676 lines
18 KiB
Groff
676 lines
18 KiB
Groff
.\" Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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.\" See https://llvm.org/LICENSE.txt for license information.
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.\" SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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.\"
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.\" This man page documents only lld's ELF linking support, obtained originally
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.\" from FreeBSD.
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.Dd February 26, 2019
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.Dt LD.LLD 1
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.Os
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.Sh NAME
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.Nm ld.lld
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.Nd ELF linker from the LLVM project
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.Sh SYNOPSIS
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.Nm ld.lld
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.Op Ar options
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.Ar objfile ...
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.Sh DESCRIPTION
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A linker takes one or more object, archive, and library files, and combines
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them into an output file (an executable, a shared library, or another object
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file).
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It relocates code and data from the input files and resolves symbol
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references between them.
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.Pp
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.Nm
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is a drop-in replacement for the GNU BFD and gold linkers.
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It accepts most of the same command line arguments and linker scripts
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as GNU linkers.
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.Pp
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.Nm
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currently supports i386, x86-64, ARM, AArch64, PowerPC32, PowerPC64,
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MIPS32, MIPS64, RISC-V, AMDGPU, Hexagon and SPARC V9 targets.
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.Nm
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acts as a Microsoft link.exe-compatible linker if invoked as
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.Nm lld-link
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and as macOS's ld if invoked as
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.Nm ld.ld64.
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All these targets are always supported however
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.Nm
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was built, so you can always use
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.Nm
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as a native linker as well as a cross linker.
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.Sh OPTIONS
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.Bl -tag -width indent
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.It Fl -allow-multiple-definition
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Do not error if a symbol is defined multiple times.
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The first definition will be used.
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.It Fl -allow-shlib-undefined
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Allow unresolved references in shared libraries.
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This option is enabled by default when linking a shared library.
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.It Fl -apply-dynamic-relocs
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Apply link-time values for dynamic relocations.
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.It Fl -as-needed
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Only set
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.Dv DT_NEEDED
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for shared libraries if used.
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.It Fl -auxiliary Ns = Ns Ar value
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Set the
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.Dv DT_AUXILIARY
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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 -Bsymbolic
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Bind defined symbols locally.
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.It Fl -Bsymbolic-functions
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Bind defined function symbols locally.
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.It Fl -build-id Ns = Ns Ar value
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Generate a build ID note.
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.Ar value
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may be one of
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.Cm fast ,
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.Cm md5 ,
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.Cm sha1 ,
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.Cm tree ,
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.Cm uuid ,
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.Cm 0x Ns Ar hex-string ,
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and
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.Cm none .
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.Cm tree
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is an alias for
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.Cm sha1 .
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Build-IDs of type
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.Cm fast ,
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.Cm md5 ,
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.Cm sha1 ,
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and
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.Cm tree
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are calculated from the object contents.
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.Cm fast
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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 -color-diagnostics Ns = Ns Ar value
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Use colors in diagnostics.
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.Ar value
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may be one of
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.Cm always ,
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.Cm auto ,
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and
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.Cm never .
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.Cm auto
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enables color if and only if output is to a terminal.
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.It Fl -color-diagnostics
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Alias for
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.Fl -color-diagnostics Ns = Ns Cm auto .
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.It Fl -compress-debug-sections Ns = Ns Ar value
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Compress DWARF debug sections.
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.Ar value
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may be
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.Cm none
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or
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.Cm zlib .
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.It Fl -cref
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Output cross reference table.
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.It Fl -define-common , Fl d
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Assign space to common symbols.
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.It Fl -defsym Ns = Ns Ar symbol Ns = Ns Ar expression
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Define a symbol alias.
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.Ar expression
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may be another symbol or a linker script expression.
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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
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Demangle symbol names.
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.It Fl -disable-new-dtags
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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.
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.It Fl -discard-none
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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.
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This is recorded in an ELF segment of type
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.Dv PT_INTERP .
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.It Fl -dynamic-list Ns = Ns Ar file
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Read a list of dynamic symbols from
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.Ar file .
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.It Fl -eh-frame-hdr
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Request creation of
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.Li .eh_frame_hdr
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section and
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.Dv PT_GNU_EH_FRAME
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segment header.
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.It Fl -emit-relocs , Fl q
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Generate relocations in the output.
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.It Fl -enable-new-dtags
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Enable new dynamic tags.
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.It Fl -end-lib
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End a grouping of objects that should be treated as if they were together
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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.
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A value of zero indicates that there is no limit.
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.It Fl -error-unresolved-symbols
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Report unresolved symbols as errors.
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.It Fl -execute-only
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Mark executable sections unreadable. This option is currently only
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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
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Put symbols in the dynamic symbol table.
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.It Fl -export-dynamic-symbol Ns = Ns Ar symbol
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Include
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.Ar symbol
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in the dynamic symbol table.
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.It Fl -fatal-warnings
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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
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.Dv DT_FILTER
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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.
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.Ar input-format
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may be one of
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.Cm binary ,
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.Cm elf ,
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and
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.Cm default .
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.Cm default
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is a synonym for
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.Cm elf .
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.It Fl -gc-sections
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Enable garbage collection of unused sections.
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.It Fl -gdb-index
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Generate
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.Li .gdb_index
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section.
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.It Fl -hash-style Ns = Ns Ar value
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Specify hash style.
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.Ar value
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may be
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.Cm sysv ,
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.Cm gnu ,
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or
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.Cm both .
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.Cm both
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is the default.
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.It Fl -help
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Print a help message.
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.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
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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
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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
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that happen to have the same value.
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.It Fl -ignore-function-address-equality
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Ignore address equality of functions. This option allows non-PIC calls to a
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function with non-default visibility in a shared object. The function may have
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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
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.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
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Do not fold
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.Ar symbol
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during ICF.
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.It Fl l Ar libName, Fl -library Ns = Ns Ar libName
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Root name of library to use.
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.It Fl L Ar dir , Fl -library-path Ns = Ns Ar dir
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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.
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Used in conjunction with
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.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
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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
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.Ar file .
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.It Fl -no-allow-shlib-undefined
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Do not allow unresolved references in shared libraries.
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This option is enabled by default when linking an executable.
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.It Fl -no-as-needed
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Always set
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.Dv DT_NEEDED
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for shared libraries.
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.It Fl -no-color-diagnostics
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Do not use colors in diagnostics.
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.It Fl -no-define-common
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Do not assign space to common symbols.
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.It Fl -no-demangle
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Do not demangle symbol names.
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.It Fl -no-dynamic-linker
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Inhibit output of an
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.Li .interp
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section.
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.It Fl -no-gc-sections
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Disable garbage collection of unused sections.
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.It Fl -no-gnu-unique
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Disable STB_GNU_UNIQUE symbol binding.
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.It Fl -no-merge-exidx-entries
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Disable merging .ARM.exidx entries.
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.It Fl -no-rosegment
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Do not put read-only non-executable sections in their own segment.
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.It Fl -no-threads
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Do not run the linker multi-threaded.
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.It Fl -no-undefined-version
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Report version scripts that refer undefined symbols.
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.It Fl -no-undefined
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Report unresolved symbols even if the linker is creating a shared library.
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.It Fl -no-warn-symbol-ordering
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Do not warn about problems with the symbol ordering file or call graph profile.
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.It Fl -no-whole-archive
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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
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Retain the executable output file whenever it is still usable.
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.It Fl -nostdlib
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Only search directories specified on the command line.
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.It Fl o Ar path
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Write the output executable, library, or object to
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.Ar path .
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If not specified,
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.Dv a.out
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is used as a default.
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.It Fl O Ns Ar value
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Optimize output file size.
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.Ar value
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may be:
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.Pp
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.Bl -tag -width 2n -compact
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.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.
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.El
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.Pp
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.Fl O Ns Cm 1
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is the default.
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.It Fl -oformat Ns = Ns Ar format
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Specify the format for the output object file.
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The only supported
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.Ar format
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is
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.Cm binary ,
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which produces output with no ELF header.
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.It Fl -omagic , Fl N
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Set the text and data sections to be readable and writable.
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.It Fl -opt-remarks-filename Ar file
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Write optimization remarks in YAML format to
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.Ar file .
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.It Fl -opt-remarks-passes Ar pass-regex
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Filter optimization remarks by only allowing the passes matching
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.Ar pass-regex .
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.It Fl -opt-remarks-with-hotness
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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
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specifically mentioned in a linker script.
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.Ar mode
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may be:
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.Pp
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.Bl -tag -width 2n -compact
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.It Cm place
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Place orphan sections in suitable output sections.
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.It Cm warn
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Place orphan sections as for
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.Cm place
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and also report a warning.
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.It Cm error
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Place orphan sections as for
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.Cm place
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and also report an error.
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.El
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.Pp
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.Cm place
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is the default.
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.It Fl -pack-dyn-relocs Ns = Ns Ar format
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Pack dynamic relocations in the given format.
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.Ar format
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may be:
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.Pp
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.Bl -tag -width 2n -compact
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.It Cm none
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Don't pack. Dynamic relocations are encoded in SHT_REL(A).
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.It Cm android
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Pack dynamic relocations in SHT_ANDROID_REL(A).
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.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
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.Pp
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.Cm none
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is the default. If
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.Fl -use-android-relr-tags
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is specified, use SHT_ANDROID_RELR instead of SHT_RELR.
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.Pp
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.It Fl -pic-veneer
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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 -print-gc-sections
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List removed unused sections.
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.It Fl -print-icf-sections
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List identical folded sections.
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.It Fl -print-map
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Print a link map to the standard output.
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.It Fl -push-state
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Save the current state of
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.Fl -as-needed ,
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.Fl -static ,
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and
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.Fl -whole-archive.
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.It Fl -pop-state
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Undo the effect of
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.Fl -push-state.
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.It Fl -relocatable , Fl r
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Create relocatable object file.
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.It Fl -reproduce Ns = Ns Ar value
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Dump linker invocation and input files for debugging.
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.It Fl -retain-symbols-file Ns = Ns Ar file
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Retain only the symbols listed in the file.
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.It Fl -rpath Ns = Ns Ar value , Fl R Ar value
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Add a
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.Dv DT_RUNPATH
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to the output.
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.It Fl -rsp-quoting Ns = Ns Ar value
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Quoting style for response files.
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The supported values are
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.Cm windows
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and
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.Cm posix .
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.It Fl -script Ns = Ns Ar file , Fl T Ar file
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Read linker script from
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.Ar file .
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.It Fl -section-start Ns = Ns Ar section Ns = Ns Ar address
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Set address of section.
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.It Fl -shared , Fl -Bsharable
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Build a shared object.
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.It Fl -soname Ns = Ns Ar value , Fl h Ar value
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Set
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.Dv DT_SONAME
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to
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.Ar value .
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.It Fl -sort-section Ns = Ns Ar value
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Specifies sections sorting rule when linkerscript is used.
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.It Fl -start-lib
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Start a grouping of objects that should be treated as if they were together
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in an archive.
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.It Fl -strip-all , Fl s
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Strip all symbols.
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.It Fl -strip-debug , Fl S
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Strip debugging information.
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.It Fl -symbol-ordering-file Ns = Ns Ar file
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Lay out sections in the order specified by
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.Ar file .
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.It Fl -sysroot Ns = Ns Ar value
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Set the system root.
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|
.It Fl -target1-abs
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Interpret
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.Dv R_ARM_TARGET1
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as
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.Dv R_ARM_ABS32 .
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.It Fl -target1-rel
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Interpret
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.Dv R_ARM_TARGET1
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as
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.Dv R_ARM_REL32 .
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.It Fl -target2 Ns = Ns Ar type
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Interpret
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.Dv R_ARM_TARGET2
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as
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.Ar type ,
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where
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.Ar type
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is one of
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.Cm rel ,
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|
.Cm abs ,
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or
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.Cm got-rel .
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|
.It Fl -Tbss Ns = Ns Ar value
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|
Same as
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.Fl -section-start
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with
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.Li .bss
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as the sectionname.
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|
.It Fl -Tdata Ns = Ns Ar value
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Same as
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.Fl -section-start
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with
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.Li .data
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as the sectionname.
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.It Fl -Ttext Ns = Ns Ar value
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|
Same as
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|
.Fl -section-start
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with
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.Li .text
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as the sectionname.
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|
.It Fl -thinlto-cache-dir Ns = Ns Ar value
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Path to ThinLTO cached object file directory.
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.It Fl -thinlto-cache-policy Ns = Ns Ar value
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Pruning policy for the ThinLTO cache.
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.It Fl -thinlto-jobs Ns = Ns Ar value
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Number of ThinLTO jobs.
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.It Fl -threads
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Run the linker multi-threaded.
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This option is enabled by default.
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.It Fl -trace
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Print the names of the input files.
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.It Fl -trace-symbol Ns = Ns Ar symbol , Fl y Ar symbol
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Trace references to
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.Ar symbol .
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.It Fl -undefined Ns = Ns Ar symbol , Fl u Ar symbol
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Force
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.Ar symbol
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to be an undefined symbol during linking.
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.It Fl -unresolved-symbols Ns = Ns Ar value
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Determine how to handle unresolved symbols.
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.It Fl -use-android-relr-tags
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Use SHT_ANDROID_RELR / DT_ANDROID_RELR* tags instead of SHT_RELR / DT_RELR*.
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.It Fl v
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Display the version number and proceed with linking if object files are
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specified.
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.It Fl V , Fl -version
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Display the version number and exit.
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.It Fl -verbose
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Verbose mode.
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|
.It Fl -version-script Ns = Ns Ar file
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Read version script from
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.Ar file .
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.It Fl -warn-backrefs
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Warn about reverse or cyclic dependencies to or between static archives.
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|
This can be used to ensure linker invocation remains compatible with
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traditional Unix-like linkers.
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.It Fl -warn-common
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Warn about duplicate common symbols.
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|
.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
|
|
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.
|
|
.It Fl -warn-unresolved-symbols
|
|
Report unresolved symbols as warnings.
|
|
.It Fl -whole-archive
|
|
Force load of all members in a static library.
|
|
.It Fl -wrap Ns = Ns Ar symbol
|
|
Use wrapper functions for symbol.
|
|
.It Fl z Ar option
|
|
Linker option extensions.
|
|
.Bl -tag -width indent
|
|
.It Cm execstack
|
|
Make the main stack executable.
|
|
Stack permissions are recorded in the
|
|
.Dv PT_GNU_STACK
|
|
segment.
|
|
.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.
|
|
.It Cm initfirst
|
|
Sets the
|
|
.Dv DF_1_INITFIRST
|
|
flag to indicate the module should be initialized first.
|
|
.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.
|
|
.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.
|
|
.It Cm nocombreloc
|
|
Disable combining and sorting multiple relocation sections.
|
|
.It Cm nocopyreloc
|
|
Disable the creation of copy relocations.
|
|
.It Cm nodefaultlib
|
|
Set the
|
|
.Dv DF_1_NODEFLIB
|
|
flag to indicate that default library search paths should be ignored.
|
|
.It Cm nodelete
|
|
Set the
|
|
.Dv DF_1_NODELETE
|
|
flag to indicate that the object cannot be unloaded from a process.
|
|
.It Cm nodlopen
|
|
Set the
|
|
.Dv DF_1_NOOPEN
|
|
flag to indicate that the object may not be opened by
|
|
.Xr dlopen 3 .
|
|
.It Cm norelro
|
|
Do not indicate that portions of the object shold be mapped read-only
|
|
after initial relocation processing.
|
|
The object will omit the
|
|
.Dv PT_GNU_RELRO
|
|
segment.
|
|
.It Cm notext
|
|
Allow relocations against read-only segments.
|
|
Sets the
|
|
.Dv DT_TEXTREL flag in the
|
|
.Dv DYNAMIC
|
|
section.
|
|
.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.
|
|
.It Cm origin
|
|
Set the
|
|
.Dv DF_ORIGIN
|
|
flag to indicate that the object requires
|
|
$ORIGIN
|
|
processing.
|
|
.It Cm retpolineplt
|
|
Emit retpoline format PLT entries as a mitigation for CVE-2017-5715.
|
|
.It Cm rodynamic
|
|
Make the
|
|
.Li .dynamic
|
|
section read-only.
|
|
The
|
|
.Dv DT_DEBUG
|
|
tag will not be emitted.
|
|
.It Cm stack-size Ns = Ns Ar size
|
|
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.
|
|
.It Cm text
|
|
Do not allow relocations against read-only segments.
|
|
This is the default.
|
|
.It Cm wxneeded
|
|
Create a
|
|
.Dv PT_OPENBSD_WXNEEDED
|
|
segment.
|
|
.El
|
|
.El
|
|
.Sh IMPLEMENTATION NOTES
|
|
.Nm Ap s
|
|
handing of archive files (those with a
|
|
.Pa .a
|
|
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.
|
|
.Pp
|
|
The
|
|
.Fl -warn-backrefs
|
|
option may be used to identify a linker invocation that may be incompatible
|
|
with traditional Unix-like linker behavior.
|