ld.lld-7(1)

NAME

ld.lld – ELF linker from the LLVM project

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.

These options are available:

--allow-multiple-definition

Do not error if a symbol is defined multiple times. The first definition will be used.

--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.

--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.

--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.

--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.

--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-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-whole-archive

Restores the default behavior of loading archive members.

--no-pie

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.

-Ovalue

Optimize output file size. value may be:

0

Disable string merging.

1

Enable string merging.

2

Enable string tail merging.

-O1 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.

--opt-remarks-filename file

Write optimization remarks in YAML format to file.

--opt-remarks-with-hotness

Include hotness information in the optimization remarks file.

--pie

Create a position independent executable.

--print-gc-sections

List removed unused sections.

--print-map

Print a link map to the standard output.

--push-state

Save the current state of --as-needed, --static, and --while-archive.

--pop-state

Undo the effect of --push-state.

--relocatable, -r

Create relocatable object file.

--reproduce=value

Dump linker invocation and input files for debugging.

--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.

--section-start=section=address

Set address of section.

--shared, --Bsharable

Build a shared object.

--soname=value, -h value

Set DT_SONAME to value.

--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

Force symbol to be an undefined symbol during linking.

--unresolved-symbols=value

Determine how to handle unresolved symbols.

-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-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.

initfirst

Sets the DF_1_INITFIRST flag to indicate the module should be initialized first.

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.

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 indcate that the object may not be opened by dlopen(3).

norelro

Do not indicate that portions of the object shold 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.

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.

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

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.