LD.LLD(1)

🎀 NAME 🎀

ld.lld — ELF linker from the LLVM project. (Yes bestie, this is the ld.lld(1) page and she's literally the moment. 💅)

✨ SYNOPSIS ✨

ld.lld [options] objfile ...

🌈 DESCRIPTION 🌈

Okay so picture this: a linker is the friend who takes all your object, archive, and library files and combines them into one output file — could be an executable, a shared library, or another object file. She relocates code and data from the input files and resolves symbol references between them. It's giving matchmaker, but for symbols. 💖

ld.lld is a drop-in replacement for the GNU BFD and gold linkers. She accepts most of the same command line arguments and linker scripts as GNU linkers. No cap, she just slides right in. ✨

Right now ld.lld supports these targets: i386, x86-64, ARM, AArch64, LoongArch, PowerPC32, PowerPC64, MIPS32, MIPS64, RISC-V, AMDGPU, Hexagon and SPARC V9. And get this — ld.lld acts as a Microsoft link.exe-compatible linker if invoked as lld-link, and as macOS's ld if invoked as ld.ld64. All these targets are always supported however ld.lld was built, so you can always use ld.lld as a native linker as well as a cross linker. Versatility? She invented it. 👑

💅 OPTIONS 💅

Many options have both a single-letter and long form. When using the long form options other than those beginning with the letter o may be specified using either one or two dashes preceding the option name. Long options beginning with o require two dashes to avoid confusion with the -o path option. (So like, don't be messy with the dashes, bestie. 🎀)

• --allow-multiple-definition — Do not error if a symbol is defined multiple times. The first definition will be used.
• --allow-shlib-undefined — Allow unresolved references in shared libraries. This option is enabled by default when linking a shared library.
• --apply-dynamic-relocs — Apply link-time values for dynamic relocations.
• --as-needed — Only set DT_NEEDED for shared libraries if used.
• --auxiliary=value — Set the DT_AUXILIARY field to the specified name.
• --Bdynamic, --dy — Link against shared libraries.
• --Bstatic, --static, --dn — Do not link against shared libraries.
• -Bno-symbolic — Don't bind default visibility defined symbols locally for -shared (default).
• -Bsymbolic — Bind default visibility defined symbols locally for -shared. Also set the DF_SYMBOLIC flag.
• -Bsymbolic-non-weak — Bind default visibility defined STB_GLOBAL symbols locally for -shared.
• -Bsymbolic-functions — Bind default visibility defined function symbols locally for -shared.
• -Bsymbolic-non-weak-functions — Bind default visibility defined STB_GLOBAL function symbols locally for -shared.
• ---be8 — Write a Big Endian ELF File using BE8 format(AArch32 only). (Yes, that's three dashes. She's extra. 💅)
• --build-id=value — Generate a build ID note. value may be one of fast, md5, sha1, tree, uuid, 0xhex-string, and none. tree is an alias for sha1. Build-IDs of type fast, md5, sha1, and tree are calculated from the object contents. fast is not intended to be cryptographically secure. (So like, don't use it for your secret diary, bestie. 🔐)
• --build-id — Synonym for --build-id=fast.
• --call-graph-profile-sort=algorithm — algorithm may be:
  • none — Ignore call graph profile.
  • hfsort — Use hfsort.
  • cdsort — Use cdsort (default).
• --color-diagnostics=value — Use colors in diagnostics. value may be one of always, auto, and never. auto enables color if and only if output is to a terminal.
• --color-diagnostics — Alias for --color-diagnostics=auto.
• --compress-debug-sections=value — Compress DWARF debug sections. value may be:
  • none — No compression.
  • zlib — The default compression level is 1 (fastest) as the debug info usually compresses well at that level. If you want to compress it more, you can specify -O2 to set the compression level to 6.
  • zstd — The compression level is 5.
• --cref — Output cross reference table. If -Map is specified, print to the map file.
• --defsym=symbol=expression — Define a symbol alias. expression may be another symbol or a linker script expression. For example, --defsym=foo=bar or --defsym=foo=bar+0x100.
• --demangle — Demangle symbol names.
• --disable-new-dtags — Disable new dynamic tags.
• --discard-all, -x — Delete all local symbols.
• --discard-locals, -X — Delete temporary local symbols.
• --discard-none — Keep all symbols in the symbol table.
• --dynamic-linker=value — Specify the dynamic linker to be used for a dynamically linked executable. This is recorded in an ELF segment of type PT_INTERP.
• --dynamic-list=file — Similar to --export-dynamic-symbol-list. When creating a shared object, implies -Bsymbolic but does not set DF_SYMBOLIC
• --EB — Select the big-endian format in the OUTPUT_FORMAT command.
• --EL — Select the little-endian format in the OUTPUT_FORMAT command.
• --eh-frame-hdr — Request creation of .eh_frame_hdr section and PT_GNU_EH_FRAME segment header.
• --emit-relocs, -q — Generate relocations in the output.
• --enable-new-dtags — Enable new dynamic tags.
• --end-lib — End a grouping of objects that should be treated as if they were together in an archive.
• --entry=entry — Name of entry point symbol.
• --error-limit=value — Maximum number of errors to emit before stopping. A value of zero indicates that there is no limit.
• --error-unresolved-symbols — Report unresolved symbols as errors.
• --error-handing-script=script_path — Call script script_path upon some error, with tag as first argument, and an extra parameter as second argument. The script is expected to return 0 on success. Any other value is considered a generic error. tag may be missing-lib followed by the name of the missing library. undefined-symbol followed by the name of the undefined symbol. (Yes, it says "handing" not "handling" — we don't make the rules, bestie. 😭)
• --execute-only — Mark executable sections unreadable. This option is currently only supported on AArch64.
• --exclude-libs=value — Exclude static libraries from automatic export.
• --export-dynamic, -E — Put symbols in the dynamic symbol table.
• --export-dynamic-symbol=glob — (executable) Put matched non-local defined symbols to the dynamic symbol table. (shared object) References to matched non-local STV_DEFAULT symbols shouldn't be bound to definitions within the shared object even if they would otherwise be due to -Bsymbolic , -Bsymbolic-functions or --dynamic-list
• --export-dynamic-symbol-list=file — Read a list of dynamic symbol patterns from file. Apply --export-dynamic-symbol on each pattern.
• --fatal-warnings — Treat warnings as errors.
• --filter=value, -F value — Set the DT_FILTER field to the specified value.
• --fini=symbol — Specify a finalizer function.
• --format=input-format, -b input-format — Specify the format of the inputs following this option. input-format may be one of binary, elf, and default. default is a synonym for elf.
• --gc-sections — Enable garbage collection of unused sections.
• --gdb-index — Generate .gdb_index section.
• --hash-style=value — Specify hash style. value may be sysv, gnu, or both. both is the default.
• --help — Print a help message.
• --icf=all — Enable identical code folding.
• --icf=safe — Enable safe identical code folding.
• --icf=none — Disable identical code folding.
• --ignore-data-address-equality — Ignore address equality of data. C/C++ requires each data to have a unique address. This option allows lld to do unsafe optimization that breaks the requirement: create copies of read-only data or merge two or more read-only data that happen to have the same value. (Unsafe, bestie. She said what she said. ⚠️)
• --ignore-function-address-equality — Ignore address equality of functions. This option allows non-PIC calls to a function with non-default visibility in a shared object. The function may have different addresses within the executable and within the shared object.
• --image-base=value — Set the base address to value.
• --init=symbol — Specify an initializer function.
• --keep-unique=symbol — Do not fold symbol during ICF.
• -l libName, --library=libName — Root name of library to use.
• -L dir, --library-path=dir — Add a directory to the library search path.
• --lto-aa-pipeline=value — AA pipeline to run during LTO. Used in conjunction with --lto-newpm-passes.
• --lto-newpm-passes=value — Passes to run during LTO.
• --lto-Oopt-level — Optimization level for LTO.
• --lto-partitions=value — Number of LTO codegen partitions.
• -m value — Set target emulation.
• --Map=file, -M file — Print a link map to file.
• --nmagic, -n — Do not page align sections, link against static libraries.
• --no-allow-shlib-undefined — Do not allow unresolved references in shared libraries. This option is enabled by default when linking an executable.
• --no-as-needed — Always set DT_NEEDED for shared libraries.
• --no-color-diagnostics — Do not use colors in diagnostics.
• --no-demangle — Do not demangle symbol names.
• --no-dynamic-linker — Inhibit output of an .interp section.
• --no-fortran-common — Do not search archive members for definitions to override COMMON symbols.
• --no-gc-sections — Disable garbage collection of unused sections.
• --no-gnu-unique — Disable STB_GNU_UNIQUE symbol binding.
• --no-merge-exidx-entries — Disable merging .ARM.exidx entries.
• --no-nmagic — Page align sections.
• --no-omagic — Do not set the text data sections to be writable, page align sections.
• --no-relax — Disable target-specific relaxations. For x86-64 this disables R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX GOT optimization.
• --no-rosegment — Do not put read-only non-executable sections in their own segment.
• --undefined-version — Do not report version scripts that refer to undefined symbols.
• --no-undefined — bestie, this one reports unresolved symbols even if the linker is busy creating a shared library. no hiding, we're being strict ✨
• --no-warn-symbol-ordering — do not warn about problems with the symbol ordering file or the call graph profile. silence is golden 🎀
• --no-warnings, -w — suppress warnings, and cancel out --fatal-warnings while you're at it.
• --no-whole-archive — restores the default behavior of loading archive members. we're back to normal, periodt 💅
• --no-pie, --no-pic-executable — do not create a position independent executable.
• --noinhibit-exec — retain the executable output file whenever it's still usable. keep the artifact, queen 👑
• --nostdlib — only search directories specified on the command line. nowhere else, no extras.
• -o path — write the output executable, library, or object to path. if you don't specify it, a.out is used as a default. iconic default behavior, honestly 🌸
• -Ovalue — optimize output file size. value may be:
  • 0 — disable string merging.
  • 1 — enable string merging.
  • 2 — enable string tail merging. if --compress-debug-sections is given, compress debug sections at compression level 6 instead of 1.

-O1 is the default. so if you say nothing, you get 1 🦋

• --oformat=format — specify the format for the output object file. the only supported format is binary, which produces output with no ELF header. that's the whole list, fr fr.
• --omagic, -N — set the text and data sections to be readable and writable, don't page align sections, and link against static libraries.
• --opt-remarks-filename file — write optimization remarks in YAML format to file.
• --opt-remarks-passes pass-regex — filter optimization remarks by only allowing the passes matching pass-regex.
• --opt-remarks-with-hotness — include hotness information in the optimization remarks file. spicy metadata 🔥
• --orphan-handling=mode — control how orphan sections are handled. an orphan section is one that's not specifically mentioned in a linker script (sad, unclaimed, we love them anyway 🥺). mode may be:
  • place — place orphan sections in suitable output sections.
  • warn — place orphan sections as for place, and also report a warning.
  • error — place orphan sections as for place, and also report an error.

place is the default.

• --pack-dyn-relocs=format — pack dynamic relocations in the given format. format may be:
  • none — do not pack. dynamic relocations are encoded in SHT_REL(A).
  • android — pack dynamic relocations in SHT_ANDROID_REL(A).
  • relr — pack relative relocations in SHT_RELR, and the rest of dynamic relocations in SHT_REL(A).
  • android+relr — pack relative relocations in SHT_RELR, and the rest of dynamic relocations in SHT_ANDROID_REL(A).

none is the default. and if --use-android-relr-tags is specified, use SHT_ANDROID_RELR instead of SHT_RELR.

• --pic-veneer — always generate position independent thunks.
• --pie, --pic-executable — create a position independent executable.
• --power10-stubs=mode — whether to use Power10 instructions in call stubs for R_PPC64_REL24_NOTOC and TOC/NOTOC interworking. mode may be:
  • yes — (default) use.
  • auto — currently the same as yes.
  • no — don't use.
• --print-gc-sections — list removed unused sections. bye bye, garbage 🗑️
• --print-icf-sections — list identical folded sections.
• --print-map — print a link map to the standard output.
• --print-archive-stats=file — write archive usage statistics to the specified file. print the numbers of members and fetched members for each archive.
• --push-state — save the current state of --as-needed, --static, and --whole-archive. little save point, like a video game 🎮
• --pop-state — restore the states saved by --push-state. load that save file back up.
• ---relax-gp — enable global pointer relaxation for RISC-V. (yes, three dashes, that's not a typo bestie, copy it exactly 🙈)
• --relocatable, -r — create relocatable object file.
• --remap-inputs=from-glob=to-file — input files matching from-glob are mapped to to-file. use /dev/null to ignore an input file. love a glow-up for your inputs ✨
• --remap-inputs-file=file — remap input files based on patterns in file. each line in the remap file is of the format from-glob=to-file or a comment starting with #.
• --reproduce=path — write a tar file to path, containing all the input files needed to reproduce the link, a text file called response.txt containing the command line options, and a text file called version.txt containing the output of ld.lld --version. the archive, when unpacked, can be used to re-run the linker with the same options and input files. it's giving time capsule 🕰️
• --retain-symbols-file=file — retain only the symbols listed in file.
• --rpath=value, -R value — add a DT_RUNPATH to the output.
• --rsp-quoting=value — quoting style for response files. the supported values are windows and posix.
• --script=file, -T file — read linker script from file. if multiple linker scripts are given, they are processed as if they were concatenated in the order they appeared on the command line.
• --section-start=section=address — set address of section.
• --shared, --Bsharable — build a shared object. (and yes, --Bsharable is spelled exactly like that, don't come for me 💀)
• --shuffle-sections=seed — shuffle matched sections using the given seed before mapping them to the output sections. if -1, reverse the section order. if 0, use a random seed. chaotic and I respect it 🌈
• --soname=value, -h value — set DT_SONAME to value.
• --sort-common — this option is ignored for GNU compatibility. it's just there, vibing, doing nothing 🫶
• --sort-section=value — specifies sections sorting rule when linkerscript is used.
• --start-lib — start a grouping of objects that should be treated as if they were together in an archive.
• --strip-all, -s — strip all symbols. implies --strip-debug.
• --strip-debug, -S — strip debugging information.
• --symbol-ordering-file=file — lay out sections in the order specified by file.
• --sysroot=value — set the system root.
• --target1-abs — interpret R_ARM_TARGET1 as R_ARM_ABS32.
• --target1-rel — interpret R_ARM_TARGET1 as R_ARM_REL32.
• --target2=type — interpret R_ARM_TARGET2 as type, where type is one of rel, abs, or got-rel.
• --Tbss=value — same as --section-start with .bss as the sectionname.
• --Tdata=value — same as --section-start with .data as the sectionname.
• --Ttext=value — same as --section-start with .text as the sectionname.
• --thinlto-cache-dir=value — path to ThinLTO cached object file directory.
• --thinlto-cache-policy=value — pruning policy for the ThinLTO cache.
• --thinlto-jobs=value — number of ThinLTO jobs.
• --threads=N — number of threads. all (default) means all of concurrent threads supported. 1 disables multi-threading. parallelize, bestie 🧚
• --fat-lto-objects — use the .llvm.lto section, which contains LLVM bitcode, in fat LTO object files to perform LTO.
• --no-fat-lto-objects — ignore the .llvm.lto section in relocatable object files (default).
• --time-trace — record time trace. ⏱️
• --time-trace-file=file — write time trace output to file.
• --time-trace-granularity=value — minimum time granularity (in microseconds) traced by time profiler.
• --trace — print the names of the input files.
• --trace-symbol=symbol, -y symbol — trace references to symbol. following it around like a stan 👀
• --undefined=symbol, -u symbol — if symbol is not defined after symbol resolution, and there's a static library that contains an object file defining the symbol, load the member to include the object file in the output file.
• --undefined-glob=pattern — synonym for --undefined, except that it takes a glob pattern. in a glob pattern, * matches zero or more characters, ? matches any single character, and [...] matches the characters within brackets. all symbols that match a given pattern are handled as if they were given as arguments of --undefined.
• --unique — creates a separate output section for every orphan input section.
• --unresolved-symbols=value — determine how to handle unresolved symbols.
• --use-android-relr-tags — use SHT_ANDROID_RELR / DT_ANDROID_RELR* tags instead of SHT_RELR / DT_RELR*.
• -v, -V — display the version number and proceed with linking if object files are specified.
• --version — display the version number and exit.
• --verbose — verbose mode. tell me everything, I'm nosy 💅
• --version-script=file — read version script from file.
• --warn-backrefs — warn about reverse or cyclic dependencies to or between static archives. this can be used to ensure linker invocation remains compatible with traditional Unix-like linkers.
• --warn-backrefs-exclude=glob — glob describing an archive (or an object file within --start-lib) which should be ignored for --warn-backrefs.
• --warn-common — warn about duplicate common symbols.
• --warn-ifunc-textrel — warn about using ifunc symbols in conjunction with text relocations. older versions of glibc library (2.28 and earlier) has a bug that causes the segment that includes ifunc symbols to be marked as not executable when they are relocated. as a result, although the program compiles and links successfully, it gives a segmentation fault when the instruction pointer reaches an ifunc symbol. use -warn-ifunc-textrel to let lld give a warning, if the code may include ifunc symbols, may do text relocations and be linked with an older glibc version. otherwise, there is no need to use it, as the default value does not give a warning. this flag has been introduced in late 2018, has no counter part in ld and gold linkers, and may be removed in the future.

ok that one is a whole saga 😭 read it twice, it's literally a real segfault warning. not a drill.

• --warn-unresolved-symbols — report unresolved symbols as warnings.
• --whole-archive — force load of all members in a static library.
• --why-extract=file — print to a file about why archive members are extracted. the receipts, finally 🧾
• --wrap=symbol — redirect symbol references to __wrap_symbol and __real_symbol references to symbol.
• -z option — linker option extensions.

okay so the -z option list keeps going, bestie — no skips, periodt: 💅

• dead-reloc-in-nonalloc=section_glob=value — resolve a relocation in a matched non-SHF_ALLOC section that references a discarded symbol to value. It accepts globs, and if a section matches more than one option, the last option takes precedence. An order of least specific to most specific match is recommended. 🦋
• execstack — make the main stack executable. Stack permissions are recorded in the PT_GNU_STACK segment. 🫶
• bti-report=[none|warning|error] — specify how to report the missing GNU_PROPERTY_AARCH64_FEATURE_1_BTI property. none is the default, so the linker will not report the missing property; otherwise it will be reported as a warning or an error. ✨
• cet-report=[none|warning|error] — same energy, but for the missing GNU_PROPERTY_X86_FEATURE_1_IBT or GNU_PROPERTY_X86_FEATURE_1_SHSTK properties. none is the default, so the linker will not report the missing property; otherwise it will be reported as a warning or an error. 🎀
• force-bti — force-enable AArch64 BTI instruction in PLT, and warn if an input ELF file does not have the GNU_PROPERTY_AARCH64_FEATURE_1_BTI property. 💅
• force-ibt — force-enable Intel Indirect Branch Tracking in PLT, and warn if an input ELF file does not have the GNU_PROPERTY_X86_FEATURE_1_IBT property. 🦋
• global — sets the DF_1_GLOBAL flag in the DYNAMIC section. Different loaders can decide how to handle this flag on their own. no cap. 👑
• ifunc-noplt — do not emit PLT entries for ifunc symbols. Instead, emit text relocations referencing the resolver. This is an experimental optimization and only suitable for standalone environments where text relocations do not have the usual drawbacks. This option must be combined with the -z notext option. 🧚
• initfirst — sets the DF_1_INITFIRST flag to indicate the module should be initialized first. 🌸
• interpose — set the DF_1_INTERPOSE flag to indicate to the runtime linker that the object is an interposer. During symbol resolution, interposers are searched after the application but before other dependencies. 💜
• muldefs — do not error if a symbol is defined multiple times. The first definition will be used. This is a synonym for --allow-multiple-definition. 🔥
• nocombreloc — disable combining and sorting multiple relocation sections. 💅
• nocopyreloc — disable the creation of copy relocations. 🦋
• nodefaultlib — set the DF_1_NODEFLIB flag to indicate that default library search paths should be ignored. 🌈
• nodelete — set the DF_1_NODELETE flag to indicate that the object cannot be unloaded from a process. 🫶
• nodlopen — set the DF_1_NOOPEN flag to indicate that the object may not be opened by dlopen(3). 😭
• nognustack — do not emit the PT_GNU_STACK segment. 💀
• norelro — do not indicate that portions of the object should be mapped read-only after initial relocation processing. The object will omit the PT_GNU_RELRO segment. 🙈
• notext — allow relocations against read-only segments. Sets the DT_TEXTREL flag in the DYNAMIC section. 🍓
• now — set the DF_BIND_NOW flag to indicate that the run-time loader should perform all relocation processing as part of object initialization. By default, relocations may be performed on demand. ⭐
• origin — set the DF_ORIGIN flag to indicate that the object requires $ORIGIN processing. 💖
• pac-plt — AArch64 only, use pointer authentication in PLT. 🎀
• pack-relative-relocs — similar to -pack-dyn-relocs=relr , but synthesizes the GLIBC_ABI_DT_RELR version dependency if there is a GLIBC_2.* version dependency. glibc ld.so rejects loading a dynamically linked object without the GLIBC_ABI_DT_RELR version dependency. 🦋
• rel — use REL format for dynamic relocations. 💅
• rela — use RELA format for dynamic relocations. ✨
• retpolineplt — emit retpoline format PLT entries as a mitigation for CVE-2017-5715. 🔥
• rodynamic — make the .dynamic section read-only. The DT_DEBUG tag will not be emitted. 💜
• separate-loadable-segments, separate-code, noseparate-code — specify whether two adjacent PT_LOAD segments are allowed to overlap in pages. noseparate-code (default) allows overlap. separate-code allows overlap between two executable segments, or two non-executable segments. separate-loadable-segments disallows overlap. 👑
• shstk — x86 only, use shadow stack. 🌸
• stack-size=size — set the main thread's stack size to size. The stack size is recorded as the size of the size. PT_GNU_STACK program segment. 🫶
• start-stop-gc — don't let __start_/__stop_ references retain the associated C identifier name sections (default). 💅
• nostart-stop-gc — let __start_/__stop_ references retain the associated C identifier name sections. 🦋
• text — do not allow relocations against read-only segments. This is the default. ⭐
• wxneeded — create a PT_OPENBSD_WXNEEDED segment. 🌈

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🌸 ENVIRONMENT VARIABLES 🌸

• LLD_REPRODUCE — create a reproduce tarball with the specified filename. If --reproduce is specified, --reproduce takes precedence. 💖
• LLD_VERSION — ld.lld creates a section named .comment containing the LLD version string. The version string can be overridden by this environment variable, which is useful to eliminate differences in the binary caused by LLD version number differences. 🎀

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🧠 IMPLEMENTATION NOTES 🧠

okay so ld.lld's handing of archive files (those with a .a file extension) is different from traditional linkers used on Unix-like systems. 👀

Traditional linkers maintain a set of undefined symbols during linking. The linker processes each file in the order in which it appears on the command line, until the set of undefined symbols becomes empty. An object file is linked into the output object when it is encountered, with its undefined symbols added to the set. Upon encountering an archive file, a traditional linker searches the objects contained therein, and processes those that satisfy symbols in the unresolved set. 🧚

Handling mutually dependent archives may be awkward when using a traditional linker. Archive files may have to be specified multiple times, or the special command line options --start-group and --end-group may be used to have the linker loop over the files in the group until no new symbols are added to the set. 😭

ld.lld records all symbols found in objects and archives as it iterates over command line arguments. When ld.lld encounters an undefined symbol that can be resolved by an object file contained in a previously processed archive file, it immediately extracts and links it into the output object. 💅

With certain archive inputs, ld.lld may produce different results compared to traditional linkers. In practice, large bodies of third party software have been linked with ld.lld without material issues. 🔥

The --warn-backrefs option may be used to identify a linker invocation that may be incompatible with traditional Unix-like linker behavior. ⭐

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and that's a wrap! this page came from Debian, dated Jul 25, 2023, and it's LD.LLD(1). slay. 💖