port of the
1942 linker]
1943 --output-def file
1945 The linker will create the file file which will contain a DEF file
1946 corresponding to the DLL the linker is generating. This DEF file
1947 (which should be called "*.def") may be used to create an import
1948 library with "dlltool" or may be used as a reference to
1949 automatically or implicitly exported symbols. [This option is
1950 specific to the i386 PE targeted port of the linker]
1951 --out-implib file
1953 The linker will create the file file which will contain an import
1954 lib corresponding to the DLL the linker is generating. This import
1955 lib (which should be called "*.dll.a" or "*.a" may be used to link
1956 clients against the generated DLL; this behaviour makes it possible
1957 to skip a separate "dlltool" import library creation step. [This
1958 option is specific to the i386 PE targeted port of the linker]
1959 --enable-auto-image-base
1961 --enable-auto-image-base=value
1962 Automatically choose the image base for DLLs, optionally starting
1963 with base value, unless one is specified using the "--image-base"
1964 argument. By using a hash generated from the dllname to create
1965 unique image bases for each DLL, in-memory collisions and
1966 relocations which can delay program execution are avoided. [This
1967 option is specific to the i386 PE targeted port of the linker]
1968 --disable-auto-image-base
1970 Do not automatically generate a unique image base. If there is no
1971 user-specified image base ("--image-base") then use the platform
1972 default. [This option is specific to the i386 PE targeted port of
1973 the linker]
1974 --dll-search-prefix string
1976 When linking dynamically to a dll without an import library, search
1977 for "<string><basename>.dll" in preference to "lib<basename>.dll".
1978 This behaviour allows easy distinction between DLLs built for the
1979 various "subplatforms": native, cygwin, uwin, pw, etc. For
1980 instance, cygwin DLLs typically use "--dll-search-prefix=cyg".
1981 [This option is specific to the i386 PE targeted port of the
1982 linker]
1983 --enable-auto-import
1985 Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA
1986 imports from DLLs, and create the necessary thunking symbols when
1987 building the import libraries with those DATA exports. Note: Use of
1988 the 'auto-import' extension will cause the text section of the
1989 image file to be made writable. This does not conform to the PE-
1990 COFF format specification published by Microsoft.
1991 Note - use of the 'auto-import' extension will also cause read only
1993 data which would normally be placed into the .rdata section to be
1994 placed into the .data section instead. This is in order to work
1995 around a problem with consts that is described here:
1996 http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
1997 Using 'auto-import' generally will 'just work' -- but sometimes you
1999 may see this message:
2000 "variable '<var>' can't be auto-imported. Please read the
2002 documentation for ld's "--enable-auto-import" for details."
2003 This message occurs when some (sub)expression accesses an address
2005 ultimately given by the sum of two constants (Win32 import tables
2006 only allow one). Instances where this may occur include accesses
2007 to member fields of struct variables imported from a DLL, as well
2008 as using a constant index into an array variable imported from a
2009 DLL. Any multiword variable (arrays, structs, long long, etc) may
2010 trigger this error condition. However, regardless of the exact
2011 data type of the offending exported variable, ld will always detect
2012 it, issue the warning, and exit.
2013 There are several ways to address this difficulty, regardless of
2015 the data type of the exported variable:
2016 One way is to use --enable-runtime-pseudo-reloc switch. This leaves
2018 the task of adjusting references in your client code for runtime
2019 environment, so this method works only when runtime environment
2020 supports this feature.
2021 A second solution is to force one of the 'constants' to be a
2023 variable -- that is, unknown and un-optimizable at compile time.
2024 For arrays, there are two possibilities: a) make the indexee (the
2025 array's address) a variable, or b) make the 'constant' index a
2026 variable. Thus:
2027 extern type extern_array[];
2029 extern_array[1] -->
2030 { volatile type *t=extern_array; t[1] }
2031 or
2033 extern type extern_array[];
2035 extern_array[1] -->
2036 { volatile int t=1; extern_array[t] }
2037 For structs (and most other multiword data types) the only option
2039 is to make the struct itself (or the long long, or the ...)
2040 variable:
2041 extern struct s extern_struct;
2043 extern_struct.field -->
2044 { volatile struct s *t=&extern_struct; t->field }
2045 or
2047 extern long long extern_ll;
2049 extern_ll -->
2050 { volatile long long * local_ll=&extern_ll; *local_ll }
2051 A third method of dealing with this difficulty is to abandon
2053 'auto-import' for the offending symbol and mark it with
2054 "__declspec(dllimport)". However, in practice that requires using
2055 compile-time #defines to indicate whether you are building a DLL,
2056 building client code that will link to the DLL, or merely
2057 building/linking to a static library. In making the choice
2058 between the various methods of resolving the 'direct address with
2059 constant offset' problem, you should consider typical real-world
2060 usage:
2061 Original:
2063 --foo.h
2065 extern int arr[];
2066 --foo.c
2067 #include "foo.h"
2068 void main(int argc, char **argv){
2069 printf("%d\n",arr[1]);
2070 }
2071 Solution 1:
2073 --foo.h
2075 extern int arr[];
2076 --foo.c
2077 #include "foo.h"
2078 void main(int argc, char **argv){
2079 /* This workaround is for win32 and cygwin; do not "optimize" */
2080 volatile int *parr = arr;
2081 printf("%d\n",parr[1]);
2082 }
2083 Solution 2:
2085 --foo.h
2087 /* Note: auto-export is assumed (no __declspec(dllexport)) */
2088 #if (defined(_WIN32) || defined(__CYGWIN__)) && \
2089 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
2090 #define FOO_IMPORT __declspec(dllimport)
2091 #else
2092 #define FOO_IMPORT
2093 #endif
2094 extern FOO_IMPORT int arr[];
2095 --foo.c
2096 #include "foo.h"
2097 void main(int argc, char **argv){
2098 printf("%d\n",arr[1]);
2099 }
2100 A fourth way to avoid this problem is to re-code your library to
2102 use a functional interface rather than a data interface for the
2103 offending variables (e.g. set_foo() and get_foo() accessor
2104 functions). [This option is specific to the i386 PE targeted port
2105 of the linker]
2106 --disable-auto-import
2108 Do not attempt to do sophisticated linking of "_symbol" to
2109 "__imp__symbol" for DATA imports from DLLs. [This option is
2110 specific to the i386 PE targeted port of the linker]
2111 --enable-runtime-pseudo-reloc
2113 If your code contains expressions described in --enable-auto-import
2114 section, that is, DATA imports from DLL with non-zero offset, this
2115 switch will create a vector of 'runtime pseudo relocations' which
2116 can be used by runtime environment to adjust references to such
2117 data in your client code. [This option is specific to the i386 PE
2118 targeted port of the linker]
2119 --disable-runtime-pseudo-reloc
2121 Do not create pseudo relocations for non-zero offset DATA imports
2122 from DLLs. [This option is specific to the i386 PE targeted port
2123 of the linker]
2124 --enable-extra-pe-debug
2126 Show additional debug info related to auto-import symbol thunking.
2127 [This option is specific to the i386 PE targeted port of the
2128 linker]
2129 --section-alignment
2131 Sets the section alignment. Sections in memory will always begin
2132 at addresses which are a multiple of this number. Defaults to
2133 0x1000. [This option is specific to the i386 PE targeted port of
2134 the linker]
2135 --stack reserve
2137 --stack reserve,commit
2138 Specify the number of bytes of memory to reserve (and optionally
2139 commit) to be used as stack for this program. The default is 2MB
2140 reserved, 4K committed. [This option is specific to the i386 PE
2141 targeted port of the linker]
2142 --subsystem which
2144 --subsystem which:major
2145 --subsystem which:major.minor
2146 Specifies the subsystem under which your program will execute. The
2147 legal values for which are "native", "windows", "console", "posix",
2148 and "xbox". You may optionally set the subsystem version also.
2149 Numeric values are also accepted for which. [This option is
2150 specific to the i386 PE targeted port of the linker]
2151 The following options set flags in the "DllCharacteristics" field
2153 of the PE file header: [These options are specific to PE targeted
2154 ports of the linker]
2155 --high-entropy-va
2157 Image is compatible with 64-bit address space layout randomization
2158 (ASLR).
2159 --dynamicbase
2161 The image base address may be relocated using address space layout
2162 randomization (ASLR). This feature was introduced with MS Windows
2163 Vista for i386 PE targets.
2164 --forceinteg
2166 Code integrity checks are enforced.
2167 --nxcompat
2169 The image is compatible with the Data Execution Prevention. This
2170 feature was introduced with MS Windows XP SP2 for i386 PE targets.
2171 --no-isolation
2173 Although the image understands isolation, do not isolate the image.
2174 --no-seh
2176 The image does not use SEH. No SE handler may be called from this
2177 image.
2178 --no-bind
2180 Do not bind this image.
2181 --wdmdriver
2183 The driver uses the MS Windows Driver Model.
2184 --tsaware
2186 The image is Terminal Server aware.
2187 --insert-timestamp
2189 --no-insert-timestamp
2190 Insert a real timestamp into the image. This is the default
2191 behaviour as it matches legacy code and it means that the image
2192 will work with other, proprietary tools. The problem with this
2193 default is that it will result in slightly different images being
2194 produced each time the same sources are linked. The option
2195 --no-insert-timestamp can be used to insert a zero value for the
2196 timestamp, this ensuring that binaries produced from identical
2197 sources will compare identically.
2198 The C6X uClinux target uses a binary format called DSBT to support
2200 shared libraries. Each shared library in the system needs to have a
2201 unique index; all executables use an index of 0.
2202 --dsbt-size size
2204 This option sets the number of entries in the DSBT of the current
2205 executable or shared library to size. The default is to create a
2206 table with 64 entries.
2207 --dsbt-index index
2209 This option sets the DSBT index of the current executable or shared
2210 library to index. The default is 0, which is appropriate for
2211 generating executables. If a shared library is generated with a
2212 DSBT index of 0, the "R_C6000_DSBT_INDEX" relocs are copied into
2213 the output file.
2214 The --no-merge-exidx-entries switch disables the merging of
2216 adjacent exidx entries in frame unwind info.
2217 The 68HC11 and 68HC12 linkers support specific options to control the
2219 memory bank switching mapping and trampoline code generation.
2220 --no-trampoline
2222 This option disables the generation of trampoline. By default a
2223 trampoline is generated for each far function which is called using
2224 a "jsr" instruction (this happens when a pointer to a far function
2225 is taken).
2226 --bank-window name
2228 This option indicates to the linker the name of the memory region
2229 in the MEMORY specification that describes the memory bank window.
2230 The definition of such region is then used by the linker to compute
2231 paging and addresses within the memory window.
2232 The following options are supported to control handling of GOT
2234 generation when linking for 68K targets.
2235 --got=type
2237 This option tells the linker which GOT generation scheme to use.
2238 type should be one of single, negative, multigot or target. For
2239 more information refer to the Info entry for ld.
2240 The following options are supported to control microMIPS instruction
2242 generation when linking for MIPS targets.
2243 --insn32
2245 --no-insn32
2246 These options control the choice of microMIPS instructions used in
2247 code generated by the linker, such as that in the PLT or lazy
2248 binding stubs, or in relaxation. If --insn32 is used, then the
2249 linker only uses 32-bit instruction encodings. By default or if
2250 --no-insn32 is used, all instruction encodings are used, including
2251 16-bit ones where possible.
2252
2254 You can change the behaviour of ld with the environment variables
2255 "GNUTARGET", "LDEMULATION" and "COLLECT_NO_DEMANGLE".
2256 "GNUTARGET" determines the input-file object format if you don't use -b
2258 (or its synonym --format). Its value should be one of the BFD names
2259 for an input format. If there is no "GNUTARGET" in the environment, ld
2260 uses the natural format of the target. If "GNUTARGET" is set to
2261 "default" then BFD attempts to discover the input format by examining
2262 binary input files; this method often succeeds, but there are potential
2263 ambiguities, since there is no method of ensuring that the magic number
2264 used to specify object-file formats is unique. However, the
2265 configuration procedure for BFD on each system places the conventional
2266 format for that system first in the search-list, so ambiguities are
2267 resolved in favor of convention.
2268 "LDEMULATION" determines the default emulation if you don't use the -m
2270 option. The emulation can affect various aspects of linker behaviour,
2271 particularly the default linker script. You can list the available
2272 emulations with the --verbose or -V options. If the -m option is not
2273 used, and the "LDEMULATION" environment variable is not defined, the
2274 default emulation depends upon how the linker was configured.
2275 Normally, the linker will default to demangling symbols. However, if
2277 "COLLECT_NO_DEMANGLE" is set in the environment, then it will default
2278 to not demangling symbols. This environment variable is used in a
2279 similar fashion by the "gcc" linker wrapper program. The default may
2280 be overridden by the --demangle and --no-demangle options.
2281
2283 ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries
2284 for binutils and ld.
2285
2287 Copyright (c) 1991-2016 Free Software Foundation, Inc.
2288 Permission is granted to copy, distribute and/or modify this document
2290 under the terms of the GNU Free Documentation License, Version 1.3 or
2291 any later version published by the Free Software Foundation; with no
2292 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
2293 Texts. A copy of the license is included in the section entitled "GNU
2294 Free Documentation License".
2295binutils-2.27 2018-10-30 LD(1)