ld(1)                 GNU Development Tools                 ld(1)


NAME
       ld - the GNU linker


SYNOPSIS
       ld     [-o output] objfile...
              [-Aarchitecture] [-b input-format] [-Bstatic]
              [-Bgroup] [-Bdynamic] [-Bsymbolic] [-c commandfile]
              [--cref] [-d|-dc|-dp]
              [-defsym symbol=expression] [--demangle]
              [--no-demangle] [-e entry] [-embedded-relocs] [-E]
              [-export-dynamic] [-f name] [--auxiliary name]
              [-F name] [--filter name] [-format input-format]
              [-g] [-G size] [-h name] [-soname name] [--help]
              [-i] [-lar] [-Lsearchdir] [-M] [-Map mapfile] [-m
              emulation] [-n|-N] [-noinhibit-exec]
              [-no-keep-memory] [-no-warn-mismatch] [-Olevel]
              [--oformat output-format] [-R filename] [-relax]
              [-r|-Ur] [-rpath directory] [-rpath-link directory]
              [-S] [-s] [-shared] [-sort-common]
              [-split-by-reloc count] [-split-by-file]
              [-T commandfile]
              [--section-start sectionname=sectionorg]
              [-Ttext textorg] [-Tdata dataorg] [-Tbss bssorg]
              [-t] [-u sym] [-V] [-v] [--verbose] [--version]
              [-warn-common] [-warn-constructors]
              [-warn-multiple-gp] [-warn-once]
              [-warn-section-align] [--whole-archive]
              [--no-whole-archive] [--wrap symbol] [-X] [-x]

DESCRIPTION
       ld combines a number of object and  archive  files,  relo-
       cates  their data and ties up symbol references. Often the
       last step in building a new compiled program to run  is  a
       call to ld.

       ld  accepts  Linker  Command Language files to provide ex-
       plicit and total control over the linking  process.   This
       man  page  does not describe the command language; see the
       `ld' entry in `info', or the manual ld: the GNU  linker  ,
       for  full details on the command language and on other as-
       pects of the GNU linker.

       This version of ld uses the general purpose BFD  libraries
       to  operate  on object files. This allows ld to read, com-
       bine, and write object files in many  different  formats--
       for  example,  COFF  or  a.out.   Different formats may be
       linked together to produce any available  kind  of  object
       file.   You  can use `objdump -i' to get a list of formats
       supported on various architectures; see objdump(1).

       Aside from its flexibility, the GNU linker is more helpful
       than  other  linkers  in providing diagnostic information.
       Many linkers abandon execution immediately upon encounter-



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ld(1)                 GNU Development Tools                 ld(1)


       ing  an  error; whenever possible, ld continues executing,
       allowing you to identify other errors (or, in some  cases,
       to get an output file in spite of the error).

       The GNU linker ld is meant to cover a broad range of situ-
       ations, and to be as compatible  as  possible  with  other
       linkers.   As  a  result, you have many choices to control
       its behavior through the command line, and  through  envi-
       ronment variables.


OPTIONS
       The  plethora  of command-line options may seem intimidat-
       ing, but in actual practice few of them are  used  in  any
       particular context.  For instance, a frequent use of ld is
       to link standard Unix object files on a standard, support-
       ed Unix system.  On such a system, to link a file hello.o:

       $ ld -o output /lib/crt0.o hello.o -lc

       This tells ld to produce a file called output as  the  re-
       sult  of linking the file /lib/crt0.o with hello.o and the
       library libc.a which will come from  the  standard  search
       directories.

       The command-line options to ld may be specified in any or-
       der, and may be repeated at will.  For the most part,  re-
       peating  an  option  with a different argument will either
       have no further  effect,  or  override  prior  occurrences
       (those  further to the left on the command line) of an op-
       tion.

       The exceptions--which may meaningfully be used  more  than
       once--are -A, -b (or its synonym -format), -defsym, --sec-
       tion-start, -L, -l, -R, and -u.

       The list of object files to be linked together,  shown  as
       objfile, may follow, precede, or be mixed in with command-
       line options; save that an objfile  argument  may  not  be
       placed between an option flag and its argument.

       Usually  the  linker  is  invoked with at least one object
       file, but other forms of binary input files  can  also  be
       specified  with  -l,  -R, and the script command language.
       If no binary input files at all are specified, the  linker
       does  not  produce  any output, and issues the message `No
       input files'.

       Option arguments must  either  follow  the  option  letter
       without  intervening  whitespace,  or be given as separate
       arguments immediately following the option  that  requires
       them.





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ld(1)                 GNU Development Tools                 ld(1)


       -Aarchitecture
              In the current release of ld, this option is useful
              only for the Intel 960 family of architectures.  In
              that ld configuration, the architecture argument is
              one of the two-letter names identifying members  of
              the  960  family;  the option specifies the desired
              output target, and warns of  any  incompatible  in-
              structions  in  the  input files.  It also modifies
              the linker's search strategy for archive libraries,
              to  support  the  use of libraries specific to each
              particular architecture, by including in the search
              loop names suffixed with the string identifying the
              architecture.

              For example,  if  your  ld  command  line  included
              `-ACA'  as  well  as `-ltry', the linker would look
              (in its built-in search paths, and in any paths you
              specify with -L) for a library with the names

              try
              libtry.a
              tryca
              libtryca.a


              The  first two possibilities would be considered in
              any event; the last two  are  due  to  the  use  of
              `-ACA'.

              Future releases of ld may support similar function-
              ality for other architecture families.

              You can meaningfully use -A more  than  once  on  a
              command line, if an architecture family allows com-
              bination of target architectures; each use will add
              another pair of name variants to search for when -l
              specifies a library.


       -b input-format
              Specify the binary format for  input  object  files
              that  follow  this option on the command line.  You
              don't usually need to specify this, as ld  is  con-
              figured  to  expect  as  a default input format the
              most usual format on each machine.  input-format is
              a text string, the name of a particular format sup-
              ported by the BFD libraries.  -format  input-format
              has  the  same  effect,  as does the script command
              TARGET.

              You may want to use this option if you are  linking
              files  with an unusual binary format.  You can also
              use -b to switch formats explicitly  (when  linking
              object files of different formats), by including -b



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ld(1)                 GNU Development Tools                 ld(1)


              input-format before each group of object files in a
              particular format.

              The  default  format  is taken from the environment
              variable GNUTARGET.  You can also define the  input
              format from a script, using the command TARGET.


       -Bstatic
              Do not link against shared libraries.  This is only
              meaningful on platforms for which shared  libraries
              are supported.


       -Bdynamic
              Link against dynamic libraries.  This is only mean-
              ingful on platforms for which shared libraries  are
              supported.   This option is normally the default on
              such platforms.


       -Bgroup
              Set the DF_1_GROUP flag in the DT_FLAGS_1 entry  in
              the dynamic section.  This causes the runtime link-
              er to handle lookups in this object and its  depen-
              dencies  to be performed only inside the group.  No
              undefined symbols are allowed.  This option is only
              meaningful  on  ELF  platforms which support shared
              libraries.


       -Bsymbolic
              When creating a shared library, bind references  to
              global  symbols to the definition within the shared
              library, if any.  Normally, it is  possible  for  a
              program linked against a shared library to override
              the definition within the shared library.  This op-
              tion is only meaningful on ELF platforms which sup-
              port shared libraries.


       -c commandfile
              Directs ld to read link commands from the file com-
              mandfile.   These commands will completely override
              ld's default link format  (rather  than  adding  to
              it);  commandfile must specify everything necessary
              to describe the target format.


              You may also include a script of link commands  di-
              rectly in the command line by bracketing it between
              `{' and `}' characters.





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ld(1)                 GNU Development Tools                 ld(1)


       --cref Output a cross reference table.  If  a  linker  map
              file  is being generated, the cross reference table
              is printed to  the  map  file.   Otherwise,  it  is
              printed on the standard output.


       -d

       -dc

       -dp    These  three options are equivalent; multiple forms
              are supported for compatibility with other linkers.
              Use  any  of them to make ld assign space to common
              symbols even if a relocatable output file is speci-
              fied (-r).  The script command FORCE_COMMON_ALLOCA-
              TION has the same effect.


       -defsym symbol=expression
              Create a global symbol in the output file, contain-
              ing  the absolute address given by expression.  You
              may use this option as many times as  necessary  to
              define  multiple  symbols  in  the command line.  A
              limited form of arithmetic is supported for the ex-
              pression  in this context: you may give a hexadeci-
              mal constant or the name of an existing symbol,  or
              use  +  and  -  to add or subtract hexadecimal con-
              stants or symbols.  If you need more elaborate  ex-
              pressions,  consider  using the linker command lan-
              guage from a script.


       --demangle

       --no-demangle
              These options control whether  to  demangle  symbol
              names in error messages and other output.  When the
              linker is told to demangle,  it  tries  to  present
              symbol names in a readable fashion: it strips lead-
              ing underscores if they are used by the object file
              format,  and converts C++ mangled symbol names into
              user readable names.  The linker will  demangle  by
              default   unless   the  environment  variable  COL-
              LECT_NO_DEMANGLE is set.  These options may be used
              to override the default.


       -e entry
               Use entry as the explicit symbol for beginning ex-
              ecution of your program, rather  than  the  default
              entry  point.   See  the `ld' entry in `info' for a
              discussion of defaults and other ways of specifying
              the entry point.




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ld(1)                 GNU Development Tools                 ld(1)


       -embedded-relocs
              This  option  is  only meaningful when linking MIPS
              embedded PIC code, generated by the  -membedded-pic
              option to the GNU compiler and assembler.  It caus-
              es the linker to create a table which may  be  used
              at runtime to relocate any data which was statical-
              ly initialized to pointer values.  See the code  in
              testsuite/ld-empic for details.


       -E

       -export-dynamic
              When  creating  an ELF file, add all symbols to the
              dynamic symbol table.  Normally, the dynamic symbol
              table contains only symbols which are used by a dy-
              namic object.  This option is needed for some  uses
              of dlopen.


       -f name

       --auxiliary name
              When  creating an ELF shared object, set the inter-
              nal DT_AUXILIARY field to the specified name.  This
              tells  the  dynamic linker that the symbol table of
              the shared object should be used  as  an  auxiliary
              filter  on  the  symbol  table of the shared object
              name.


       -F name

       --filter name
              When creating an ELF shared object, set the  inter-
              nal  DT_FILTER  field  to the specified name.  This
              tells the dynamic linker that the symbol  table  of
              the shared object should be used as a filter on the
              symbol table of the shared object name.


       -format input-format
              Synonym for -b input-format.


       -g     Accepted, but ignored; provided  for  compatibility
              with other tools.


       -G size
              Set the maximum size of objects to be optimized us-
              ing the GP register to size under MIPS ECOFF.   Ig-
              nored for other object file formats.




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ld(1)                 GNU Development Tools                 ld(1)


       -h name

       -soname name
              When  creating an ELF shared object, set the inter-
              nal DT_SONAME field to the specified name.  When an
              executable is linked with a shared object which has
              a DT_SONAME field, then when the executable is  run
              the  dynamic linker will attempt to load the shared
              object specified by the DT_SONAME field rather than
              the using the file name given to the linker.


       --help Print  a summary of the command-line options on the
              standard output and exit.  This option  and  --ver-
              sion  begin with two dashes instead of one for com-
              patibility with other GNU programs.  The other  op-
              tions  start  with  only one dash for compatibility
              with other linkers.


       -i     Perform an incremental link (same as option -r).


       -lar    Add an archive file ar to the  list  of  files  to
              link.  This option may be used any number of times.
              ld will search its  path-list  for  occurrences  of
              libar.a for every ar specified.


       -Lsearchdir
              This  command  adds  path  searchdir to the list of
              paths that ld will search  for  archive  libraries.
              You may use this option any number of times.

              The  default  set  of paths searched (without being
              specified with -L) depends on what  emulation  mode
              ld  is  using, and in some cases also on how it was
              configured.    The paths can also be specified in a
              link script with the SEARCH_DIR command.


       -M     Print (to the standard output file) a link map--di-
              agnostic information about where symbols are mapped
              by ld, and information on global common storage al-
              location.


       -Map mapfile
              Print to the file mapfile  a  link  map--diagnostic
              information  about  where symbols are mapped by ld,
              and information on global  common  storage  alloca-
              tion.





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ld(1)                 GNU Development Tools                 ld(1)


       -m emulation
              Emulate  the  emulation  linker.   You can list the
              available emulations with the --verbose or  -V  op-
              tions.   This  option overrides the compiled-in de-
              fault, which is the system for which you configured
              ld.


       -N     specifies  readable and writable text and data sec-
              tions. If the output  format  supports  Unix  style
              magic numbers, the output is marked as OMAGIC.

              When  you  use the `-N' option, the linker does not
              page-align the data segment.


       -n     sets the text segment to be read only,  and  NMAGIC
              is written if possible.


       -noinhibit-exec
              Normally,  the  linker  will  not produce an output
              file if it encounters errors during the  link  pro-
              cess.   With  this  flag,  you can specify that you
              wish the output file retained even after  non-fatal
              errors.


       -no-keep-memory
              The linker normally optimizes for speed over memory
              usage by caching the symbol tables of  input  files
              in memory.  This option tells the linker to instead
              optimize for memory usage, by rereading the  symbol
              tables  as  necessary.  This may be required if the
              linker runs out of memory  space  while  linking  a
              large executable.


       -no-warn-mismatch
              Normally  the  linker will give an error if you try
              to link together input files  that  are  mismatched
              for  some  reason,  perhaps  because they have been
              compiled for different processors or for  different
              endiannesses.  This option tells the linker that it
              should silently permit such possible errors.   This
              option should only be used with care, in cases when
              you have taken some  special  action  that  ensures
              that the linker errors are inappropriate.


       -o output
              output is a name for the program produced by ld; if
              this option is not specified, the name  `a.out'  is
              used by default.  The script command OUTPUT can al-



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ld(1)                 GNU Development Tools                 ld(1)


              so specify the output file name.


       -Olevel
              Generate optimized output files.   This  might  use
              significantly  more  time  and  therefore  probably
              should be enabled only for generating the final bi-
              nary.   level  is  supposed  to be a numeric value.
              Any value greater than zero enables  the  optimiza-
              tions.


       --oformat output-format
              Specify  the  binary  format  for the output object
              file.  You don't usually need to specify  this,  as
              ld  is  configured  to  produce as a default output
              format the most usual format on each machine.  out-
              put-format is a text string, the name of a particu-
              lar format supported by  the  BFD  libraries.   The
              script  command  OUTPUT_FORMAT can also specify the
              output format, but this option overrides it.


       -R filename
              Read symbol names and their  addresses  from  file-
              name,  but  do not relocate it or include it in the
              output.  This allows your output file to refer sym-
              bolically  to  absolute locations of memory defined
              in other programs.


       -relax An option with machine dependent effects.  Current-
              ly this option is only supported on the H8/300.

              On some platforms, use this option to perform glob-
              al optimizations  that  become  possible  when  the
              linker resolves addressing in your program, such as
              relaxing address modes  and  synthesizing  new  in-
              structions in the output object file.

              On  platforms where this is not supported, `-relax'
              is accepted, but has no effect.


       -r     Generates  relocatable  output--i.e.,  generate  an
              output  file that can in turn serve as input to ld.
              This is often called partial linking.   As  a  side
              effect,  in environments that support standard Unix
              magic numbers, this option  also  sets  the  output
              file's  magic  number to OMAGIC.  If this option is
              not specified, an absolute file is produced.   When
              linking  C++ programs, this option will not resolve
              references to constructors; -Ur is an  alternative.




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ld(1)                 GNU Development Tools                 ld(1)


              This option does the same as -i.


       -rpath directory
              Add a directory to the runtime library search path.
              This is used when linking an  ELF  executable  with
              shared  objects.  All -rpath arguments are concate-
              nated and passed to the runtime linker, which  uses
              them  to  locate  shared  objects  at runtime.  The
              -rpath option is also used when locating shared ob-
              jects which are needed by shared objects explicitly
              included in the link; see the  description  of  the
              -rpath-link  option.   If  -rpath  is not used when
              linking an ELF executable, the contents of the  en-
              vironment  variable  LD_RUN_PATH will be used if it
              is defined.

              The -rpath option may also be used  on  SunOS.   By
              default,  on  SunOS, the linker will form a runtime
              search path out of all the -L options it is  given.
              If a -rpath option is used, the runtime search path
              will be formed exclusively  using  the  -rpath  op-
              tions, ignoring the -L options.  This can be useful
              when using gcc, which adds many  -L  options  which
              may be on NFS mounted filesystems.


       -rpath-link directory
              When using ELF or SunOS, one shared library may re-
              quire another.  This  happens  when  an  ld -shared
              link  includes a shared library as one of the input
              files.

              When the linker encounters such a  dependency  when
              doing  a non-shared, non-relocateable link, it will
              automatically try to locate the required shared li-
              brary  and include it in the link, if it is not in-
              cluded explicitly.  In such a case, the -rpath-link
              option  specifies  the  first set of directories to
              search.  The -rpath-link option may specify  a  se-
              quence  of  directory  names either by specifying a
              list of names separated by colons, or by  appearing
              multiple times.

              If  the  required  shared library is not found, the
              linker will issue a warning and continue  with  the
              link.


       -S     Omits debugger symbol information (but not all sym-
              bols) from the output file.


       -s     Omits all symbol information from the output  file.



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ld(1)                 GNU Development Tools                 ld(1)


       -shared
              Create  a  shared  library.  This is currently only
              supported on ELF and SunOS platforms (on  SunOS  it
              is  not  required, as the linker will automatically
              create a shared library when  there  are  undefined
              symbols and the -e option is not used).


       -sort-common
              Normally,  when ld places the global common symbols
              in the appropriate output sections, it  sorts  them
              by size.  First come all the one byte symbols, then
              all the two bytes, then all  the  four  bytes,  and
              then  everything else.  This is to prevent gaps be-
              tween symbols due to alignment  constraints.   This
              option disables that sorting.


       -split-by-reloc count
              Trys  to  creates extra sections in the output file
              so that no single output section in the  file  con-
              tains  more than count relocations.  This is useful
              when generating huge  relocatable  for  downloading
              into certain real time kernels with the COFF object
              file format; since COFF cannot represent more  than
              65535  relocations  in a single section.  Note that
              this will fail to work  with  object  file  formats
              which do not support arbitrary sections.  The link-
              er will not split up individual input sections  for
              redistribution,  so  if a single input section con-
              tains more than count relocations one  output  sec-
              tion will contain that many relocations.


       -split-by-file
              Similar to -split-by-reloc but creates a new output
              section for each input file.


       --section-start sectionname=org
              Locate a section in the output file at the absolute
              address  given  by  org.  org must be a hexadecimal
              integer.  You may use this option as many times  as
              necessary  to  locate multiple sections in the com-
              mand line.  If you need more elaborate expressions,
              consider  using  the linker command language from a
              script.


       -Tbss org

       -Tdata org





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ld(1)                 GNU Development Tools                 ld(1)


       -Ttext org
              Use org as the starting address for--respectively--
              the  bss,  data,  or the text segment of the output
              file.  org must be a hexadecimal integer.


       -T commandfile
              Equivalent to -c commandfile; supported for compat-
              ibility with other tools.


       -t     Prints names of input files as ld processes them.


       -u sym Forces  sym  to be entered in the output file as an
              undefined symbol.  This may, for  example,  trigger
              linking  of  additional  modules  from standard li-
              braries.  -u may be repeated with different  option
              arguments to enter additional undefined symbols.


       -Ur    For  anything  other than C++ programs, this option
              is equivalent to -r: it generates relocatable  out-
              put--i.e., an output file that can in turn serve as
              input to ld.  When linking C++ programs,  -Ur  will
              resolve references to constructors, unlike -r.


       --verbose
              Display the version number for ld and list the sup-
              ported emulations.  Display which input  files  can
              and can not be opened.


       -v, -V Display  the  version number for ld.  The -V option
              also lists the supported emulations.


       --version
              Display the version number for ld and exit.


       -warn-common
              Warn when a common symbol is combined with  another
              common  symbol  or  with a symbol definition.  Unix
              linkers allow this somewhat  sloppy  practice,  but
              linkers  on  some  other  operating systems do not.
              This option allows you to find  potential  problems
              from combining global symbols.


       -warn-constructors
              Warn  if any global constructors are used.  This is
              only useful for a few  object  file  formats.   For



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ld(1)                 GNU Development Tools                 ld(1)


              formats like COFF or ELF, the linker can not detect
              the use of global constructors.


       -warn-multiple-gp
              Warn if the output file requires  multiple  global-
              pointer values.  This option is only meaningful for
              certain processors, such as the Alpha.


       -warn-once
              Only warn once for each  undefined  symbol,  rather
              than once per module which refers to it.


       -warn-section-align
              Warn if the address of an output section is changed
              because of  alignment.   Typically,  the  alignment
              will  be set by an input section.  The address will
              only be changed if  it  not  explicitly  specified;
              that is, if the SECTIONS command does not specify a
              start address for the section.


       --whole-archive
              For each archive mentioned on the command line  af-
              ter  the  --whole-archive option, include every ob-
              ject file in the archive in the link,  rather  than
              searching  the  archive  for  the  required  object
              files.  This is normally used to  turn  an  archive
              file into a shared library, forcing every object to
              be included in the resulting shared library.


       --no-whole-archive
              Turn off the effect of the  --whole-archive  option
              for  archives  which  appear  later  on the command
              line.


       --wrap symbol
              Use a wrapper function for symbol.   Any  undefined
              reference to symbol will be resolved to __wrap_sym-
              bol.  Any undefined reference to __real_symbol will
              be resolved to symbol.


       -X     Delete  all temporary local symbols.  For most tar-
              gets, this is all local symbols whose  names  begin
              with `L'.


       -x     Delete all local symbols.




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ld(1)                 GNU Development Tools                 ld(1)


ENVIRONMENT
       You  can  change  the  behavior of ld with the environment
       variable GNUTARGET.

       GNUTARGET determines the input-file object format  if  you
       don't  use  -b (or its synonym -format).  Its value should
       be one of the BFD names for an input format.  If there  is
       no  GNUTARGET in the environment, ld uses the natural for-
       mat of the host. If GNUTARGET is set to default  then  BFD
       attempts  to discover the input format by examining binary
       input files; this method often succeeds, but there are po-
       tential  ambiguities, since there is no method of ensuring
       that the magic number used to flag object-file formats  is
       unique.   However,  the configuration procedure for BFD on
       each system places the conventional format for that system
       first  in  the search-list, so ambiguities are resolved in
       favor of convention.




SEE ALSO
       objdump(1)
       `ld' and `binutils' entries in info
       ld: the GNU linker, Steve Chamberlain  and  Roland  Pesch;
       The GNU Binary Utilities, Roland H. Pesch.


COPYING
       Copyright  (c)  1991,  92,  93, 94, 95, 96, 97, 1998, 2000
       Free Software Foundation, Inc.

       This document is distributed under the terms  of  the  GNU
       Free  Documentation License, version 1.1.  That license is
       described in the sources for this manual page, but  it  is
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Free Software Foundation                                       14





ld(1)                 GNU Development Tools                 ld(1)



























































Free Software Foundation                                       15



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