LD.LLD(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-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 --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.