Ubuntu Manpage: ld.lld — ELF linker from the LLVM project

Provided by: lld-12_12.0.1-19ubuntu3_amd64

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.

     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. (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. Implies -Bsymbolic but does not set DF_SYMBOLIC

--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.

--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

--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-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-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-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. This is currently a no-op.

--no-rosegment
Do not put read-only non-executable sections in their own segment.

--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.

-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.

--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.

--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.

--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.

--shuffle-sections=seed
Shuffle input sections using the given seed. If 0, use a random seed.

--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=N
Number of threads. all (default) means all of concurrent threads supported. 1
disables multi-threading.

--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.

--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 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-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 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
Redirect symbol references to __wrap_symbol and __real_symbol references to symbol.

-z option
Linker option extensions.

dead-reloc-in-nonalloc=section_glob=value
Resolve a relocation in a matched non-SHF_ALLOC section referencing a
discarded symbol to value Accepts globs, in the event of a section matching
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.

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 -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.

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.

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.