1MOLD(1) BSD General Commands Manual MOLD(1)
2
4 mold — a modern linker
5
7 mold [-options] objfile ...
8
10 mold is a faster drop-in replacement for the default GNU ld(1).
11 How to use mold
13 See https://github.com/rui314/mold#how-to-use
14 Compatibility
16 mold is designed to be a drop-in replacement for the GNU linkers for
17 linking user-land programs. If your user-land program cannot be built
18 due to missing command-line options, please file a bug at
19 https://github.com/rui314/mold/issues
20 mold supports a very limited set of linker script features, which is just
22 sufficient to read /usr/lib/x86_64-linux-gnu/libc.so on Linux systems (on
23 Linux, that file is despite its name not a shared library but an ASCII
24 linker script that loads a real libc.so file.) Beyond that, we have no
25 plan to support any linker script features. The linker script is an ad-
26 hoc, over-designed, complex language which we believe needs to be dis‐
27 rupted by a simpler mechanism. We have a plan to add a replacement for
28 the linker script to mold instead.
29 Archive symbol resolution
31 Traditionally, Unix linkers are sensitive to the order in which input
32 files appear on command line. They process input files from the first
33 (left-most) file to the last (right-most) file one-by-one. While reading
34 input files, they maintain sets of defined and undefined symbols. When
35 visiting an archive file (.a files), they pull out object files to re‐
36 solve as many undefined symbols as possible and go on to the next input
37 file. Object files that weren't pulled out will never have a chance for
38 a second look.
39 Due to this semantics, you usually have to add archive files at the end
41 of a command line, so that when a linker reaches archive files, it knows
42 what symbols are remain undefined. If you put archive files at the be‐
43 ginning of a command line, a linker doesn't have any undefined symbol,
44 and thus no object files will be pulled out from archives.
45 You can change the processing order by --start-group and --end-group op‐
47 tions, though they make a linker slower.
48 mold as well as LLVM lld(1) linker take a different approach. They memo‐
50 rize what symbols can be resolved from archive files instead of forget‐
51 ting it after processing each archive. Therefore, mold and lld(1) can
52 "go back" in a command line to pull out object files from archives, if
53 they are needed to resolve remaining undefined symbols. They are not
54 sensitive to the input file order.
55 --start-group and --end-group are still accepted by mold and lld(1) for
57 compatibility with traditional linkers, but they are silently ignored.
58 Dynamic symbol resolution
60 Some Unix linker features are unable to be understood without understand‐
61 ing the semantics of dynamic symbol resolution. Therefore, even though
62 that's not specific to mold, we'll explain it here.
63 We use "ELF module" or just "module" as a collective term to refer an ex‐
65 ecutable or a shared library file in the ELF format.
66 An ELF module may have lists of imported symbols and exported symbols, as
68 well as a list of shared library names from which imported symbols should
69 be imported. The point is that imported symbols are not bound to any
70 specific shared library until runtime.
71 Here is how the Unix dynamic linker resolves dynamic symbols. Upon the
73 start of an ELF program, the dynamic linker construct a list of ELF mod‐
74 ules which as a whole consist of a complete program. The executable file
75 is always at the beginning of the list followed by its depending shared
76 libraries. An imported symbol is searched from the beginning of the list
77 to the end. If two or more modules define the same symbol, the one that
78 appears first in the list takes precedence over the others.
79 This Unix semantics are contrary to systems such as Windows that have the
81 two-level namespace for dynamic symbols. On Windows, for example, dy‐
82 namic symbols are represented as a tuple of (symbol-name,
83 shared-library-name), so that each dynamic symbol is guaranteed to be re‐
84 solved from some specific library.
85 Typically, an ELF module that exports a symbol also imports the same sym‐
87 bol. Such a symbol is usually resolved to itself, but that's not the
88 case if a module that appears before in the symbol search list provides
89 another definition of the same symbol.
90 Let me take malloc(3) as an example. Assume that you define your version
92 of malloc(3) in your main executable file. Then, all malloc calls from
93 any module are resolved to your function instead of that in libc, because
94 the executable is always at the beginning of the dynamic symbol search
95 list. Note that even malloc(3) calls within libc are resolved to your
96 definition since libc exports and imports malloc. Therefore, by defining
97 malloc yourself, you can overwrite a library function, and the malloc(3)
98 in libc becomes dead code.
99 These Unix semantics are tricky and sometimes considered harmful. For
101 example, assume that you accidentally define atoi(3) as a global function
102 in your executable that behaves completely differently from the one in
103 the C standard. Then, all atoi function calls from any modules (even
104 function calls within libc) are redirected to your function instead of
105 the one in libc which obviously causes a problem. That is a somewhat
106 surprising consequence for an accidental name conflict. On the other
107 hand, this semantic is sometimes considered useful because it allows
108 users to overwrite library functions without recompiling modules contain‐
109 ing them. Whether good or bad, you should keep this semantic in mind to
110 understand the Unix linkers behaviors.
111 Build reproducibility
113 mold's output is deterministic. That is, if you pass the same object
114 files and the same command-line options to the same version of mold, it
115 is guaranteed to always produce the same output. The linker's internal
116 randomness, such as the timing of thread scheduling or iteration orders
117 of hash tables, doesn't affect the output.
118 mold does not have any host-specific default settings. This is contrary
120 to the GNU linkers to which some configurable values, such as system-de‐
121 pendent library search paths, are hard-coded. mold depends only on its
122 command-line arguments.
123
125 --chroot=dir
126 Set dir to root directory.
127 --color-diagnostics=[auto | always | never]
129 --color-diagnostics
130 --no-color-diagnostics
131 Show diagnostics messages in color using ANSI escape sequences.
133 auto means that mold prints out messages in color only if the
134 standard output is connected to a TTY. Default is auto.
135 --fork
137 --no-fork
138 Spawn a child process and let it do the actual linking. When
139 linking a large program, the OS kernel can take a few hundred
140 milliseconds to terminate a mold process. --fork hides that la‐
141 tency. By default, it does fork.
142 --perf Print performance statistics.
144 --print-dependencies
146 Print out dependency information for input files.
147 Each line of the output for this option shows that which file de‐
149 pends on which file to use which symbol. This option is useful to
150 debug why some object file in a static archive got linked or why
151 some shared library is kept in an output file's dependency list
152 even with --as-needed.
153 -N, --omagic
155 --no-omagic
156 Force mold to emit an output file with an old-fashioned memory
157 layout. First, it makes the first data segment to not be aligned
158 to a page boundary. Second, text segments are marked as writable
159 if the option is given.
160 --repro
163 Archive input files as a tar file.
164 --reverse-sections
166 Reverses the order of input sections before assigning them the
167 offsets in the output file.
168 This option is useful for finding a bug that depends on an ini‐
170 tialization order of global objects. In C++, constructors of
171 global objects in a single source file are guaranteed to be exe‐
172 cuted in the source order, but there's no such guarantee across
173 compilation units. Usually, constructors are executed in the or‐
174 der given to the linker, but depending on it is a mistake.
175 By reversing the order of input sections using
177 --reverse-sections, you can easily test that your program works
178 in the reversed initialization order.
179 --run command arg file ...
181 Run command with mold as /usr/bin/ld. Specifically, mold runs a
182 given command with the LD_PRELOAD environment set to intercept
183 exec(3) family functions and replaces argv[0] with itself if it
184 is ld, ld.gold or ld.lld.
185 --shuffle-sections
187 --shuffle-sections=number
188 Randomizes the output by shuffling the order of input sections
189 before assigning them the offsets in the output file. If number
190 is given, it's used as a seed for the random number generator, so
191 that the linker produces the same output as for the same seed. If
192 no seed is given, a random number is used as a seed.
193 This option is useful for benchmarking. Modern CPUs are sensitive
195 to program's memory layout. A seeming benign change in program
196 layout (such as a small size increase of a function in the middle
197 of a program) can affect program's performance. Therefore, even
198 if you write new code and get a good benchmark result, it is hard
199 to say whether or not the new code improves the programs perfor‐
200 mance. It is possible that the new memory layout happens to per‐
201 form better.
202 By running a benchmark multiple time with shuffling memory layout
204 using --shuffle-sections, you can isolate your program's real
205 performance number from the randomness caused by memory layout
206 changes.
207 --stats
209 Print input statistics.
210 --thread-count=count
212 Use count number of threads.
213 --threads
215 --no-threads
216 Use multiple threads. By default, mold uses as many threads as
217 the number of cores or 32, whichever is the smallest. The reason
218 why it is capped to 32 is because mold doesn't scale well beyond
219 that point. To use only one thread, pass --no-threads or
220 --thread-count=1.
221 --quick-exit
223 --no-quick-exit
224 Use or do not use quick_exit to exit.
225
227 --help Report usage information to stdout and exit.
228 -v, --version
230 Report version information to stdout.
231 -V Report version and target information to stdout.
233 -C dir, --directory dir
235 Change to dir before doing anything.
236 -E, --export-dynamic
238 --no-export-dynamic
239 When creating an executable, using the -E option causes all
240 global symbols to be put into the dynamic symbol table, so that
241 the symbols are visible from other ELF modules at runtime.
242 By default, or if --no-export-dynamic is given, only symbols that
244 are referenced by DSOs at link-time are exported from an exe‐
245 cutable.
246 -F libname, --filter=libname
248 Set the DT_FILTER dynamic section field to libname.
249 -Ifile, --dynamic-linker=file
251 --no-dynamic-linker
252 Set the dynamic linker path to file. If no -I option is given,
253 or if --no-dynamic-linker is given, no dynamic linker path is set
254 to an output file. This is contrary to the GNU linkers which
255 sets a default dynamic linker path in that case. However, this
256 difference doesn't usually make any difference because the com‐
257 piler driver always passes -I to a linker.
258 -Ldir, --library-path=dir
260 Add dir to the list of library search paths from which mold
261 searches libraries for the -l option.
262 Unlike the GNU linkers, mold does not have the default search
264 paths. This difference doesn't usually make any difference be‐
265 cause the compiler driver always passes all necessary search
266 paths to a linker.
267 -M, --print-map
269 Write a map file to stdout.
270 -N, --omagic
272 --no-omagic
273 Force mold to emit an output file with an old-fashioned memory
274 layout. First, it makes the first data segment to not be aligned
275 to a page boundary. Second, text segments are marked as writable
276 if the option is given.
277 -S, --strip-debug
279 Omit .debug_* sections from the output file.
280 -T file, --script=file
282 Read linker script from file.
283 -X, --discard-locals
285 Discard temporary local symbols to reduce the sizes of the symbol
286 table and the string table. Temporary local symbols are local
287 symbols starting with .L. Compilers usually generate such sym‐
288 bols for unnamed program elements such as string literals or
289 floating-point literals.
290 -e symbol, --entry=symbol
292 Use symbol as the entry point symbol instead of the default entry
293 point symbol _start.
294 -f shlib, --auxiliary=shlib
296 Set the DT_AUXILIARY dynamic section field to shlib.
297 -h libname, --soname=libname
299 Set the DT_SONAME dynamic section field to libname. This option
300 is used when creating a shared object file. Typically, when you
301 create SyXXX lib foo.so, you want to pass --soname=foo to a
302 linker.
303 -llibname
305 Search for Sylib libname.so or Sylib libname.a from library
306 search paths.
307 -m [target]
309 Choose a target.
310 -o file, --output=file
312 Use file as the output file name instead of the default name
313 a.out.
314 -r, --relocatable
316 Instead of generating an executable or a shared object file, com‐
317 bine input object files to generate another object file that can
318 be used as an input to a linker.
319 --relocatable-merge-sections
321 By default, mold doesn't merge input sections by name when merg‐
322 ing input object files into a single output object file for -r.
323 For example, .text.foo and .text.bar aren't merged for -r even
324 though they are merged into .text according to the default sec‐
325 tion merging rules.
326 This option changes the behavior so that mold merges input sec‐
328 tions by name by the default section merging rules.
329 -s, --strip-all
331 Omit .symtab section from the output file.
332 -u symbol, --undefined=symbol
334 If symbol remains as an undefined symbol after reading all object
335 files, and if there is an static archive that contains an object
336 file defining symbol, pull out the object file and link it so
337 that the output file contains a definition of symbol.
338 --Bdynamic
340 Link against shared libraries.
341 --Bstatic
343 Do not link against shared libraries.
344 --Bsymbolic
346 When creating a shared library, make global symbols export-only
347 (i.e. do not import the same symbol). As a result, references
348 within a shared library is always resolved locally, negating sym‐
349 bol override at runtime. See Dynamic symbol resolution for more
350 information about symbol imports and exports.
351 --Bsymbolic-functions
353 Have the same effect as --Bsymbolic but works only for function
354 symbols. Data symbols remains being both imported and exported.
355 --Bno-symbolic
357 Cancel --Bsymbolic and --Bsymbolic-functions.
358 --Map=file
360 Write map file to file.
361 --Tbss=address
363 Alias for --section-start=.bss=address.
364 --Tdata=address
366 Alias for --section-start=.data=address.
367 --Ttext=address
369 Alias for --section-start=.text=address.
370 --allow-multiple-definition
372 Normally, the linker reports an error if there are more than one
373 definition of a symbol. This option changes the default behavior
374 so that it doesn't report an error for duplicate definitions and
375 instead use the first definition.
376 --as-needed
378 --no-as-needed
379 By default, shared libraries given to a linker are uncondition‐
380 ally added to the list of required libraries in an output file.
381 However, shared libraries after --as-needed are added to the list
382 only when at least one symbol is actually used by an object file.
383 In other words, shared libraries after --as-needed are not added
384 to the list of needed libraries if they are not needed by a pro‐
385 gram.
386 The --no-as-needed option restores the default behavior for sub‐
388 sequent files.
389 --build-id
391 --build-id=[none | md5 | sha1 | sha256 | uuid | 0xhexstring]
392 --no-build-id
393 Create a .note.gnu.build-id section containing a byte string to
394 uniquely identify an output file. --build-id and
395 --build-id=sha256 compute a 256-bit cryptographic hash of an out‐
396 put file and set it to build-id. md5 and sha1 compute the same
397 hash but truncate it to 128 and 160 bits, respectively, before
398 setting it to build-id. uuid sets a random 128-bit UUID.
399 0xhexstring sets hexstring.
400 --defsym=symbol=value
402 --compress-debug-sections=[none | zlib | zlib-gabi | zstd]
404 Compress DWARF debug info (.debug_* sections) using the zlib or
405 zstd compression algorithm. -zlib-gabi is an alias for -zlib.
406 --defsym=symbol=value
408 Define symbol as an alias for value.
409 value is either an integer (in decimal or hexadecimal with ‘0x’
411 prefix) or a symbol name. If an integer is given as a value,
412 symbol is defined as an absolute symbol with the given value.
413 --default-symver
415 Use soname as a symbol version and append that version to all
416 symbols.
417 --demangle
419 --no-demangle
420 Demangle C++ symbols in log messages.
421 --dependency-file=file
423 Write a dependency file to file. The contents of the written
424 file is readable by make, which defines only one rule with the
425 linker's output file as a target and all input files as its pre‐
426 requisite. Users are expected to include the generated dependency
427 file into a Makefile to automate the dependency management. This
428 option is analogous to the compiler's -MM -MF options.
429 --dynamic-list=file
431 Read a list of dynamic symbols from file. Same as
432 --export-dynamic-symbol-list, except that it implies --Bsymbolic.
433 If file does not exist in the current directory, it is searched
435 from library search paths for the sake of compatibility with GNU
436 ld.
437 --eh-frame-hdr
439 --no-eh-frame-hdr
440 Create .eh_frame_hdr section.
441 --emit-relocs
443 A linker usually "consumes" relocation sections. That is, a
444 linker applies relocations to other sections, and relocation sec‐
445 tions themselves are discarded.
446 The --emit-relocs instructs the linker to leave relocation sec‐
448 tions in the output file. Some post-link binary analysis or opti‐
449 mization tools such as LLVM Bolt need them.
450 --enable-new-dtags
452 --disable-new-dtags
453 By default, mold emits DT_RUNPATH for --rpath. If you pass
454 --disable-new-dtags, mold emits DT_RPATH for --rpath instead.
455 --execute-only
457 Traditionally, most processors require both executable and read‐
458 able bits to 1 to make the page executable, which allows machine
459 code to read itself as data at runtime. This is actually what an
460 attacker often does after gaining a limited control of a process
461 to find pieces of machine code they can use to gain the full con‐
462 trol of the process.
463 As a mitigation, some recent processors allows "execute-only"
465 pages. If a page is execute-only, you can call a function there
466 as long as you know its address but can't read it as data.
467 This option marks text segments execute-only. This option cur‐
469 rently works only on some ARM64 processors.
470 --exclude-libs=libraries...
472 Mark all symbols in the given libraries hidden.
473 --export-dynamic-symbol=sym
475 Put symbols matching sym in the dynamic symbol table. sym may be
476 a glob, with the same syntax as the globs used in
477 --export-dynamic-symbol-list or --version-script.
478 --export-dynamic-symbol-list=file
480 Read a list of dynamic symbols from file.
481 --fatal-warnings
483 --no-fatal-warnings
484 Treat warnings as errors.
485 --fini=symbol
487 Call symbol at unload-time.
488 --gc-sections
490 --no-gc-sections
491 Remove unreferenced sections.
492 --gdb-index
494 Create a .gdb_index section to speed up GNU debugger. To use
495 this, you need to compile source files with the -ggnu-pubnames
496 compiler flag.
497 --hash-style=[sysv | gnu | both]
499 Set hash style.
500 --icf=[none | safe | all]
502 --no-icf
503 It is not uncommon for a program to contain many identical func‐
504 tions that differ only in name. For example, a C++ template
505 std::vector is very likely to be instantiated to the identical
506 code for std::vector<int> and std::vector<unsigned> because the
507 container cares only about the size of the parameter type. Iden‐
508 tical Code Folding (ICF) is a size optimization to identify and
509 merge such identical functions.
510 If --icf=all is given, mold tries to merge all identical func‐
512 tions. This reduces the size of the output most, but it is not
513 “safe” optimization. It is guaranteed in C and C++ that two
514 pointers pointing two different functions will never be equal,
515 but --icf=all breaks that assumption as two functions have the
516 same address after merging. So a care must be taken when you use
517 that flag that your program does not depend on the function
518 pointer uniqueness.
519 --icf=safe is a flag to merge functions only when it is safe to
521 do so. That is, if a program does not take an address of a func‐
522 tion, it is safe to merge that function with other function, as
523 you cannot compare a function pointer with something else without
524 taking an address of a function. needs to be used with a com‐
525 piler that supports .llvm_addrsig section which contains the in‐
526 formation as to what symbols are address-taken. LLVM/Clang sup‐
527 ports that section by default. Since GCC does not support it yet,
528 you cannot use --icf=safe with GCC (it doesn't do any harm but
529 can't optimize at all.)
530 --icf=none and --no-icf disables ICF.
532 --ignore-data-address-equality
534 Make ICF to merge not only functions but also data. This option
535 should be used in combination with --icf=all.
536 --image-base=addr
538 Set the base address to addr.
539 --init=symbol
541 Call symbol at load-time.
542 --no-undefined
544 Report undefined symbols (even with --shared).
545 --noinhibit-exec
547 Create an output file even if errors occur.
548 --pack-dyn-relocs=[none | relr]
550 If relr is specified, all R_*_RELATIVE relocations are put into
551 .relr.dyn section instead of .rel.dyn or .rela.dyn section. Since
552 .relr.dyn section uses a space-efficient encoding scheme, speci‐
553 fying this flag can reduce the size of the output. This is typi‐
554 cally most effective for position-independent executable.
555 Note that a runtime loader has to support .relr.dyn to run exe‐
557 cutables or shared libraries linked with --pack-dyn-relocs=relr,
558 and only ChromeOS, Android and Fuchsia support it as of now in
559 2022.
560 --package-metadata=string
562 Embed string to a .note.package section. This option in intended
563 to be used by a package management command such as rpm to embed
564 metadata regarding a package to each executable file.
565 --pie, --pic-executable
567 --no-pie, --no-pic-executable
568 Create a position-independent executable.
569 --print-gc-sections
571 --no-print-gc-sections
572 Print removed unreferenced sections.
573 --print-icf-sections
575 --no-print-icf-sections
576 Print folded identical sections.
577 --push-state
579 --pop-state
580 --push-state saves the current values of --as-needed,
581 --whole-archive, --static, and --start-lib. The saved values can
582 be restored by --pop-state.
583 --push-state and --pop-state pairs can nest.
585 These options are useful when you want to construct linker com‐
587 mand line options programmatically. For example, if you want to
588 link libfoo.so by as-needed basis but don't want to change the
589 global state of --as-needed, you can append "--push-state --as-
590 needed -lfoo --pop-state" to the linker command line options.
591 --relax
593 --no-relax
594 Rewrite machine instructions with more efficient ones for some
595 relocations. The feature is enabled by default.
596 --require-defined=symbol
598 Like --undefined, except the new symbol must be defined by the
599 end of the link.
600 --retain-symbols-file=file
602 Keep only symbols listed in file.
603 file is a text file containing a symbol name on each line. mold
605 discards all local symbols as well as global symbol that are not
606 in file. Note that this option removes symbols only from .symtab
607 section and does not affect .dynsym section, which is used for
608 dynamic linking.
609 --rpath=dir
611 Add dir to runtime search path.
612 --section-start=section=address
614 Set address to section. address is a hexadecimal number that may
615 start with an optional ‘0x’.
616 --shared, --Bshareable
618 Create a share library.
619 --spare-dynamic-tags=number
621 Reserve given number of tags in .dynamic section.
622 --start-lib
624 --end-lib
625 Handle object files between --start-lib and --end-lib as if they
626 were in an archive file. That means object files between them are
627 linked only when they are needed to resolve undefined symbols.
628 The options are useful if you want to link object files only when
629 they are needed but want to avoid the overhead of running ar(3).
630 --static
632 Do not link against shared libraries.
633 --sysroot=dir
635 Set target system root directory to dir.
636 --trace
637 Print name of each input file.
638 --undefined-version
640 --no-undefined-version
641 By default, mold warns on a symbol specified by a version script
642 or by --export-dynamic-symbol if it is not defined. You can si‐
643 lence the warning by --undefined-version.
644 --unique=pattern
646 Don't merge input sections that match pattern.
647 --unresolved-symbols=[report-all | ignore-all | ignore-in-object-files |
649 ignore-in-shared-libs]
650 How to handle undefined symbols.
651 --version-script=file
653 Read version script from file. If file does not exist in the
654 current directory, it is searched from library search paths for
655 the sake of compatibility with GNU ld.
656 --warn-common
658 --no-warn-common
659 Warn about common symbols.
660 --warn-once
662 Only warn once for each undefined symbol instead of warn for each
663 relocation referring an undefined symbol.
664 --warn-unresolved-symbols
666 --error-unresolved-symbols
667 Normally, the linker reports an error for unresolved symbols.
668 --warn-unresolved-symbols option turns it into a warning.
669 --error-unresolved-symbols option restores the default behavior.
670 --whole-archive
672 --no-whole-archive
673 When archive files (.a files) are given to a linker, only object
674 files that are needed to resolve undefined symbols are extracted
675 from them and linked to an output file. --whole-archive changes
676 that behavior for subsequent archives so that a linker extracts
677 all object files and link them to an output. For example, if you
678 are creating a shared object file and you want to include all ar‐
679 chive members to the output, you should pass --whole-archive.
680 --no-whole-archive restores the default behavior for subsequent
681 archives.
682 --wrap=symbol
684 Make symbol to be resolved to __wrap_symbol. The original symbol
685 can be resolved as __real_symbol. This option is typically used
686 for wrapping an existing function.
687 -z cet-report=[none | warning | error]
689 Intel Control-flow Enforcement Technology (CET) is a new x86 fea‐
690 ture available since Tiger Lake which is released in 2020. It
691 defines new instructions to harden security to protect programs
692 from control hijacking attacks. You can tell compiler to use the
693 feature by specifying the -fcf-protection flag.
694 -z cet-report flag is used to make sure that all object files
696 were compiled with a correct -fcf-protection flag. If warning or
697 error are given, mold prints out a warning or an error message if
698 an object file was not compiled with the compiler flag.
699 mold looks for GNU_PROPERTY_X86_FEATURE_1_IBT bit and
701 GNU_PROPERTY_X86_FEATURE_1_SHSTK bit in .note.gnu.property sec‐
702 tion to determine whether or not an object file was compiled with
703 -fcf-protection.
704 -z now
706 -z lazy
707 By default, functions referring other ELF modules are resolved by
708 the dynamic linker when they are called for the first time. -z
709 now marks an executable or a shared library file so that all dy‐
710 namic symbols are loaded when a file is loaded to memory. -z
711 lazy restores the default behavior.
712 -z origin
714 Mark object requiring immediate $ORIGIN processing at runtime.
715 -z ibt Turn on GNU_PROPERTY_X86_FEATURE_1_IBT bit in .note.gnu.property
717 section to indicate that the output uses IBT-enabled PLT. This
718 option implies -z ibtplt.
719 -z ibtplt
721 Generate Intel Branch Tracking (IBT)-enabled PLT which is the de‐
722 fault on x86-64.
723 -z execstack
725 -z noexecstack
726 By default, the pages for the stack area (i.e. the pages where
727 local variables reside) are not executable for security reasons.
728 -z execstack makes it executable. -z noexecstack restores the
729 default behavior.
730 -z keep-text-section-prefix
732 -z nokeep-text-section-prefix
733 Keep .text.hot, .text.unknown, .text.unlikely, .text.startup and
734 .text.exit as separate sections in the final binary.
735 -z relro
737 -z norelro
738 Some sections such as .dynamic have to be writable only during an
739 executable or a shared library file is being loaded to memory.
740 Once the dynamic linker finishes its job, such sections won't be
741 mutated by anyone. As a security mitigation, it is preferred to
742 make such segments read-only during program execution.
743 -z relro puts such sections into a special segment called relro.
745 The dynamic linker make a relro segment read-only after it fin‐
746 ishes its job.
747 By default, mold generates a relro segment. -z norelro disables
749 the feature.
750 -z separate-loadable-segments
752 -z separate-code
753 -z noseparate-code
754 If one memory page contains multiple segments, the page protec‐
755 tion bits are set in such a way that needed attributes (writable
756 or executable) are satisfied for all segments. This usually hap‐
757 pens at a boundary of two segments with two different attributes.
758 separate-loadable-segments adds paddings between segments with
760 different attributes so that they do not share the same page.
761 This is the default.
762 separate-code adds paddings only between executable and non-exe‐
764 cutable segments.
765 noseparate-code does not add any paddings between segments.
767 -z defs
769 -z nodefs
770 Report undefined symbols (even with --shared).
771 -z shstk
773 Enforce shadow stack by turning GNU_PROPERTY_X86_FEATURE_1_SHSTK
774 bit in .note.gnu.property output section. Shadow stack is part of
775 Intel Control-flow Enforcement Technology (CET), which is avail‐
776 able since Tiger Lake (2020).
777 -z text
779 -z notext, -z textoff
780 mold by default reports an error if dynamic relocations are cre‐
781 ated in read-only sections. If -z notext or -z textoff are
782 given, mold creates such dynamic relocations without reporting an
783 error. -z text restores the default behavior.
784 -z max-page-size
786 Some CPU ISAs support multiple different memory page sizes. This
787 option specifies the maximum page size that an output binary can
788 run on. If you specify a large value, the output can run on both
789 large and small page systems, but it wastes a bit of memory at
790 page boundaries on systems with small pages.
791 The default value is 4 KiB for i386, x86-64 and RISC-V, and 64
793 KiB for ARM64.
794 -z nodefaultlib
796 Make the dynamic loader to ignore default search paths.
797 -z nodelete
799 Mark DSO non-deletable at runtime.
800 -z nodlopen
802 Mark DSO not available to dlopen(3). This option makes it possi‐
803 ble for the linker to optimize thread-local variable accesses by
804 rewriting instructions for some targets.
805 -z nodump
807 Mark DSO not available to dldump(3).
808 -z nocopyreloc
810 Do not create copy relocations.
811 -z initfirst
813 Mark DSO to be initialized first at runtime.
814 -z interpose
816 Mark object to interpose all DSOs but executable.
817
819 gold(1), ld(1), elf(5), ld.so(8)
820
822 Rui Ueyama <ruiu@cs.stanford.edu>
823
825 Report bugs to https://github.com/rui314/mold/issues
826BSD February 6, 2023 BSD