MAN page from RedHat EL 6 toolchain-armiwmmx-2012-2012.12.1-oselas.2.2.x86_64.rpm
Section: GNU Development Tools (1)
ld - The GNU linker
combines a number of object and archive files, relocatestheir data and ties up symbol references. Usually the last step incompiling a program is to run ld
ld accepts Linker Command Language files written ina superset of AT&T's Link Editor Command Language syntax,to provide explicit and total control over the linking process.
This man page does not describe the command language; see theld entry in "info" for full details on the commandlanguage and on other aspects of the GNU linker.
This version of ld uses the general purpose BFD librariesto operate on object files. This allows ld to read, combine, andwrite object files in many different formats---for example, COFF or"a.out". Different formats may be linked together to produce anyavailable kind of object file.
Aside from its flexibility, the GNU linker is more helpful than otherlinkers in providing diagnostic information. Many linkers abandonexecution immediately upon encountering 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 situations,and to be as compatible as possible with other linkers. As a result,you have many choices to control its behavior.
The linker supports a plethora of command-line options, but in actualpractice few of them are used in any particular context.For instance, a frequent use of ld
is to link standard Unixobject files on a standard, supported Unix system. On such a system, tolink a file "hello.o"
ld -o <output> /lib/crt0.o hello.o -lc
This tells ld to produce a file called output as theresult of linking the file "/lib/crt0.o" with "hello.o" andthe library "libc.a", which will come from the standard searchdirectories. (See the discussion of the -l option below.)
Some of the command-line options to ld may be specified at anypoint in the command line. However, options which refer to files, suchas -l or -T, cause the file to be read at the point atwhich the option appears in the command line, relative to the objectfiles and other file options. Repeating non-file options with adifferent argument will either have no further effect, or override prioroccurrences (those further to the left on the command line) of thatoption. Options which may be meaningfully specified more than once arenoted in the descriptions below.
Non-option arguments are object files or archives which are to be linkedtogether. They may follow, precede, or be mixed in with command-lineoptions, except that an object file argument may not be placed betweenan option and its argument.
Usually the linker is invoked with at least one object file, but you canspecify other forms of binary input files using -l, -R,and the script command language. If no binary input files at allare specified, the linker does not produce any output, and issues themessage No input files.
If the linker cannot recognize the format of an object file, it willassume that it is a linker script. A script specified in this wayaugments the main linker script used for the link (either the defaultlinker script or the one specified by using -T). This featurepermits the linker to link against a file which appears to be an objector an archive, but actually merely defines some symbol values, or uses"INPUT" or "GROUP" to load other objects. Specifying ascript in this way merely augments the main linker script, with theextra commands placed after the main script; use the -T optionto replace the default linker script entirely, but note the effect ofthe "INSERT" command.
For options whose names are a single letter,option arguments must either follow the option letter without interveningwhitespace, or be given as separate arguments immediately following theoption that requires them.
For options whose names are multiple letters, either one dash or two canprecede the option name; for example, -trace-symbol and--trace-symbol are equivalent. Note---there is one exception tothis rule. Multiple letter options that start with a lower case 'o' canonly be preceded by two dashes. This is to reduce confusion with the-o option. So for example -omagic sets the output filename to magic whereas --omagic sets the NMAGIC flag on theoutput.
Arguments to multiple-letter options must either be separated from theoption name by an equals sign, or be given as separate argumentsimmediately following the option that requires them. For example,--trace-symbol foo and --trace-symbol=foo are equivalent.Unique abbreviations of the names of multiple-letter options areaccepted.
Note---if the linker is being invoked indirectly, via a compiler driver(e.g. gcc) then all the linker command line options should beprefixed by -Wl, (or whatever is appropriate for the particularcompiler driver) like this:
gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
This is important, because otherwise the compiler driver program maysilently drop the linker options, resulting in a bad link. Confusionmay also arise when passing options that require values through adriver, as the use of a space between option and argument acts asa separator, and causes the driver to pass only the option to the linkerand the argument to the compiler. In this case, it is simplest to usethe joined forms of both single- and multiple-letter options, such as:
gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
Here is a table of the generic command line switches accepted by the GNUlinker:
- Read command-line options from file. The options read areinserted in place of the original @file option. If filedoes not exist, or cannot be read, then the option will be treatedliterally, and not removed.
Options in file are separated by whitespace. A whitespacecharacter may be included in an option by surrounding the entireoption in either single or double quotes. Any character (including abackslash) may be included by prefixing the character to be includedwith a backslash. The file may itself contain additional@file options; any such options will be processed recursively.
- -a keyword
- This option is supported for HP/UX compatibility. The keywordargument must be one of the strings archive, shared, ordefault. -aarchive is functionally equivalent to-Bstatic, and the other two keywords are functionally equivalentto -Bdynamic. This option may be used any number of times.
- --audit AUDITLIB
- Adds AUDITLIB to the "DT_AUDIT" entry of the dynamic section.AUDITLIB is not checked for existence, nor will it use the DT_SONAMEspecified in the library. If specified multiple times "DT_AUDIT"will contain a colon separated list of audit interfaces to use. If the linkerfinds an object with an audit entry while searching for shared libraries,it will add a corresponding "DT_DEPAUDIT" entry in the output file. This option is only meaningful on ELF platforms supporting the rtld-auditinterface.
- -A architecture
- In the current release of ld, this option is useful only for theIntel 960 family of architectures. In that ld configuration, thearchitecture argument identifies the particular architecture inthe 960 family, enabling some safeguards and modifying thearchive-library search path.
Future releases of ld may support similar functionality forother architecture families.
- -b input-format
- ld may be configured to support more than one kind of objectfile. If your ld is configured this way, you can use the-b option to specify the binary format for input object filesthat follow this option on the command line. Even when ld isconfigured to support alternative object formats, you don't usually needto specify this, as ld should be configured to expect as adefault input format the most usual format on each machine.input-format is a text string, the name of a particular formatsupported by the BFD libraries. (You can list the available binaryformats with objdump -i.)
You may want to use this option if you are linking files with an unusualbinary format. You can also use -b to switch formats explicitly (whenlinking object files of different formats), by including-b input-format before each group of object files in aparticular 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";
- -c MRI-commandfile
- For compatibility with linkers produced by MRI, ld accepts scriptfiles written in an alternate, restricted command language, described inthe MRI Compatible Script Files section of GNU ld documentation.Introduce MRI script files withthe option -c; use the -T option to run linkerscripts written in the general-purpose ld scripting language.If MRI-cmdfile does not exist, ld looks for it in the directoriesspecified by any -L options.
- These three options are equivalent; multiple forms are supported forcompatibility with other linkers. They assign space to common symbolseven if a relocatable output file is specified (with -r). Thescript command "FORCE_COMMON_ALLOCATION" has the same effect.
- --depaudit AUDITLIB
- -P AUDITLIB
- Adds AUDITLIB to the "DT_DEPAUDIT" entry of the dynamic section.AUDITLIB is not checked for existence, nor will it use the DT_SONAMEspecified in the library. If specified multiple times "DT_DEPAUDIT"will contain a colon separated list of audit interfaces to use. Thisoption is only meaningful on ELF platforms supporting the rtld-audit interface.The -P option is provided for Solaris compatibility.
- -e entry
- Use entry as the explicit symbol for beginning execution of yourprogram, rather than the default entry point. If there is no symbolnamed entry, the linker will try to parse entry as a number,and use that as the entry address (the number will be interpreted inbase 10; you may use a leading 0x for base 16, or a leading0 for base 8).
- --exclude-libs lib,lib,...
- Specifies a list of archive libraries from which symbols should not be automaticallyexported. The library names may be delimited by commas or colons. Specifying"--exclude-libs ALL" excludes symbols in all archive libraries fromautomatic export. This option is available only for the i386 PE targetedport of the linker and for ELF targeted ports. For i386 PE, symbolsexplicitly listed in a .def file are still exported, regardless of thisoption. For ELF targeted ports, symbols affected by this option willbe treated as hidden.
- --exclude-modules-for-implib module,module,...
- Specifies a list of object files or archive members, from which symbolsshould not be automatically exported, but which should be copied wholesaleinto the import library being generated during the link. The module namesmay be delimited by commas or colons, and must match exactly the filenamesused by ld to open the files; for archive members, this is simplythe member name, but for object files the name listed must include andmatch precisely any path used to specify the input file on the linker'scommand-line. This option is available only for the i386 PE targeted portof the linker. Symbols explicitly listed in a .def file are still exported,regardless of this option.
- When creating a dynamically linked executable, using the -Eoption or the --export-dynamic option causes the linker to addall symbols to the dynamic symbol table. The dynamic symbol table is theset of symbols which are visible from dynamic objects at run time.
If you do not use either of these options (or use the--no-export-dynamic option to restore the default behavior), thedynamic symbol table will normally contain only those symbols which arereferenced by some dynamic object mentioned in the link.
If you use "dlopen" to load a dynamic object which needs to referback to the symbols defined by the program, rather than some otherdynamic object, then you will probably need to use this option whenlinking the program itself.
You can also use the dynamic list to control what symbols shouldbe added to the dynamic symbol table if the output format supports it.See the description of --dynamic-list.
Note that this option is specific to ELF targeted ports. PE targetssupport a similar function to export all symbols from a DLL or EXE; seethe description of --export-all-symbols below.
- Link big-endian objects. This affects the default output format.
- Link little-endian objects. This affects the default output format.
- -f name
- When creating an ELF shared object, set the internal DT_AUXILIARY fieldto the specified name. This tells the dynamic linker that the symboltable of the shared object should be used as an auxiliary filter on thesymbol table of the shared object name.
If you later link a program against this filter object, then, when yourun the program, the dynamic linker will see the DT_AUXILIARY field. Ifthe dynamic linker resolves any symbols from the filter object, it willfirst check whether there is a definition in the shared objectname. If there is one, it will be used instead of the definitionin the filter object. The shared object name need not exist.Thus the shared object name may be used to provide an alternativeimplementation of certain functions, perhaps for debugging or formachine specific performance.
This option may be specified more than once. The DT_AUXILIARY entrieswill be created in the order in which they appear on the command line.
- -F name
- When creating an ELF shared object, set the internal DT_FILTER field tothe specified name. This tells the dynamic linker that the symbol tableof the shared object which is being created should be used as a filteron the symbol table of the shared object name.
If you later link a program against this filter object, then, when yourun the program, the dynamic linker will see the DT_FILTER field. Thedynamic linker will resolve symbols according to the symbol table of thefilter object as usual, but it will actually link to the definitionsfound in the shared object name. Thus the filter object can beused to select a subset of the symbols provided by the objectname.
Some older linkers used the -F option throughout a compilationtoolchain for specifying object-file format for both input and outputobject files.The GNU linker uses other mechanisms for this purpose: the-b, --format, --oformat options, the"TARGET" command in linker scripts, and the "GNUTARGET"environment variable.The GNU linker will ignore the -F option when notcreating an ELF shared object.
- When creating an ELF executable or shared object, call NAME when theexecutable or shared object is unloaded, by setting DT_FINI to theaddress of the function. By default, the linker uses "_fini" asthe function to call.
- Ignored. Provided for compatibility with other tools.
- -G value
- Set the maximum size of objects to be optimized using the GP register tosize. This is only meaningful for object file formats such asMIPS ECOFF which supports putting large and small objects into differentsections. This is ignored for other object file formats.
- -h name
- When creating an ELF shared object, set the internal DT_SONAME field tothe specified name. When an executable is linked with a shared objectwhich has a DT_SONAME field, then when the executable is run the dynamiclinker will attempt to load the shared object specified by the DT_SONAMEfield rather than the using the file name given to the linker.
- Perform an incremental link (same as option -r).
- When creating an ELF executable or shared object, call NAME when theexecutable or shared object is loaded, by setting DT_INIT to the addressof the function. By default, the linker uses "_init" as thefunction to call.
- -l namespec
- Add the archive or object file specified by namespec to thelist of files to link. This option may be used any number of times.If namespec is of the form :filename, ldwill search the library path for a file called filename, otherwise itwill search the library path for a file called libnamespec.a.
On systems which support shared libraries, ld may also search forfiles other than libnamespec.a. Specifically, on ELFand SunOS systems, ld will search a directory for a librarycalled libnamespec.so before searching for one calledlibnamespec.a. (By convention, a ".so" extensionindicates a shared library.) Note that this behavior does not applyto :filename, which always specifies a file calledfilename.
The linker will search an archive only once, at the location where it isspecified on the command line. If the archive defines a symbol whichwas undefined in some object which appeared before the archive on thecommand line, the linker will include the appropriate file(s) from thearchive. However, an undefined symbol in an object appearing later onthe command line will not cause the linker to search the archive again.
See the -( option for a way to force the linker to searcharchives multiple times.
You may list the same archive multiple times on the command line.
This type of archive searching is standard for Unix linkers. However,if you are using ld on AIX, note that it is different from thebehaviour of the AIX linker.
- -L searchdir
- Add path searchdir to the list of paths that ld will searchfor archive libraries and ld control scripts. You may use thisoption any number of times. The directories are searched in the orderin which they are specified on the command line. Directories specifiedon the command line are searched before the default directories. All-L options apply to all -l options, regardless of theorder in which the options appear. -L options do not affecthow ld searches for a linker script unless -Toption is specified.
If searchdir begins with "=", then the "=" will be replacedby the sysroot prefix, a path specified when the linker is configured.
The default set of paths searched (without being specified with-L) depends on which emulation mode ld is using, and insome cases also on how it was configured.
The paths can also be specified in a link script with the"SEARCH_DIR" command. Directories specified this way are searchedat the point in which the linker script appears in the command line.
- -m emulation
- Emulate the emulation linker. You can list the availableemulations with the --verbose or -V options.
If the -m option is not used, the emulation is taken from the"LDEMULATION" environment variable, if that is defined.
Otherwise, the default emulation depends upon how the linker wasconfigured.
- Print a link map to the standard output. A link map providesinformation about the link, including the following:
- Where object files are mapped into memory.
- How common symbols are allocated.
- All archive members included in the link, with a mention of the symbolwhich caused the archive member to be brought in.
- The values assigned to symbols.
Note - symbols whose values are computed by an expression whichinvolves a reference to a previous value of the same symbol may nothave correct result displayed in the link map. This is because thelinker discards intermediate results and only retains the final valueof an expression. Under such circumstances the linker will displaythe final value enclosed by square brackets. Thus for example alinker script containing:
foo = 1 foo = foo * 4 foo = foo + 8
will produce the following output in the link map if the -Moption is used:
0x00000001 foo = 0x1 [0x0000000c] foo = (foo * 0x4) [0x0000000c] foo = (foo + 0x8)
See Expressions for more information about expressions in linkerscripts.
- Turn off page alignment of sections, and disable linking against sharedlibraries. If the output format supports Unix style magic numbers,mark the output as "NMAGIC".
- Set the text and data sections to be readable and writable. Also, donot page-align the data segment, and disable linking against sharedlibraries. If the output format supports Unix style magic numbers,mark the output as "OMAGIC". Note: Although a writable text sectionis allowed for PE-COFF targets, it does not conform to the formatspecification published by Microsoft.
- This option negates most of the effects of the -N option. Itsets the text section to be read-only, and forces the data segment tobe page-aligned. Note - this option does not enable linking againstshared libraries. Use -Bdynamic for this.
- -o output
- Use output as the name for the program produced by ld; if thisoption is not specified, the name a.out is used by default. Thescript command "OUTPUT" can also specify the output file name.
- -O level
- If level is a numeric values greater than zero ld optimizesthe output. This might take significantly longer and therefore probablyshould only be enabled for the final binary. At the moment thisoption only affects ELF shared library generation. Future releases ofthe linker may make more use of this option. Also currently there isno difference in the linker's behaviour for different non-zero valuesof this option. Again this may change with future releases.
- Leave relocation sections and contents in fully linked executables.Post link analysis and optimization tools may need this information inorder to perform correct modifications of executables. This resultsin larger executables.
This option is currently only supported on ELF platforms.
- Force the output file to have dynamic sections. This option is specificto VxWorks targets.
- Generate relocatable output---i.e., generate an output file that can inturn serve as input to ld. This is often called partiallinking. As a side effect, in environments that support standard Unixmagic numbers, this option also sets the output file's magic number to"OMAGIC".If this option is not specified, an absolute file is produced. Whenlinking C++ programs, this option will not resolve references toconstructors; to do that, use -Ur.
When an input file does not have the same format as the output file,partial linking is only supported if that input file does not contain anyrelocations. Different output formats can have further restrictions; forexample some "a.out"-based formats do not support partial linkingwith input files in other formats at all.
This option does the same thing as -i.
- -R filename
- Read symbol names and their addresses from filename, but do notrelocate it or include it in the output. This allows your output fileto refer symbolically to absolute locations of memory defined in otherprograms. You may use this option more than once.
For compatibility with other ELF linkers, if the -R option isfollowed by a directory name, rather than a file name, it is treated asthe -rpath option.
- Omit all symbol information from the output file.
- Omit debugger symbol information (but not all symbols) from the output file.
- Print the names of the input files as ld processes them.
- -T scriptfile
- Use scriptfile as the linker script. This script replacesld's default linker script (rather than adding to it), socommandfile must specify everything necessary to describe theoutput file. If scriptfile does not exist inthe current directory, "ld" looks for it in the directoriesspecified by any preceding -L options. Multiple -Toptions accumulate.
- -dT scriptfile
- Use scriptfile as the default linker script.
This option is similar to the --script option except thatprocessing of the script is delayed until after the rest of thecommand line has been processed. This allows options placed after the--default-script option on the command line to affect thebehaviour of the linker script, which can be important when the linkercommand line cannot be directly controlled by the user. (eg becausethe command line is being constructed by another tool, such asgcc).
- -u symbol
- Force symbol to be entered in the output file as an undefinedsymbol. Doing this may, for example, trigger linking of additionalmodules from standard libraries. -u may be repeated withdifferent option arguments to enter additional undefined symbols. Thisoption is equivalent to the "EXTERN" linker script command.
- For anything other than C++ programs, this option is equivalent to-r: it generates relocatable output---i.e., an output file that can inturn serve as input to ld. When linking C++ programs, -Urdoes resolve references to constructors, unlike -r.It does not work to use -Ur on files that were themselves linkedwith -Ur; once the constructor table has been built, it cannotbe added to. Use -Ur only for the last partial link, and-r for the others.
- Creates a separate output section for every input section matchingSECTION, or if the optional wildcard SECTION argument ismissing, for every orphan input section. An orphan section is one notspecifically mentioned in a linker script. You may use this optionmultiple times on the command line; It prevents the normal merging ofinput sections with the same name, overriding output section assignmentsin a linker script.
- Display the version number for ld. The -V option alsolists the supported emulations.
- Delete all local symbols.
- Delete all temporary local symbols. (These symbols start withsystem-specific local label prefixes, typically .L for ELF systemsor L for traditional a.out systems.)
- -y symbol
- Print the name of each linked file in which symbol appears. Thisoption may be given any number of times. On many systems it is necessaryto prepend an underscore.
This option is useful when you have an undefined symbol in your link butdon't know where the reference is coming from.
- -Y path
- Add path to the default library search path. This option existsfor Solaris compatibility.
- -z keyword
- The recognized keywords are:
- Combines multiple reloc sections and sorts them to make dynamic symbollookup caching possible.
- Disallows undefined symbols in object files. Undefined symbols inshared libraries are still allowed.
- Marks the object as requiring executable stack.
- This option is only meaningful when building a shared object.It marks the object so that its runtime initialization will occurbefore the runtime initialization of any other objects brought intothe process at the same time. Similarly the runtime finalization ofthe object will occur after the runtime finalization of any otherobjects.
- Marks the object that its symbol table interposes before all symbolsbut the primary executable.
- When generating an executable or shared library, mark it to tell thedynamic linker to defer function call resolution to the point whenthe function is called (lazy binding), rather than at load time.Lazy binding is the default.
- Marks the object that its filters be processed immediately atruntime.
- Allows multiple definitions.
- Disables multiple reloc sections combining.
- Disables production of copy relocs.
- Marks the object that the search for dependencies of this object willignore any default library search paths.
- Marks the object shouldn't be unloaded at runtime.
- Marks the object not available to "dlopen".
- Marks the object can not be dumped by "dldump".
- Marks the object as not requiring executable stack.
- Don't create an ELF "PT_GNU_RELRO" segment header in the object.
- When generating an executable or shared library, mark it to tell thedynamic linker to resolve all symbols when the program is started, orwhen the shared library is linked to using dlopen, instead ofdeferring function call resolution to the point when the function isfirst called.
- Marks the object may contain $ORIGIN.
- Create an ELF "PT_GNU_RELRO" segment header in the object.
- Set the emulation maximum page size to value.
- Set the emulation common page size to value.
Other keywords are ignored for Solaris compatibility.
- -( archives -)
- --start-group archives --end-group
- The archives should be a list of archive files. They may beeither explicit file names, or -l options.
The specified archives are searched repeatedly until no new undefinedreferences are created. Normally, an archive is searched only once inthe order that it is specified on the command line. If a symbol in thatarchive is needed to resolve an undefined symbol referred to by anobject in an archive that appears later on the command line, the linkerwould not be able to resolve that reference. By grouping the archives,they all be searched repeatedly until all possible references areresolved.
Using this option has a significant performance cost. It is best to useit only when there are unavoidable circular references between two ormore archives.
- Tells the linker to accept input files whose architecture cannot berecognised. The assumption is that the user knows what they are doingand deliberately wants to link in these unknown input files. This wasthe default behaviour of the linker, before release 2.14. The defaultbehaviour from release 2.14 onwards is to reject such input files, andso the --accept-unknown-input-arch option has been added torestore the old behaviour.
- This option affects ELF DT_NEEDED tags for dynamic libraries mentionedon the command line after the --as-needed option. Normallythe linker will add a DT_NEEDED tag for each dynamic library mentionedon the command line, regardless of whether the library is actuallyneeded or not. --as-needed causes a DT_NEEDED tag to only beemitted for a library that satisfies an undefined symbol referencefrom a regular object file or, if the library is not found in theDT_NEEDED lists of other libraries linked up to that point, anundefined symbol reference from another dynamic library.--no-as-needed restores the default behaviour.
- These two options have been deprecated because of the similarity oftheir names to the --as-needed and --no-as-neededoptions. They have been replaced by --copy-dt-needed-entriesand --no-copy-dt-needed-entries.
- -assert keyword
- This option is ignored for SunOS compatibility.
- Link against dynamic libraries. This is only meaningful on platformsfor which shared libraries are supported. This option is normally thedefault on such platforms. The different variants of this option arefor compatibility with various systems. You may use this optionmultiple times on the command line: it affects library searching for-l options which follow it.
- Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the dynamicsection. This causes the runtime linker to handle lookups in thisobject and its dependencies to be performed only inside the group.--unresolved-symbols=report-all is implied. This option isonly meaningful on ELF platforms which support shared libraries.
- Do not link against shared libraries. This is only meaningful onplatforms for which shared libraries are supported. The differentvariants of this option are for compatibility with various systems. Youmay use this option multiple times on the command line: it affectslibrary searching for -l options which follow it. Thisoption also implies --unresolved-symbols=report-all. Thisoption can be used with -shared. Doing so means that ashared library is being created but that all of the library's externalreferences must be resolved by pulling in entries from staticlibraries.
- When creating a shared library, bind references to global symbols to thedefinition within the shared library, if any. Normally, it is possiblefor a program linked against a shared library to override the definitionwithin the shared library. This option is only meaningful on ELFplatforms which support shared libraries.
- When creating a shared library, bind references to global functionsymbols to the definition within the shared library, if any.This option is only meaningful on ELF platforms which support sharedlibraries.
- Specify the name of a dynamic list file to the linker. This istypically used when creating shared libraries to specify a list ofglobal symbols whose references shouldn't be bound to the definitionwithin the shared library, or creating dynamically linked executablesto specify a list of symbols which should be added to the symbol tablein the executable. This option is only meaningful on ELF platformswhich support shared libraries.
The format of the dynamic list is the same as the version node withoutscope and node name. See VERSION for more information.
- Include all global data symbols to the dynamic list.
- Provide the builtin dynamic list for C++ operator new and delete. Itis mainly useful for building shared libstdc++.
- Provide the builtin dynamic list for C++ runtime type identification.
- Asks the linker not to check section addresses after they havebeen assigned to see if there are any overlaps. Normally the linker willperform this check, and if it finds any overlaps it will producesuitable error messages. The linker does know about, and does makeallowances for sections in overlays. The default behaviour can berestored by using the command line switch --check-sections.Section overlap is not usually checked for relocatable links. You canforce checking in that case by using the --check-sectionsoption.
- This option affects the treatment of dynamic libraries referred to by DT_NEEDED tags inside ELF dynamic libraries mentioned on thecommand line. Normally the linker will add a DT_NEEDED tag to theoutput binary for each library mentioned in a DT_NEEDED tag in aninput dynamic library. With --no-copy-dt-needed-entriesspecified on the command line however any dynamic libraries thatfollow it will have their DT_NEEDED entries ignored. The defaultbehaviour can be restored with --copy-dt-needed-entries.
This option also has an effect on the resolution of symbols in dynamiclibraries. With the default setting dynamic libraries mentioned onthe command line will be recursively searched, following theirDT_NEEDED tags to other libraries, in order to resolve symbolsrequired by the output binary. With--no-copy-dt-needed-entries specified however the searchingof dynamic libraries that follow it will stop with the dynamiclibrary itself. No DT_NEEDED links will be traversed to resolvesymbols.
- Output a cross reference table. If a linker map file is beinggenerated, the cross reference table is printed to the map file.Otherwise, it is printed on the standard output.
The format of the table is intentionally simple, so that it may beeasily processed by a script if necessary. The symbols are printed out,sorted by name. For each symbol, a list of file names is given. If thesymbol is defined, the first file listed is the location of thedefinition. The remaining files contain references to the symbol.
- This option inhibits the assignment of addresses to common symbols.The script command "INHIBIT_COMMON_ALLOCATION" has the same effect.
The --no-define-common option allows decouplingthe decision to assign addresses to Common symbols from the choiceof the output file type; otherwise a non-Relocatable output typeforces assigning addresses to Common symbols.Using --no-define-common allows Common symbols that are referencedfrom a shared library to be assigned addresses only in the main program.This eliminates the unused duplicate space in the shared library,and also prevents any possible confusion over resolving to the wrongduplicate when there are many dynamic modules with specialized searchpaths for runtime symbol resolution.
- Create a global symbol in the output file, containing the absoluteaddress given by expression. You may use this option as manytimes as necessary to define multiple symbols in the command line. Alimited form of arithmetic is supported for the expression in thiscontext: you may give a hexadecimal constant or the name of an existingsymbol, or use "+" and "-" to add or subtract hexadecimalconstants or symbols. If you need more elaborate expressions, considerusing the linker command language from a script. Note: there should be no whitespace between symbol, the equals sign ("="), andexpression.
- These options control whether to demangle symbol names in error messagesand other output. When the linker is told to demangle, it tries topresent symbol names in a readable fashion: it strips leadingunderscores if they are used by the object file format, and converts C++mangled symbol names into user readable names. Different compilers havedifferent mangling styles. The optional demangling style argument can be usedto choose an appropriate demangling style for your compiler. The linker willdemangle by default unless the environment variable COLLECT_NO_DEMANGLEis set. These options may be used to override the default.
- Set the name of the dynamic linker. This is only meaningful whengenerating dynamically linked ELF executables. The default dynamiclinker is normally correct; don't use this unless you know what you aredoing.
- Treat all warnings as errors. The default behaviour can be restoredwith the option --no-fatal-warnings.
- Make sure that an output file has a .exe suffix.
If a successfully built fully linked output file does not have a".exe" or ".dll" suffix, this option forces the linker to copythe output file to one of the same name with a ".exe" suffix. Thisoption is useful when using unmodified Unix makefiles on a MicrosoftWindows host, since some versions of Windows won't run an image unlessit ends in a ".exe" suffix.
- Enable garbage collection of unused input sections. It is ignored ontargets that do not support this option. The default behaviour (of notperforming this garbage collection) can be restored by specifying--no-gc-sections on the command line.
--gc-sections decides which input sections are used byexamining symbols and relocations. The section containing the entrysymbol and all sections containing symbols undefined on thecommand-line will be kept, as will sections containing symbolsreferenced by dynamic objects. Note that when building sharedlibraries, the linker must assume that any visible symbol isreferenced. Once this initial set of sections has been determined,the linker recursively marks as used any section referenced by theirrelocations. See --entry and --undefined.
This option can be set when doing a partial link (enabled with option-r). In this case the root of symbols kept must be explicitly specified either by an --entry or --undefined option or bya "ENTRY" command in the linker script.
- List all sections removed by garbage collection. The listing isprinted on stderr. This option is only effective if garbagecollection has been enabled via the --gc-sections) option. Thedefault behaviour (of not listing the sections that are removed) canbe restored by specifying --no-print-gc-sections on the commandline.
- Print a summary of the command-line options on the standard output and exit.
- Print a summary of all target specific options on the standard output and exit.
- Print a link map to the file mapfile. See the description of the-M option, above.
- ld normally optimizes for speed over memory usage by caching thesymbol tables of input files in memory. This option tells ld toinstead optimize for memory usage, by rereading the symbol tables asnecessary. This may be required if ld runs out of memory spacewhile linking a large executable.
- -z defs
- Report unresolved symbol references from regular object files. Thisis done even if the linker is creating a non-symbolic shared library.The switch --[no-]allow-shlib-undefined controls thebehaviour for reporting unresolved references found in sharedlibraries being linked in.
- -z muldefs
- Normally when a symbol is defined multiple times, the linker willreport a fatal error. These options allow multiple definitions and thefirst definition will be used.
- Allows or disallows undefined symbols in shared libraries.This switch is similar to --no-undefined except that itdetermines the behaviour when the undefined symbols are in ashared library rather than a regular object file. It does not affecthow undefined symbols in regular object files are handled.
The default behaviour is to report errors for any undefined symbolsreferenced in shared libraries if the linker is being used to createan executable, but to allow them if the linker is being used to createa shared library.
The reasons for allowing undefined symbol references in sharedlibraries specified at link time are that:
- A shared library specified at link time may not be the same as the onethat is available at load time, so the symbol might actually beresolvable at load time.
- There are some operating systems, eg BeOS and HPPA, where undefinedsymbols in shared libraries are normal.
The BeOS kernel for example patches shared libraries at load time toselect whichever function is most appropriate for the currentarchitecture. This is used, for example, to dynamically select anappropriate memset function.
- Normally when a symbol has an undefined version, the linker will ignoreit. This option disallows symbols with undefined version and a fatal errorwill be issued instead.
- Create and use a default symbol version (the soname) for unversionedexported symbols.
- Create and use a default symbol version (the soname) for unversionedimported symbols.
- Normally ld will give an error if you try to link together inputfiles that are mismatched for some reason, perhaps because they havebeen compiled for different processors or for different endiannesses.This option tells ld that it should silently permit such possibleerrors. This option should only be used with care, in cases when youhave taken some special action that ensures that the linker errors areinappropriate.
- Normally ld will give a warning if it finds an incompatiblelibrary during a library search. This option silences the warning.
- Turn off the effect of the --whole-archive option for subsequentarchive files.
- Retain the executable output file whenever it is still usable.Normally, the linker will not produce an output file if it encounterserrors during the link process; it exits without writing an output filewhen it issues any error whatsoever.
- Only search library directories explicitly specified on thecommand line. Library directories specified in linker scripts(including linker scripts specified on the command line) are ignored.
- ld may be configured to support more than one kind of objectfile. If your ld is configured this way, you can use the--oformat option to specify the binary format for the outputobject file. Even when ld is configured to support alternativeobject formats, you don't usually need to specify this, as ldshould be configured to produce as a default output format the mostusual format on each machine. output-format is a text string, thename of a particular format supported by the BFD libraries. (You canlist the available binary formats with objdump -i.) The scriptcommand "OUTPUT_FORMAT" can also specify the output format, butthis option overrides it.
- Create a position independent executable. This is currently only supported onELF platforms. Position independent executables are similar to sharedlibraries in that they are relocated by the dynamic linker to the virtualaddress the OS chooses for them (which can vary between invocations). Likenormal dynamically linked executables they can be executed and symbolsdefined in the executable cannot be overridden by shared libraries.
- This option is ignored for Linux compatibility.
- This option is ignored for SVR4 compatibility.
- An option with machine dependent effects.This option is only supported on a few targets.
On some platforms the --relax option performs target specific,global optimizations that become possible when the linker resolvesaddressing in the program, such as relaxing address modes,synthesizing new instructions, selecting shorter version of currentinstructions, and combinig constant values.
On some platforms these link time global optimizations may make symbolicdebugging of the resulting executable impossible.This is known to be the case for the Matsushita MN10200 and MN10300family of processors.
On platforms where this is not supported, --relax is accepted,but ignored.
On platforms where --relax is accepted the option--no-relax can be used to disable the feature.
- Retain only the symbols listed in the file filename,discarding all others. filename is simply a flat file, with onesymbol name per line. This option is especially useful in environments(such as VxWorks)where a large global symbol table is accumulated gradually, to conserverun-time memory.
--retain-symbols-file does not discard undefined symbols,or symbols needed for relocations.
You may only specify --retain-symbols-file once in the commandline. It overrides -s and -S.
- Add a directory to the runtime library search path. This is used whenlinking an ELF executable with shared objects. All -rpatharguments are concatenated and passed to the runtime linker, which usesthem to locate shared objects at runtime. The -rpath option isalso used when locating shared objects which are needed by sharedobjects explicitly included in the link; see the description of the-rpath-link option. If -rpath is not used when linking anELF executable, the contents of the environment variable"LD_RUN_PATH" will be used if it is defined.
The -rpath option may also be used on SunOS. By default, onSunOS, the linker will form a runtime search patch out of all the-L options it is given. If a -rpath option is used, theruntime search path will be formed exclusively using the -rpathoptions, ignoring the -L options. This can be useful when usinggcc, which adds many -L options which may be on NFS mountedfile systems.
For compatibility with other ELF linkers, if the -R option isfollowed by a directory name, rather than a file name, it is treated asthe -rpath option.
- When using ELF or SunOS, one shared library may require another. Thishappens when an "ld -shared" link includes a shared library as oneof the input files.
When the linker encounters such a dependency when doing a non-shared,non-relocatable link, it will automatically try to locate the requiredshared library and include it in the link, if it is not includedexplicitly. In such a case, the -rpath-link optionspecifies the first set of directories to search. The-rpath-link option may specify a sequence of directory nameseither by specifying a list of names separated by colons, or byappearing multiple times.
This option should be used with caution as it overrides the search paththat may have been hard compiled into a shared library. In such a case itis possible to use unintentionally a different search path than theruntime linker would do.
The linker uses the following search paths to locate required sharedlibraries:
- Any directories specified by -rpath-link options.
- Any directories specified by -rpath options. The differencebetween -rpath and -rpath-link is that directoriesspecified by -rpath options are included in the executable andused at runtime, whereas the -rpath-link option is only effectiveat link time. Searching -rpath in this way is only supportedby native linkers and cross linkers which have been configured withthe --with-sysroot option.
- On an ELF system, for native linkers, if the -rpath and-rpath-link options were not used, search the contents of theenvironment variable "LD_RUN_PATH".
- On SunOS, if the -rpath option was not used, search anydirectories specified using -L options.
- For a native linker, the search the contents of the environmentvariable "LD_LIBRARY_PATH".
- For a native ELF linker, the directories in "DT_RUNPATH" or"DT_RPATH" of a shared library are searched for sharedlibraries needed by it. The "DT_RPATH" entries are ignored if"DT_RUNPATH" entries exist.
- The default directories, normally /lib and /usr/lib.
- For a native linker on an ELF system, if the file /etc/ld.so.confexists, the list of directories found in that file.
If the required shared library is not found, the linker will issue awarning and continue with the link.
- Create a shared library. This is currently only supported on ELF, XCOFFand SunOS platforms. On SunOS, the linker will automatically create ashared library if the -e option is not used and there areundefined symbols in the link.
- This option tells ld to sort the common symbols by alignment inascending or descending order when it places them in the appropriate outputsections. The symbol alignments considered are sixteen-byte or larger,eight-byte, four-byte, two-byte, and one-byte. This is to prevent gapsbetween symbols due to alignment constraints. If no sorting order isspecified, then descending order is assumed.
- This option will apply "SORT_BY_NAME" to all wildcard sectionpatterns in the linker script.
- This option will apply "SORT_BY_ALIGNMENT" to all wildcard sectionpatterns in the linker script.
- Similar to --split-by-reloc but creates a new output section foreach input file when size is reached. size defaults to asize