1LD(1) GNU Development Tools LD(1)
2
3
4
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
16 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
20 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
24 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
30 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
36 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
47 ld -o <output> /lib/crt0.o hello.o -lc
48
49 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
54 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
64 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
69 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
75 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
86 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
91 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
99 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
105 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
110 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
111
112 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
120 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
121
122 Here is a table of the generic command-line switches accepted by the
123 GNU linker:
124
125 @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
131 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
138 -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
145 --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
155 -b input-format
156 --format=input-format
157 ld may be configured to support more than one kind of object file.
158 If your ld is configured this way, you can use the -b option to
159 specify the binary format for input object files that follow this
160 option on the command line. Even when ld is configured to support
161 alternative object formats, you don't usually need to specify this,
162 as ld should be configured to expect as a default input format the
163 most usual format on each machine. input-format is a text string,
164 the name of a particular format supported by the BFD libraries.
165 (You can list the available binary formats with objdump -i.)
166
167 You may want to use this option if you are linking files with an
168 unusual binary format. You can also use -b to switch formats
169 explicitly (when linking object files of different formats), by
170 including -b input-format before each group of object files in a
171 particular format.
172
173 The default format is taken from the environment variable
174 "GNUTARGET".
175
176 You can also define the input format from a script, using the
177 command "TARGET";
178
179 -c MRI-commandfile
180 --mri-script=MRI-commandfile
181 For compatibility with linkers produced by MRI, ld accepts script
182 files written in an alternate, restricted command language,
183 described in the MRI Compatible Script Files section of GNU ld
184 documentation. Introduce MRI script files with the option -c; use
185 the -T option to run linker scripts written in the general-purpose
186 ld scripting language. If MRI-cmdfile does not exist, ld looks for
187 it in the directories specified by any -L options.
188
189 -d
190 -dc
191 -dp These three options are equivalent; multiple forms are supported
192 for compatibility with other linkers. They assign space to common
193 symbols even if a relocatable output file is specified (with -r).
194 The script command "FORCE_COMMON_ALLOCATION" has the same effect.
195
196 --depaudit AUDITLIB
197 -P AUDITLIB
198 Adds AUDITLIB to the "DT_DEPAUDIT" entry of the dynamic section.
199 AUDITLIB is not checked for existence, nor will it use the
200 DT_SONAME specified in the library. If specified multiple times
201 "DT_DEPAUDIT" will contain a colon separated list of audit
202 interfaces to use. This option is only meaningful on ELF platforms
203 supporting the rtld-audit interface. The -P option is provided for
204 Solaris compatibility.
205
206 --enable-non-contiguous-regions
207 This option avoids generating an error if an input section does not
208 fit a matching output section. The linker tries to allocate the
209 input section to subseque nt matching output sections, and
210 generates an error only if no output section is large enough. This
211 is useful when several non-contiguous memory regions are available
212 and the input section does not require a particular one. The order
213 in which input sections are evaluated does not change, for
214 instance:
215
216 MEMORY {
217 MEM1 (rwx) : ORIGIN : 0x1000, LENGTH = 0x14
218 MEM2 (rwx) : ORIGIN : 0x1000, LENGTH = 0x40
219 MEM3 (rwx) : ORIGIN : 0x2000, LENGTH = 0x40
220 }
221 SECTIONS {
222 mem1 : { *(.data.*); } > MEM1
223 mem2 : { *(.data.*); } > MEM2
224 mem3 : { *(.data.*); } > MEM2
225 }
226
227 with input sections:
228 .data.1: size 8
229 .data.2: size 0x10
230 .data.3: size 4
231
232 results in .data.1 affected to mem1, and .data.2 and .data.3
233 affected to mem2, even though .data.3 would fit in mem3.
234
235 This option is incompatible with INSERT statements because it
236 changes the way input sections are mapped to output sections.
237
238 --enable-non-contiguous-regions-warnings
239 This option enables warnings when "--enable-non-contiguous-regions"
240 allows possibly unexpected matches in sections mapping, potentially
241 leading to silently discarding a section instead of failing because
242 it does not fit any output region.
243
244 -e entry
245 --entry=entry
246 Use entry as the explicit symbol for beginning execution of your
247 program, rather than the default entry point. If there is no
248 symbol named entry, the linker will try to parse entry as a number,
249 and use that as the entry address (the number will be interpreted
250 in base 10; you may use a leading 0x for base 16, or a leading 0
251 for base 8).
252
253 --exclude-libs lib,lib,...
254 Specifies a list of archive libraries from which symbols should not
255 be automatically exported. The library names may be delimited by
256 commas or colons. Specifying "--exclude-libs ALL" excludes symbols
257 in all archive libraries from automatic export. This option is
258 available only for the i386 PE targeted port of the linker and for
259 ELF targeted ports. For i386 PE, symbols explicitly listed in a
260 .def file are still exported, regardless of this option. For ELF
261 targeted ports, symbols affected by this option will be treated as
262 hidden.
263
264 --exclude-modules-for-implib module,module,...
265 Specifies a list of object files or archive members, from which
266 symbols should not be automatically exported, but which should be
267 copied wholesale into the import library being generated during the
268 link. The module names may be delimited by commas or colons, and
269 must match exactly the filenames used by ld to open the files; for
270 archive members, this is simply the member name, but for object
271 files the name listed must include and match precisely any path
272 used to specify the input file on the linker's command-line. This
273 option is available only for the i386 PE targeted port of the
274 linker. Symbols explicitly listed in a .def file are still
275 exported, regardless of this option.
276
277 -E
278 --export-dynamic
279 --no-export-dynamic
280 When creating a dynamically linked executable, using the -E option
281 or the --export-dynamic option causes the linker to add all symbols
282 to the dynamic symbol table. The dynamic symbol table is the set
283 of symbols which are visible from dynamic objects at run time.
284
285 If you do not use either of these options (or use the
286 --no-export-dynamic option to restore the default behavior), the
287 dynamic symbol table will normally contain only those symbols which
288 are referenced by some dynamic object mentioned in the link.
289
290 If you use "dlopen" to load a dynamic object which needs to refer
291 back to the symbols defined by the program, rather than some other
292 dynamic object, then you will probably need to use this option when
293 linking the program itself.
294
295 You can also use the dynamic list to control what symbols should be
296 added to the dynamic symbol table if the output format supports it.
297 See the description of --dynamic-list.
298
299 Note that this option is specific to ELF targeted ports. PE
300 targets support a similar function to export all symbols from a DLL
301 or EXE; see the description of --export-all-symbols below.
302
303 --export-dynamic-symbol=glob
304 When creating a dynamically linked executable, symbols matching
305 glob will be added to the dynamic symbol table. When creating a
306 shared library, references to symbols matching glob will not be
307 bound to the definitions within the shared library. This option is
308 a no-op when creating a shared library and -Bsymbolic or
309 --dynamic-list are not specified. This option is only meaningful on
310 ELF platforms which support shared libraries.
311
312 --export-dynamic-symbol-list=file
313 Specify a --export-dynamic-symbol for each pattern in the file.
314 The format of the file is the same as the version node without
315 scope and node name. See VERSION for more information.
316
317 -EB Link big-endian objects. This affects the default output format.
318
319 -EL Link little-endian objects. This affects the default output
320 format.
321
322 -f name
323 --auxiliary=name
324 When creating an ELF shared object, set the internal DT_AUXILIARY
325 field to the specified name. This tells the dynamic linker that
326 the symbol table of the shared object should be used as an
327 auxiliary filter on the symbol table of the shared object name.
328
329 If you later link a program against this filter object, then, when
330 you run the program, the dynamic linker will see the DT_AUXILIARY
331 field. If the dynamic linker resolves any symbols from the filter
332 object, it will first check whether there is a definition in the
333 shared object name. If there is one, it will be used instead of
334 the definition in the filter object. The shared object name need
335 not exist. Thus the shared object name may be used to provide an
336 alternative implementation of certain functions, perhaps for
337 debugging or for machine-specific performance.
338
339 This option may be specified more than once. The DT_AUXILIARY
340 entries will be created in the order in which they appear on the
341 command line.
342
343 -F name
344 --filter=name
345 When creating an ELF shared object, set the internal DT_FILTER
346 field to the specified name. This tells the dynamic linker that
347 the symbol table of the shared object which is being created should
348 be used as a filter on the symbol table of the shared object name.
349
350 If you later link a program against this filter object, then, when
351 you run the program, the dynamic linker will see the DT_FILTER
352 field. The dynamic linker will resolve symbols according to the
353 symbol table of the filter object as usual, but it will actually
354 link to the definitions found in the shared object name. Thus the
355 filter object can be used to select a subset of the symbols
356 provided by the object name.
357
358 Some older linkers used the -F option throughout a compilation
359 toolchain for specifying object-file format for both input and
360 output object files. The GNU linker uses other mechanisms for this
361 purpose: the -b, --format, --oformat options, the "TARGET" command
362 in linker scripts, and the "GNUTARGET" environment variable. The
363 GNU linker will ignore the -F option when not creating an ELF
364 shared object.
365
366 -fini=name
367 When creating an ELF executable or shared object, call NAME when
368 the executable or shared object is unloaded, by setting DT_FINI to
369 the address of the function. By default, the linker uses "_fini"
370 as the function to call.
371
372 -g Ignored. Provided for compatibility with other tools.
373
374 -G value
375 --gpsize=value
376 Set the maximum size of objects to be optimized using the GP
377 register to size. This is only meaningful for object file formats
378 such as MIPS ELF that support putting large and small objects into
379 different sections. This is ignored for other object file formats.
380
381 -h name
382 -soname=name
383 When creating an ELF shared object, set the internal DT_SONAME
384 field to the specified name. When an executable is linked with a
385 shared object which has a DT_SONAME field, then when the executable
386 is run the dynamic linker will attempt to load the shared object
387 specified by the DT_SONAME field rather than the using the file
388 name given to the linker.
389
390 -i Perform an incremental link (same as option -r).
391
392 -init=name
393 When creating an ELF executable or shared object, call NAME when
394 the executable or shared object is loaded, by setting DT_INIT to
395 the address of the function. By default, the linker uses "_init"
396 as the function to call.
397
398 -l namespec
399 --library=namespec
400 Add the archive or object file specified by namespec to the list of
401 files to link. This option may be used any number of times. If
402 namespec is of the form :filename, ld will search the library path
403 for a file called filename, otherwise it will search the library
404 path for a file called libnamespec.a.
405
406 On systems which support shared libraries, ld may also search for
407 files other than libnamespec.a. Specifically, on ELF and SunOS
408 systems, ld will search a directory for a library called
409 libnamespec.so before searching for one called libnamespec.a. (By
410 convention, a ".so" extension indicates a shared library.) Note
411 that this behavior does not apply to :filename, which always
412 specifies a file called filename.
413
414 The linker will search an archive only once, at the location where
415 it is specified on the command line. If the archive defines a
416 symbol which was undefined in some object which appeared before the
417 archive on the command line, the linker will include the
418 appropriate file(s) from the archive. However, an undefined symbol
419 in an object appearing later on the command line will not cause the
420 linker to search the archive again.
421
422 See the -( option for a way to force the linker to search archives
423 multiple times.
424
425 You may list the same archive multiple times on the command line.
426
427 This type of archive searching is standard for Unix linkers.
428 However, if you are using ld on AIX, note that it is different from
429 the behaviour of the AIX linker.
430
431 -L searchdir
432 --library-path=searchdir
433 Add path searchdir to the list of paths that ld will search for
434 archive libraries and ld control scripts. You may use this option
435 any number of times. The directories are searched in the order in
436 which they are specified on the command line. Directories
437 specified on the command line are searched before the default
438 directories. All -L options apply to all -l options, regardless of
439 the order in which the options appear. -L options do not affect
440 how ld searches for a linker script unless -T option is specified.
441
442 If searchdir begins with "=" or $SYSROOT, then this prefix will be
443 replaced by the sysroot prefix, controlled by the --sysroot option,
444 or specified when the linker is configured.
445
446 The default set of paths searched (without being specified with -L)
447 depends on which emulation mode ld is using, and in some cases also
448 on how it was configured.
449
450 The paths can also be specified in a link script with the
451 "SEARCH_DIR" command. Directories specified this way are searched
452 at the point in which the linker script appears in the command
453 line.
454
455 -m emulation
456 Emulate the emulation linker. You can list the available
457 emulations with the --verbose or -V options.
458
459 If the -m option is not used, the emulation is taken from the
460 "LDEMULATION" environment variable, if that is defined.
461
462 Otherwise, the default emulation depends upon how the linker was
463 configured.
464
465 -M
466 --print-map
467 Print a link map to the standard output. A link map provides
468 information about the link, including the following:
469
470 • Where object files are mapped into memory.
471
472 • How common symbols are allocated.
473
474 • All archive members included in the link, with a mention of the
475 symbol which caused the archive member to be brought in.
476
477 • The values assigned to symbols.
478
479 Note - symbols whose values are computed by an expression which
480 involves a reference to a previous value of the same symbol may
481 not have correct result displayed in the link map. This is
482 because the linker discards intermediate results and only
483 retains the final value of an expression. Under such
484 circumstances the linker will display the final value enclosed
485 by square brackets. Thus for example a linker script
486 containing:
487
488 foo = 1
489 foo = foo * 4
490 foo = foo + 8
491
492 will produce the following output in the link map if the -M
493 option is used:
494
495 0x00000001 foo = 0x1
496 [0x0000000c] foo = (foo * 0x4)
497 [0x0000000c] foo = (foo + 0x8)
498
499 See Expressions for more information about expressions in
500 linker scripts.
501
502 • How GNU properties are merged.
503
504 When the linker merges input .note.gnu.property sections into
505 one output .note.gnu.property section, some properties are
506 removed or updated. These actions are reported in the link
507 map. For example:
508
509 Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
510
511 This indicates that property 0xc0000002 is removed from output
512 when merging properties in foo.o, whose property 0xc0000002
513 value is 0x1, and bar.o, which doesn't have property
514 0xc0000002.
515
516 Updated property 0xc0010001 (0x1) to merge foo.o (0x1) and bar.o (0x1)
517
518 This indicates that property 0xc0010001 value is updated to 0x1
519 in output when merging properties in foo.o, whose 0xc0010001
520 property value is 0x1, and bar.o, whose 0xc0010001 property
521 value is 0x1.
522
523 --print-map-discarded
524 --no-print-map-discarded
525 Print (or do not print) the list of discarded and garbage collected
526 sections in the link map. Enabled by default.
527
528 -n
529 --nmagic
530 Turn off page alignment of sections, and disable linking against
531 shared libraries. If the output format supports Unix style magic
532 numbers, mark the output as "NMAGIC".
533
534 -N
535 --omagic
536 Set the text and data sections to be readable and writable. Also,
537 do not page-align the data segment, and disable linking against
538 shared libraries. If the output format supports Unix style magic
539 numbers, mark the output as "OMAGIC". Note: Although a writable
540 text section is allowed for PE-COFF targets, it does not conform to
541 the format specification published by Microsoft.
542
543 --no-omagic
544 This option negates most of the effects of the -N option. It sets
545 the text section to be read-only, and forces the data segment to be
546 page-aligned. Note - this option does not enable linking against
547 shared libraries. Use -Bdynamic for this.
548
549 -o output
550 --output=output
551 Use output as the name for the program produced by ld; if this
552 option is not specified, the name a.out is used by default. The
553 script command "OUTPUT" can also specify the output file name.
554
555 --dependency-file=depfile
556 Write a dependency file to depfile. This file contains a rule
557 suitable for "make" describing the output file and all the input
558 files that were read to produce it. The output is similar to the
559 compiler's output with -M -MP. Note that there is no option like
560 the compiler's -MM, to exclude "system files" (which is not a well-
561 specified concept in the linker, unlike "system headers" in the
562 compiler). So the output from --dependency-file is always specific
563 to the exact state of the installation where it was produced, and
564 should not be copied into distributed makefiles without careful
565 editing.
566
567 -O level
568 If level is a numeric values greater than zero ld optimizes the
569 output. This might take significantly longer and therefore
570 probably should only be enabled for the final binary. At the
571 moment this option only affects ELF shared library generation.
572 Future releases of the linker may make more use of this option.
573 Also currently there is no difference in the linker's behaviour for
574 different non-zero values of this option. Again this may change
575 with future releases.
576
577 -plugin name
578 Involve a plugin in the linking process. The name parameter is the
579 absolute filename of the plugin. Usually this parameter is
580 automatically added by the complier, when using link time
581 optimization, but users can also add their own plugins if they so
582 wish.
583
584 Note that the location of the compiler originated plugins is
585 different from the place where the ar, nm and ranlib programs
586 search for their plugins. In order for those commands to make use
587 of a compiler based plugin it must first be copied into the
588 ${libdir}/bfd-plugins directory. All gcc based linker plugins are
589 backward compatible, so it is sufficient to just copy in the newest
590 one.
591
592 --push-state
593 The --push-state allows one to preserve the current state of the
594 flags which govern the input file handling so that they can all be
595 restored with one corresponding --pop-state option.
596
597 The option which are covered are: -Bdynamic, -Bstatic, -dn, -dy,
598 -call_shared, -non_shared, -static, -N, -n, --whole-archive,
599 --no-whole-archive, -r, -Ur, --copy-dt-needed-entries,
600 --no-copy-dt-needed-entries, --as-needed, --no-as-needed, and -a.
601
602 One target for this option are specifications for pkg-config. When
603 used with the --libs option all possibly needed libraries are
604 listed and then possibly linked with all the time. It is better to
605 return something as follows:
606
607 -Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
608
609 --pop-state
610 Undoes the effect of --push-state, restores the previous values of
611 the flags governing input file handling.
612
613 -q
614 --emit-relocs
615 Leave relocation sections and contents in fully linked executables.
616 Post link analysis and optimization tools may need this information
617 in order to perform correct modifications of executables. This
618 results in larger executables.
619
620 This option is currently only supported on ELF platforms.
621
622 --force-dynamic
623 Force the output file to have dynamic sections. This option is
624 specific to VxWorks targets.
625
626 -r
627 --relocatable
628 Generate relocatable output---i.e., generate an output file that
629 can in turn serve as input to ld. This is often called partial
630 linking. As a side effect, in environments that support standard
631 Unix magic numbers, this option also sets the output file's magic
632 number to "OMAGIC". If this option is not specified, an absolute
633 file is produced. When linking C++ programs, this option will not
634 resolve references to constructors; to do that, use -Ur.
635
636 When an input file does not have the same format as the output
637 file, partial linking is only supported if that input file does not
638 contain any relocations. Different output formats can have further
639 restrictions; for example some "a.out"-based formats do not support
640 partial linking with input files in other formats at all.
641
642 This option does the same thing as -i.
643
644 -R filename
645 --just-symbols=filename
646 Read symbol names and their addresses from filename, but do not
647 relocate it or include it in the output. This allows your output
648 file to refer symbolically to absolute locations of memory defined
649 in other programs. You may use this option more than once.
650
651 For compatibility with other ELF linkers, if the -R option is
652 followed by a directory name, rather than a file name, it is
653 treated as the -rpath option.
654
655 -s
656 --strip-all
657 Omit all symbol information from the output file.
658
659 -S
660 --strip-debug
661 Omit debugger symbol information (but not all symbols) from the
662 output file.
663
664 --strip-discarded
665 --no-strip-discarded
666 Omit (or do not omit) global symbols defined in discarded sections.
667 Enabled by default.
668
669 -t
670 --trace
671 Print the names of the input files as ld processes them. If -t is
672 given twice then members within archives are also printed. -t
673 output is useful to generate a list of all the object files and
674 scripts involved in linking, for example, when packaging files for
675 a linker bug report.
676
677 -T scriptfile
678 --script=scriptfile
679 Use scriptfile as the linker script. This script replaces ld's
680 default linker script (rather than adding to it), so commandfile
681 must specify everything necessary to describe the output file.
682 If scriptfile does not exist in the current directory, "ld" looks
683 for it in the directories specified by any preceding -L options.
684 Multiple -T options accumulate.
685
686 -dT scriptfile
687 --default-script=scriptfile
688 Use scriptfile as the default linker script.
689
690 This option is similar to the --script option except that
691 processing of the script is delayed until after the rest of the
692 command line has been processed. This allows options placed after
693 the --default-script option on the command line to affect the
694 behaviour of the linker script, which can be important when the
695 linker command line cannot be directly controlled by the user. (eg
696 because the command line is being constructed by another tool, such
697 as gcc).
698
699 -u symbol
700 --undefined=symbol
701 Force symbol to be entered in the output file as an undefined
702 symbol. Doing this may, for example, trigger linking of additional
703 modules from standard libraries. -u may be repeated with different
704 option arguments to enter additional undefined symbols. This
705 option is equivalent to the "EXTERN" linker script command.
706
707 If this option is being used to force additional modules to be
708 pulled into the link, and if it is an error for the symbol to
709 remain undefined, then the option --require-defined should be used
710 instead.
711
712 --require-defined=symbol
713 Require that symbol is defined in the output file. This option is
714 the same as option --undefined except that if symbol is not defined
715 in the output file then the linker will issue an error and exit.
716 The same effect can be achieved in a linker script by using
717 "EXTERN", "ASSERT" and "DEFINED" together. This option can be used
718 multiple times to require additional symbols.
719
720 -Ur For anything other than C++ programs, this option is equivalent to
721 -r: it generates relocatable output---i.e., an output file that can
722 in turn serve as input to ld. When linking C++ programs, -Ur does
723 resolve references to constructors, unlike -r. It does not work to
724 use -Ur on files that were themselves linked with -Ur; once the
725 constructor table has been built, it cannot be added to. Use -Ur
726 only for the last partial link, and -r for the others.
727
728 --orphan-handling=MODE
729 Control how orphan sections are handled. An orphan section is one
730 not specifically mentioned in a linker script.
731
732 MODE can have any of the following values:
733
734 "place"
735 Orphan sections are placed into a suitable output section
736 following the strategy described in Orphan Sections. The
737 option --unique also affects how sections are placed.
738
739 "discard"
740 All orphan sections are discarded, by placing them in the
741 /DISCARD/ section.
742
743 "warn"
744 The linker will place the orphan section as for "place" and
745 also issue a warning.
746
747 "error"
748 The linker will exit with an error if any orphan section is
749 found.
750
751 The default if --orphan-handling is not given is "place".
752
753 --unique[=SECTION]
754 Creates a separate output section for every input section matching
755 SECTION, or if the optional wildcard SECTION argument is missing,
756 for every orphan input section. An orphan section is one not
757 specifically mentioned in a linker script. You may use this option
758 multiple times on the command line; It prevents the normal merging
759 of input sections with the same name, overriding output section
760 assignments in a linker script.
761
762 -v
763 --version
764 -V Display the version number for ld. The -V option also lists the
765 supported emulations.
766
767 -x
768 --discard-all
769 Delete all local symbols.
770
771 -X
772 --discard-locals
773 Delete all temporary local symbols. (These symbols start with
774 system-specific local label prefixes, typically .L for ELF systems
775 or L for traditional a.out systems.)
776
777 -y symbol
778 --trace-symbol=symbol
779 Print the name of each linked file in which symbol appears. This
780 option may be given any number of times. On many systems it is
781 necessary to prepend an underscore.
782
783 This option is useful when you have an undefined symbol in your
784 link but don't know where the reference is coming from.
785
786 -Y path
787 Add path to the default library search path. This option exists
788 for Solaris compatibility.
789
790 -z keyword
791 The recognized keywords are:
792
793 bndplt
794 Always generate BND prefix in PLT entries. Supported for
795 Linux/x86_64.
796
797 call-nop=prefix-addr
798 call-nop=suffix-nop
799 call-nop=prefix-byte
800 call-nop=suffix-byte
801 Specify the 1-byte "NOP" padding when transforming indirect
802 call to a locally defined function, foo, via its GOT slot.
803 call-nop=prefix-addr generates "0x67 call foo".
804 call-nop=suffix-nop generates "call foo 0x90".
805 call-nop=prefix-byte generates "byte call foo".
806 call-nop=suffix-byte generates "call foo byte". Supported for
807 i386 and x86_64.
808
809 cet-report=none
810 cet-report=warning
811 cet-report=error
812 Specify how to report the missing
813 GNU_PROPERTY_X86_FEATURE_1_IBT and
814 GNU_PROPERTY_X86_FEATURE_1_SHSTK properties in input
815 .note.gnu.property section. cet-report=none, which is the
816 default, will make the linker not report missing properties in
817 input files. cet-report=warning will make the linker issue a
818 warning for missing properties in input files.
819 cet-report=error will make the linker issue an error for
820 missing properties in input files. Note that ibt will turn off
821 the missing GNU_PROPERTY_X86_FEATURE_1_IBT property report and
822 shstk will turn off the missing
823 GNU_PROPERTY_X86_FEATURE_1_SHSTK property report. Supported
824 for Linux/i386 and Linux/x86_64.
825
826 combreloc
827 nocombreloc
828 Combine multiple dynamic relocation sections and sort to
829 improve dynamic symbol lookup caching. Do not do this if
830 nocombreloc.
831
832 common
833 nocommon
834 Generate common symbols with STT_COMMON type during a
835 relocatable link. Use STT_OBJECT type if nocommon.
836
837 common-page-size=value
838 Set the page size most commonly used to value. Memory image
839 layout will be optimized to minimize memory pages if the system
840 is using pages of this size.
841
842 defs
843 Report unresolved symbol references from regular object files.
844 This is done even if the linker is creating a non-symbolic
845 shared library. This option is the inverse of -z undefs.
846
847 dynamic-undefined-weak
848 nodynamic-undefined-weak
849 Make undefined weak symbols dynamic when building a dynamic
850 object, if they are referenced from a regular object file and
851 not forced local by symbol visibility or versioning. Do not
852 make them dynamic if nodynamic-undefined-weak. If neither
853 option is given, a target may default to either option being in
854 force, or make some other selection of undefined weak symbols
855 dynamic. Not all targets support these options.
856
857 execstack
858 Marks the object as requiring executable stack.
859
860 global
861 This option is only meaningful when building a shared object.
862 It makes the symbols defined by this shared object available
863 for symbol resolution of subsequently loaded libraries.
864
865 globalaudit
866 This option is only meaningful when building a dynamic
867 executable. This option marks the executable as requiring
868 global auditing by setting the "DF_1_GLOBAUDIT" bit in the
869 "DT_FLAGS_1" dynamic tag. Global auditing requires that any
870 auditing library defined via the --depaudit or -P command-line
871 options be run for all dynamic objects loaded by the
872 application.
873
874 ibtplt
875 Generate Intel Indirect Branch Tracking (IBT) enabled PLT
876 entries. Supported for Linux/i386 and Linux/x86_64.
877
878 ibt Generate GNU_PROPERTY_X86_FEATURE_1_IBT in .note.gnu.property
879 section to indicate compatibility with IBT. This also implies
880 ibtplt. Supported for Linux/i386 and Linux/x86_64.
881
882 initfirst
883 This option is only meaningful when building a shared object.
884 It marks the object so that its runtime initialization will
885 occur before the runtime initialization of any other objects
886 brought into the process at the same time. Similarly the
887 runtime finalization of the object will occur after the runtime
888 finalization of any other objects.
889
890 interpose
891 Specify that the dynamic loader should modify its symbol search
892 order so that symbols in this shared library interpose all
893 other shared libraries not so marked.
894
895 unique
896 nounique
897 When generating a shared library or other dynamically loadable
898 ELF object mark it as one that should (by default) only ever be
899 loaded once, and only in the main namespace (when using
900 "dlmopen"). This is primarily used to mark fundamental
901 libraries such as libc, libpthread et al which do not usually
902 function correctly unless they are the sole instances of
903 themselves. This behaviour can be overridden by the "dlmopen"
904 caller and does not apply to certain loading mechanisms (such
905 as audit libraries).
906
907 lam-u48
908 Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U48 in
909 .note.gnu.property section to indicate compatibility with Intel
910 LAM_U48. Supported for Linux/x86_64.
911
912 lam-u57
913 Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U57 in
914 .note.gnu.property section to indicate compatibility with Intel
915 LAM_U57. Supported for Linux/x86_64.
916
917 lam-u48-report=none
918 lam-u48-report=warning
919 lam-u48-report=error
920 Specify how to report the missing
921 GNU_PROPERTY_X86_FEATURE_1_LAM_U48 property in input
922 .note.gnu.property section. lam-u48-report=none, which is the
923 default, will make the linker not report missing properties in
924 input files. lam-u48-report=warning will make the linker issue
925 a warning for missing properties in input files.
926 lam-u48-report=error will make the linker issue an error for
927 missing properties in input files. Supported for Linux/x86_64.
928
929 lam-u57-report=none
930 lam-u57-report=warning
931 lam-u57-report=error
932 Specify how to report the missing
933 GNU_PROPERTY_X86_FEATURE_1_LAM_U57 property in input
934 .note.gnu.property section. lam-u57-report=none, which is the
935 default, will make the linker not report missing properties in
936 input files. lam-u57-report=warning will make the linker issue
937 a warning for missing properties in input files.
938 lam-u57-report=error will make the linker issue an error for
939 missing properties in input files. Supported for Linux/x86_64.
940
941 lam-report=none
942 lam-report=warning
943 lam-report=error
944 Specify how to report the missing
945 GNU_PROPERTY_X86_FEATURE_1_LAM_U48 and
946 GNU_PROPERTY_X86_FEATURE_1_LAM_U57 properties in input
947 .note.gnu.property section. lam-report=none, which is the
948 default, will make the linker not report missing properties in
949 input files. lam-report=warning will make the linker issue a
950 warning for missing properties in input files.
951 lam-report=error will make the linker issue an error for
952 missing properties in input files. Supported for Linux/x86_64.
953
954 lazy
955 When generating an executable or shared library, mark it to
956 tell the dynamic linker to defer function call resolution to
957 the point when the function is called (lazy binding), rather
958 than at load time. Lazy binding is the default.
959
960 loadfltr
961 Specify that the object's filters be processed immediately at
962 runtime.
963
964 max-page-size=value
965 Set the maximum memory page size supported to value.
966
967 muldefs
968 Allow multiple definitions.
969
970 nocopyreloc
971 Disable linker generated .dynbss variables used in place of
972 variables defined in shared libraries. May result in dynamic
973 text relocations.
974
975 nodefaultlib
976 Specify that the dynamic loader search for dependencies of this
977 object should ignore any default library search paths.
978
979 nodelete
980 Specify that the object shouldn't be unloaded at runtime.
981
982 nodlopen
983 Specify that the object is not available to "dlopen".
984
985 nodump
986 Specify that the object can not be dumped by "dldump".
987
988 noexecstack
989 Marks the object as not requiring executable stack.
990
991 noextern-protected-data
992 Don't treat protected data symbols as external when building a
993 shared library. This option overrides the linker backend
994 default. It can be used to work around incorrect relocations
995 against protected data symbols generated by compiler. Updates
996 on protected data symbols by another module aren't visible to
997 the resulting shared library. Supported for i386 and x86-64.
998
999 noreloc-overflow
1000 Disable relocation overflow check. This can be used to disable
1001 relocation overflow check if there will be no dynamic
1002 relocation overflow at run-time. Supported for x86_64.
1003
1004 now When generating an executable or shared library, mark it to
1005 tell the dynamic linker to resolve all symbols when the program
1006 is started, or when the shared library is loaded by dlopen,
1007 instead of deferring function call resolution to the point when
1008 the function is first called.
1009
1010 origin
1011 Specify that the object requires $ORIGIN handling in paths.
1012
1013 relro
1014 norelro
1015 Create an ELF "PT_GNU_RELRO" segment header in the object.
1016 This specifies a memory segment that should be made read-only
1017 after relocation, if supported. Specifying common-page-size
1018 smaller than the system page size will render this protection
1019 ineffective. Don't create an ELF "PT_GNU_RELRO" segment if
1020 norelro.
1021
1022 report-relative-reloc
1023 Report dynamic relative relocations generated by linker.
1024 Supported for Linux/i386 and Linux/x86_64.
1025
1026 separate-code
1027 noseparate-code
1028 Create separate code "PT_LOAD" segment header in the object.
1029 This specifies a memory segment that should contain only
1030 instructions and must be in wholly disjoint pages from any
1031 other data. Don't create separate code "PT_LOAD" segment if
1032 noseparate-code is used.
1033
1034 shstk
1035 Generate GNU_PROPERTY_X86_FEATURE_1_SHSTK in .note.gnu.property
1036 section to indicate compatibility with Intel Shadow Stack.
1037 Supported for Linux/i386 and Linux/x86_64.
1038
1039 stack-size=value
1040 Specify a stack size for an ELF "PT_GNU_STACK" segment.
1041 Specifying zero will override any default non-zero sized
1042 "PT_GNU_STACK" segment creation.
1043
1044 start-stop-gc
1045 nostart-stop-gc
1046 When --gc-sections is in effect, a reference from a retained
1047 section to "__start_SECNAME" or "__stop_SECNAME" causes all
1048 input sections named "SECNAME" to also be retained, if
1049 "SECNAME" is representable as a C identifier and either
1050 "__start_SECNAME" or "__stop_SECNAME" is synthesized by the
1051 linker. -z start-stop-gc disables this effect, allowing
1052 sections to be garbage collected as if the special synthesized
1053 symbols were not defined. -z start-stop-gc has no effect on a
1054 definition of "__start_SECNAME" or "__stop_SECNAME" in an
1055 object file or linker script. Such a definition will prevent
1056 the linker providing a synthesized "__start_SECNAME" or
1057 "__stop_SECNAME" respectively, and therefore the special
1058 treatment by garbage collection for those references.
1059
1060 start-stop-visibility=value
1061 Specify the ELF symbol visibility for synthesized
1062 "__start_SECNAME" and "__stop_SECNAME" symbols. value must be
1063 exactly default, internal, hidden, or protected. If no -z
1064 start-stop-visibility option is given, protected is used for
1065 compatibility with historical practice. However, it's highly
1066 recommended to use -z start-stop-visibility=hidden in new
1067 programs and shared libraries so that these symbols are not
1068 exported between shared objects, which is not usually what's
1069 intended.
1070
1071 text
1072 notext
1073 textoff
1074 Report an error if DT_TEXTREL is set, i.e., if the position-
1075 independent or shared object has dynamic relocations in read-
1076 only sections. Don't report an error if notext or textoff.
1077
1078 undefs
1079 Do not report unresolved symbol references from regular object
1080 files, either when creating an executable, or when creating a
1081 shared library. This option is the inverse of -z defs.
1082
1083 unique-symbol
1084 nounique-symbol
1085 Avoid duplicated local symbol names in the symbol string table.
1086 Append "."number"" to duplicated local symbol names if unique-
1087 symbol is used. nounique-symbol is the default.
1088
1089 x86-64-baseline
1090 x86-64-v2
1091 x86-64-v3
1092 x86-64-v4
1093 Specify the x86-64 ISA level needed in .note.gnu.property
1094 section. x86-64-baseline generates
1095 "GNU_PROPERTY_X86_ISA_1_BASELINE". x86-64-v2 generates
1096 "GNU_PROPERTY_X86_ISA_1_V2". x86-64-v3 generates
1097 "GNU_PROPERTY_X86_ISA_1_V3". x86-64-v4 generates
1098 "GNU_PROPERTY_X86_ISA_1_V4". Supported for Linux/i386 and
1099 Linux/x86_64.
1100
1101 Other keywords are ignored for Solaris compatibility.
1102
1103 -( archives -)
1104 --start-group archives --end-group
1105 The archives should be a list of archive files. They may be either
1106 explicit file names, or -l options.
1107
1108 The specified archives are searched repeatedly until no new
1109 undefined references are created. Normally, an archive is searched
1110 only once in the order that it is specified on the command line.
1111 If a symbol in that archive is needed to resolve an undefined
1112 symbol referred to by an object in an archive that appears later on
1113 the command line, the linker would not be able to resolve that
1114 reference. By grouping the archives, they will all be searched
1115 repeatedly until all possible references are resolved.
1116
1117 Using this option has a significant performance cost. It is best
1118 to use it only when there are unavoidable circular references
1119 between two or more archives.
1120
1121 --accept-unknown-input-arch
1122 --no-accept-unknown-input-arch
1123 Tells the linker to accept input files whose architecture cannot be
1124 recognised. The assumption is that the user knows what they are
1125 doing and deliberately wants to link in these unknown input files.
1126 This was the default behaviour of the linker, before release 2.14.
1127 The default behaviour from release 2.14 onwards is to reject such
1128 input files, and so the --accept-unknown-input-arch option has been
1129 added to restore the old behaviour.
1130
1131 --as-needed
1132 --no-as-needed
1133 This option affects ELF DT_NEEDED tags for dynamic libraries
1134 mentioned on the command line after the --as-needed option.
1135 Normally the linker will add a DT_NEEDED tag for each dynamic
1136 library mentioned on the command line, regardless of whether the
1137 library is actually needed or not. --as-needed causes a DT_NEEDED
1138 tag to only be emitted for a library that at that point in the link
1139 satisfies a non-weak undefined symbol reference from a regular
1140 object file or, if the library is not found in the DT_NEEDED lists
1141 of other needed libraries, a non-weak undefined symbol reference
1142 from another needed dynamic library. Object files or libraries
1143 appearing on the command line after the library in question do not
1144 affect whether the library is seen as needed. This is similar to
1145 the rules for extraction of object files from archives.
1146 --no-as-needed restores the default behaviour.
1147
1148 Note: On Linux based systems the --as-needed option also has an
1149 affect on the behaviour of the --rpath and --rpath-link options.
1150 See the description of --rpath-link for more details.
1151
1152 --add-needed
1153 --no-add-needed
1154 These two options have been deprecated because of the similarity of
1155 their names to the --as-needed and --no-as-needed options. They
1156 have been replaced by --copy-dt-needed-entries and
1157 --no-copy-dt-needed-entries.
1158
1159 -assert keyword
1160 This option is ignored for SunOS compatibility.
1161
1162 -Bdynamic
1163 -dy
1164 -call_shared
1165 Link against dynamic libraries. This is only meaningful on
1166 platforms for which shared libraries are supported. This option is
1167 normally the default on such platforms. The different variants of
1168 this option are for compatibility with various systems. You may
1169 use this option multiple times on the command line: it affects
1170 library searching for -l options which follow it.
1171
1172 -Bgroup
1173 Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the dynamic
1174 section. This causes the runtime linker to handle lookups in this
1175 object and its dependencies to be performed only inside the group.
1176 --unresolved-symbols=report-all is implied. This option is only
1177 meaningful on ELF platforms which support shared libraries.
1178
1179 -Bstatic
1180 -dn
1181 -non_shared
1182 -static
1183 Do not link against shared libraries. This is only meaningful on
1184 platforms for which shared libraries are supported. The different
1185 variants of this option are for compatibility with various systems.
1186 You may use this option multiple times on the command line: it
1187 affects library searching for -l options which follow it. This
1188 option also implies --unresolved-symbols=report-all. This option
1189 can be used with -shared. Doing so means that a shared library is
1190 being created but that all of the library's external references
1191 must be resolved by pulling in entries from static libraries.
1192
1193 -Bsymbolic
1194 When creating a shared library, bind references to global symbols
1195 to the definition within the shared library, if any. Normally, it
1196 is possible for a program linked against a shared library to
1197 override the definition within the shared library. This option is
1198 only meaningful on ELF platforms which support shared libraries.
1199
1200 -Bsymbolic-functions
1201 When creating a shared library, bind references to global function
1202 symbols to the definition within the shared library, if any. This
1203 option is only meaningful on ELF platforms which support shared
1204 libraries.
1205
1206 -Bno-symbolic
1207 This option can cancel previously specified -Bsymbolic and
1208 -Bsymbolic-functions.
1209
1210 --dynamic-list=dynamic-list-file
1211 Specify the name of a dynamic list file to the linker. This is
1212 typically used when creating shared libraries to specify a list of
1213 global symbols whose references shouldn't be bound to the
1214 definition within the shared library, or creating dynamically
1215 linked executables to specify a list of symbols which should be
1216 added to the symbol table in the executable. This option is only
1217 meaningful on ELF platforms which support shared libraries.
1218
1219 The format of the dynamic list is the same as the version node
1220 without scope and node name. See VERSION for more information.
1221
1222 --dynamic-list-data
1223 Include all global data symbols to the dynamic list.
1224
1225 --dynamic-list-cpp-new
1226 Provide the builtin dynamic list for C++ operator new and delete.
1227 It is mainly useful for building shared libstdc++.
1228
1229 --dynamic-list-cpp-typeinfo
1230 Provide the builtin dynamic list for C++ runtime type
1231 identification.
1232
1233 --check-sections
1234 --no-check-sections
1235 Asks the linker not to check section addresses after they have been
1236 assigned to see if there are any overlaps. Normally the linker
1237 will perform this check, and if it finds any overlaps it will
1238 produce suitable error messages. The linker does know about, and
1239 does make allowances for sections in overlays. The default
1240 behaviour can be restored by using the command-line switch
1241 --check-sections. Section overlap is not usually checked for
1242 relocatable links. You can force checking in that case by using
1243 the --check-sections option.
1244
1245 --copy-dt-needed-entries
1246 --no-copy-dt-needed-entries
1247 This option affects the treatment of dynamic libraries referred to
1248 by DT_NEEDED tags inside ELF dynamic libraries mentioned on the
1249 command line. Normally the linker won't add a DT_NEEDED tag to the
1250 output binary for each library mentioned in a DT_NEEDED tag in an
1251 input dynamic library. With --copy-dt-needed-entries specified on
1252 the command line however any dynamic libraries that follow it will
1253 have their DT_NEEDED entries added. The default behaviour can be
1254 restored with --no-copy-dt-needed-entries.
1255
1256 This option also has an effect on the resolution of symbols in
1257 dynamic libraries. With --copy-dt-needed-entries dynamic libraries
1258 mentioned on the command line will be recursively searched,
1259 following their DT_NEEDED tags to other libraries, in order to
1260 resolve symbols required by the output binary. With the default
1261 setting however the searching of dynamic libraries that follow it
1262 will stop with the dynamic library itself. No DT_NEEDED links will
1263 be traversed to resolve symbols.
1264
1265 --cref
1266 Output a cross reference table. If a linker map file is being
1267 generated, the cross reference table is printed to the map file.
1268 Otherwise, it is printed on the standard output.
1269
1270 The format of the table is intentionally simple, so that it may be
1271 easily processed by a script if necessary. The symbols are printed
1272 out, sorted by name. For each symbol, a list of file names is
1273 given. If the symbol is defined, the first file listed is the
1274 location of the definition. If the symbol is defined as a common
1275 value then any files where this happens appear next. Finally any
1276 files that reference the symbol are listed.
1277
1278 --ctf-variables
1279 --no-ctf-variables
1280 The CTF debuginfo format supports a section which encodes the names
1281 and types of variables found in the program which do not appear in
1282 any symbol table. These variables clearly cannot be looked up by
1283 address by conventional debuggers, so the space used for their
1284 types and names is usually wasted: the types are usually small but
1285 the names are often not. --ctf-variables causes the generation of
1286 such a section. The default behaviour can be restored with
1287 --no-ctf-variables.
1288
1289 --ctf-share-types=method
1290 Adjust the method used to share types between translation units in
1291 CTF.
1292
1293 share-unconflicted
1294 Put all types that do not have ambiguous definitions into the
1295 shared dictionary, where debuggers can easily access them, even
1296 if they only occur in one translation unit. This is the
1297 default.
1298
1299 share-duplicated
1300 Put only types that occur in multiple translation units into
1301 the shared dictionary: types with only one definition go into
1302 per-translation-unit dictionaries. Types with ambiguous
1303 definitions in multiple translation units always go into per-
1304 translation-unit dictionaries. This tends to make the CTF
1305 larger, but may reduce the amount of CTF in the shared
1306 dictionary. For very large projects this may speed up opening
1307 the CTF and save memory in the CTF consumer at runtime.
1308
1309 --no-define-common
1310 This option inhibits the assignment of addresses to common symbols.
1311 The script command "INHIBIT_COMMON_ALLOCATION" has the same effect.
1312
1313 The --no-define-common option allows decoupling the decision to
1314 assign addresses to Common symbols from the choice of the output
1315 file type; otherwise a non-Relocatable output type forces assigning
1316 addresses to Common symbols. Using --no-define-common allows
1317 Common symbols that are referenced from a shared library to be
1318 assigned addresses only in the main program. This eliminates the
1319 unused duplicate space in the shared library, and also prevents any
1320 possible confusion over resolving to the wrong duplicate when there
1321 are many dynamic modules with specialized search paths for runtime
1322 symbol resolution.
1323
1324 --force-group-allocation
1325 This option causes the linker to place section group members like
1326 normal input sections, and to delete the section groups. This is
1327 the default behaviour for a final link but this option can be used
1328 to change the behaviour of a relocatable link (-r). The script
1329 command "FORCE_GROUP_ALLOCATION" has the same effect.
1330
1331 --defsym=symbol=expression
1332 Create a global symbol in the output file, containing the absolute
1333 address given by expression. You may use this option as many times
1334 as necessary to define multiple symbols in the command line. A
1335 limited form of arithmetic is supported for the expression in this
1336 context: you may give a hexadecimal constant or the name of an
1337 existing symbol, or use "+" and "-" to add or subtract hexadecimal
1338 constants or symbols. If you need more elaborate expressions,
1339 consider using the linker command language from a script. Note:
1340 there should be no white space between symbol, the equals sign
1341 ("="), and expression.
1342
1343 The linker processes --defsym arguments and -T arguments in order,
1344 placing --defsym before -T will define the symbol before the linker
1345 script from -T is processed, while placing --defsym after -T will
1346 define the symbol after the linker script has been processed. This
1347 difference has consequences for expressions within the linker
1348 script that use the --defsym symbols, which order is correct will
1349 depend on what you are trying to achieve.
1350
1351 --demangle[=style]
1352 --no-demangle
1353 These options control whether to demangle symbol names in error
1354 messages and other output. When the linker is told to demangle, it
1355 tries to present symbol names in a readable fashion: it strips
1356 leading underscores if they are used by the object file format, and
1357 converts C++ mangled symbol names into user readable names.
1358 Different compilers have different mangling styles. The optional
1359 demangling style argument can be used to choose an appropriate
1360 demangling style for your compiler. The linker will demangle by
1361 default unless the environment variable COLLECT_NO_DEMANGLE is set.
1362 These options may be used to override the default.
1363
1364 -Ifile
1365 --dynamic-linker=file
1366 Set the name of the dynamic linker. This is only meaningful when
1367 generating dynamically linked ELF executables. The default dynamic
1368 linker is normally correct; don't use this unless you know what you
1369 are doing.
1370
1371 --no-dynamic-linker
1372 When producing an executable file, omit the request for a dynamic
1373 linker to be used at load-time. This is only meaningful for ELF
1374 executables that contain dynamic relocations, and usually requires
1375 entry point code that is capable of processing these relocations.
1376
1377 --embedded-relocs
1378 This option is similar to the --emit-relocs option except that the
1379 relocs are stored in a target-specific section. This option is
1380 only supported by the BFIN, CR16 and M68K targets.
1381
1382 --disable-multiple-abs-defs
1383 Do not allow multiple definitions with symbols included in filename
1384 invoked by -R or --just-symbols
1385
1386 --fatal-warnings
1387 --no-fatal-warnings
1388 Treat all warnings as errors. The default behaviour can be
1389 restored with the option --no-fatal-warnings.
1390
1391 --force-exe-suffix
1392 Make sure that an output file has a .exe suffix.
1393
1394 If a successfully built fully linked output file does not have a
1395 ".exe" or ".dll" suffix, this option forces the linker to copy the
1396 output file to one of the same name with a ".exe" suffix. This
1397 option is useful when using unmodified Unix makefiles on a
1398 Microsoft Windows host, since some versions of Windows won't run an
1399 image unless it ends in a ".exe" suffix.
1400
1401 --gc-sections
1402 --no-gc-sections
1403 Enable garbage collection of unused input sections. It is ignored
1404 on targets that do not support this option. The default behaviour
1405 (of not performing this garbage collection) can be restored by
1406 specifying --no-gc-sections on the command line. Note that garbage
1407 collection for COFF and PE format targets is supported, but the
1408 implementation is currently considered to be experimental.
1409
1410 --gc-sections decides which input sections are used by examining
1411 symbols and relocations. The section containing the entry symbol
1412 and all sections containing symbols undefined on the command-line
1413 will be kept, as will sections containing symbols referenced by
1414 dynamic objects. Note that when building shared libraries, the
1415 linker must assume that any visible symbol is referenced. Once
1416 this initial set of sections has been determined, the linker
1417 recursively marks as used any section referenced by their
1418 relocations. See --entry, --undefined, and --gc-keep-exported.
1419
1420 This option can be set when doing a partial link (enabled with
1421 option -r). In this case the root of symbols kept must be
1422 explicitly specified either by one of the options --entry,
1423 --undefined, or --gc-keep-exported or by a "ENTRY" command in the
1424 linker script.
1425
1426 As a GNU extension, ELF input sections marked with the
1427 "SHF_GNU_RETAIN" flag will not be garbage collected.
1428
1429 --print-gc-sections
1430 --no-print-gc-sections
1431 List all sections removed by garbage collection. The listing is
1432 printed on stderr. This option is only effective if garbage
1433 collection has been enabled via the --gc-sections) option. The
1434 default behaviour (of not listing the sections that are removed)
1435 can be restored by specifying --no-print-gc-sections on the command
1436 line.
1437
1438 --gc-keep-exported
1439 When --gc-sections is enabled, this option prevents garbage
1440 collection of unused input sections that contain global symbols
1441 having default or protected visibility. This option is intended to
1442 be used for executables where unreferenced sections would otherwise
1443 be garbage collected regardless of the external visibility of
1444 contained symbols. Note that this option has no effect when
1445 linking shared objects since it is already the default behaviour.
1446 This option is only supported for ELF format targets.
1447
1448 --print-output-format
1449 Print the name of the default output format (perhaps influenced by
1450 other command-line options). This is the string that would appear
1451 in an "OUTPUT_FORMAT" linker script command.
1452
1453 --print-memory-usage
1454 Print used size, total size and used size of memory regions created
1455 with the MEMORY command. This is useful on embedded targets to
1456 have a quick view of amount of free memory. The format of the
1457 output has one headline and one line per region. It is both human
1458 readable and easily parsable by tools. Here is an example of an
1459 output:
1460
1461 Memory region Used Size Region Size %age Used
1462 ROM: 256 KB 1 MB 25.00%
1463 RAM: 32 B 2 GB 0.00%
1464
1465 --help
1466 Print a summary of the command-line options on the standard output
1467 and exit.
1468
1469 --target-help
1470 Print a summary of all target-specific options on the standard
1471 output and exit.
1472
1473 -Map=mapfile
1474 Print a link map to the file mapfile. See the description of the
1475 -M option, above. If mapfile is just the character "-" then the
1476 map will be written to stdout.
1477
1478 Specifying a directory as mapfile causes the linker map to be
1479 written as a file inside the directory. Normally name of the file
1480 inside the directory is computed as the basename of the output file
1481 with ".map" appended. If however the special character "%" is
1482 used then this will be replaced by the full path of the output
1483 file. Additionally if there are any characters after the % symbol
1484 then ".map" will no longer be appended.
1485
1486 -o foo.exe -Map=bar [Creates ./bar]
1487 -o ../dir/foo.exe -Map=bar [Creates ./bar]
1488 -o foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
1489 -o ../dir2/foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
1490 -o foo.exe -Map=% [Creates ./foo.exe.map]
1491 -o ../dir/foo.exe -Map=% [Creates ../dir/foo.exe.map]
1492 -o foo.exe -Map=%.bar [Creates ./foo.exe.bar]
1493 -o ../dir/foo.exe -Map=%.bar [Creates ../dir/foo.exe.bar]
1494 -o ../dir2/foo.exe -Map=../dir/% [Creates ../dir/../dir2/foo.exe.map]
1495 -o ../dir2/foo.exe -Map=../dir/%.bar [Creates ../dir/../dir2/foo.exe.bar]
1496
1497 It is an error to specify more than one "%" character.
1498
1499 If the map file already exists then it will be overwritten by this
1500 operation.
1501
1502 --no-keep-memory
1503 ld normally optimizes for speed over memory usage by caching the
1504 symbol tables of input files in memory. This option tells ld to
1505 instead optimize for memory usage, by rereading the symbol tables
1506 as necessary. This may be required if ld runs out of memory space
1507 while linking a large executable.
1508
1509 --no-undefined
1510 -z defs
1511 Report unresolved symbol references from regular object files.
1512 This is done even if the linker is creating a non-symbolic shared
1513 library. The switch --[no-]allow-shlib-undefined controls the
1514 behaviour for reporting unresolved references found in shared
1515 libraries being linked in.
1516
1517 The effects of this option can be reverted by using "-z undefs".
1518
1519 --allow-multiple-definition
1520 -z muldefs
1521 Normally when a symbol is defined multiple times, the linker will
1522 report a fatal error. These options allow multiple definitions and
1523 the first definition will be used.
1524
1525 --allow-shlib-undefined
1526 --no-allow-shlib-undefined
1527 Allows or disallows undefined symbols in shared libraries. This
1528 switch is similar to --no-undefined except that it determines the
1529 behaviour when the undefined symbols are in a shared library rather
1530 than a regular object file. It does not affect how undefined
1531 symbols in regular object files are handled.
1532
1533 The default behaviour is to report errors for any undefined symbols
1534 referenced in shared libraries if the linker is being used to
1535 create an executable, but to allow them if the linker is being used
1536 to create a shared library.
1537
1538 The reasons for allowing undefined symbol references in shared
1539 libraries specified at link time are that:
1540
1541 • A shared library specified at link time may not be the same as
1542 the one that is available at load time, so the symbol might
1543 actually be resolvable at load time.
1544
1545 • There are some operating systems, eg BeOS and HPPA, where
1546 undefined symbols in shared libraries are normal.
1547
1548 The BeOS kernel for example patches shared libraries at load
1549 time to select whichever function is most appropriate for the
1550 current architecture. This is used, for example, to
1551 dynamically select an appropriate memset function.
1552
1553 --error-handling-script=scriptname
1554 If this option is provided then the linker will invoke scriptname
1555 whenever an error is encountered. Currently however only two kinds
1556 of error are supported: missing symbols and missing libraries. Two
1557 arguments will be passed to script: the keyword "undefined-symbol"
1558 or `missing-lib" and the name of the undefined symbol or missing
1559 library. The intention is that the script will provide suggestions
1560 to the user as to where the symbol or library might be found.
1561 After the script has finished then the normal linker error message
1562 will be displayed.
1563
1564 The availability of this option is controlled by a configure time
1565 switch, so it may not be present in specific implementations.
1566
1567 --no-undefined-version
1568 Normally when a symbol has an undefined version, the linker will
1569 ignore it. This option disallows symbols with undefined version and
1570 a fatal error will be issued instead.
1571
1572 --default-symver
1573 Create and use a default symbol version (the soname) for
1574 unversioned exported symbols.
1575
1576 --default-imported-symver
1577 Create and use a default symbol version (the soname) for
1578 unversioned imported symbols.
1579
1580 --no-warn-mismatch
1581 Normally ld will give an error if you try to link together input
1582 files that are mismatched for some reason, perhaps because they
1583 have been compiled for different processors or for different
1584 endiannesses. This option tells ld that it should silently permit
1585 such possible errors. This option should only be used with care,
1586 in cases when you have taken some special action that ensures that
1587 the linker errors are inappropriate.
1588
1589 --no-warn-search-mismatch
1590 Normally ld will give a warning if it finds an incompatible library
1591 during a library search. This option silences the warning.
1592
1593 --no-whole-archive
1594 Turn off the effect of the --whole-archive option for subsequent
1595 archive files.
1596
1597 --noinhibit-exec
1598 Retain the executable output file whenever it is still usable.
1599 Normally, the linker will not produce an output file if it
1600 encounters errors during the link process; it exits without writing
1601 an output file when it issues any error whatsoever.
1602
1603 -nostdlib
1604 Only search library directories explicitly specified on the command
1605 line. Library directories specified in linker scripts (including
1606 linker scripts specified on the command line) are ignored.
1607
1608 --oformat=output-format
1609 ld may be configured to support more than one kind of object file.
1610 If your ld is configured this way, you can use the --oformat option
1611 to specify the binary format for the output object file. Even when
1612 ld is configured to support alternative object formats, you don't
1613 usually need to specify this, as ld should be configured to produce
1614 as a default output format the most usual format on each machine.
1615 output-format is a text string, the name of a particular format
1616 supported by the BFD libraries. (You can list the available binary
1617 formats with objdump -i.) The script command "OUTPUT_FORMAT" can
1618 also specify the output format, but this option overrides it.
1619
1620 --out-implib file
1621 Create an import library in file corresponding to the executable
1622 the linker is generating (eg. a DLL or ELF program). This import
1623 library (which should be called "*.dll.a" or "*.a" for DLLs) may be
1624 used to link clients against the generated executable; this
1625 behaviour makes it possible to skip a separate import library
1626 creation step (eg. "dlltool" for DLLs). This option is only
1627 available for the i386 PE and ELF targetted ports of the linker.
1628
1629 -pie
1630 --pic-executable
1631 Create a position independent executable. This is currently only
1632 supported on ELF platforms. Position independent executables are
1633 similar to shared libraries in that they are relocated by the
1634 dynamic linker to the virtual address the OS chooses for them
1635 (which can vary between invocations). Like normal dynamically
1636 linked executables they can be executed and symbols defined in the
1637 executable cannot be overridden by shared libraries.
1638
1639 -no-pie
1640 Create a position dependent executable. This is the default.
1641
1642 -qmagic
1643 This option is ignored for Linux compatibility.
1644
1645 -Qy This option is ignored for SVR4 compatibility.
1646
1647 --relax
1648 --no-relax
1649 An option with machine dependent effects. This option is only
1650 supported on a few targets.
1651
1652 On some platforms the --relax option performs target specific,
1653 global optimizations that become possible when the linker resolves
1654 addressing in the program, such as relaxing address modes,
1655 synthesizing new instructions, selecting shorter version of current
1656 instructions, and combining constant values.
1657
1658 On some platforms these link time global optimizations may make
1659 symbolic debugging of the resulting executable impossible. This is
1660 known to be the case for the Matsushita MN10200 and MN10300 family
1661 of processors.
1662
1663 On platforms where the feature is supported, the option --no-relax
1664 will disable it.
1665
1666 On platforms where the feature is not supported, both --relax and
1667 --no-relax are accepted, but ignored.
1668
1669 --retain-symbols-file=filename
1670 Retain only the symbols listed in the file filename, discarding all
1671 others. filename is simply a flat file, with one symbol name per
1672 line. This option is especially useful in environments (such as
1673 VxWorks) where a large global symbol table is accumulated
1674 gradually, to conserve run-time memory.
1675
1676 --retain-symbols-file does not discard undefined symbols, or
1677 symbols needed for relocations.
1678
1679 You may only specify --retain-symbols-file once in the command
1680 line. It overrides -s and -S.
1681
1682 -rpath=dir
1683 Add a directory to the runtime library search path. This is used
1684 when linking an ELF executable with shared objects. All -rpath
1685 arguments are concatenated and passed to the runtime linker, which
1686 uses them to locate shared objects at runtime.
1687
1688 The -rpath option is also used when locating shared objects which
1689 are needed by shared objects explicitly included in the link; see
1690 the description of the -rpath-link option. Searching -rpath in
1691 this way is only supported by native linkers and cross linkers
1692 which have been configured with the --with-sysroot option.
1693
1694 If -rpath is not used when linking an ELF executable, the contents
1695 of the environment variable "LD_RUN_PATH" will be used if it is
1696 defined.
1697
1698 The -rpath option may also be used on SunOS. By default, on SunOS,
1699 the linker will form a runtime search path out of all the -L
1700 options it is given. If a -rpath option is used, the runtime
1701 search path will be formed exclusively using the -rpath options,
1702 ignoring the -L options. This can be useful when using gcc, which
1703 adds many -L options which may be on NFS mounted file systems.
1704
1705 For compatibility with other ELF linkers, if the -R option is
1706 followed by a directory name, rather than a file name, it is
1707 treated as the -rpath option.
1708
1709 -rpath-link=dir
1710 When using ELF or SunOS, one shared library may require another.
1711 This happens when an "ld -shared" link includes a shared library as
1712 one of the input files.
1713
1714 When the linker encounters such a dependency when doing a non-
1715 shared, non-relocatable link, it will automatically try to locate
1716 the required shared library and include it in the link, if it is
1717 not included explicitly. In such a case, the -rpath-link option
1718 specifies the first set of directories to search. The -rpath-link
1719 option may specify a sequence of directory names either by
1720 specifying a list of names separated by colons, or by appearing
1721 multiple times.
1722
1723 The tokens $ORIGIN and $LIB can appear in these search directories.
1724 They will be replaced by the full path to the directory containing
1725 the program or shared object in the case of $ORIGIN and either lib
1726 - for 32-bit binaries - or lib64 - for 64-bit binaries - in the
1727 case of $LIB.
1728
1729 The alternative form of these tokens - ${ORIGIN} and ${LIB} can
1730 also be used. The token $PLATFORM is not supported.
1731
1732 This option should be used with caution as it overrides the search
1733 path that may have been hard compiled into a shared library. In
1734 such a case it is possible to use unintentionally a different
1735 search path than the runtime linker would do.
1736
1737 The linker uses the following search paths to locate required
1738 shared libraries:
1739
1740 1. Any directories specified by -rpath-link options.
1741
1742 2. Any directories specified by -rpath options. The difference
1743 between -rpath and -rpath-link is that directories specified by
1744 -rpath options are included in the executable and used at
1745 runtime, whereas the -rpath-link option is only effective at
1746 link time. Searching -rpath in this way is only supported by
1747 native linkers and cross linkers which have been configured
1748 with the --with-sysroot option.
1749
1750 3. On an ELF system, for native linkers, if the -rpath and
1751 -rpath-link options were not used, search the contents of the
1752 environment variable "LD_RUN_PATH".
1753
1754 4. On SunOS, if the -rpath option was not used, search any
1755 directories specified using -L options.
1756
1757 5. For a native linker, search the contents of the environment
1758 variable "LD_LIBRARY_PATH".
1759
1760 6. For a native ELF linker, the directories in "DT_RUNPATH" or
1761 "DT_RPATH" of a shared library are searched for shared
1762 libraries needed by it. The "DT_RPATH" entries are ignored if
1763 "DT_RUNPATH" entries exist.
1764
1765 7. For a linker for a Linux system, if the file /etc/ld.so.conf
1766 exists, the list of directories found in that file. Note: the
1767 path to this file is prefixed with the "sysroot" value, if that
1768 is defined, and then any "prefix" string if the linker was
1769 configured with the --prefix=<path> option.
1770
1771 8. For a native linker on a FreeBSD system, any directories
1772 specified by the "_PATH_ELF_HINTS" macro defined in the
1773 elf-hints.h header file.
1774
1775 9. Any directories specified by a "SEARCH_DIR" command in a linker
1776 script given on the command line, including scripts specified
1777 by -T (but not -dT).
1778
1779 10. The default directories, normally /lib and /usr/lib.
1780
1781 11. Any directories specified by a plugin
1782 LDPT_SET_EXTRA_LIBRARY_PATH.
1783
1784 12. Any directories specified by a "SEARCH_DIR" command in a
1785 default linker script.
1786
1787 Note however on Linux based systems there is an additional caveat:
1788 If the --as-needed option is active and a shared library is located
1789 which would normally satisfy the search and this library does not
1790 have DT_NEEDED tag for libc.so and there is a shared library later
1791 on in the set of search directories which also satisfies the search
1792 and this second shared library does have a DT_NEEDED tag for
1793 libc.so then the second library will be selected instead of the
1794 first.
1795
1796 If the required shared library is not found, the linker will issue
1797 a warning and continue with the link.
1798
1799 -shared
1800 -Bshareable
1801 Create a shared library. This is currently only supported on ELF,
1802 XCOFF and SunOS platforms. On SunOS, the linker will automatically
1803 create a shared library if the -e option is not used and there are
1804 undefined symbols in the link.
1805
1806 --sort-common
1807 --sort-common=ascending
1808 --sort-common=descending
1809 This option tells ld to sort the common symbols by alignment in
1810 ascending or descending order when it places them in the
1811 appropriate output sections. The symbol alignments considered are
1812 sixteen-byte or larger, eight-byte, four-byte, two-byte, and one-
1813 byte. This is to prevent gaps between symbols due to alignment
1814 constraints. If no sorting order is specified, then descending
1815 order is assumed.
1816
1817 --sort-section=name
1818 This option will apply "SORT_BY_NAME" to all wildcard section
1819 patterns in the linker script.
1820
1821 --sort-section=alignment
1822 This option will apply "SORT_BY_ALIGNMENT" to all wildcard section
1823 patterns in the linker script.
1824
1825 --spare-dynamic-tags=count
1826 This option specifies the number of empty slots to leave in the
1827 .dynamic section of ELF shared objects. Empty slots may be needed
1828 by post processing tools, such as the prelinker. The default is 5.
1829
1830 --split-by-file[=size]
1831 Similar to --split-by-reloc but creates a new output section for
1832 each input file when size is reached. size defaults to a size of 1
1833 if not given.
1834
1835 --split-by-reloc[=count]
1836 Tries to creates extra sections in the output file so that no
1837 single output section in the file contains more than count
1838 relocations. This is useful when generating huge relocatable files
1839 for downloading into certain real time kernels with the COFF object
1840 file format; since COFF cannot represent more than 65535
1841 relocations in a single section. Note that this will fail to work
1842 with object file formats which do not support arbitrary sections.
1843 The linker will not split up individual input sections for
1844 redistribution, so if a single input section contains more than
1845 count relocations one output section will contain that many
1846 relocations. count defaults to a value of 32768.
1847
1848 --stats
1849 Compute and display statistics about the operation of the linker,
1850 such as execution time and memory usage.
1851
1852 --sysroot=directory
1853 Use directory as the location of the sysroot, overriding the
1854 configure-time default. This option is only supported by linkers
1855 that were configured using --with-sysroot.
1856
1857 --task-link
1858 This is used by COFF/PE based targets to create a task-linked
1859 object file where all of the global symbols have been converted to
1860 statics.
1861
1862 --traditional-format
1863 For some targets, the output of ld is different in some ways from
1864 the output of some existing linker. This switch requests ld to use
1865 the traditional format instead.
1866
1867 For example, on SunOS, ld combines duplicate entries in the symbol
1868 string table. This can reduce the size of an output file with full
1869 debugging information by over 30 percent. Unfortunately, the SunOS
1870 "dbx" program can not read the resulting program ("gdb" has no
1871 trouble). The --traditional-format switch tells ld to not combine
1872 duplicate entries.
1873
1874 --section-start=sectionname=org
1875 Locate a section in the output file at the absolute address given
1876 by org. You may use this option as many times as necessary to
1877 locate multiple sections in the command line. org must be a single
1878 hexadecimal integer; for compatibility with other linkers, you may
1879 omit the leading 0x usually associated with hexadecimal values.
1880 Note: there should be no white space between sectionname, the
1881 equals sign ("="), and org.
1882
1883 -Tbss=org
1884 -Tdata=org
1885 -Ttext=org
1886 Same as --section-start, with ".bss", ".data" or ".text" as the
1887 sectionname.
1888
1889 -Ttext-segment=org
1890 When creating an ELF executable, it will set the address of the
1891 first byte of the text segment.
1892
1893 -Trodata-segment=org
1894 When creating an ELF executable or shared object for a target where
1895 the read-only data is in its own segment separate from the
1896 executable text, it will set the address of the first byte of the
1897 read-only data segment.
1898
1899 -Tldata-segment=org
1900 When creating an ELF executable or shared object for x86-64 medium
1901 memory model, it will set the address of the first byte of the
1902 ldata segment.
1903
1904 --unresolved-symbols=method
1905 Determine how to handle unresolved symbols. There are four
1906 possible values for method:
1907
1908 ignore-all
1909 Do not report any unresolved symbols.
1910
1911 report-all
1912 Report all unresolved symbols. This is the default.
1913
1914 ignore-in-object-files
1915 Report unresolved symbols that are contained in shared
1916 libraries, but ignore them if they come from regular object
1917 files.
1918
1919 ignore-in-shared-libs
1920 Report unresolved symbols that come from regular object files,
1921 but ignore them if they come from shared libraries. This can
1922 be useful when creating a dynamic binary and it is known that
1923 all the shared libraries that it should be referencing are
1924 included on the linker's command line.
1925
1926 The behaviour for shared libraries on their own can also be
1927 controlled by the --[no-]allow-shlib-undefined option.
1928
1929 Normally the linker will generate an error message for each
1930 reported unresolved symbol but the option --warn-unresolved-symbols
1931 can change this to a warning.
1932
1933 --dll-verbose
1934 --verbose[=NUMBER]
1935 Display the version number for ld and list the linker emulations
1936 supported. Display which input files can and cannot be opened.
1937 Display the linker script being used by the linker. If the optional
1938 NUMBER argument > 1, plugin symbol status will also be displayed.
1939
1940 --version-script=version-scriptfile
1941 Specify the name of a version script to the linker. This is
1942 typically used when creating shared libraries to specify additional
1943 information about the version hierarchy for the library being
1944 created. This option is only fully supported on ELF platforms
1945 which support shared libraries; see VERSION. It is partially
1946 supported on PE platforms, which can use version scripts to filter
1947 symbol visibility in auto-export mode: any symbols marked local in
1948 the version script will not be exported.
1949
1950 --warn-common
1951 Warn when a common symbol is combined with another common symbol or
1952 with a symbol definition. Unix linkers allow this somewhat sloppy
1953 practice, but linkers on some other operating systems do not. This
1954 option allows you to find potential problems from combining global
1955 symbols. Unfortunately, some C libraries use this practice, so you
1956 may get some warnings about symbols in the libraries as well as in
1957 your programs.
1958
1959 There are three kinds of global symbols, illustrated here by C
1960 examples:
1961
1962 int i = 1;
1963 A definition, which goes in the initialized data section of the
1964 output file.
1965
1966 extern int i;
1967 An undefined reference, which does not allocate space. There
1968 must be either a definition or a common symbol for the variable
1969 somewhere.
1970
1971 int i;
1972 A common symbol. If there are only (one or more) common
1973 symbols for a variable, it goes in the uninitialized data area
1974 of the output file. The linker merges multiple common symbols
1975 for the same variable into a single symbol. If they are of
1976 different sizes, it picks the largest size. The linker turns a
1977 common symbol into a declaration, if there is a definition of
1978 the same variable.
1979
1980 The --warn-common option can produce five kinds of warnings. Each
1981 warning consists of a pair of lines: the first describes the symbol
1982 just encountered, and the second describes the previous symbol
1983 encountered with the same name. One or both of the two symbols
1984 will be a common symbol.
1985
1986 1. Turning a common symbol into a reference, because there is
1987 already a definition for the symbol.
1988
1989 <file>(<section>): warning: common of `<symbol>'
1990 overridden by definition
1991 <file>(<section>): warning: defined here
1992
1993 2. Turning a common symbol into a reference, because a later
1994 definition for the symbol is encountered. This is the same as
1995 the previous case, except that the symbols are encountered in a
1996 different order.
1997
1998 <file>(<section>): warning: definition of `<symbol>'
1999 overriding common
2000 <file>(<section>): warning: common is here
2001
2002 3. Merging a common symbol with a previous same-sized common
2003 symbol.
2004
2005 <file>(<section>): warning: multiple common
2006 of `<symbol>'
2007 <file>(<section>): warning: previous common is here
2008
2009 4. Merging a common symbol with a previous larger common symbol.
2010
2011 <file>(<section>): warning: common of `<symbol>'
2012 overridden by larger common
2013 <file>(<section>): warning: larger common is here
2014
2015 5. Merging a common symbol with a previous smaller common symbol.
2016 This is the same as the previous case, except that the symbols
2017 are encountered in a different order.
2018
2019 <file>(<section>): warning: common of `<symbol>'
2020 overriding smaller common
2021 <file>(<section>): warning: smaller common is here
2022
2023 --warn-constructors
2024 Warn if any global constructors are used. This is only useful for
2025 a few object file formats. For formats like COFF or ELF, the
2026 linker can not detect the use of global constructors.
2027
2028 --warn-multiple-gp
2029 Warn if multiple global pointer values are required in the output
2030 file. This is only meaningful for certain processors, such as the
2031 Alpha. Specifically, some processors put large-valued constants in
2032 a special section. A special register (the global pointer) points
2033 into the middle of this section, so that constants can be loaded
2034 efficiently via a base-register relative addressing mode. Since
2035 the offset in base-register relative mode is fixed and relatively
2036 small (e.g., 16 bits), this limits the maximum size of the constant
2037 pool. Thus, in large programs, it is often necessary to use
2038 multiple global pointer values in order to be able to address all
2039 possible constants. This option causes a warning to be issued
2040 whenever this case occurs.
2041
2042 --warn-once
2043 Only warn once for each undefined symbol, rather than once per
2044 module which refers to it.
2045
2046 --warn-section-align
2047 Warn if the address of an output section is changed because of
2048 alignment. Typically, the alignment will be set by an input
2049 section. The address will only be changed if it not explicitly
2050 specified; that is, if the "SECTIONS" command does not specify a
2051 start address for the section.
2052
2053 --warn-textrel
2054 Warn if the linker adds DT_TEXTREL to a position-independent
2055 executable or shared object.
2056
2057 --warn-alternate-em
2058 Warn if an object has alternate ELF machine code.
2059
2060 --warn-unresolved-symbols
2061 If the linker is going to report an unresolved symbol (see the
2062 option --unresolved-symbols) it will normally generate an error.
2063 This option makes it generate a warning instead.
2064
2065 --error-unresolved-symbols
2066 This restores the linker's default behaviour of generating errors
2067 when it is reporting unresolved symbols.
2068
2069 --whole-archive
2070 For each archive mentioned on the command line after the
2071 --whole-archive option, include every object file in the archive in
2072 the link, rather than searching the archive for the required object
2073 files. This is normally used to turn an archive file into a shared
2074 library, forcing every object to be included in the resulting
2075 shared library. This option may be used more than once.
2076
2077 Two notes when using this option from gcc: First, gcc doesn't know
2078 about this option, so you have to use -Wl,-whole-archive. Second,
2079 don't forget to use -Wl,-no-whole-archive after your list of
2080 archives, because gcc will add its own list of archives to your
2081 link and you may not want this flag to affect those as well.
2082
2083 --wrap=symbol
2084 Use a wrapper function for symbol. Any undefined reference to
2085 symbol will be resolved to "__wrap_symbol". Any undefined
2086 reference to "__real_symbol" will be resolved to symbol.
2087
2088 This can be used to provide a wrapper for a system function. The
2089 wrapper function should be called "__wrap_symbol". If it wishes to
2090 call the system function, it should call "__real_symbol".
2091
2092 Here is a trivial example:
2093
2094 void *
2095 __wrap_malloc (size_t c)
2096 {
2097 printf ("malloc called with %zu\n", c);
2098 return __real_malloc (c);
2099 }
2100
2101 If you link other code with this file using --wrap malloc, then all
2102 calls to "malloc" will call the function "__wrap_malloc" instead.
2103 The call to "__real_malloc" in "__wrap_malloc" will call the real
2104 "malloc" function.
2105
2106 You may wish to provide a "__real_malloc" function as well, so that
2107 links without the --wrap option will succeed. If you do this, you
2108 should not put the definition of "__real_malloc" in the same file
2109 as "__wrap_malloc"; if you do, the assembler may resolve the call
2110 before the linker has a chance to wrap it to "malloc".
2111
2112 Only undefined references are replaced by the linker. So,
2113 translation unit internal references to symbol are not resolved to
2114 "__wrap_symbol". In the next example, the call to "f" in "g" is
2115 not resolved to "__wrap_f".
2116
2117 int
2118 f (void)
2119 {
2120 return 123;
2121 }
2122
2123 int
2124 g (void)
2125 {
2126 return f();
2127 }
2128
2129 --eh-frame-hdr
2130 --no-eh-frame-hdr
2131 Request (--eh-frame-hdr) or suppress (--no-eh-frame-hdr) the
2132 creation of ".eh_frame_hdr" section and ELF "PT_GNU_EH_FRAME"
2133 segment header.
2134
2135 --no-ld-generated-unwind-info
2136 Request creation of ".eh_frame" unwind info for linker generated
2137 code sections like PLT. This option is on by default if linker
2138 generated unwind info is supported.
2139
2140 --enable-new-dtags
2141 --disable-new-dtags
2142 This linker can create the new dynamic tags in ELF. But the older
2143 ELF systems may not understand them. If you specify
2144 --enable-new-dtags, the new dynamic tags will be created as needed
2145 and older dynamic tags will be omitted. If you specify
2146 --disable-new-dtags, no new dynamic tags will be created. By
2147 default, the new dynamic tags are not created. Note that those
2148 options are only available for ELF systems.
2149
2150 --hash-size=number
2151 Set the default size of the linker's hash tables to a prime number
2152 close to number. Increasing this value can reduce the length of
2153 time it takes the linker to perform its tasks, at the expense of
2154 increasing the linker's memory requirements. Similarly reducing
2155 this value can reduce the memory requirements at the expense of
2156 speed.
2157
2158 --hash-style=style
2159 Set the type of linker's hash table(s). style can be either "sysv"
2160 for classic ELF ".hash" section, "gnu" for new style GNU
2161 ".gnu.hash" section or "both" for both the classic ELF ".hash" and
2162 new style GNU ".gnu.hash" hash tables. The default depends upon
2163 how the linker was configured, but for most Linux based systems it
2164 will be "both".
2165
2166 --compress-debug-sections=none
2167 --compress-debug-sections=zlib
2168 --compress-debug-sections=zlib-gnu
2169 --compress-debug-sections=zlib-gabi
2170 On ELF platforms, these options control how DWARF debug sections
2171 are compressed using zlib.
2172
2173 --compress-debug-sections=none doesn't compress DWARF debug
2174 sections. --compress-debug-sections=zlib-gnu compresses DWARF
2175 debug sections and renames them to begin with .zdebug instead of
2176 .debug. --compress-debug-sections=zlib-gabi also compresses DWARF
2177 debug sections, but rather than renaming them it sets the
2178 SHF_COMPRESSED flag in the sections' headers.
2179
2180 The --compress-debug-sections=zlib option is an alias for
2181 --compress-debug-sections=zlib-gabi.
2182
2183 Note that this option overrides any compression in input debug
2184 sections, so if a binary is linked with
2185 --compress-debug-sections=none for example, then any compressed
2186 debug sections in input files will be uncompressed before they are
2187 copied into the output binary.
2188
2189 The default compression behaviour varies depending upon the target
2190 involved and the configure options used to build the toolchain.
2191 The default can be determined by examining the output from the
2192 linker's --help option.
2193
2194 --reduce-memory-overheads
2195 This option reduces memory requirements at ld runtime, at the
2196 expense of linking speed. This was introduced to select the old
2197 O(n^2) algorithm for link map file generation, rather than the new
2198 O(n) algorithm which uses about 40% more memory for symbol storage.
2199
2200 Another effect of the switch is to set the default hash table size
2201 to 1021, which again saves memory at the cost of lengthening the
2202 linker's run time. This is not done however if the --hash-size
2203 switch has been used.
2204
2205 The --reduce-memory-overheads switch may be also be used to enable
2206 other tradeoffs in future versions of the linker.
2207
2208 --build-id
2209 --build-id=style
2210 Request the creation of a ".note.gnu.build-id" ELF note section or
2211 a ".buildid" COFF section. The contents of the note are unique
2212 bits identifying this linked file. style can be "uuid" to use 128
2213 random bits, "sha1" to use a 160-bit SHA1 hash on the normative
2214 parts of the output contents, "md5" to use a 128-bit MD5 hash on
2215 the normative parts of the output contents, or "0xhexstring" to use
2216 a chosen bit string specified as an even number of hexadecimal
2217 digits ("-" and ":" characters between digit pairs are ignored).
2218 If style is omitted, "sha1" is used.
2219
2220 The "md5" and "sha1" styles produces an identifier that is always
2221 the same in an identical output file, but will be unique among all
2222 nonidentical output files. It is not intended to be compared as a
2223 checksum for the file's contents. A linked file may be changed
2224 later by other tools, but the build ID bit string identifying the
2225 original linked file does not change.
2226
2227 Passing "none" for style disables the setting from any "--build-id"
2228 options earlier on the command line.
2229
2230 The i386 PE linker supports the -shared option, which causes the output
2231 to be a dynamically linked library (DLL) instead of a normal
2232 executable. You should name the output "*.dll" when you use this
2233 option. In addition, the linker fully supports the standard "*.def"
2234 files, which may be specified on the linker command line like an object
2235 file (in fact, it should precede archives it exports symbols from, to
2236 ensure that they get linked in, just like a normal object file).
2237
2238 In addition to the options common to all targets, the i386 PE linker
2239 support additional command-line options that are specific to the i386
2240 PE target. Options that take values may be separated from their values
2241 by either a space or an equals sign.
2242
2243 --add-stdcall-alias
2244 If given, symbols with a stdcall suffix (@nn) will be exported as-
2245 is and also with the suffix stripped. [This option is specific to
2246 the i386 PE targeted port of the linker]
2247
2248 --base-file file
2249 Use file as the name of a file in which to save the base addresses
2250 of all the relocations needed for generating DLLs with dlltool.
2251 [This is an i386 PE specific option]
2252
2253 --dll
2254 Create a DLL instead of a regular executable. You may also use
2255 -shared or specify a "LIBRARY" in a given ".def" file. [This
2256 option is specific to the i386 PE targeted port of the linker]
2257
2258 --enable-long-section-names
2259 --disable-long-section-names
2260 The PE variants of the COFF object format add an extension that
2261 permits the use of section names longer than eight characters, the
2262 normal limit for COFF. By default, these names are only allowed in
2263 object files, as fully-linked executable images do not carry the
2264 COFF string table required to support the longer names. As a GNU
2265 extension, it is possible to allow their use in executable images
2266 as well, or to (probably pointlessly!) disallow it in object
2267 files, by using these two options. Executable images generated
2268 with these long section names are slightly non-standard, carrying
2269 as they do a string table, and may generate confusing output when
2270 examined with non-GNU PE-aware tools, such as file viewers and
2271 dumpers. However, GDB relies on the use of PE long section names
2272 to find Dwarf-2 debug information sections in an executable image
2273 at runtime, and so if neither option is specified on the command-
2274 line, ld will enable long section names, overriding the default and
2275 technically correct behaviour, when it finds the presence of debug
2276 information while linking an executable image and not stripping
2277 symbols. [This option is valid for all PE targeted ports of the
2278 linker]
2279
2280 --enable-stdcall-fixup
2281 --disable-stdcall-fixup
2282 If the link finds a symbol that it cannot resolve, it will attempt
2283 to do "fuzzy linking" by looking for another defined symbol that
2284 differs only in the format of the symbol name (cdecl vs stdcall)
2285 and will resolve that symbol by linking to the match. For example,
2286 the undefined symbol "_foo" might be linked to the function
2287 "_foo@12", or the undefined symbol "_bar@16" might be linked to the
2288 function "_bar". When the linker does this, it prints a warning,
2289 since it normally should have failed to link, but sometimes import
2290 libraries generated from third-party dlls may need this feature to
2291 be usable. If you specify --enable-stdcall-fixup, this feature is
2292 fully enabled and warnings are not printed. If you specify
2293 --disable-stdcall-fixup, this feature is disabled and such
2294 mismatches are considered to be errors. [This option is specific
2295 to the i386 PE targeted port of the linker]
2296
2297 --leading-underscore
2298 --no-leading-underscore
2299 For most targets default symbol-prefix is an underscore and is
2300 defined in target's description. By this option it is possible to
2301 disable/enable the default underscore symbol-prefix.
2302
2303 --export-all-symbols
2304 If given, all global symbols in the objects used to build a DLL
2305 will be exported by the DLL. Note that this is the default if
2306 there otherwise wouldn't be any exported symbols. When symbols are
2307 explicitly exported via DEF files or implicitly exported via
2308 function attributes, the default is to not export anything else
2309 unless this option is given. Note that the symbols "DllMain@12",
2310 "DllEntryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will
2311 not be automatically exported. Also, symbols imported from other
2312 DLLs will not be re-exported, nor will symbols specifying the DLL's
2313 internal layout such as those beginning with "_head_" or ending
2314 with "_iname". In addition, no symbols from "libgcc", "libstd++",
2315 "libmingw32", or "crtX.o" will be exported. Symbols whose names
2316 begin with "__rtti_" or "__builtin_" will not be exported, to help
2317 with C++ DLLs. Finally, there is an extensive list of cygwin-
2318 private symbols that are not exported (obviously, this applies on
2319 when building DLLs for cygwin targets). These cygwin-excludes are:
2320 "_cygwin_dll_entry@12", "_cygwin_crt0_common@8",
2321 "_cygwin_noncygwin_dll_entry@12", "_fmode", "_impure_ptr",
2322 "cygwin_attach_dll", "cygwin_premain0", "cygwin_premain1",
2323 "cygwin_premain2", "cygwin_premain3", and "environ". [This option
2324 is specific to the i386 PE targeted port of the linker]
2325
2326 --exclude-symbols symbol,symbol,...
2327 Specifies a list of symbols which should not be automatically
2328 exported. The symbol names may be delimited by commas or colons.
2329 [This option is specific to the i386 PE targeted port of the
2330 linker]
2331
2332 --exclude-all-symbols
2333 Specifies no symbols should be automatically exported. [This
2334 option is specific to the i386 PE targeted port of the linker]
2335
2336 --file-alignment
2337 Specify the file alignment. Sections in the file will always begin
2338 at file offsets which are multiples of this number. This defaults
2339 to 512. [This option is specific to the i386 PE targeted port of
2340 the linker]
2341
2342 --heap reserve
2343 --heap reserve,commit
2344 Specify the number of bytes of memory to reserve (and optionally
2345 commit) to be used as heap for this program. The default is 1MB
2346 reserved, 4K committed. [This option is specific to the i386 PE
2347 targeted port of the linker]
2348
2349 --image-base value
2350 Use value as the base address of your program or dll. This is the
2351 lowest memory location that will be used when your program or dll
2352 is loaded. To reduce the need to relocate and improve performance
2353 of your dlls, each should have a unique base address and not
2354 overlap any other dlls. The default is 0x400000 for executables,
2355 and 0x10000000 for dlls. [This option is specific to the i386 PE
2356 targeted port of the linker]
2357
2358 --kill-at
2359 If given, the stdcall suffixes (@nn) will be stripped from symbols
2360 before they are exported. [This option is specific to the i386 PE
2361 targeted port of the linker]
2362
2363 --large-address-aware
2364 If given, the appropriate bit in the "Characteristics" field of the
2365 COFF header is set to indicate that this executable supports
2366 virtual addresses greater than 2 gigabytes. This should be used in
2367 conjunction with the /3GB or /USERVA=value megabytes switch in the
2368 "[operating systems]" section of the BOOT.INI. Otherwise, this bit
2369 has no effect. [This option is specific to PE targeted ports of
2370 the linker]
2371
2372 --disable-large-address-aware
2373 Reverts the effect of a previous --large-address-aware option.
2374 This is useful if --large-address-aware is always set by the
2375 compiler driver (e.g. Cygwin gcc) and the executable does not
2376 support virtual addresses greater than 2 gigabytes. [This option
2377 is specific to PE targeted ports of the linker]
2378
2379 --major-image-version value
2380 Sets the major number of the "image version". Defaults to 1.
2381 [This option is specific to the i386 PE targeted port of the
2382 linker]
2383
2384 --major-os-version value
2385 Sets the major number of the "os version". Defaults to 4. [This
2386 option is specific to the i386 PE targeted port of the linker]
2387
2388 --major-subsystem-version value
2389 Sets the major number of the "subsystem version". Defaults to 4.
2390 [This option is specific to the i386 PE targeted port of the
2391 linker]
2392
2393 --minor-image-version value
2394 Sets the minor number of the "image version". Defaults to 0.
2395 [This option is specific to the i386 PE targeted port of the
2396 linker]
2397
2398 --minor-os-version value
2399 Sets the minor number of the "os version". Defaults to 0. [This
2400 option is specific to the i386 PE targeted port of the linker]
2401
2402 --minor-subsystem-version value
2403 Sets the minor number of the "subsystem version". Defaults to 0.
2404 [This option is specific to the i386 PE targeted port of the
2405 linker]
2406
2407 --output-def file
2408 The linker will create the file file which will contain a DEF file
2409 corresponding to the DLL the linker is generating. This DEF file
2410 (which should be called "*.def") may be used to create an import
2411 library with "dlltool" or may be used as a reference to
2412 automatically or implicitly exported symbols. [This option is
2413 specific to the i386 PE targeted port of the linker]
2414
2415 --enable-auto-image-base
2416 --enable-auto-image-base=value
2417 Automatically choose the image base for DLLs, optionally starting
2418 with base value, unless one is specified using the "--image-base"
2419 argument. By using a hash generated from the dllname to create
2420 unique image bases for each DLL, in-memory collisions and
2421 relocations which can delay program execution are avoided. [This
2422 option is specific to the i386 PE targeted port of the linker]
2423
2424 --disable-auto-image-base
2425 Do not automatically generate a unique image base. If there is no
2426 user-specified image base ("--image-base") then use the platform
2427 default. [This option is specific to the i386 PE targeted port of
2428 the linker]
2429
2430 --dll-search-prefix string
2431 When linking dynamically to a dll without an import library, search
2432 for "<string><basename>.dll" in preference to "lib<basename>.dll".
2433 This behaviour allows easy distinction between DLLs built for the
2434 various "subplatforms": native, cygwin, uwin, pw, etc. For
2435 instance, cygwin DLLs typically use "--dll-search-prefix=cyg".
2436 [This option is specific to the i386 PE targeted port of the
2437 linker]
2438
2439 --enable-auto-import
2440 Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA
2441 imports from DLLs, thus making it possible to bypass the dllimport
2442 mechanism on the user side and to reference unmangled symbol names.
2443 [This option is specific to the i386 PE targeted port of the
2444 linker]
2445
2446 The following remarks pertain to the original implementation of the
2447 feature and are obsolete nowadays for Cygwin and MinGW targets.
2448
2449 Note: Use of the 'auto-import' extension will cause the text
2450 section of the image file to be made writable. This does not
2451 conform to the PE-COFF format specification published by Microsoft.
2452
2453 Note - use of the 'auto-import' extension will also cause read only
2454 data which would normally be placed into the .rdata section to be
2455 placed into the .data section instead. This is in order to work
2456 around a problem with consts that is described here:
2457 http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
2458
2459 Using 'auto-import' generally will 'just work' -- but sometimes you
2460 may see this message:
2461
2462 "variable '<var>' can't be auto-imported. Please read the
2463 documentation for ld's "--enable-auto-import" for details."
2464
2465 This message occurs when some (sub)expression accesses an address
2466 ultimately given by the sum of two constants (Win32 import tables
2467 only allow one). Instances where this may occur include accesses
2468 to member fields of struct variables imported from a DLL, as well
2469 as using a constant index into an array variable imported from a
2470 DLL. Any multiword variable (arrays, structs, long long, etc) may
2471 trigger this error condition. However, regardless of the exact
2472 data type of the offending exported variable, ld will always detect
2473 it, issue the warning, and exit.
2474
2475 There are several ways to address this difficulty, regardless of
2476 the data type of the exported variable:
2477
2478 One way is to use --enable-runtime-pseudo-reloc switch. This leaves
2479 the task of adjusting references in your client code for runtime
2480 environment, so this method works only when runtime environment
2481 supports this feature.
2482
2483 A second solution is to force one of the 'constants' to be a
2484 variable -- that is, unknown and un-optimizable at compile time.
2485 For arrays, there are two possibilities: a) make the indexee (the
2486 array's address) a variable, or b) make the 'constant' index a
2487 variable. Thus:
2488
2489 extern type extern_array[];
2490 extern_array[1] -->
2491 { volatile type *t=extern_array; t[1] }
2492
2493 or
2494
2495 extern type extern_array[];
2496 extern_array[1] -->
2497 { volatile int t=1; extern_array[t] }
2498
2499 For structs (and most other multiword data types) the only option
2500 is to make the struct itself (or the long long, or the ...)
2501 variable:
2502
2503 extern struct s extern_struct;
2504 extern_struct.field -->
2505 { volatile struct s *t=&extern_struct; t->field }
2506
2507 or
2508
2509 extern long long extern_ll;
2510 extern_ll -->
2511 { volatile long long * local_ll=&extern_ll; *local_ll }
2512
2513 A third method of dealing with this difficulty is to abandon
2514 'auto-import' for the offending symbol and mark it with
2515 "__declspec(dllimport)". However, in practice that requires using
2516 compile-time #defines to indicate whether you are building a DLL,
2517 building client code that will link to the DLL, or merely
2518 building/linking to a static library. In making the choice
2519 between the various methods of resolving the 'direct address with
2520 constant offset' problem, you should consider typical real-world
2521 usage:
2522
2523 Original:
2524
2525 --foo.h
2526 extern int arr[];
2527 --foo.c
2528 #include "foo.h"
2529 void main(int argc, char **argv){
2530 printf("%d\n",arr[1]);
2531 }
2532
2533 Solution 1:
2534
2535 --foo.h
2536 extern int arr[];
2537 --foo.c
2538 #include "foo.h"
2539 void main(int argc, char **argv){
2540 /* This workaround is for win32 and cygwin; do not "optimize" */
2541 volatile int *parr = arr;
2542 printf("%d\n",parr[1]);
2543 }
2544
2545 Solution 2:
2546
2547 --foo.h
2548 /* Note: auto-export is assumed (no __declspec(dllexport)) */
2549 #if (defined(_WIN32) || defined(__CYGWIN__)) && \
2550 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
2551 #define FOO_IMPORT __declspec(dllimport)
2552 #else
2553 #define FOO_IMPORT
2554 #endif
2555 extern FOO_IMPORT int arr[];
2556 --foo.c
2557 #include "foo.h"
2558 void main(int argc, char **argv){
2559 printf("%d\n",arr[1]);
2560 }
2561
2562 A fourth way to avoid this problem is to re-code your library to
2563 use a functional interface rather than a data interface for the
2564 offending variables (e.g. set_foo() and get_foo() accessor
2565 functions).
2566
2567 --disable-auto-import
2568 Do not attempt to do sophisticated linking of "_symbol" to
2569 "__imp__symbol" for DATA imports from DLLs. [This option is
2570 specific to the i386 PE targeted port of the linker]
2571
2572 --enable-runtime-pseudo-reloc
2573 If your code contains expressions described in --enable-auto-import
2574 section, that is, DATA imports from DLL with non-zero offset, this
2575 switch will create a vector of 'runtime pseudo relocations' which
2576 can be used by runtime environment to adjust references to such
2577 data in your client code. [This option is specific to the i386 PE
2578 targeted port of the linker]
2579
2580 --disable-runtime-pseudo-reloc
2581 Do not create pseudo relocations for non-zero offset DATA imports
2582 from DLLs. [This option is specific to the i386 PE targeted port
2583 of the linker]
2584
2585 --enable-extra-pe-debug
2586 Show additional debug info related to auto-import symbol thunking.
2587 [This option is specific to the i386 PE targeted port of the
2588 linker]
2589
2590 --section-alignment
2591 Sets the section alignment. Sections in memory will always begin
2592 at addresses which are a multiple of this number. Defaults to
2593 0x1000. [This option is specific to the i386 PE targeted port of
2594 the linker]
2595
2596 --stack reserve
2597 --stack reserve,commit
2598 Specify the number of bytes of memory to reserve (and optionally
2599 commit) to be used as stack for this program. The default is 2MB
2600 reserved, 4K committed. [This option is specific to the i386 PE
2601 targeted port of the linker]
2602
2603 --subsystem which
2604 --subsystem which:major
2605 --subsystem which:major.minor
2606 Specifies the subsystem under which your program will execute. The
2607 legal values for which are "native", "windows", "console", "posix",
2608 and "xbox". You may optionally set the subsystem version also.
2609 Numeric values are also accepted for which. [This option is
2610 specific to the i386 PE targeted port of the linker]
2611
2612 The following options set flags in the "DllCharacteristics" field
2613 of the PE file header: [These options are specific to PE targeted
2614 ports of the linker]
2615
2616 --high-entropy-va
2617 --disable-high-entropy-va
2618 Image is compatible with 64-bit address space layout randomization
2619 (ASLR). This option is enabled by default for 64-bit PE images.
2620
2621 This option also implies --dynamicbase and --enable-reloc-section.
2622
2623 --dynamicbase
2624 --disable-dynamicbase
2625 The image base address may be relocated using address space layout
2626 randomization (ASLR). This feature was introduced with MS Windows
2627 Vista for i386 PE targets. This option is enabled by default but
2628 can be disabled via the --disable-dynamicbase option. This option
2629 also implies --enable-reloc-section.
2630
2631 --forceinteg
2632 --disable-forceinteg
2633 Code integrity checks are enforced. This option is disabled by
2634 default.
2635
2636 --nxcompat
2637 --disable-nxcompat
2638 The image is compatible with the Data Execution Prevention. This
2639 feature was introduced with MS Windows XP SP2 for i386 PE targets.
2640 The option is enabled by default.
2641
2642 --no-isolation
2643 --disable-no-isolation
2644 Although the image understands isolation, do not isolate the image.
2645 This option is disabled by default.
2646
2647 --no-seh
2648 --disable-no-seh
2649 The image does not use SEH. No SE handler may be called from this
2650 image. This option is disabled by default.
2651
2652 --no-bind
2653 --disable-no-bind
2654 Do not bind this image. This option is disabled by default.
2655
2656 --wdmdriver
2657 --disable-wdmdriver
2658 The driver uses the MS Windows Driver Model. This option is
2659 disabled by default.
2660
2661 --tsaware
2662 --disable-tsaware
2663 The image is Terminal Server aware. This option is disabled by
2664 default.
2665
2666 --insert-timestamp
2667 --no-insert-timestamp
2668 Insert a real timestamp into the image. This is the default
2669 behaviour as it matches legacy code and it means that the image
2670 will work with other, proprietary tools. The problem with this
2671 default is that it will result in slightly different images being
2672 produced each time the same sources are linked. The option
2673 --no-insert-timestamp can be used to insert a zero value for the
2674 timestamp, this ensuring that binaries produced from identical
2675 sources will compare identically.
2676
2677 --enable-reloc-section
2678 --disable-reloc-section
2679 Create the base relocation table, which is necessary if the image
2680 is loaded at a different image base than specified in the PE
2681 header. This option is enabled by default.
2682
2683 The C6X uClinux target uses a binary format called DSBT to support
2684 shared libraries. Each shared library in the system needs to have a
2685 unique index; all executables use an index of 0.
2686
2687 --dsbt-size size
2688 This option sets the number of entries in the DSBT of the current
2689 executable or shared library to size. The default is to create a
2690 table with 64 entries.
2691
2692 --dsbt-index index
2693 This option sets the DSBT index of the current executable or shared
2694 library to index. The default is 0, which is appropriate for
2695 generating executables. If a shared library is generated with a
2696 DSBT index of 0, the "R_C6000_DSBT_INDEX" relocs are copied into
2697 the output file.
2698
2699 The --no-merge-exidx-entries switch disables the merging of
2700 adjacent exidx entries in frame unwind info.
2701
2702 --branch-stub
2703 This option enables linker branch relaxation by inserting branch
2704 stub sections when needed to extend the range of branches. This
2705 option is usually not required since C-SKY supports branch and call
2706 instructions that can access the full memory range and branch
2707 relaxation is normally handled by the compiler or assembler.
2708
2709 --stub-group-size=N
2710 This option allows finer control of linker branch stub creation.
2711 It sets the maximum size of a group of input sections that can be
2712 handled by one stub section. A negative value of N locates stub
2713 sections after their branches, while a positive value allows stub
2714 sections to appear either before or after the branches. Values of
2715 1 or -1 indicate that the linker should choose suitable defaults.
2716
2717 The 68HC11 and 68HC12 linkers support specific options to control the
2718 memory bank switching mapping and trampoline code generation.
2719
2720 --no-trampoline
2721 This option disables the generation of trampoline. By default a
2722 trampoline is generated for each far function which is called using
2723 a "jsr" instruction (this happens when a pointer to a far function
2724 is taken).
2725
2726 --bank-window name
2727 This option indicates to the linker the name of the memory region
2728 in the MEMORY specification that describes the memory bank window.
2729 The definition of such region is then used by the linker to compute
2730 paging and addresses within the memory window.
2731
2732 The following options are supported to control handling of GOT
2733 generation when linking for 68K targets.
2734
2735 --got=type
2736 This option tells the linker which GOT generation scheme to use.
2737 type should be one of single, negative, multigot or target. For
2738 more information refer to the Info entry for ld.
2739
2740 The following options are supported to control microMIPS instruction
2741 generation and branch relocation checks for ISA mode transitions when
2742 linking for MIPS targets.
2743
2744 --insn32
2745 --no-insn32
2746 These options control the choice of microMIPS instructions used in
2747 code generated by the linker, such as that in the PLT or lazy
2748 binding stubs, or in relaxation. If --insn32 is used, then the
2749 linker only uses 32-bit instruction encodings. By default or if
2750 --no-insn32 is used, all instruction encodings are used, including
2751 16-bit ones where possible.
2752
2753 --ignore-branch-isa
2754 --no-ignore-branch-isa
2755 These options control branch relocation checks for invalid ISA mode
2756 transitions. If --ignore-branch-isa is used, then the linker
2757 accepts any branch relocations and any ISA mode transition required
2758 is lost in relocation calculation, except for some cases of "BAL"
2759 instructions which meet relaxation conditions and are converted to
2760 equivalent "JALX" instructions as the associated relocation is
2761 calculated. By default or if --no-ignore-branch-isa is used a
2762 check is made causing the loss of an ISA mode transition to produce
2763 an error.
2764
2765 --compact-branches
2766 --no-compact-branches
2767 These options control the generation of compact instructions by the
2768 linker in the PLT entries for MIPS R6.
2769
2770 For the pdp11-aout target, three variants of the output format can be
2771 produced as selected by the following options. The default variant for
2772 pdp11-aout is the --omagic option, whereas for other targets --nmagic
2773 is the default. The --imagic option is defined only for the pdp11-aout
2774 target, while the others are described here as they apply to the
2775 pdp11-aout target.
2776
2777 -N
2778 --omagic
2779 Mark the output as "OMAGIC" (0407) in the a.out header to indicate
2780 that the text segment is not to be write-protected and shared.
2781 Since the text and data sections are both readable and writable,
2782 the data section is allocated immediately contiguous after the text
2783 segment. This is the oldest format for PDP11 executable programs
2784 and is the default for ld on PDP11 Unix systems from the beginning
2785 through 2.11BSD.
2786
2787 -n
2788 --nmagic
2789 Mark the output as "NMAGIC" (0410) in the a.out header to indicate
2790 that when the output file is executed, the text portion will be
2791 read-only and shareable among all processes executing the same
2792 file. This involves moving the data areas up to the first possible
2793 8K byte page boundary following the end of the text. This option
2794 creates a pure executable format.
2795
2796 -z
2797 --imagic
2798 Mark the output as "IMAGIC" (0411) in the a.out header to indicate
2799 that when the output file is executed, the program text and data
2800 areas will be loaded into separate address spaces using the split
2801 instruction and data space feature of the memory management unit in
2802 larger models of the PDP11. This doubles the address space
2803 available to the program. The text segment is again pure, write-
2804 protected, and shareable. The only difference in the output format
2805 between this option and the others, besides the magic number, is
2806 that both the text and data sections start at location 0. The -z
2807 option selected this format in 2.11BSD. This option creates a
2808 separate executable format.
2809
2810 --no-omagic
2811 Equivalent to --nmagic for pdp11-aout.
2812
2814 You can change the behaviour of ld with the environment variables
2815 "GNUTARGET", "LDEMULATION" and "COLLECT_NO_DEMANGLE".
2816
2817 "GNUTARGET" determines the input-file object format if you don't use -b
2818 (or its synonym --format). Its value should be one of the BFD names
2819 for an input format. If there is no "GNUTARGET" in the environment, ld
2820 uses the natural format of the target. If "GNUTARGET" is set to
2821 "default" then BFD attempts to discover the input format by examining
2822 binary input files; this method often succeeds, but there are potential
2823 ambiguities, since there is no method of ensuring that the magic number
2824 used to specify object-file formats is unique. However, the
2825 configuration procedure for BFD on each system places the conventional
2826 format for that system first in the search-list, so ambiguities are
2827 resolved in favor of convention.
2828
2829 "LDEMULATION" determines the default emulation if you don't use the -m
2830 option. The emulation can affect various aspects of linker behaviour,
2831 particularly the default linker script. You can list the available
2832 emulations with the --verbose or -V options. If the -m option is not
2833 used, and the "LDEMULATION" environment variable is not defined, the
2834 default emulation depends upon how the linker was configured.
2835
2836 Normally, the linker will default to demangling symbols. However, if
2837 "COLLECT_NO_DEMANGLE" is set in the environment, then it will default
2838 to not demangling symbols. This environment variable is used in a
2839 similar fashion by the "gcc" linker wrapper program. The default may
2840 be overridden by the --demangle and --no-demangle options.
2841
2843 ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries
2844 for binutils and ld.
2845
2847 Copyright (c) 1991-2021 Free Software Foundation, Inc.
2848
2849 Permission is granted to copy, distribute and/or modify this document
2850 under the terms of the GNU Free Documentation License, Version 1.3 or
2851 any later version published by the Free Software Foundation; with no
2852 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
2853 Texts. A copy of the license is included in the section entitled "GNU
2854 Free Documentation License".
2855
2856
2857
2858binutils-2.37 2022-03-10 LD(1)