.\" Copyright (c) 2016 Joseph Koshy.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" This software is provided by the author and contributors ``as is''
.\" and any express or implied warranties, including, but not limited
.\" to, the implied warranties of merchantability and fitness for a
.\" particular purpose are disclaimed.  In no event shall the author or
.\" contributors be liable for any direct, indirect, incidental, special,
.\" exemplary, or consequential damages (including, but not limited to,
.\" procurement of substitute goods or services; loss of use, data, or
.\" profits; or business interruption) however caused and on any
.\" theory of liability, whether in contract, strict liability, or
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.\" out of the use of this software, even if advised of the
.\" possibility of such damage.
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.\" $Id$
.\"
.Dd February 14, 2016
.Os
.Dt LD 1
.Sh NAME
.Nm ld
.Nd link editor
.Sh SYNOPSIS
.Nm
.Op Fl \&(
.Op Fl \&)
.Op Fl Bdynamic
.Op Fl Bshareable
.Op Fl Bstatic
.Op Fl I Ar file | Fl -dynamic-linker= Ns Ar file
.Op Fl L Ar dir | Fl -library-path= Ns Ar dir
.Op Fl M | Fl -print-map
.Op Fl T Ar script-file | Fl -script= Ns Ar script-file
.Op Fl V | Fl v | Fl -version
.Op Fl a Ar linkmode
.Op Fl b Ar input-format | Fl -format= Ns Ar input-format
.Op Fl call_shared
.Op Fl d | Fl dc | Fl dp
.Op Fl dn
.Op Fl dy
.Op Fl e Ar symbol | Fl -entry= Ns Ar symbol
.Op Fl h Ar name | Fl soname= Ns Ar name
.Op Fl l Ar library | Fl -library= Ns Ar library
.Op Fl o Ar output-file | Fl -output= Ns Ar output-file
.Op Fl q | Fl -emit-relocs
.Op Fl r | Fl -relocatable
.Op Fl u Ar name | Fl -undefined= Ns Ar name
.Op Fl z Ar keyword
.Op Fl -as-needed
.Op Fl -eh-frame-hdr
.Op Fl -end-group
.Op Fl -gc-sections
.Op Fl -no-as-needed
.Op Fl -no-define-common
.Op Fl -no-gc-sections
.Op Fl -no-print-gc-sections
.Op Fl -no-whole-archive
.Op Fl -oformat= Ns Ar format
.Op Fl -pic-executable | Fl pie
.Op Fl -print-gc-sections
.Op Fl -rpath= Ns Ar dirs
.Op Fl -rpath-link= Ns Ar dirs
.Op Fl -start-group
.Op Fl shared
.Op Fl static
.Op Fl -version-script= Ns Ar script
.Op Fl -whole-archive
.Ar
.Sh DESCRIPTION
The
.Nm
utility combines ELF objects and
.Xr ar 1
archives containing ELF objects into an executable or a partially
relocated object.
.Pp
The
.Nm
utility processes options and files in the order presented on the
command line.
Unlike most
.Ux
utilities, options and file names may be interspersed.
Options seen on the command line will generally apply to subsequent
files, or till overridden by another option.
.Sh OPTIONS
.Pp
The
.Nm
utility supports the following options:
.Bl -tag -width indent
.It Xo
.Fl \&(
.Ar archives Ns ...
.Fl \&)
.Xc
Start a group of archives that are to be searched repeatedly until no new
undefined references are created.
This option is used when there are circular references between one or
more archives in the archive group.
.Pp
The files named by the arguments
.Ar archives
are expected to be archive files.
.Pp
Each use of the
.Fl \&(
option starts a new archive group that is ended by a matching
.Fl \&)
option.
.It Fl Bdynamic
Choose dynamic libraries for the libraries specified by subsequent
.Fl l
options.
.It Fl Bshareable
Create a shared library.
.It Fl Bstatic
Choose static libraries for the libraries specified by subsequent
.Fl l
options.
.It Fl I Ar file | Fl -dynamic-linker= Ns Ar file
Set the name of the dynamic linker when generating ELF executables.
.It Fl L Ar dir | Fl -library-path= Ns Ar dir
Add directory
.Ar dir
to the list of paths that
.Nm
will search for archive libraries.
This option may be specified multiple times.
User supplied directories are searched in the order specified on
the command line.
.It Fl M | Fl -print-map
Print a link map to standard output.
.It Fl T Ar script-file | Fl -script= Ns Ar script-file
Use the file name by argument
.Ar script-file
as the linker script instead of the default.
.It Fl V | Fl v | Fl version
Print a version identifier for
.Nm
and exit.
.It Fl a Ar linkmode
Select linking mode.
The value of the argument
.Ar linkmode
should be one of the following literals:
.Bl -tag -width ".Li default" -compact
.It Cm default
Equivalent to specifying
.Fl Bdynamic .
.It Cm archive
Equivalent to specifying
.Fl Bstatic .
.It Cm shared
Equivalent to specifying
.Fl Bdynamic .
.El
.It Fl b Ar input-format | Fl -format Ar input-format
Set the input format to that specified by argument
.Ar input-format .
The legal values for the argument
.Ar input-format
are those supported by
.Xr elftc_bfd_find_target 3 .
.It Fl d | Fl dc | Fl dp
Assign space for common symbols even if generating a relocatable object.
.It Fl dn
Equivalent to specifying option
.Fl Bstatic .
.It Fl dy
Equivalent to specifying option
.Fl Bdynamic .
.It Fl e Ar entry | Fl -entry Ar entry
Set execution to start at the symbol named by the argument
.Ar entry .
The argument should be the name of a symbol.
.It Fl h Ar name | Fl soname Ar name
Set the
.Li DT_SONAME
field in the object to that specified by the argument
.Ar name .
.It Fl l Ar name | Fl -library= Ns Ar name
Add the archive library or shared library named by argument
.Ar name
to the set of files to link.
This file is looked for in the list of directories specified by prior
.Fl L
options on the command line.
.It Fl o Ar output-file | Fl -output= Ns Ar output-file
Use the file specified by argument
.Ar output-file
for the output, instead of the default file name of
.Sq a.out .
.It Fl q | Fl -emit-relocs
Preserve relocation information in executables, for use by post-link
analysis tools.
.It Fl r | Fl -relocatable
Generate a relocatable output file that can be used as input for subsequent
linker runs.
.It Fl u Ar name | Fl -undefined= Ns Ar name
Add the symbol specified by argument
.Ar name
to the output file as an undefined symbol.
This option may be specified multiple times.
.It Fl z Ar keyword
Recognized keywords include:
.Bl -tag -width ".Li defaultextract" -compact
.It Cm execstack
Require the object to use an executable stack.
.It Cm noexecstack
Do not require the object to use an executable stack.
.El
.It Fl -as-needed
Add
.Li DT_NEEDED
tags for only those shared libraries that satisfy non-weak
unresolved references from object files or other dynamic libraries
seen so far on the command line.
.It Fl call_shared
Equivalent to specifying option
.Fl Bdynamic .
.It Fl -eh-frame-hdr
Create a
.Dq ".eh_frame_hdr"
section, and a
.Li PT_GNU_EH_FRAME
segment header, containing exception handling information.
.It Fl -end-group
Equivalent to specifying option
.Fl \&) .
.It Fl -gc-sections
Garbage collect unused input sections.
.It Fl -no-as-needed
Insert
.Li DT_NEEDED
tags for all shared libraries seen henceforth on the command line,
irrespective of whether the shared library is needed to resolve an
undefined symbol or not.
This behavior is the default.
.It Fl -no-define-common
Do not assign addresses to common symbols.
.It Fl -no-gc-sections
Do not garbage collect input sections that contain unreferenced
symbols.
.It Fl -no-print-gc-sections
Do not print the list of sections removed when the
.Fl -gc-sections
directive is active.
.It Fl -no-whole-archive
Only include objects in an archive that satisfy an unresolved reference
in the link.
This behavior is the default.
.It Fl non_shared
Equivalent to specifying option
.Fl Bstatic .
.It Fl -oformat= Ns Ar format
Set the desired output format to that specified by the argument
.Ar format .
Supported values for argument
.Ar format
are those understood by
.Xr elftc_bfd_find_target 3 .
.It Fl -pic-executable | Fl pie
Create a position-independent executable.
.It Fl -print-gc-sections
Print the list of sections removed when the
.Fl -gc-sections
directive is active.
The output is printed to stderr.
.It Fl -rpath= Ns Ar dirs
Add the colon-separated list of directories named by the argument
.Ar dirs
to the runtime library search path and to the link-time search
path.
.It Fl -rpath-link= Ns Ar dirs
Add the directories specified by the colon-separated list of directories
in argument
.Ar dirs
to the link-time search path for libraries.
The directories specified by this option are searched before those
specified by
.Fl -rpath
options.
.It Fl shared
Equivalent to specifying option
.Fl Bshareable .
.It Fl -start-group
Equivalent to specifying option
.Fl \&( .
.It Fl static
Equivalent to specifying option
.Fl Bstatic .
.It Fl -version-script= Ns Ar script-file
Use the version script in the file named by argument
.Ar script-file .
.It Fl -whole-archive
Include the entire contents of every archive file encountered on the
command line after this option in the link.
.El
.Sh DIAGNOSTICS
.Ex -std
.Sh SEE ALSO
.Xr ar 1 ,
.Xr ranlib 1 ,
.Xr archive 3 ,
.Xr elf 3 ,
.Xr elftc_bfd_find_target 3 ,
.Xr dwarf 3
.Sh IMPLEMENTATION NOTES
The
.Nm
utility differs from its GNU equivalent in the following:
.Bl -bullet
.It
The
.Nm
utility currently supports a limited range of output formats.
.It
The
.Fl e
and
.Fl -entry
options only accept a symbol name as an argument, and not a numeric
address.
.It
The
.Fl l
option only searches files in the directories specified by
prior
.Fl L
options.
.It
The
.Fl T | Fl -script
option does not search for script files in the directories specified
by prior
.Fl L
options.
.It
The
.Fl -rpath
option accepts a colon-separated list of directories instead of
single directory.
.El
.Pp
The following options are recognized, but are currently unimplemented:
.Fl Bgroup ,
.Fl Bsymbolic ,
.Fl Bsymbolic_functions ,
.Fl E ,
.Fl EB ,
.Fl EL ,
.Fl F ,
.Fl Map ,
.Fl N ,
.Fl O ,
.Fl Qy ,
.Fl R ,
.Fl S ,
.Fl Tbss ,
.Fl Tdata ,
.Fl Ttext ,
.Fl X ,
.Fl Y ,
.Fl Ur ,
.Fl c ,
.Fl f ,
.Fl g ,
.Fl i ,
.Fl m ,
.Fl n ,
.Fl s ,
.Fl t ,
.Fl x ,
.Fl y ,
.Fl -accept-unknown-input-arch ,
.Fl -allow-multiple-definition ,
.Fl -allow-shlib-undefined ,
.Fl -assert ,
.Fl -auxiliary ,
.Fl -build-id ,
.Fl -check-sections ,
.Fl -cref ,
.Fl -defsym ,
.Fl -demangle ,
.Fl -disable-new-dtags ,
.Fl -discard-all ,
.Fl -discard-locals ,
.Fl -error-unresolved-symbols ,
.Fl -export-dynamic ,
.Fl -emulation ,
.Fl -enable-new-dtags ,
.Fl -fatal-warnings ,
.Fl -filter ,
.Fl -fini ,
.Fl -hash-style ,
.Fl -help ,
.Fl -init ,
.Fl -just-symbols ,
.Fl -mri-script ,
.Fl -nmagic ,
.Fl nostdlib ,
.Fl -no-accept-unknown-input-arch ,
.Fl -no-allow-shlib-undefined ,
.Fl -no-assert ,
.Fl -no-check-sections ,
.Fl -no-demangle ,
.Fl -no-keep-memory ,
.Fl -no-omagic ,
.Fl -no-undefined ,
.Fl -no-undefined-version ,
.Fl -no-warn-mismatch ,
.Fl -omagic ,
.Fl -qmagic ,
.Fl -relax ,
.Fl -retain-symbols-file ,
.Fl -runpath ,
.Fl -section-start ,
.Fl -sort-common ,
.Fl -split-by-file ,
.Fl -split-by-reloc ,
.Fl -stats ,
.Fl -strip-all ,
.Fl -strip-debug ,
.Fl -trace ,
.Fl -trace_symbol ,
.Fl -traditional-format ,
.Fl -unique ,
.Fl -unresolved-symbols ,
.Fl -verbose ,
.Fl -warn-common ,
.Fl -warn-constructors ,
.Fl -warn-multiple-gp ,
.Fl -warn-once ,
.Fl -warn-section-align ,
.Fl -warn-shared-textrel ,
.Fl -warn-unresolved-symbols ,
.Fl -wrap .
.Pp
The following keywords are recognized by the
.Fl z
option, but are currently unimplemented:
.Cm allextract ,
.Cm defaultextract ,
.Cm defs ,
.Cm ignore ,
.Cm initfirst ,
.Cm lazyload ,
.Cm muldefs ,
.Cm nodefaultlib ,
.Cm nodefs ,
.Cm nodelete ,
.Cm nodlopen ,
.Cm nolazyload ,
.Cm now ,
.Cm origin ,
.Cm record ,
.Cm systemlibrary ,
.Cm weakextract .
.Sh HISTORY
A
.Nm
command first appeared in AT&T UNIX Version 1.
.Pp
The Elftoolchain implementation of
.Nm
was written by
.An Kai Wang Aq Mt kaiwang27@gmail.com .