LD.LLD
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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.
- -Bno-symbolic
-
Don't bind default visibility defined symbols locally for
-shared
(default).
- -Bsymbolic
-
Bind default visibility defined symbols locally for
-shared.
Also set the
DF_SYMBOLIC
flag.
- -Bsymbolic-functions
-
Bind default visibility defined function symbols locally for
-shared.
- -Bsymbolic-non-weak-functions
-
Bind default visibility defined STB_GLOBAL function symbols locally for
-shared.
- --build-id = value
-
Generate a build ID note.
value
may be one of
fast
md5
sha1
tree
uuid
0x hex-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. If
-Map
is specified, print to the map file.
- --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
-
Similar to
--export-dynamic-symbol-list
When creating a shared object, implies
-Bsymbolic
but does not set DF_SYMBOLIC
- --EB
-
Select the big-endian format in the OUTPUT_FORMAT command.
- --EL
-
Select the little-endian format in the OUTPUT_FORMAT command.
- --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
- --export-dynamic-symbol-list = file
-
Read a list of dynamic symbol patterns from
file
Apply
--export-dynamic-symbol
on each pattern.
- --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-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. For x86-64 this disables R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX GOT optimization.
- --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.
- -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.
- --power10-stubs = mode
-
Whether to use Power10 instructions in call stubs for R_PPC64_REL24_NOTOC and TOC/NOTOC interworking.
mode
may be:
- yes
-
(default) Use.
- auto
-
Currently the same as yes.
- no
-
Don't use.
- --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
-
Restore the states saved by
--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 matched sections using the given seed before mapping them to the output sections.
If -1, reverse the section order. 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.
Implies
--strip-debug
- --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.
- --why-extract = file
-
Print to a file about why archive members are extracted.
- --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.
- bti-report = [none|warning|error]
-
Specify how to report the missing GNU_PROPERTY_AARCH64_FEATURE_1_BTI property.
none
is the default, linker will not report the missing property otherwise will be reported as a warning or an error.
- cet-report = [none|warning|error]
-
Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_IBT or GNU_PROPERTY_X86_FEATURE_1_SHSTK properties.
none
is the default, linker will not report the missing property otherwise will be reported as a warning or an error.
- 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.
- start-stop-gc
-
Don't let __start_/__stop_ references retain the associated C identifier name sections (default).
- nostart-stop-gc
-
Let __start_/__stop_ references retain the associated C identifier name sections.
- text
-
Do not allow relocations against read-only segments.
This is the default.
- wxneeded
-
Create a
PT_OPENBSD_WXNEEDED
segment.
IMPLEMENTATION NOTES
Ap 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.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- IMPLEMENTATION NOTES
-
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Time: 08:07:00 GMT, April 28, 2024