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LD.LLD(1) General Commands Manual LD.LLD(1)

ld.lld
ELF linker from the LLVM project

ld.lld [options] objfile ...

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:

Do not error if a symbol is defined multiple times. The first definition will be used.
Apply link-time values for dynamic relocations.
Only set DT_NEEDED for shared libraries if used.
=value
Set the DT_AUXILIARY field to the specified name.
, --dy
Link against shared libraries.
, --static, --dn
Do not link against shared libraries.
Bind defined symbols locally.
Bind defined function symbols locally.
=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.
Synonym for --build-id=fast.
=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.
Alias for --color-diagnostics=auto.
=value
Compress DWARF debug sections. value may be none or zlib.
Output cross reference table.
, -d
Assign space to common symbols.
=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 symbol names.
Disable new dynamic tags.
, -x
Delete all local symbols.
, -X
Delete temporary local symbols.
Keep all symbols in the symbol table.
=value
Specify the dynamic linker to be used for a dynamically linked executable. This is recorded in an ELF segment of type PT_INTERP.
=file
Read a list of dynamic symbols from file.
Request creation of .eh_frame_hdr section and PT_GNU_EH_FRAME segment header.
, -q
Generate relocations in the output.
Enable new dynamic tags.
End a grouping of objects that should be treated as if they were together in an archive.
=entry
Name of entry point symbol.
=value
Maximum number of errors to emit before stopping. A value of zero indicates that there is no limit.
Report unresolved symbols as errors.
=value
Exclude static libraries from automatic export.
, -E
Put symbols in the dynamic symbol table.
=symbol
Include symbol in the dynamic symbol table.
Treat warnings as errors.
=value, -F value
Set the DT_FILTER field to the specified value.
=symbol
Specify a finalizer function.
=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.
Enable garbage collection of unused sections.
Generate .gdb_index section.
=value
Specify hash style. value may be sysv, gnu, or both. both is the default.
Print a help message.
=all
Enable identical code folding.
=safe
Enable safe identical code folding.
=none
Disable identical code folding.
=value
Set the base address to value.
=symbol
Specify an initializer function.
=symbol
Do not fold symbol during ICF.
libName, --library=libName
Root name of library to use.
dir, --library-path=dir
Add a directory to the library search path.
=value
AA pipeline to run during LTO. Used in conjunction with --lto-newpm-passes.
=value
Passes to run during LTO.
opt-level
Optimization level for LTO.
=value
Number of LTO codegen partitions.
value
Set target emulation.
=file, -M file
Print a link map to file.
Always set DT_NEEDED for shared libraries.
Do not use colors in diagnostics.
Do not assign space to common symbols.
Do not demangle symbol names.
Inhibit output of an .interp section.
Disable garbage collection of unused sections.
Disable STB_GNU_UNIQUE symbol binding.
Do not put read-only non-executable sections in their own segment.
Do not run the linker multi-threaded.
Report version scripts that refer undefined symbols.
Report unresolved symbols even if the linker is creating a shared library.
Restores the default behavior of loading archive members.
Do not create a position independent executable.
Retain the executable output file whenever it is still usable.
Only search directories specified on the command line.
path
Write the output executable, library, or object to path. If not specified, a.out is used as a default.
value
Optimize output file size. value may be:

Disable string merging.
Enable string merging.
Enable string tail merging.

-O1 is the default.

=format
Specify the format for the output object file. The only supported format is binary, which produces output with no ELF header.
, -N
Set the text and data sections to be readable and writable.
file
Write optimization remarks in YAML format to file.
Include hotness information in the optimization remarks file.
Create a position independent executable.
List removed unused sections.
Print a link map to the standard output.
Save the current state of --as-needed, --static, and --while-archive.
Undo the effect of --push-state.
, -r
Create relocatable object file.
=value
Dump linker invocation and input files for debugging.
=file
Retain only the symbols listed in the file.
=value, -R value
Add a DT_RUNPATH to the output.
=value
Quoting style for response files. The supported values are windows and posix.
=file, -T file
Read linker script from file.
=section=address
Set address of section.
, --Bsharable
Build a shared object.
=value, -h value
Set DT_SONAME to value.
=value
Specifies sections sorting rule when linkerscript is used.
Start a grouping of objects that should be treated as if they were together in an archive.
, -s
Strip all symbols.
, -S
Strip debugging information.
=file
Lay out sections in the order specified by file.
=value
Set the system root.
Interpret R_ARM_TARGET1 as R_ARM_ABS32.
Interpret R_ARM_TARGET1 as R_ARM_REL32.
=type
Interpret R_ARM_TARGET2 as type, where type is one of rel, abs, or got-rel.
=value
Same as --section-start with .bss as the sectionname.
=value
Same as --section-start with .data as the sectionname.
=value
Same as --section-start with .text as the sectionname.
=value
Path to ThinLTO cached object file directory.
=value
Pruning policy for the ThinLTO cache.
=value
Number of ThinLTO jobs.
Run the linker multi-threaded. This option is enabled by default.
Print the names of the input files.
=symbol, -y symbol
Trace references to symbol.
=symbol, -u symbol
Force symbol to be an undefined symbol during linking.
=value
Determine how to handle unresolved symbols.
Display the version number and proceed with linking if object files are specified.
, --version
Display the version number and exit.
Verbose mode.
=file
Read version script from file.
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 about duplicate common symbols.
Report unresolved symbols as warnings.
Force load of all members in a static library.
=symbol
Use wrapper functions for symbol.
option
Linker option extensions.
Make the main stack executable. Stack permissions are recorded in the PT_GNU_STACK segment.
Sets the DF_1_INITFIRST flag to indicate the module should be initialized first.
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.
Do not error if a symbol is defined multiple times. The first definition will be used. This is a synonym for --allow-multiple-definition.
Disable combining and sorting multiple relocation sections.
Disable the creation of copy relocations.
Set the DF_1_NODELETE flag to indicate that the object cannot be unloaded from a process.
Set the DF_1_NOOPEN flag to indcate that the object may not be opened by dlopen(3).
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.
Allow relocations against read-only segments. Sets the DT_TEXTREL flag in the DYNAMIC section.
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.
Set the DF_ORIGIN flag to indicate that the object requires $ORIGIN processing.
Emit retpoline format PLT entries as a mitigation for CVE-2017-5715.
Make the .dynamic section read-only. The DT_DEBUG tag will not be emitted.
=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.
Do not allow relocations against read-only segments. This is the default.
Create a PT_OPENBSD_WXNEEDED segment.

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.

September 14, 2018 OpenBSD-current