ld(1) GNU Development Tools ld(1) NAME ld - the GNU linker SYNOPSIS ld [-o output] objfile... [-Aarchitecture] [-b input-format] [-Bstatic] [-Bdynamic] [-Bsymbolic] [-c commandfile] [--cref] [-d|-dc|-dp] [-defsym symbol = expression] [-e entry] [-embedded-relocs] [-E] [-export-dynamic] [-F] [-F format] [-format input-format] [-g] [-G size] [--help] [-i] [-lar] [-Lsearchdir] [-M] [-Map mapfile] [-m emulation] [-n|-N] [-noinhibit-exec] [-no-keep-memory] [-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] [-Ttext textorg] [-Tdata dataorg] [-Tbss bssorg] [-t] [-u sym] [-V] [-v] [--verbose] [--version] [-warn-common] [-warn-constructors] [-warn-multiple-gp] [-warn-once] [--whole-archive] [--no-whole-archive] [--wrap symbol] [-X] [-x] DESCRIPTION ld combines a number of object and archive files, relocates 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 explicit 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 de- tails on the command language and on other aspects of the GNU linker. This version of ld uses the general purpose BFD libraries to operate on object files. This allows ld to read, combine, and write object files in many different formats-for exam- ple, COFF or a.out. Different formats may be linked togeth- er to produce any available kind of object file. You can use `objdump -i' to get a list of formats supported on vari- ous 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 encountering an error; whenever possible, ld continues executing, allow- ing you to identify other errors (or, in some cases, to get an output file in spite of the error). cygnus support Last change: 17 August 1992 1 ld(1) GNU Development Tools ld(1) The GNU linker ld is meant to cover a broad range of situa- tions, and to be as compatible as possible with other link- ers. As a result, you have many choices to control its behavior through the command line, and through environment variables. OPTIONS The plethora of command-line options may seem intimidating, but in actual practice few of them are used in any particu- lar context. For instance, a frequent use of ld is to link standard Unix object files on a standard, supported 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 result 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 ord- er, and may be repeated at will. For the most part, repeat- ing 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 option. The exceptions-which may meaningfully be used more than once-are -A, -b (or its synonym -format), -defsym, -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 pro- duce 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 ar- guments immediately following the option that requires them. -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, cygnus support Last change: 17 August 1992 2 ld(1) GNU Development Tools ld(1) and warns of any incompatible instructions 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 iden- tifying 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 functionality for other architecture families. You can meaningfully use -A more than once on a command line, if an architecture family allows combination of target architectures; each use will add another pair of name variants to search for when -l specifies a li- brary. -b input-format Specify the binary format for input object files that follow this option on the command line. You don't usu- ally need to specify this, as ld is configured to ex- pect as a default input format the most usual format on each machine. input-format is a text string, the name of a particular format supported 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 input- format before each group of object files in a particu- lar format. The default format is taken from the environment vari- able GNUTARGET. You can also define the input format from a script, using the command TARGET. cygnus support Last change: 17 August 1992 3 ld(1) GNU Development Tools ld(1) -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 meaning- ful on platforms for which shared libraries are sup- ported. This option is normally the default on such platforms. -Bsymbolic When creating a shared library, bind references to glo- bal symbols to the definition within the shared li- brary, if any. Normally, it is possible for a program linked against a shared library to override the defini- tion within the shared library. This option is only meaningful on ELF platforms which support shared li- braries. -c commandfile Directs ld to read link commands from the file command- file. These commands will completely override ld's de- fault link format (rather than adding to it); command- file must specify everything necessary to describe the target format. You may also include a script of link commands directly in the command line by bracketing it between `{' and `}' characters. --cref Output a cross reference table. If a linker map file is being generated, the cross reference table is print- ed 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 specified (-r). The script command FORCECOMMON_ALLOCATION has the same cygnus support Last change: 17 August 1992 4 ld(1) GNU Development Tools ld(1) effect. -defsym symbol = expression Create a global symbol in the output file, containing the absolute address given by expression. You may use this option as many times as necessary to define multi- ple symbols in the command line. A limited form of ar- ithmetic is supported for the expression in this con- text: you may give a hexadecimal constant or the name of an existing symbol, or use + and - to add or sub- tract hexadecimal constants or symbols. If you need more elaborate expressions, consider using the linker command language from a script. -e entry Use entry as the explicit symbol for beginning execu- tion of your program, rather than the default entry point. for a discussion of defaults and other ways of specifying the entry point. -embedded-relocs This option is only meaningful when linking MIPS embed- ded PIC code, generated by the -membedded-pic option to the GNU compiler and assembler. It causes the linker to create a table which may be used at runtime to relo- cate any data which was statically 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 dynamic object. This option is needed for some uses of dlopen. -F -Fformat Some older linkers used this option throughout a compi- lation toolchain for specifying object-file format for both input and output object files. ld's mechanisms (the -b or -format options for input files, the TARGET command in linker scripts for output files, the GNUTAR- GET environment variable) are more flexible, but but it accepts (and ignores) the -F option flag for compati- cygnus support Last change: 17 August 1992 5 ld(1) GNU Development Tools ld(1) bility with scripts written to call the old linker. -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 using the GP register to size under MIPS ECOFF. Ignored for other object file formats. --help Print a summary of the command-line options on the standard output and exit. This option and --version begin with two dashes instead of one for compatibility with other GNU programs. The other options 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 speci- fied with -L) depends on what emulation mode ld is us- ing, and in some cases also on how it was configured. The paths can also be specified in a link script with the SEARCHDIR command. -M Print (to the standard output file) a link map- diagnostic information about where symbols are mapped by ld, and information on global common storage alloca- tion. cygnus support Last change: 17 August 1992 6 ld(1) GNU Development Tools ld(1) -Map mapfile Print to the file mapfile a link map-diagnostic infor- mation about where symbols are mapped by ld, and infor- mation on global common storage allocation. -m emulation Emulate the emulation linker. You can list the avail- able emulations with the --verbose or -V options. This option overrides the compiled-in default, which is the system for which you configured ld. -N specifies readable and writable text and data sections. 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 process. 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 optim- ize 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. -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 also specify the output file name. -oformat output-format Specify the binary format for the output object file. You don't usually need to specify this, as ld is con- figured to produce as a default output format the most cygnus support Last change: 17 August 1992 7 ld(1) GNU Development Tools ld(1) usual format on each machine. output-format is a text string, the name of a particular format supported by the BFD libraries. The script command OUTPUTFORMAT can also specify the output format, but this option over- rides it. -R filename Read symbol names and their addresses from filename, but do not relocate it or include it in the output. This allows your output file to refer symbolically to absolute locations of memory defined in other programs. -relax An option with machine dependent effects. Currently this option is only supported on the H8/300. On some platforms, use this option to perform global optimizations that become possible when the linker resolves addressing in your program, such as relaxing address modes and synthesizing new instructions 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 en- vironments 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 op- tion will not resolve references to constructors; -Ur is an alternative. 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 concatenated and passed to the runtime linker, which uses them to locate shared objects at runtime. The -rpath option is also used when locating shared objects 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 environment variable LDRUN_PATH will be used if cygnus support Last change: 17 August 1992 8 ld(1) GNU Development Tools ld(1) it is defined. The -rpath option may also be used on SunOS. By de- fault, on SunOS, the linker will form a runtime search patch 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 options, 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 require 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 automati- cally try to locate the required shared library and in- clude it in the link, if it is not included explicitly. In such a case, the -rpath-link option specifies the first set of directories to search. The -rpath-link option may specify a sequence 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 symbols) from the output file. -s Omits all symbol information from the output file. -shared Create a shared library. This is currently only sup- ported 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 between symbols due to cygnus support Last change: 17 August 1992 9 ld(1) GNU Development Tools ld(1) alignment constraints. This option disables that sort- ing. -split-by-reloc count Trys to creates extra sections in the output file so that no single output section in the file contains 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 sin- gle section. Note that this will fail to work with ob- ject file formats which do not support arbitrary sec- tions. The linker will not split up individual input sections for redistribution, so if a single input sec- tion contains more than count relocations one output section will contain that many relocations. -split-by-file Similar to -split-by-reloc but creates a new output section for each input file. -Tbss org -Tdata org -Ttext org Use org as the starting address for-respectively-the bss, data, or the text segment of the output file. textorg must be a hexadecimal integer. -T commandfile Equivalent to -c commandfile; supported for compatibil- ity 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 unde- fined symbol. This may, for example, trigger linking of additional modules from standard libraries. -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 output-i.e., cygnus support Last change: 17 August 1992 10 ld(1) GNU Development Tools ld(1) 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 support- ed 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 com- mon symbol or with a symbol definition. Unix linkers allow this somewhat sloppy practice, but linkers on some other operating systems do not. This option al- lows you to find potential problems from combining glo- bal symbols. -warn-constructors Warn if any global constructors are used. This is only useful for a few object file formats. For formats like COFF or ELF, the linker can not detect the use of glo- bal 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. --whole-archive For each archive mentioned on the command line after the --whole-archive option, include every object file in the archive in the link, rather than searching the archive for the required object files. This is normal- cygnus support Last change: 17 August 1992 11 ld(1) GNU Development Tools ld(1) ly 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 refer- ence to symbol will be resolved to __wrap symbol. Any undefined reference to __real symbol will be resolved to symbol. -X Delete all temporary local symbols. For most targets, this is all local symbols whose names begin with `L'. -x Delete all local symbols. ENVIRONMENT You can change the behavior of ld with the environment vari- able 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 format 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 potential 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 conven- tion. 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, 1992 Free Software Foundation, Inc. cygnus support Last change: 17 August 1992 12 ld(1) GNU Development Tools ld(1) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this per- mission notice are preserved on all copies. Permission is granted to copy and distribute modified ver- sions of this manual under the conditions for verbatim copy- ing, provided that the entire resulting derived work is dis- tributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above condi- tions for modified versions, except that this permission no- tice may be included in translations approved by the Free Software Foundation instead of in the original English. cygnus support Last change: 17 August 1992 13