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. \" Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
. \" See https://llvm.org/LICENSE.txt for license information.
. \" SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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. \"
. \" This man page documents only lld's ELF linking support, obtained originally
. \" from FreeBSD.
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.Dd Jul 25 , 2023
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.Dt LD.LLD 1
.Os
.Sh NAME
.Nm ld.lld
.Nd ELF linker from the LLVM project
.Sh SYNOPSIS
.Nm ld.lld
.Op Ar options
.Ar objfile ...
.Sh 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.
.Pp
.Nm
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.
.Pp
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.Nm
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currently supports i386, x86-64, ARM, AArch64, LoongArch, PowerPC32,
PowerPC64, MIPS32, MIPS64, RISC-V, AMDGPU, Hexagon and SPARC V9 targets.
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.Nm
acts as a Microsoft link.exe-compatible linker if invoked as
.Nm lld-link
and as macOS's ld if invoked as
.Nm ld.ld64.
All these targets are always supported however
.Nm
was built, so you can always use
.Nm
as a native linker as well as a cross linker.
.Sh OPTIONS
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Many options have both a single-letter and long form.
When using the long form options other than those beginning with the
letter
.Cm o
may be specified using either one or two dashes preceding the option name.
Long options beginning with
.Cm o
require two dashes to avoid confusion with the
.Fl o Ar path
option.
.Pp
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.Bl -tag -width indent
.It Fl -allow-multiple-definition
Do not error if a symbol is defined multiple times.
The first definition will be used.
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.It Fl -allow-shlib-undefined
Allow unresolved references in shared libraries.
This option is enabled by default when linking a shared library.
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.It Fl -apply-dynamic-relocs
Apply link-time values for dynamic relocations.
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.It Fl -as-needed
Only set
.Dv DT_NEEDED
for shared libraries if used.
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.It Fl -auxiliary Ns = Ns Ar value
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Set the
.Dv DT_AUXILIARY
field to the specified name.
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.It Fl -Bdynamic , Fl -dy
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Link against shared libraries.
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.It Fl -Bstatic , Fl -static , Fl -dn
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Do not link against shared libraries.
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.It Fl Bno-symbolic
Don't bind default visibility defined symbols locally for
.Fl shared
(default).
.It Fl Bsymbolic
Bind default visibility defined symbols locally for
.Fl shared.
Also set the
.Dv DF_SYMBOLIC
flag.
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.It Fl Bsymbolic-non-weak
Bind default visibility defined STB_GLOBAL symbols locally for
.Fl shared.
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.It Fl Bsymbolic-functions
Bind default visibility defined function symbols locally for
.Fl shared.
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.It Fl Bsymbolic-non-weak-functions
Bind default visibility defined STB_GLOBAL function symbols locally for
.Fl shared.
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.It Fl --be8
Write a Big Endian ELF File using BE8 format(AArch32 only)
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.It Fl -build-id Ns = Ns Ar value
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Generate a build ID note.
.Ar value
may be one of
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.Cm fast ,
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.Cm md5 ,
.Cm sha1 ,
.Cm tree ,
.Cm uuid ,
.Cm 0 x Ns Ar hex-string ,
and
.Cm none .
.Cm tree
is an alias for
.Cm sha1 .
Build-IDs of type
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.Cm fast ,
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.Cm md5 ,
.Cm sha1 ,
and
.Cm tree
are calculated from the object contents.
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.Cm fast
is not intended to be cryptographically secure.
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.It Fl -build-id
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Synonym for
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.Fl -build-id Ns = Ns Cm fast .
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.It Fl -call-graph-profile-sort Ns = Ns Ar algorithm
.Ar algorithm
may be:
.Pp
.Bl -tag -width 2 n -compact
.It Cm none
Ignore call graph profile.
.It Cm hfsort
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Use hfsort.
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.It Cm cdsort
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Use cdsort (default).
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.El
.Pp
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.It Fl -color-diagnostics Ns = Ns Ar value
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Use colors in diagnostics.
.Ar value
may be one of
.Cm always ,
.Cm auto ,
and
.Cm never .
.Cm auto
enables color if and only if output is to a terminal.
.It Fl -color-diagnostics
Alias for
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.Fl -color-diagnostics Ns = Ns Cm auto .
.It Fl -compress-debug-sections Ns = Ns Ar value
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Compress DWARF debug sections.
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.Cm value
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may be
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.Pp
.Bl -tag -width 2 n -compact
.It Cm none
No compression.
.It Cm zlib
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The default compression level is 1 (fastest) as the debug info usually
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compresses well at that level. If you want to compress it more,
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you can specify
.Fl O2
to set the compression level to 6.
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.It Cm zstd
The compression level is 5.
.El
.Pp
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.It Fl -cref
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Output cross reference table. If
.Fl Map
is specified, print to the map file.
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.It Fl -defsym Ns = Ns Ar symbol Ns = Ns Ar expression
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Define a symbol alias.
.Ar expression
may be another symbol or a linker script expression.
For example,
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.Ql --defsym=foo=bar
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or
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.Ql --defsym=foo=bar+0x100 .
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.It Fl -demangle
Demangle symbol names.
.It Fl -disable-new-dtags
Disable new dynamic tags.
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.It Fl -discard-all , Fl x
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Delete all local symbols.
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.It Fl -discard-locals , Fl X
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Delete temporary local symbols.
.It Fl -discard-none
Keep all symbols in the symbol table.
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.It Fl -dynamic-linker Ns = Ns Ar value
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Specify the dynamic linker to be used for a dynamically linked executable.
This is recorded in an ELF segment of type
.Dv PT_INTERP .
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.It Fl -dynamic-list Ns = Ns Ar file
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Similar to
.Cm --export-dynamic-symbol-list .
When creating a shared object, implies
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.Cm -Bsymbolic
but does not set DF_SYMBOLIC
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.It Fl -EB
Select the big-endian format in the OUTPUT_FORMAT command.
.It Fl -EL
Select the little-endian format in the OUTPUT_FORMAT command.
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.It Fl -eh-frame-hdr
Request creation of
.Li .eh_frame_hdr
section and
.Dv PT_GNU_EH_FRAME
segment header.
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.It Fl -emit-relocs , Fl q
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Generate relocations in the output.
.It Fl -enable-new-dtags
Enable new dynamic tags.
.It Fl -end-lib
End a grouping of objects that should be treated as if they were together
in an archive.
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.It Fl -entry Ns = Ns Ar entry
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Name of entry point symbol.
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.It Fl -error-limit Ns = Ns Ar value
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Maximum number of errors to emit before stopping.
A value of zero indicates that there is no limit.
.It Fl -error-unresolved-symbols
Report unresolved symbols as errors.
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.It Fl -error-handing-script Ns = Ns Ar script_path
Call script
.Ar script_path
upon some error, with
.Ar 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.
.Ar tag
may be
.Cm missing-lib
followed by the name of the missing library.
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.Cm undefined-symbol
followed by the name of the undefined symbol.
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.It Fl -execute-only
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Mark executable sections unreadable.
This option is currently only supported on AArch64.
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.It Fl -exclude-libs Ns = Ns Ar value
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Exclude static libraries from automatic export.
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.It Fl -export-dynamic , Fl E
Put symbols in the dynamic symbol table.
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.It Fl -export-dynamic-symbol Ns = Ns Ar 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
.Cm -Bsymbolic
,
.Cm -Bsymbolic-functions
or
.Cm --dynamic-list
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.It Fl -export-dynamic-symbol-list Ns = Ns Ar file
Read a list of dynamic symbol patterns from
.Ar file .
Apply
.Cm --export-dynamic-symbol
on each pattern.
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.It Fl -fatal-warnings
Treat warnings as errors.
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.It Fl -filter Ns = Ns Ar value , Fl F Ar value
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Set the
.Dv DT_FILTER
field to the specified value.
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.It Fl -fini Ns = Ns Ar symbol
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Specify a finalizer function.
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.It Fl -format Ns = Ns Ar input-format , Fl b Ar input-format
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Specify the format of the inputs following this option.
.Ar input-format
may be one of
.Cm binary ,
.Cm elf ,
and
.Cm default .
.Cm default
is a synonym for
.Cm elf .
.It Fl -gc-sections
Enable garbage collection of unused sections.
.It Fl -gdb-index
Generate
.Li .gdb_index
section.
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.It Fl -hash-style Ns = Ns Ar value
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Specify hash style.
.Ar value
may be
.Cm sysv ,
.Cm gnu ,
or
.Cm both .
.Cm both
is the default.
.It Fl -help
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Print a help message.
.It Fl -icf Ns = Ns Cm all
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Enable identical code folding.
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.It Fl -icf Ns = Ns Cm safe
Enable safe identical code folding.
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.It Fl -icf Ns = Ns Cm none
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Disable identical code folding.
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.It Fl -ignore-data-address-equality
Ignore address equality of data. C/C++ requires each data to have a unique
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address.
This option allows lld to do unsafe optimization that breaks the
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requirement: create copies of read-only data or merge two or more read-only data
that happen to have the same value.
.It Fl -ignore-function-address-equality
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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.
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.It Fl -image-base Ns = Ns Ar value
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Set the base address to
.Ar value .
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.It Fl -init Ns = Ns Ar symbol
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Specify an initializer function.
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.It Fl -keep-unique Ns = Ns Ar symbol
Do not fold
.Ar symbol
during ICF.
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.It Fl l Ar libName, Fl -library Ns = Ns Ar libName
Root name of library to use.
.It Fl L Ar dir , Fl -library-path Ns = Ns Ar dir
Add a directory to the library search path.
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.It Fl -lto-aa-pipeline Ns = Ns Ar value
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AA pipeline to run during LTO.
Used in conjunction with
.Fl -lto-newpm-passes .
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.It Fl -lto-newpm-passes Ns = Ns Ar value
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Passes to run during LTO.
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.It Fl -lto-O Ns Ar opt-level
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Optimization level for LTO.
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.It Fl -lto-partitions Ns = Ns Ar value
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Number of LTO codegen partitions.
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.It Fl m Ar value
Set target emulation.
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.It Fl -Map Ns = Ns Ar file , Fl M Ar file
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Print a link map to
.Ar file .
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.It Fl -nmagic , Fl n
Do not page align sections, link against static libraries.
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.It Fl -no-allow-shlib-undefined
Do not allow unresolved references in shared libraries.
This option is enabled by default when linking an executable.
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.It Fl -no-as-needed
Always set
.Dv DT_NEEDED
for shared libraries.
.It Fl -no-color-diagnostics
Do not use colors in diagnostics.
.It Fl -no-demangle
Do not demangle symbol names.
.It Fl -no-dynamic-linker
Inhibit output of an
.Li .interp
section.
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.It Fl -no-fortran-common
Do not search archive members for definitions to override COMMON symbols.
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.It Fl -no-gc-sections
Disable garbage collection of unused sections.
.It Fl -no-gnu-unique
Disable STB_GNU_UNIQUE symbol binding.
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.It Fl -no-merge-exidx-entries
Disable merging .ARM.exidx entries.
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.It Fl -no-nmagic
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Page align sections.
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.It Fl -no-omagic
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Do not set the text data sections to be writable, page align sections.
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.It Fl -no-relax
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Disable target-specific relaxations. For x86-64 this disables R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX GOT optimization.
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.It Fl -no-rosegment
Do not put read-only non-executable sections in their own segment.
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.It Fl -undefined-version
Do not report version scripts that refer to undefined symbols.
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.It Fl -no-undefined
Report unresolved symbols even if the linker is creating a shared library.
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.It Fl -no-warn-symbol-ordering
Do not warn about problems with the symbol ordering file or call graph profile.
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.It Fl -no-warnings , Fl w
Suppress warnings and cancel
.Cm --fatal-warnings.
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.It Fl -no-whole-archive
Restores the default behavior of loading archive members.
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.It Fl -no-pie , Fl -no-pic-executable
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Do not create a position independent executable.
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.It Fl -noinhibit-exec
Retain the executable output file whenever it is still usable.
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.It Fl -nostdlib
Only search directories specified on the command line.
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.It Fl o Ar path
Write the output executable, library, or object to
.Ar path .
If not specified,
.Dv a.out
is used as a default.
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.It Fl O Ns Ar value
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Optimize output file size.
.Ar value
may be:
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.Pp
.Bl -tag -width 2 n -compact
.It Cm 0
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Disable string merging.
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.It Cm 1
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Enable string merging.
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.It Cm 2
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Enable string tail merging. If
.Fl -compress-debug-sections
is given, compress debug sections at compression level 6 instead of 1.
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.El
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.Pp
.Fl O Ns Cm 1
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is the default.
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.It Fl -oformat Ns = Ns Ar format
Specify the format for the output object file.
The only supported
.Ar format
is
.Cm binary ,
which produces output with no ELF header.
.It Fl -omagic , Fl N
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Set the text and data sections to be readable and writable, do not page align
sections, link against static libraries.
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.It Fl -opt-remarks-filename Ar file
Write optimization remarks in YAML format to
.Ar file .
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.It Fl -opt-remarks-passes Ar pass-regex
Filter optimization remarks by only allowing the passes matching
.Ar pass-regex .
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.It Fl -opt-remarks-with-hotness
Include hotness information in the optimization remarks file.
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.It Fl -orphan-handling Ns = Ns Ar mode
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Control how orphan sections are handled.
An orphan section is one not specifically mentioned in a linker script.
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.Ar mode
may be:
.Pp
.Bl -tag -width 2 n -compact
.It Cm place
Place orphan sections in suitable output sections.
.It Cm warn
Place orphan sections as for
.Cm place
and also report a warning.
.It Cm error
Place orphan sections as for
.Cm place
and also report an error.
.El
.Pp
.Cm place
is the default.
.It Fl -pack-dyn-relocs Ns = Ns Ar format
Pack dynamic relocations in the given format.
.Ar format
may be:
.Pp
.Bl -tag -width 2 n -compact
.It Cm none
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Do not pack.
Dynamic relocations are encoded in SHT_REL(A).
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.It Cm android
Pack dynamic relocations in SHT_ANDROID_REL(A).
.It Cm relr
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Pack relative relocations in SHT_RELR, and the rest of dynamic relocations in
SHT_REL(A).
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.It Cm android+relr
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Pack relative relocations in SHT_RELR, and the rest of dynamic relocations in
SHT_ANDROID_REL(A).
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.El
.Pp
.Cm none
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is the default.
If
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.Fl -use-android-relr-tags
is specified, use SHT_ANDROID_RELR instead of SHT_RELR.
.Pp
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.It Fl -pic-veneer
Always generate position independent thunks.
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.It Fl -pie , Fl -pic-executable
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Create a position independent executable.
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.It Fl -power10-stubs Ns = Ns Cm mode
Whether to use Power10 instructions in call stubs for R_PPC64_REL24_NOTOC and TOC/NOTOC interworking.
.Ar mode
may be:
.Pp
.Bl -tag -width 2 n -compact
.It Cm yes
(default) Use.
.It Cm auto
Currently the same as yes.
.It Cm no
Don't use.
.El
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.It Fl -print-gc-sections
List removed unused sections.
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.It Fl -print-icf-sections
List identical folded sections.
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.It Fl -print-map
Print a link map to the standard output.
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.It Fl -print-archive-stats Ns = Ns Ar file
Write archive usage statistics to the specified file.
Print the numbers of members and fetched members for each archive.
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.It Fl -push-state
Save the current state of
.Fl -as-needed ,
.Fl -static ,
and
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.Fl -whole-archive.
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.It Fl -pop-state
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Restore the states saved by
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.Fl -push-state.
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.It Fl --relax-gp
Enable global pointer relaxation for RISC-V.
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.It Fl -relocatable , Fl r
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Create relocatable object file.
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.It Fl -remap-inputs Ns = Ns Ar from-glob=to-file
Input files matching
.Cm from-glob
are mapped to
.Cm to-file.
Use
.Cm /dev/null
to ignore an input file.
.It Fl -remap-inputs-file Ns = Ns Ar file
Remap input files based on patterns in
.Ar file .
Each line in the remap file is of the format
.Cm from-glob=to-file
or a comment starting with
.Cm # .
2019-08-23 08:52:55 +00:00
.It Fl -reproduce Ns = Ns Ar path
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Write a tar file to
2019-08-23 08:52:55 +00:00
.Ar path,
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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
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version.txt containing the output of ld.lld --version.
The archive when
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unpacked can be used to re-run the linker with the same options and input files.
2018-03-01 16:02:19 +00:00
.It Fl -retain-symbols-file Ns = Ns Ar file
2018-02-07 20:38:18 +00:00
Retain only the symbols listed in the file.
2018-07-30 22:31:00 +00:00
.It Fl -rpath Ns = Ns Ar value , Fl R Ar value
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Add a
.Dv DT_RUNPATH
to the output.
2018-03-01 16:02:19 +00:00
.It Fl -rsp-quoting Ns = Ns Ar value
2018-02-07 20:38:18 +00:00
Quoting style for response files.
The supported values are
2018-03-01 16:02:19 +00:00
.Cm windows
2018-02-07 20:38:18 +00:00
and
2018-03-01 16:02:19 +00:00
.Cm posix .
2018-07-30 22:31:00 +00:00
.It Fl -script Ns = Ns Ar file , Fl T Ar file
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Read linker script from
.Ar file .
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If multiple linker scripts are given, they are processed as if they
were concatenated in the order they appeared on the command line.
2018-07-30 22:31:00 +00:00
.It Fl -section-start Ns = Ns Ar section Ns = Ns Ar address
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Set address of section.
2018-07-30 22:31:00 +00:00
.It Fl -shared , Fl -Bsharable
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Build a shared object.
2020-02-19 21:19:58 +00:00
.It Fl -shuffle-sections Ns = Ns Ar seed
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Shuffle matched sections using the given seed before mapping them to the output sections.
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If -1, reverse the section order. If 0, use a random seed.
2018-07-30 22:31:00 +00:00
.It Fl -soname Ns = Ns Ar value , Fl h Ar value
2018-02-07 20:38:18 +00:00
Set
.Dv DT_SONAME
to
.Ar value .
2019-06-03 05:11:44 +00:00
.It Fl -sort-common
This option is ignored for GNU compatibility.
2018-03-01 18:40:11 +00:00
.It Fl -sort-section Ns = Ns Ar value
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Specifies sections sorting rule when linkerscript is used.
.It Fl -start-lib
Start a grouping of objects that should be treated as if they were together
in an archive.
2018-07-30 22:31:00 +00:00
.It Fl -strip-all , Fl s
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Strip all symbols.
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Implies
.Fl -strip-debug .
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.It Fl -strip-debug , Fl S
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Strip debugging information.
2018-03-02 02:57:12 +00:00
.It Fl -symbol-ordering-file Ns = Ns Ar file
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Lay out sections in the order specified by
.Ar file .
2018-03-01 16:02:19 +00:00
.It Fl -sysroot Ns = Ns Ar value
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Set the system root.
.It Fl -target1-abs
Interpret
.Dv R_ARM_TARGET1
as
.Dv R_ARM_ABS32 .
.It Fl -target1-rel
Interpret
.Dv R_ARM_TARGET1
as
.Dv R_ARM_REL32 .
2018-03-01 16:02:19 +00:00
.It Fl -target2 Ns = Ns Ar type
2018-02-07 20:38:18 +00:00
Interpret
.Dv R_ARM_TARGET2
as
.Ar type ,
where
.Ar type
is one of
2018-03-01 16:02:19 +00:00
.Cm rel ,
.Cm abs ,
2018-02-07 20:38:18 +00:00
or
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.Cm got-rel .
2018-03-01 18:40:11 +00:00
.It Fl -Tbss Ns = Ns Ar value
2018-02-07 20:38:18 +00:00
Same as
.Fl -section-start
with
.Li .bss
as the sectionname.
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.It Fl -Tdata Ns = Ns Ar value
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Same as
.Fl -section-start
with
.Li .data
as the sectionname.
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.It Fl -Ttext Ns = Ns Ar value
Same as
.Fl -section-start
with
.Li .text
as the sectionname.
2018-03-01 16:02:19 +00:00
.It Fl -thinlto-cache-dir Ns = Ns Ar value
2018-02-07 20:38:18 +00:00
Path to ThinLTO cached object file directory.
2018-03-02 02:57:12 +00:00
.It Fl -thinlto-cache-policy Ns = Ns Ar value
2018-02-07 20:38:18 +00:00
Pruning policy for the ThinLTO cache.
2018-03-01 16:02:19 +00:00
.It Fl -thinlto-jobs Ns = Ns Ar value
2018-02-07 20:38:18 +00:00
Number of ThinLTO jobs.
[lld][COFF][ELF][WebAssembly] Replace --[no-]threads /threads[:no] with --threads={1,2,...} /threads:{1,2,...}
--no-threads is a name copied from gold.
gold has --no-thread, --thread-count and several other --thread-count-*.
There are needs to customize the number of threads (running several lld
processes concurrently or customizing the number of LTO threads).
Having a single --threads=N is a straightforward replacement of gold's
--no-threads + --thread-count.
--no-threads is used rarely. So just delete --no-threads instead of
keeping it for compatibility for a while.
If --threads= is specified (ELF,wasm; COFF /threads: is similar),
--thinlto-jobs= defaults to --threads=,
otherwise all available hardware threads are used.
There is currently no way to override a --threads={1,2,...}. It is still
a debate whether we should use --threads=all.
Reviewed By: rnk, aganea
Differential Revision: https://reviews.llvm.org/D76885
2020-03-17 19:40:19 +00:00
.It Fl -threads Ns = Ns Ar N
Number of threads.
.Cm all
(default) means all of concurrent threads supported.
.Cm 1
disables multi-threading.
2023-07-24 20:14:17 +00:00
.It Fl -fat-lto-objects
Use the .llvm.lto section, which contains LLVM bitcode, in fat LTO object files to perform LTO.
.It Fl -no-fat-lto-objects
Ignore the .llvm.lto section in relocatable object files (default).
2020-05-12 10:54:18 +00:00
.It Fl -time-trace
Record time trace.
.It Fl -time-trace-file Ns = Ns Ar file
Write time trace output to
.Ar file .
.It Fl -time-trace-granularity Ns = Ns Ar value
Minimum time granularity (in microseconds) traced by time profiler.
2018-07-30 23:07:44 +00:00
.It Fl -trace
Print the names of the input files.
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.It Fl -trace-symbol Ns = Ns Ar symbol , Fl y Ar symbol
2018-02-07 20:38:18 +00:00
Trace references to
.Ar symbol .
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.It Fl -undefined Ns = Ns Ar symbol , Fl u Ar symbol
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If
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.Ar symbol
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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.
.It Fl -undefined-glob Ns = Ns Ar pattern
Synonym for
.Fl -undefined ,
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except that it takes a glob pattern.
In a glob pattern,
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.Cm *
matches zero or more characters,
.Cm ?
matches any single character, and
.Cm [...]
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matches the characters within brackets.
All symbols that match
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a given pattern are handled as if they were given as arguments of
.Fl -undefined .
[LLD] Add support for --unique option
Summary:
Places orphan sections into a unique output section. This prevents the merging of orphan sections of the same name.
Matches behaviour of GNU ld --unique. --unique=pattern is not implemented.
Motivated user case shown in the test has 2 local symbols as they would appear if C++ source has been compiled with -ffunction-sections. The merging of these sections in the case of a partial link (-r) may limit the effectiveness of -gc-sections of a subsequent link.
Reviewers: espindola, jhenderson, bd1976llvm, edd, andrewng, JonChesterfield, MaskRay, grimar, ruiu, psmith
Reviewed By: MaskRay, grimar
Subscribers: emaste, arichardson, MaskRay, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D75536
2020-03-09 15:43:20 +00:00
.It Fl -unique
Creates a separate output section for every orphan input section.
2018-03-01 16:02:19 +00:00
.It Fl -unresolved-symbols Ns = Ns Ar value
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Determine how to handle unresolved symbols.
2019-03-01 04:49:42 +00:00
.It Fl -use-android-relr-tags
Use SHT_ANDROID_RELR / DT_ANDROID_RELR* tags instead of SHT_RELR / DT_RELR*.
2022-09-21 00:12:44 +00:00
.It Fl v , Fl V
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Display the version number and proceed with linking if object files are
specified.
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.It Fl -version
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Display the version number and exit.
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.It Fl -verbose
Verbose mode.
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.It Fl -version-script Ns = Ns Ar file
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Read version script from
.Ar file .
2018-04-29 02:18:48 +00:00
.It Fl -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.
[ELF] Add --warn-backrefs-exclude=<glob>
D77522 changed --warn-backrefs to not warn for linking sandwich
problems (-ldef1 -lref -ldef2). This removed lots of false positives.
However, glibc still has some problems. libc.a defines some symbols
which are normally in libm.a and libpthread.a, e.g. __isnanl/raise.
For a linking order `-lm -lpthread -lc`, I have seen:
```
// different resolutions: GNU ld/gold select libc.a(s_isnan.o) as the definition
backward reference detected: __isnanl in libc.a(printf_fp.o) refers to libm.a(m_isnanl.o)
// different resolutions: GNU ld/gold select libc.a(raise.o) as the definition
backward reference detected: raise in libc.a(abort.o) refers to libpthread.a(pt-raise.o)
```
To facilitate deployment of --warn-backrefs, add --warn-backrefs-exclude= so that
certain known issues (which may be impractical to fix) can be whitelisted.
Deliberate choices:
* Not a comma-separated list (`--warn-backrefs-exclude=liba.a,libb.a`).
-Wl, splits the argument at commas, so we cannot use commas.
--export-dynamic-symbol is similar.
* Not in the style of `--warn-backrefs='*' --warn-backrefs=-liba.a`.
We just need exclusion, not inclusion. For easier build system
integration, we should avoid order dependency. With the current
scheme, we enable --warn-backrefs, and indivial libraries can add
--warn-backrefs-exclude=<glob> to their LDFLAGS.
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D77512
2020-04-05 04:31:36 +00:00
.It Fl -warn-backrefs-exclude Ns = Ns Ar glob
Glob describing an archive (or an object file within --start-lib)
which should be ignored for
.Fl -warn-backrefs
2018-02-07 20:38:18 +00:00
.It Fl -warn-common
Warn about duplicate common symbols.
Introduce a flag to warn when ifunc symbols are used with text relocations.
Summary:
This patch adds a new flag, --warn-ifunc-textrel, to work around a glibc bug. When a code with ifunc symbols is used to produce an object file with text relocations, lld always succeeds. However, if that object file is linked using an old version of glibc, the resultant binary just crashes with segmentation fault when it is run (The bug is going to be corrected as of glibc 2.19).
Since there is no way to tell beforehand what library the object file will be linked against in the future, there does not seem to be a fool-proof way for lld to give an error only in cases where the binary will crash. So, with this change (dated 2018-09-25), lld starts to give a warning, contingent on a new command line flag that does not have a gnu counter part. The default value for --warn-ifunc-textrel is false, so lld behaviour will not change unless the user explicitly asks lld to give a warning. Users that link with a glibc library with version 2.19 or newer, or does not use ifunc symbols, or does not generate object files with text relocations do not need to take any action. Other users may consider to start passing warn-ifunc-textrel to lld to get early warnings.
Reviewers: ruiu, espindola
Reviewed By: ruiu
Subscribers: grimar, MaskRay, markj, emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D52430
llvm-svn: 343628
2018-10-02 20:30:22 +00:00
.It Fl -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
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they are relocated.
As a result, although the program compiles and links
Introduce a flag to warn when ifunc symbols are used with text relocations.
Summary:
This patch adds a new flag, --warn-ifunc-textrel, to work around a glibc bug. When a code with ifunc symbols is used to produce an object file with text relocations, lld always succeeds. However, if that object file is linked using an old version of glibc, the resultant binary just crashes with segmentation fault when it is run (The bug is going to be corrected as of glibc 2.19).
Since there is no way to tell beforehand what library the object file will be linked against in the future, there does not seem to be a fool-proof way for lld to give an error only in cases where the binary will crash. So, with this change (dated 2018-09-25), lld starts to give a warning, contingent on a new command line flag that does not have a gnu counter part. The default value for --warn-ifunc-textrel is false, so lld behaviour will not change unless the user explicitly asks lld to give a warning. Users that link with a glibc library with version 2.19 or newer, or does not use ifunc symbols, or does not generate object files with text relocations do not need to take any action. Other users may consider to start passing warn-ifunc-textrel to lld to get early warnings.
Reviewers: ruiu, espindola
Reviewed By: ruiu
Subscribers: grimar, MaskRay, markj, emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D52430
llvm-svn: 343628
2018-10-02 20:30:22 +00:00
successfully, it gives segmentation fault when the instruction pointer reaches
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an ifunc symbol.
Use -warn-ifunc-textrel to let lld give a warning, if the
Introduce a flag to warn when ifunc symbols are used with text relocations.
Summary:
This patch adds a new flag, --warn-ifunc-textrel, to work around a glibc bug. When a code with ifunc symbols is used to produce an object file with text relocations, lld always succeeds. However, if that object file is linked using an old version of glibc, the resultant binary just crashes with segmentation fault when it is run (The bug is going to be corrected as of glibc 2.19).
Since there is no way to tell beforehand what library the object file will be linked against in the future, there does not seem to be a fool-proof way for lld to give an error only in cases where the binary will crash. So, with this change (dated 2018-09-25), lld starts to give a warning, contingent on a new command line flag that does not have a gnu counter part. The default value for --warn-ifunc-textrel is false, so lld behaviour will not change unless the user explicitly asks lld to give a warning. Users that link with a glibc library with version 2.19 or newer, or does not use ifunc symbols, or does not generate object files with text relocations do not need to take any action. Other users may consider to start passing warn-ifunc-textrel to lld to get early warnings.
Reviewers: ruiu, espindola
Reviewed By: ruiu
Subscribers: grimar, MaskRay, markj, emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D52430
llvm-svn: 343628
2018-10-02 20:30:22 +00:00
code may include ifunc symbols, may do text relocations and be linked with
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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.
2018-02-07 20:38:18 +00:00
.It Fl -warn-unresolved-symbols
Report unresolved symbols as warnings.
.It Fl -whole-archive
Force load of all members in a static library.
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.It Fl -why-extract Ns = Ns Ar file
Print to a file about why archive members are extracted.
2018-03-01 18:40:11 +00:00
.It Fl -wrap Ns = Ns Ar symbol
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Redirect
.Ar symbol
references to
.Ar __wrap_symbol
and
.Ar __real_symbol
references to
.Ar symbol.
2018-02-07 20:38:18 +00:00
.It Fl z Ar option
Linker option extensions.
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.Bl -tag -width indent -compact
.Pp
2020-07-08 17:10:43 +00:00
.It Cm dead-reloc-in-nonalloc Ns = Ns Ar section_glob=value
Resolve a relocation in a matched non-SHF_ALLOC section referencing a discarded symbol to
.Ar 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.
.Pp
2018-02-07 20:38:18 +00:00
.It Cm execstack
Make the main stack executable.
Stack permissions are recorded in the
.Dv PT_GNU_STACK
segment.
2019-09-25 03:39:31 +00:00
.Pp
2021-12-16 15:18:08 +00:00
.It Cm bti-report Ns = Ns Ar [none|warning|error]
Specify how to report the missing GNU_PROPERTY_AARCH64_FEATURE_1_BTI property.
.Cm none
is the default, linker will not report the missing property otherwise will be reported as a warning or an error.
.Pp
.It Cm cet-report Ns = Ns Ar [none|warning|error]
Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_IBT or GNU_PROPERTY_X86_FEATURE_1_SHSTK properties.
.Cm none
is the default, linker will not report the missing property otherwise will be reported as a warning or an error.
.Pp
2019-12-11 06:07:17 +00:00
.It Cm force-bti
Force enable AArch64 BTI instruction in PLT, warn if Input ELF file does not have GNU_PROPERTY_AARCH64_FEATURE_1_BTI property.
.Pp
2019-12-11 02:05:36 +00:00
.It Cm 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.
.Pp
2018-09-25 09:32:31 +00:00
.It Cm global
Sets the
.Dv DF_1_GLOBAL flag in the
.Dv DYNAMIC
section.
Different loaders can decide how to handle this flag on their own.
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.Pp
2019-05-14 15:25:21 +00:00
.It Cm 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
.Fl z Li notext
option.
2019-09-25 03:39:31 +00:00
.Pp
2018-07-30 17:36:38 +00:00
.It Cm initfirst
Sets the
.Dv DF_1_INITFIRST
flag to indicate the module should be initialized first.
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.Pp
2018-09-14 14:25:37 +00:00
.It Cm interpose
Set the
.Dv 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.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm muldefs
Do not error if a symbol is defined multiple times.
The first definition will be used.
This is a synonym for
.Fl -allow-multiple-definition.
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.Pp
2018-02-07 20:38:18 +00:00
.It Cm nocombreloc
Disable combining and sorting multiple relocation sections.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm nocopyreloc
Disable the creation of copy relocations.
2019-09-25 03:39:31 +00:00
.Pp
2018-11-27 09:48:17 +00:00
.It Cm nodefaultlib
Set the
.Dv DF_1_NODEFLIB
flag to indicate that default library search paths should be ignored.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm nodelete
Set the
.Dv DF_1_NODELETE
flag to indicate that the object cannot be unloaded from a process.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm nodlopen
Set the
.Dv DF_1_NOOPEN
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flag to indicate that the object may not be opened by
2018-02-07 20:38:18 +00:00
.Xr dlopen 3 .
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.Pp
2019-10-21 17:27:51 +00:00
.It Cm nognustack
Do not emit the
.Dv PT_GNU_STACK
segment.
.Pp
2018-02-07 20:38:18 +00:00
.It Cm norelro
2020-01-10 04:09:48 +00:00
Do not indicate that portions of the object should be mapped read-only
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after initial relocation processing.
The object will omit the
.Dv PT_GNU_RELRO
segment.
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.Pp
2018-02-07 20:38:18 +00:00
.It Cm notext
Allow relocations against read-only segments.
Sets the
.Dv DT_TEXTREL flag in the
.Dv DYNAMIC
section.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm now
Set the
.Dv 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.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm origin
Set the
.Dv DF_ORIGIN
flag to indicate that the object requires
$ORIGIN
processing.
2019-09-25 03:39:31 +00:00
.Pp
2019-12-11 06:07:17 +00:00
.It Cm pac-plt
AArch64 only, use pointer authentication in PLT.
.Pp
2022-03-11 03:54:20 +00:00
.It Cm pack-relative-relocs
Similar to
.Cm -pack-dyn-relocs=relr
, but synthesizes the GLIBC_ABI_DT_RELR version dependency if there is a GLIBC_2.* version dependency.
glibc ld.so rejects loading a dynamically linked object without the GLIBC_ABI_DT_RELR version dependency.
.Pp
2020-05-29 21:22:03 +00:00
.It Cm rel
Use REL format for dynamic relocations.
.Pp
.It Cm rela
Use RELA format for dynamic relocations.
.Pp
2018-02-07 20:38:18 +00:00
.It Cm retpolineplt
Emit retpoline format PLT entries as a mitigation for CVE-2017-5715.
2019-09-25 03:39:31 +00:00
.Pp
2018-02-07 20:38:18 +00:00
.It Cm rodynamic
Make the
.Li .dynamic
section read-only.
The
.Dv DT_DEBUG
tag will not be emitted.
2019-09-25 03:39:31 +00:00
.Pp
.It Cm separate-loadable-segments
.It Cm separate-code
.It Cm noseparate-code
Specify whether two adjacent PT_LOAD segments are allowed to overlap in pages.
.Cm noseparate-code
(default) allows overlap.
.Cm separate-code
allows overlap between two executable segments, or two non-executable segments.
.Cm separate-loadable-segments
disallows overlap.
.Pp
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.It Cm shstk
x86 only, use shadow stack.
.Pp
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.It Cm stack-size Ns = Ns Ar size
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Set the main thread's stack size to
.Ar size .
The stack size is recorded as the size of the
.Ar size .
.Dv PT_GNU_STACK
program segment.
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.Pp
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.It Cm start-stop-gc
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Don't let __start_/__stop_ references retain the associated C identifier name sections (default).
.Pp
.It Cm nostart-stop-gc
Let __start_/__stop_ references retain the associated C identifier name sections.
.Pp
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.It Cm text
Do not allow relocations against read-only segments.
This is the default.
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.Pp
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.It Cm wxneeded
Create a
.Dv PT_OPENBSD_WXNEEDED
segment.
.El
.El
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.Sh ENVIRONMENT VARIABLES
.Bl -tag -width LC_CTYPE
.It Ev LLD_REPRODUCE
Create a reproduce tarball with the specified filename. If
.Fl -reproduce
is specified,
.Fl -reproduce
takes precedence.
.It Ev LLD_VERSION
ld.lld creates a section named
.Cm .comment
containing the LLD version string. The version string can be overridden by this environment variable,
which is useful to eliminate differences in the binary caused by LLD version number differences.
.El
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.Sh IMPLEMENTATION NOTES
.Nm Ap s
handing of archive files (those with a
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.Pa .a
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file extension) is different from traditional linkers used on Unix-like
systems.
.Pp
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.
.Pp
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
.Fl -start-group
and
.Fl -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.
.Pp
.Nm
records all symbols found in objects and archives as it iterates over
command line arguments.
When
.Nm
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.
.Pp
With certain archive inputs
.Nm
may produce different results compared to traditional linkers.
In practice, large bodies of third party software have been linked with
.Nm
without material issues.
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.Pp
The
.Fl -warn-backrefs
option may be used to identify a linker invocation that may be incompatible
with traditional Unix-like linker behavior.
