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Manual Pages  — LD.LLD

NAME

ld.lld – ELF linker from the LLVM project

CONTENTS

SYNOPSIS


ld.lld [options] objfile ...

DESCRIPTION

A linker takes one or more object, archive, and library files, and combines them into an output file (an executable, a shared library, or another object file). It relocates code and data from the input files and resolves symbol references between them.

ld.lld is a drop-in replacement for the GNU BFD and gold linkers. It accepts most of the same command line arguments and linker scripts as GNU linkers.

ld.lld currently supports i386, x86-64, ARM, AArch64, PowerPC32, PowerPC64, MIPS32, MIPS64, RISC-V, AMDGPU, Hexagon and SPARC V9 targets. 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.

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.

--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.
--Bsymbolic
  Bind defined symbols locally.
--Bsymbolic-functions
  Bind defined function symbols locally.
--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.
--build-id
  Synonym for --build-id -= fast.
--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 or zlib. The default compression level is 1 (fastest) as the debug info usually compresses well at that level, but if you want to compress it more, you can specify -O2 to set the compression level to 6.
--cref
  Output cross reference table.
--define-common -, -d
  Assign space to common symbols.
--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
  Read a list of dynamic symbols from file.
--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.
--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 -= symbol
  Include symbol in the dynamic symbol table.
--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.
--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-O opt-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-define-common
  Do not assign space to common symbols.
--no-demangle
  Do not demangle symbol names.
--no-dynamic-linker
  Inhibit output of an .interp section.
--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-rosegment
  Do not put read-only non-executable sections in their own segment.
--no-threads
  Do not run the linker multi-threaded.
--no-undefined-version
  Report version scripts that refer undefined symbols.
--no-undefined
  Report unresolved symbols even if the linker is creating a shared library.
--no-warn-symbol-ordering
  Do not warn about problems with the symbol ordering file or call graph profile.
--no-whole-archive
  Restores the default behavior of loading archive members.
--no-pie -, --no-pic-executable
  Do not create a position independent executable.
--noinhibit-exec
  Retain the executable output file whenever it is still usable.
--nostdlib
  Only search directories specified on the command line.
-o path
  Write the output executable, library, or object to path. If not specified, a.out is used as a default.
-O value
  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.

-O 1 is the default.
--oformat -= format
  Specify the format for the output object file. The only supported format is binary, which produces output with no ELF header.
--omagic -, -N
  Set the text and data sections to be readable and writable, do not page align sections, 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.
--orphan-handling -= mode
  Control how orphan sections are handled. An orphan section is one not specifically mentioned in a linker script. 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. 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.
--print-gc-sections
  List removed unused sections.
--print-icf-sections
  List identical folded sections.
--print-map
  Print a link map to the standard output.
--push-state
  Save the current state of --as-needed, --static, and --whole-archive.
--pop-state
  Undo the effect of --push-state.
--relocatable -, -r
  Create relocatable object file.
--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.
--retain-symbols-file -= file
  Retain only the symbols listed in the 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.
--soname -= value , -h value
  Set DT_SONAME to value.
--sort-common
  This option is ignored for GNU compatibility.
--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.
--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
  Run the linker multi-threaded. This option is enabled by default.
--trace
  Print the names of the input files.
--trace-symbol -= symbol , -y symbol
  Trace references to symbol.
--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.
--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
  Display the version number and proceed with linking if object files are specified.
-V -, --version
  Display the version number and exit.
--verbose
  Verbose mode.
--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-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 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.
--warn-unresolved-symbols
  Report unresolved symbols as warnings.
--whole-archive
  Force load of all members in a static library.
--wrap -= symbol
  Use wrapper functions for symbol.
-z option
  Linker option extensions.

execstack
  Make the main stack executable. Stack permissions are recorded in the PT_GNU_STACK segment.

force-bti
  Force enable AArch64 BTI instruction in PLT, warn if Input ELF file does not have GNU_PROPERTY_AARCH64_FEATURE_1_BTI property.

force-ibt
  Force enable Intel Indirect Branch Tracking in PLT, warn if an input ELF file does not have 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.

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 -znotext 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.

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.

text Do not allow relocations against read-only segments. This is the default.

wxneeded
  Create a PT_OPENBSD_WXNEEDED segment.

IMPLEMENTATION NOTES

Ap 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.


LD.LLD (1) May 12, 2019

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