gcc 编译连接_can not be used when making a shared object; recom

http://sourceware.org/binutils/docs-2.23.1/ld/Options.html#Options

本人的错误是gcc的时候出现了.note.gnu.build-id 这个段号

这个可以通过 编译的时候加上 -Wl,--build-id=none

通过 objdump –h (ELF文件)来查看文件的段号

详细见http://sourceware.org/binutils/docs-2.23.1/ld/Options.html#Options

问题可以参考http://stackoverflow.com/questions/15316384/do-not-pass-build-id-to-linker-from-gcc 来解决

The linker supports a plethora of command-line options, 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, 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. (See the discussion of the `-l' option below.)

Some of the command-line options to ld may be specified at any point in the command line. However, options which refer to files, such as `-l' or `-T', cause the file to be read at the point at which the option appears in the command line, relative to the object files and other file options. Repeating non-file options with a different argument will either have no further effect, or override prior occurrences (those further to the left on the command line) of that option. Options which may be meaningfully specified more than once are noted in the descriptions below.

Non-option arguments are object files or archives which are to be linked together. They may follow, precede, or be mixed in with command-line options, except that an object file argument may not be placed between an option and its argument.

Usually the linker is invoked with at least one object file, but you can specify other forms of binary input files using `-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'.

If the linker cannot recognize the format of an object file, it will assume that it is a linker script. A script specified in this way augments the main linker script used for the link (either the default linker script or the one specified by using `-T'). This feature permits the linker to link against a file which appears to be an object or an archive, but actually merely defines some symbol values, or uses INPUT or GROUP to load other objects. Specifying a script in this way merely augments the main linker script, with the extra commands placed after the main script; use the `-T' option to replace the default linker script entirely, but note the effect of the INSERT command. See Scripts.

For options whose names are a single letter, option arguments must either follow the option letter without intervening whitespace, or be given as separate arguments immediately following the option that requires them.

For options whose names are multiple letters, either one dash or two can precede the option name; for example, `-trace-symbol' and `--trace-symbol' are equivalent. Note—there is one exception to this rule. Multiple letter options that start with a lower case 'o' can only be preceded by two dashes. This is to reduce confusion with the `-o' option. So for example `-omagic' sets the output file name to `magic' whereas `--omagic' sets the NMAGIC flag on the output.

Arguments to multiple-letter options must either be separated from the option name by an equals sign, or be given as separate arguments immediately 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 are accepted.

Note—if the linker is being invoked indirectly, via a compiler driver (e.g. `gcc') then all the linker command line options should be prefixed by `-Wl,' (or whatever is appropriate for the particular compiler driver) like this:

       gcc -Wl,--start-group foo.o bar.o -Wl,--end-group

This is important, because otherwise the compiler driver program may silently drop the linker options, resulting in a bad link. Confusion may also arise when passing options that require values through a driver, as the use of a space between option and argument acts as a separator, and causes the driver to pass only the option to the linker and the argument to the compiler. In this case, it is simplest to use the 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 GNU linker:

@ file

Read command-line options from  file. The options read are inserted in place of the original @ file option. If  file does not exist, or cannot be read, then the option will be treated literally, and not removed.

Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with 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  keyword argument must be one of the strings ` archive', ` shared', or ` default'. ` -aarchive' is functionally equivalent to ` -Bstatic', and the other two keywords are functionally equivalent to ` -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_SONAME specified in the library. If specified multiple times  DT_AUDIT will contain a colon separated list of audit interfaces to use. If the linker finds 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-audit interface.

-A  architecture

--architecture= architecture

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 identifies the particular architecture in the 960 family, enabling some safeguards and modifying the archive-library search path. See  ld and the Intel 960 family, for details.

Future releases of ld may support similar functionality for other architecture families.

-b  input-format --format= input-format

ld may be configured to support more than one kind of object file. If your  ld is configured this way, you can use the ` -b' option to specify the binary format for input object files that follow this option on the command line. Even when  ld is configured to support alternative object formats, you don't usually need to specify this, as  ld should be configured 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 supported by the BFD libraries. (You can list the available binary formats with ` objdump -i'.) See  BFD.

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 particular format.

The default format is taken from the environment variable GNUTARGET. See Environment. You can also define the input format from a script, using the command TARGET; see Format Commands.

-c  MRI-commandfile --mri-script= MRI-commandfile

For compatibility with linkers produced by MRI,  ld accepts script files written in an alternate, restricted command language, described in  MRI Compatible Script Files. Introduce MRI script files with the option ` -c'; use the ` -T' option to run linker scripts written in the general-purpose  ld scripting language. If  MRI-cmdfile does not exist,  ld looks for it in the directories specified by any ` -L' options.

-d -dc -dp

These three options are equivalent; multiple forms are supported for compatibility with other linkers. They assign space to common symbols even if a relocatable output file is specified (with ` -r'). The script command  FORCE_COMMON_ALLOCATION has the same effect. See  Miscellaneous Commands.

--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_SONAME specified in the library. If specified multiple times  DT_DEPAUDIT will contain a colon separated list of audit interfaces to use. This option is only meaningful on ELF platforms supporting the rtld-audit interface. The -P option is provided for Solaris compatibility.

-e  entry --entry= entry

Use  entry as the explicit symbol for beginning execution of your program, rather than the default entry point. If there is no symbol named  entry, the linker will try to parse  entry as a number, and use that as the entry address (the number will be interpreted in base 10; you may use a leading ` 0x' for base 16, or a leading ` 0' for base 8). See  Entry Point, for a discussion of defaults and other ways of specifying the entry point.

--exclude-libs  lib , lib ,...

Specifies a list of archive libraries from which symbols should not be automatically exported. The library names may be delimited by commas or colons. Specifying  --exclude-libs ALL excludes symbols in all archive libraries from automatic export. This option is available only for the i386 PE targeted port of the linker and for ELF targeted ports. For i386 PE, symbols explicitly listed in a .def file are still exported, regardless of this option. For ELF targeted ports, symbols affected by this option will be treated as hidden.

--exclude-modules-for-implib  module , module ,...

Specifies a list of object files or archive members, from which symbols should not be automatically exported, but which should be copied wholesale into the import library being generated during the link. The module names may be delimited by commas or colons, and must match exactly the filenames used by  ld to open the files; for archive members, this is simply the member name, but for object files the name listed must include and match precisely any path used to specify the input file on the linker's command-line. This option is available only for the i386 PE targeted port of the linker. Symbols explicitly listed in a .def file are still exported, regardless of this option.

-E --export-dynamic --no-export-dynamic

When creating a dynamically linked executable, using the  -E option or the  --export-dynamic option causes the linker to add all symbols to the dynamic symbol table. The dynamic symbol table is the set 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), the dynamic symbol table will normally contain only those symbols which are referenced by some dynamic object mentioned in the link.

If you use dlopen to load a dynamic object which needs to refer back to the symbols defined by the program, rather than some other dynamic object, then you will probably need to use this option when linking the program itself.

You can also use the dynamic list to control what symbols should be 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 targets support a similar function to export all symbols from a DLL or EXE; see the description of `--export-all-symbols' below.

-EB

Link big-endian objects. This affects the default output format.

-EL

Link little-endian objects. This affects the default output format.

-f  name --auxiliary= name

When creating an ELF shared object, set the internal 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.

If you later link a program against this filter object, then, when you run the program, the dynamic linker will see the DT_AUXILIARY field. If the dynamic linker resolves any symbols from the filter object, it will first check whether there is a definition in the shared object name. If there is one, it will be used instead of the definition in the filter object. The shared object name need not exist. Thus the shared object name may be used to provide an alternative implementation of certain functions, perhaps for debugging or for machine specific performance.

This option may be specified more than once. The DT_AUXILIARY entries will be created in the order in which they appear on the command line.

-F  name --filter= name

When creating an ELF shared object, set the internal DT_FILTER field to the specified name. This tells the dynamic linker that the symbol table of the shared object which is being created should be used as a filter on the symbol table of the shared object  name.

If you later link a program against this filter object, then, when you run the program, the dynamic linker will see the DT_FILTER field. The dynamic linker will resolve symbols according to the symbol table of the filter object as usual, but it will actually link to the definitions found in the shared object name. Thus the filter object can be used to select a subset of the symbols provided by the object name.

Some older linkers used the -F option throughout a compilation toolchain for specifying object-file format for both input and output object files. The gnu linker uses other mechanisms for this purpose: the -b, --format, --oformat options, theTARGET command in linker scripts, and the GNUTARGET environment variable. The gnu linker will ignore the -F option when not creating an ELF shared object.

-fini= name

When creating an ELF executable or shared object, call NAME when the executable or shared object is unloaded, by setting DT_FINI to the address of the function. By default, the linker uses  _fini as the function to call.

-g

Ignored. Provided for compatibility with other tools.

-G  value --gpsize= value

Set the maximum size of objects to be optimized using the GP register to  size. This is only meaningful for object file formats such as MIPS ECOFF which supports putting large and small objects into different sections. This is ignored for other object file formats.

-h  name -soname= name

When creating an ELF shared object, set the internal 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.

-i

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

-init= name

When creating an ELF executable or shared object, call NAME when the executable or shared object is loaded, by setting DT_INIT to the address of the function. By default, the linker uses  _init as the function to call.

-l  namespec --library= namespec

Add the archive or object file specified by  namespec to the list of files to link. This option may be used any number of times. If  namespec is of the form  :filename,  ld will search the library path for a file called  filename, otherwise it will search the library path for a file called  libnamespec.a.

On systems which support shared libraries, ld may also search for files other than libnamespec.a. Specifically, on ELF and SunOS systems, ld will search a directory for a library called libnamespec.so before searching for one called libnamespec.a. (By convention, a .so extension indicates a shared library.) Note that this behavior does not apply to :filename, which always specifies a file called filename.

The linker will search an archive only once, at the location where it is specified on the command line. If the archive defines a symbol which was undefined in some object which appeared before the archive on the command line, the linker will include the appropriate file(s) from the archive. However, an undefined symbol in an object appearing later on the command line will not cause the linker to search the archive again.

See the -( option for a way to force the linker to search archives 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 the behaviour of the AIX linker.

-L  searchdir --library-path= searchdir

Add path  searchdir to the list of paths that  ld will search for archive libraries and  ld control scripts. You may use this option any number of times. The directories are searched in the order in which they are specified on the command line. Directories specified on the command line are searched before the default directories. All  -L options apply to all  -l options, regardless of the order in which the options appear.  -L options do not affect how  ld searches for a linker script unless  -T option is specified.

If searchdir begins with =, then the = will be replaced by 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 in some cases also on how it was configured. See Environment.

The paths can also be specified in a link script with the SEARCH_DIR command. Directories specified this way are searched at the point in which the linker script appears in the command line.

-m  emulation

Emulate the  emulation linker. You can list the available emulations 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 was configured.

-M --print-map

Print a link map to the standard output. A link map provides information 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 symbol which caused the archive member to be brought in.
• The values assigned to symbols.

  Note - symbols whose values are computed by an expression which involves a reference to a previous value of the same symbol may not have correct result displayed in the link map. This is because the linker discards intermediate results and only retains the final value of an expression. Under such circumstances the linker will display the final value enclosed by square brackets. Thus for example a linker script containing:

                    foo = 1
                    foo = foo * 4
                    foo = foo + 8
            

  will produce the following output in the link map if the -M option is used:

                    0x00000001                foo = 0x1
                    [0x0000000c]                foo = (foo * 0x4)
                    [0x0000000c]                foo = (foo + 0x8)
            

  See Expressions for more information about expressions in linker scripts.

-n --nmagic

Turn off page alignment of sections, and disable linking against shared libraries. If the output format supports Unix style magic numbers, mark the output as  NMAGIC.

-N --omagic

Set the text and data sections to be readable and writable. Also, do not page-align the data segment, and disable linking against shared libraries. If the output format supports Unix style magic numbers, mark the output as  OMAGIC. Note: Although a writable text section is allowed for PE-COFF targets, it does not conform to the format specification published by Microsoft.

--no-omagic

This option negates most of the effects of the  -N option. It sets the text section to be read-only, and forces the data segment to be page-aligned. Note - this option does not enable linking against shared libraries. Use  -Bdynamic for this.

-o  output --output= output

Use  output as the 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.

-O  level

If  level is a numeric values greater than zero  ld optimizes the output. This might take significantly longer and therefore probably should only be enabled for the final binary. At the moment this option only affects ELF shared library generation. Future releases of the linker may make more use of this option. Also currently there is no difference in the linker's behaviour for different non-zero values of this option. Again this may change with future releases.

-q --emit-relocs

Leave relocation sections and contents in fully linked executables. Post link analysis and optimization tools may need this information in order to perform correct modifications of executables. This results in larger executables.

This option is currently only supported on ELF platforms.

--force-dynamic

Force the output file to have dynamic sections. This option is specific to VxWorks targets.

-r --relocatable

Generate 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; 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 any relocations. Different output formats can have further restrictions; for example some a.out-based formats do not support partial linking with input files in other formats at all.

This option does the same thing as `-i'.

-R  filename --just-symbols= 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. You may use this option more than once.

For compatibility with other ELF linkers, if the -R option is followed by a directory name, rather than a file name, it is treated as the -rpath option.

-s --strip-all

Omit all symbol information from the output file.

-S --strip-debug

Omit debugger symbol information (but not all symbols) from the output file.

-t --trace

Print the names of the input files as  ld processes them.

-T  scriptfile --script= scriptfile

Use  scriptfile as the linker script. This script replaces  ld's default linker script (rather than adding to it), so  commandfile must specify everything necessary to describe the output file. See  Scripts. If  scriptfile does not exist in the current directory,  ld looks for it in the directories specified by any preceding ` -L' options. Multiple ` -T' options accumulate.

-dT  scriptfile --default-script= scriptfile

Use  scriptfile as the default linker script. See  Scripts.

This option is similar to the --script option except that processing of the script is delayed until after the rest of the command line has been processed. This allows options placed after the --default-script option on the command line to affect the behaviour of the linker script, which can be important when the linker command line cannot be directly controlled by the user. (eg because the command line is being constructed by another tool, such as `gcc').

-u  symbol --undefined= symbol

Force  symbol to be entered in the output file as an undefined symbol. Doing 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. This option is equivalent to the  EXTERN linker script command.

-Ur

For anything other than C++ programs, this option is equivalent to ` -r': it generates relocatable output—i.e., an output file that can in turn serve as input to  ld. When linking C++ programs, ` -Ur'  does resolve references to constructors, unlike ` -r'. It does not work to use ` -Ur' on files that were themselves linked with ` -Ur'; once the constructor table has been built, it cannot be added to. Use ` -Ur' only for the last partial link, and ` -r' for the others.

--unique[= SECTION ]

Creates a separate output section for every input section matching  SECTION, or if the optional wildcard  SECTION argument is missing, for every orphan input section. An orphan section is one not specifically mentioned in a linker script. You may use this option multiple times on the command line; It prevents the normal merging of input sections with the same name, overriding output section assignments in a linker script.

-v --version -V

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

-x --discard-all

Delete all local symbols.

-X --discard-locals

Delete all temporary local symbols. (These symbols start with system-specific local label prefixes, typically ` .L' for ELF systems or ` L' for traditional a.out systems.)

-y  symbol --trace-symbol= symbol

Print the name of each linked file in which  symbol appears. This option may be given any number of times. On many systems it is necessary to prepend an underscore.

This option is useful when you have an undefined symbol in your link but don't know where the reference is coming from.

-Y  path

Add  path to the default library search path. This option exists for Solaris compatibility.

-z  keyword

The recognized keywords are:

` combreloc'

Combines multiple reloc sections and sorts them to make dynamic symbol lookup caching possible. 

` defs'

Disallows undefined symbols in object files. Undefined symbols in shared libraries are still allowed. 

` execstack'

Marks the object as requiring executable stack. 

` initfirst'

This option is only meaningful when building a shared object. It marks the object so that its runtime initialization will occur before the runtime initialization of any other objects brought into the process at the same time. Similarly the runtime finalization of the object will occur after the runtime finalization of any other objects. 

` interpose'

Marks the object that its symbol table interposes before all symbols but the primary executable. 

` lazy'

When generating an executable or shared library, mark it to tell the dynamic linker to defer function call resolution to the point when the function is called (lazy binding), rather than at load time. Lazy binding is the default. 

` loadfltr'

Marks the object that its filters be processed immediately at runtime. 

` muldefs'

Allows multiple definitions. 

` nocombreloc'

Disables multiple reloc sections combining. 

` nocopyreloc'

Disables production of copy relocs. 

` nodefaultlib'

Marks the object that the search for dependencies of this object will ignore any default library search paths. 

` nodelete'

Marks the object shouldn't be unloaded at runtime. 

` nodlopen'

Marks the object not available to  dlopen. 

` nodump'

Marks the object can not be dumped by  dldump. 

` noexecstack'

Marks the object as not requiring executable stack. 

` norelro'

Don't create an ELF  PT_GNU_RELRO segment header in the object. 

` now'

When generating an executable or shared library, mark it to tell the dynamic linker to resolve all symbols when the program is started, or when the shared library is linked to using dlopen, instead of deferring function call resolution to the point when the function is first called. 

` origin'

Marks the object may contain $ORIGIN. 

` relro'

Create an ELF  PT_GNU_RELRO segment header in the object. 

` max-page-size=value'

Set the emulation maximum page size to  value. 

` common-page-size=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 be either explicit file names, or ` -l' options.

The specified archives are searched repeatedly until no new undefined references are created. Normally, an archive is searched only once in the order that it is specified on the command line. If a symbol in that archive is needed to resolve an undefined symbol referred to by an object in an archive that appears later on the command line, the linker would not be able to resolve that reference. By grouping the archives, they all be searched repeatedly until all possible references are resolved.

Using this option has a significant performance cost. It is best to use it only when there are unavoidable circular references between two or more archives.

--accept-unknown-input-arch --no-accept-unknown-input-arch

Tells the linker to accept input files whose architecture cannot be recognised. The assumption is that the user knows what they are doing and deliberately wants to link in these unknown input files. This was the default behaviour of the linker, before release 2.14. The default behaviour from release 2.14 onwards is to reject such input files, and so the ` --accept-unknown-input-arch' option has been added to restore the old behaviour.

--as-needed --no-as-needed

This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the  --as-needed option. Normally the linker will add a DT_NEEDED tag for each dynamic library mentioned on the command line, regardless of whether the library is actually needed or not.  --as-needed causes a DT_NEEDED tag to only be emitted for a library that satisfies an undefined symbol reference from a regular object file or, if the library is not found in the DT_NEEDED lists of other libraries linked up to that point, an undefined symbol reference from another dynamic library.  --no-as-needed restores the default behaviour.

--add-needed --no-add-needed

These two options have been deprecated because of the similarity of their names to the  --as-needed and  --no-as-needed options. They have been replaced by  --copy-dt-needed-entries and  --no-copy-dt-needed-entries.

-assert  keyword

This option is ignored for SunOS compatibility.

-Bdynamic -dy -call_shared

Link against dynamic libraries. This is only meaningful on platforms for which shared libraries are supported. This option is normally the default on such platforms. The different variants of this option are for compatibility with various systems. You may use this option multiple times on the command line: it affects library searching for  -l options which follow it.

-Bgroup

Set the  DF_1_GROUP flag in the  DT_FLAGS_1 entry in the dynamic section. This causes the runtime linker to handle lookups in this object and its dependencies to be performed only inside the group.  --unresolved-symbols=report-all is implied. This option is only meaningful on ELF platforms which support shared libraries.

-Bstatic -dn -non_shared -static

Do not link against shared libraries. This is only meaningful on platforms for which shared libraries are supported. The different variants of this option are for compatibility with various systems. You may use this option multiple times on the command line: it affects library searching for  -l options which follow it. This option also implies  --unresolved-symbols=report-all. This option can be used with  -shared. Doing so means that a shared library is being created but that all of the library's external references must be resolved by pulling in entries from static 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 option is only meaningful on ELF platforms which support shared libraries.

-Bsymbolic-functions

When creating a shared library, bind references to global function symbols to the definition within the shared library, if any. This option is only meaningful on ELF platforms which support shared libraries.

--dynamic-list= dynamic-list-file

Specify the name of a dynamic list file to the linker. This is typically used when creating shared libraries to specify a list of global symbols whose references shouldn't be bound to the definition within the shared library, or creating dynamically linked executables to specify a list of symbols which should be added to the symbol table in the executable. This option is only meaningful on ELF platforms which support shared libraries.

The format of the dynamic list is the same as the version node without scope and node name. See VERSION for more information.

--dynamic-list-data

Include all global data symbols to the dynamic list.

--dynamic-list-cpp-new

Provide the builtin dynamic list for C++ operator new and delete. It is mainly useful for building shared libstdc++.

--dynamic-list-cpp-typeinfo

Provide the builtin dynamic list for C++ runtime type identification.

--check-sections --no-check-sections

Asks the linker  not to check section addresses after they have been assigned to see if there are any overlaps. Normally the linker will perform this check, and if it finds any overlaps it will produce suitable error messages. The linker does know about, and does make allowances for sections in overlays. The default behaviour can be restored by using the command line switch  --check-sections. Section overlap is not usually checked for relocatable links. You can force checking in that case by using the  --check-sections option.

--copy-dt-needed-entries --no-copy-dt-needed-entries

This option affects the treatment of dynamic libraries referred to by DT_NEEDED tags  inside ELF dynamic libraries mentioned on the command line. Normally the linker won't add a DT_NEEDED tag to the output binary for each library mentioned in a DT_NEEDED tag in an input dynamic library. With  --copy-dt-needed-entries specified on the command line however any dynamic libraries that follow it will have their DT_NEEDED entries added. The default behaviour can be restored with  --no-copy-dt-needed-entries.

This option also has an effect on the resolution of symbols in dynamic libraries. With --copy-dt-needed-entries dynamic libraries mentioned on the command line will be recursively searched, following their DT_NEEDED tags to other libraries, in order to resolve symbols required by the output binary. With the default setting however the searching of dynamic libraries that follow it will stop with the dynamic library itself. No DT_NEEDED links will be traversed to resolve symbols.

--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.

The format of the table is intentionally simple, so that it may be easily 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 the symbol is defined, the first file listed is the location of the definition. The remaining files contain references to the symbol.

--no-define-common

This option inhibits the assignment of addresses to common symbols. The script command  INHIBIT_COMMON_ALLOCATION has the same effect. See  Miscellaneous Commands.

The `--no-define-common' option allows decoupling the decision to assign addresses to Common symbols from the choice of the output file type; otherwise a non-Relocatable output type forces assigning addresses to Common symbols. Using `--no-define-common' allows Common symbols that are referenced from 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 wrong duplicate when there are many dynamic modules with specialized search paths for runtime symbol resolution.

--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 multiple symbols in the command line. A limited form of arithmetic is supported for the  expression in this context: you may give a hexadecimal constant or the name of an existing symbol, or use  + and  - to add or subtract hexadecimal constants or symbols. If you need more elaborate expressions, consider using the linker command language from a script (see  Assignment: Symbol Definitions).  Note: there should be no white space between  symbol, the equals sign (“<=>”), and  expression.

--demangle[= style ] --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 leading underscores if they are used by the object file format, and converts C++ mangled symbol names into user readable names. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler. The linker will demangle by default unless the environment variable ` COLLECT_NO_DEMANGLE' is set. These options may be used to override the default.

-I file --dynamic-linker= file

Set the name of the dynamic linker. This is only meaningful when generating dynamically linked ELF executables. The default dynamic linker is normally correct; don't use this unless you know what you are doing.

--fatal-warnings --no-fatal-warnings

Treat all warnings as errors. The default behaviour can be restored with the option  --no-fatal-warnings.

--force-exe-suffix

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 copy the output file to one of the same name with a .exe suffix. This option is useful when using unmodified Unix makefiles on a Microsoft Windows host, since some versions of Windows won't run an image unless it ends in a .exe suffix.

--gc-sections --no-gc-sections

Enable garbage collection of unused input sections. It is ignored on targets that do not support this option. The default behaviour (of not performing this garbage collection) can be restored by specifying ` --no-gc-sections' on the command line.

`--gc-sections' decides which input sections are used by examining symbols and relocations. The section containing the entry symbol and all sections containing symbols undefined on the command-line will be kept, as will sections containing symbols referenced by dynamic objects. Note that when building shared libraries, the linker must assume that any visible symbol is referenced. Once this initial set of sections has been determined, the linker recursively marks as used any section referenced by their relocations. 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 by a ENTRY command in the linker script.

--print-gc-sections --no-print-gc-sections

List all sections removed by garbage collection. The listing is printed on stderr. This option is only effective if garbage collection has been enabled via the ` --gc-sections') option. The default behaviour (of not listing the sections that are removed) can be restored by specifying ` --no-print-gc-sections' on the command line.

--print-output-format

Print the name of the default output format (perhaps influenced by other command-line options). This is the string that would appear in an  OUTPUT_FORMAT linker script command (see  File Commands).

--help

Print a summary of the command-line options on the standard output and exit.

--target-help

Print a summary of all target specific options on the standard output and exit.

-Map= mapfile

Print a link map to the file  mapfile. See the description of the  -M option, above.

--no-keep-memory

ld normally optimizes for speed over memory usage by caching the symbol tables of input files in memory. This option tells  ld to instead optimize for memory usage, by rereading the symbol tables as necessary. This may be required if  ld runs out of memory space while linking a large executable.

--no-undefined -z defs

Report unresolved symbol references from regular object files. This is done even if the linker is creating a non-symbolic shared library. The switch  --[no-]allow-shlib-undefined controls the behaviour for reporting unresolved references found in shared libraries being linked in.

--allow-multiple-definition -z muldefs

Normally when a symbol is defined multiple times, the linker will report a fatal error. These options allow multiple definitions and the first definition will be used.

--allow-shlib-undefined --no-allow-shlib-undefined

Allows or disallows undefined symbols in shared libraries. This switch is similar to  --no-undefined except that it determines the behaviour when the undefined symbols are in a shared library rather than a regular object file. It does not affect how undefined symbols in regular object files are handled.

The default behaviour is to report errors for any undefined symbols referenced in shared libraries if the linker is being used to create an executable, but to allow them if the linker is being used to create a shared library.

The reasons for allowing undefined symbol references in shared libraries specified at link time are that:

• A shared library specified at link time may not be the same as the one that is available at load time, so the symbol might actually be resolvable at load time.
• There are some operating systems, eg BeOS and HPPA, where undefined symbols in shared libraries are normal.

  The BeOS kernel for example patches shared libraries at load time to select whichever function is most appropriate for the current architecture. This is used, for example, to dynamically select an appropriate memset function.

--no-undefined-version

Normally when a symbol has an undefined version, the linker will ignore it. This option disallows symbols with undefined version and a fatal error will be issued instead.

--default-symver

Create and use a default symbol version (the soname) for unversioned exported symbols.

--default-imported-symver

Create and use a default symbol version (the soname) for unversioned imported symbols.

--no-warn-mismatch

Normally  ld 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  ld 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.

--no-warn-search-mismatch

Normally  ld will give a warning if it finds an incompatible library during a library search. This option silences the warning.

--no-whole-archive

Turn off the effect of the  --whole-archive option for subsequent archive files.

--noinhibit-exec

Retain the executable output file whenever it is still usable. Normally, the linker will not produce an output file if it encounters errors during the link process; it exits without writing an output file when it issues any error whatsoever.

-nostdlib

Only search library directories explicitly specified on the command line. Library directories specified in linker scripts (including linker scripts specified on the command line) are ignored.

--oformat= output-format

ld may be configured to support more than one kind of object file. If your  ld is configured this way, you can use the ` --oformat' option to specify the binary format for the output object file. Even when  ld is configured to support alternative object formats, you don't usually need to specify this, as  ld should be configured to produce as a default output format the most usual format on each machine.  output-format is a text string, the name of a particular format supported by the BFD libraries. (You can list the available binary formats with ` objdump -i'.) The script command  OUTPUT_FORMAT can also specify the output format, but this option overrides it. See  BFD.

-pie --pic-executable

Create a position independent executable. This is currently only supported on ELF platforms. Position independent executables are similar to shared libraries in that they are relocated by the dynamic linker to the virtual address the OS chooses for them (which can vary between invocations). Like normal dynamically linked executables they can be executed and symbols defined in the executable cannot be overridden by shared libraries.

-qmagic

This option is ignored for Linux compatibility.

-Qy

This option is ignored for SVR4 compatibility.

--relax --no-relax

An option with machine dependent effects. This option is only supported on a few targets. See  ld and the H8/300. See  ld and the Intel 960 family. See  ld and Xtensa Processors. See  ld and the 68HC11 and 68HC12. See  ld and PowerPC 32-bit ELF Support.

On some platforms the `--relax' option performs target specific, global optimizations that become possible when the linker resolves addressing in the program, such as relaxing address modes, synthesizing new instructions, selecting shorter version of current instructions, and combinig constant values.

On some platforms these link time global optimizations may make symbolic debugging of the resulting executable impossible. This is known to be the case for the Matsushita MN10200 and MN10300 family 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-symbols-file= filename

Retain  only the symbols listed in the file  filename, discarding all others.  filename is simply a flat file, with one symbol name per line. This option is especially useful in environments (such as VxWorks) where a large global symbol table is accumulated gradually, to conserve run-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 command line. It overrides `-s' and `-S'. 

-rpath= dir

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  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 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 -rpathoptions, ignoring the -L options. This can be useful when using gcc, which adds many -L options which may be on NFS mounted file systems.

For compatibility with other ELF linkers, if the -R option is followed by a directory name, rather than a file name, it is treated as the -rpath option.

-rpath-link= dir

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-relocatable link, it will automatically try to locate the required shared library and include it in the link, if it is not included explicitly. In such a case, the -rpath-linkoption 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.

This option should be used with caution as it overrides the search path that may have been hard compiled into a shared library. In such a case it is possible to use unintentionally a different search path than the runtime linker would do.

The linker uses the following search paths to locate required shared libraries:

1. Any directories specified by -rpath-link options.
2. Any directories specified by -rpath options. The difference between -rpath and -rpath-link is that directories specified by -rpath options are included in the executable and used at runtime, whereas the -rpath-link option is only effective at link time. Searching -rpath in this way is only supported by native linkers and cross linkers which have been configured with the --with-sysroot option.
3. On an ELF system, for native linkers, if the -rpath and -rpath-link options were not used, search the contents of the environment variable LD_RUN_PATH.
4. On SunOS, if the -rpath option was not used, search any directories specified using -L options.
5. For a native linker, the search the contents of the environment variable LD_LIBRARY_PATH.
6. For a native ELF linker, the directories in DT_RUNPATH or DT_RPATH of a shared library are searched for shared libraries needed by it. The DT_RPATH entries are ignored if DT_RUNPATH entries exist.
7. The default directories, normally /lib and /usr/lib.
8. For a native linker on an ELF system, if the file /etc/ld.so.conf exists, the list of directories found in that file.

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

-shared -Bshareable

Create a shared library. This is currently only supported on ELF, XCOFF and SunOS platforms. On SunOS, the linker will automatically create a shared library if the  -e option is not used and there are undefined symbols in the link.

--sort-common --sort-common=ascending --sort-common=descending

This option tells  ld to sort the common symbols by alignment in ascending or descending order when it places them in the appropriate output sections. The symbol alignments considered are sixteen-byte or larger, eight-byte, four-byte, two-byte, and one-byte. This is to prevent gaps between symbols due to alignment constraints. If no sorting order is specified, then descending order is assumed.

--sort-section=name

This option will apply  SORT_BY_NAME to all wildcard section patterns in the linker script.

--sort-section=alignment

This option will apply  SORT_BY_ALIGNMENT to all wildcard section patterns in the linker script.

--split-by-file[= size ]

Similar to  --split-by-reloc but creates a new output section for each input file when  size is reached.  size defaults to a size of 1 if not given.

--split-by-reloc[= count ]

Tries 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 files 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 linker will not split up individual input sections for redistribution, so if a single input section contains more than  count relocations one output section will contain that many relocations.  count defaults to a value of 32768.

--stats

Compute and display statistics about the operation of the linker, such as execution time and memory usage.

--sysroot= directory

Use  directory as the location of the sysroot, overriding the configure-time default. This option is only supported by linkers that were configured using  --with-sysroot.

--traditional-format

For some targets, the output of  ld is different in some ways from the output of some existing linker. This switch requests  ld to use the traditional format instead.

For example, on SunOS, ld combines duplicate entries in the symbol string table. This can reduce the size of an output file with full debugging information by over 30 percent. Unfortunately, the SunOS dbx program can not read the resulting program (gdb has no trouble). The `--traditional-format' switch tells ld to not combine duplicate entries.

--section-start= sectionname = org

Locate a section in the output file at the absolute address given by  org. You may use this option as many times as necessary to locate multiple sections in the command line.  org must be a single hexadecimal integer; for compatibility with other linkers, you may omit the leading ` 0x' usually associated with hexadecimal values.  Note: there should be no white space between  sectionname, the equals sign (“<=>”), and  org.

-Tbss= org -Tdata= org -Ttext= org

Same as  --section-start, with  .bss,  .data or  .text as the  sectionname.

-Ttext-segment= org

When creating an ELF executable or shared object, it will set the address of the first byte of the text segment.

--unresolved-symbols= method

Determine how to handle unresolved symbols. There are four possible values for ` method':

` ignore-all'

Do not report any unresolved symbols. 

` report-all'

Report all unresolved symbols. This is the default. 

` ignore-in-object-files'

Report unresolved symbols that are contained in shared libraries, but ignore them if they come from regular object files. 

` ignore-in-shared-libs'

Report unresolved symbols that come from regular object files, but ignore them if they come from shared libraries. This can be useful when creating a dynamic binary and it is known that all the shared libraries that it should be referencing are included on the linker's command line.

The behaviour for shared libraries on their own can also be controlled by the --[no-]allow-shlib-undefined option.

Normally the linker will generate an error message for each reported unresolved symbol but the option --warn-unresolved-symbols can change this to a warning.

--dll-verbose --verbose[= NUMBER ]

Display the version number for  ld and list the linker emulations supported. Display which input files can and cannot be opened. Display the linker script being used by the linker. If the optional  NUMBER argument > 1, plugin symbol status will also be displayed.

--version-script= version-scriptfile

Specify the name of a version script to the linker. This is typically used when creating shared libraries to specify additional information about the version hierarchy for the library being created. This option is only fully supported on ELF platforms which support shared libraries; see  VERSION. It is partially supported on PE platforms, which can use version scripts to filter symbol visibility in auto-export mode: any symbols marked ` local' in the version script will not be exported. See  WIN32.

--warn-common

Warn when a common symbol is combined with another common symbol or with a symbol definition. Unix linkers allow this somewhat sloppy practise, but linkers on some other operating systems do not. This option allows you to find potential problems from combining global symbols. Unfortunately, some C libraries use this practise, so you may get some warnings about symbols in the libraries as well as in your programs.

There are three kinds of global symbols, illustrated here by C examples:

` int i = 1;'

A definition, which goes in the initialized data section of the output file. 

` extern int i;'

An undefined reference, which does not allocate space. There must be either a definition or a common symbol for the variable somewhere. 

` int i;'

A common symbol. If there are only (one or more) common symbols for a variable, it goes in the uninitialized data area of the output file. The linker merges multiple common symbols for the same variable into a single symbol. If they are of different sizes, it picks the largest size. The linker turns a common symbol into a declaration, if there is a definition of the same variable.

The `--warn-common' option can produce five kinds of warnings. Each warning consists of a pair of lines: the first describes the symbol just encountered, and the second describes the previous symbol encountered with the same name. One or both of the two symbols will be a common symbol.

1. Turning a common symbol into a reference, because there is already a definition for the symbol.

                  file(section): warning: common of `symbol'
                     overridden by definition
                  file(section): warning: defined here
             

2. Turning a common symbol into a reference, because a later definition for the symbol is encountered. This is the same as the previous case, except that the symbols are encountered in a different order.

                  file(section): warning: definition of `symbol'
                     overriding common
                  file(section): warning: common is here
             

3. Merging a common symbol with a previous same-sized common symbol.

                  file(section): warning: multiple common
                     of `symbol'
                  file(section): warning: previous common is here
             

4. Merging a common symbol with a previous larger common symbol.

                  file(section): warning: common of `symbol'
                     overridden by larger common
                  file(section): warning: larger common is here
             

5. Merging a common symbol with a previous smaller common symbol. This is the same as the previous case, except that the symbols are encountered in a different order.

                  file(section): warning: common of `symbol'
                     overriding smaller common
                  file(section): warning: smaller common is here
             

--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 global constructors.

--warn-multiple-gp

Warn if multiple global pointer values are required in the output file. This is only meaningful for certain processors, such as the Alpha. Specifically, some processors put large-valued constants in a special section. A special register (the global pointer) points into the middle of this section, so that constants can be loaded efficiently via a base-register relative addressing mode. Since the offset in base-register relative mode is fixed and relatively small (e.g., 16 bits), this limits the maximum size of the constant pool. Thus, in large programs, it is often necessary to use multiple global pointer values in order to be able to address all possible constants. This option causes a warning to be issued whenever this case occurs.

--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 (see  SECTIONS).

--warn-shared-textrel

Warn if the linker adds a DT_TEXTREL to a shared object.

--warn-alternate-em

Warn if an object has alternate ELF machine code.

--warn-unresolved-symbols

If the linker is going to report an unresolved symbol (see the option  --unresolved-symbols) it will normally generate an error. This option makes it generate a warning instead.

--error-unresolved-symbols

This restores the linker's default behaviour of generating errors when it is reporting unresolved symbols.

--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 normally used to turn an archive file into a shared library, forcing every object to be included in the resulting shared library. This option may be used more than once.

Two notes when using this option from gcc: First, gcc doesn't know about this option, so you have to use -Wl,-whole-archive. Second, don't forget to use -Wl,-no-whole-archive after your list of archives, because gcc will add its own list of archives to your link and you may not want this flag to affect those as well.

--wrap= symbol

Use a wrapper function for  symbol. Any undefined reference to  symbol will be resolved to  __wrap_ symbol. Any undefined reference to  __real_ symbol will be resolved to  symbol.

This can be used to provide a wrapper for a system function. The wrapper function should be called __wrap_symbol. If it wishes to call the system function, it should call __real_symbol.

Here is a trivial example:

          void *
          __wrap_malloc (size_t c)
          {
            printf ("malloc called with %zu\n", c);
            return __real_malloc (c);
          }
     

If you link other code with this file using --wrap malloc, then all calls to malloc will call the function __wrap_malloc instead. The call to __real_malloc in __wrap_malloc will call the real malloc function.

You may wish to provide a __real_malloc function as well, so that links without the --wrap option will succeed. If you do this, you should not put the definition of __real_malloc in the same file as __wrap_malloc; if you do, the assembler may resolve the call before the linker has a chance to wrap it to malloc.

--eh-frame-hdr

Request creation of  .eh_frame_hdr section and ELF  PT_GNU_EH_FRAME segment header.

--no-ld-generated-unwind-info

Request creation of  .eh_frame unwind info for linker generated code sections like PLT. This option is on by default if linker generated unwind info is supported.

--enable-new-dtags --disable-new-dtags

This linker can create the new dynamic tags in ELF. But the older ELF systems may not understand them. If you specify  --enable-new-dtags, the dynamic tags will be created as needed. If you specify  --disable-new-dtags, no new dynamic tags will be created. By default, the new dynamic tags are not created. Note that those options are only available for ELF systems.

--hash-size= number

Set the default size of the linker's hash tables to a prime number close to  number. Increasing this value can reduce the length of time it takes the linker to perform its tasks, at the expense of increasing the linker's memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed.

--hash-style= style

Set the type of linker's hash table(s).  style can be either  sysv for classic ELF  .hash section,  gnu for new style GNU  .gnu.hash section or  both for both the classic ELF  .hash and new style GNU  .gnu.hash hash tables. The default is  sysv.

--reduce-memory-overheads

This option reduces memory requirements at ld runtime, at the expense of linking speed. This was introduced to select the old O(n^2) algorithm for link map file generation, rather than the new O(n) algorithm which uses about 40% more memory for symbol storage.

Another effect of the switch is to set the default hash table size to 1021, which again saves memory at the cost of lengthening the linker's run time. This is not done however if the --hash-size switch has been used.

The --reduce-memory-overheads switch may be also be used to enable other tradeoffs in future versions of the linker.

--build-id --build-id= style

Request creation of  .note.gnu.build-id ELF note section. The contents of the note are unique bits identifying this linked file.  style can be  uuid to use 128 random bits,  sha1 to use a 160-bit  SHA1 hash on the normative parts of the output contents,  md5 to use a 128-bit  MD5 hash on the normative parts of the output contents, or  0x hexstring to use a chosen bit string specified as an even number of hexadecimal digits ( - and  : characters between digit pairs are ignored). If  style is omitted,  sha1 is used.

The md5 and sha1 styles produces an identifier that is always the same in an identical output file, but will be unique among all nonidentical output files. It is not intended to be compared as a checksum for the file's contents. A linked file may be changed later by other tools, but the build ID bit string identifying the original linked file does not change.

Passing none for style disables the setting from any --build-id options earlier on the command line.

2.1.1 Options Specific to i386 PE Targets

The i386 PE linker supports the -shared option, which causes the output to be a dynamically linked library (DLL) instead of a normal executable. You should name the output *.dll when you use this option. In addition, the linker fully supports the standard *.def files, which may be specified on the linker command line like an object file (in fact, it should precede archives it exports symbols from, to ensure that they get linked in, just like a normal object file).

In addition to the options common to all targets, the i386 PE linker support additional command line options that are specific to the i386 PE target. Options that take values may be separated from their values by either a space or an equals sign.

--add-stdcall-alias

If given, symbols with a stdcall suffix (@ nn) will be exported as-is and also with the suffix stripped. [This option is specific to the i386 PE targeted port of the linker]

--base-file  file

Use  file as the name of a file in which to save the base addresses of all the relocations needed for generating DLLs with  dlltool. [This is an i386 PE specific option]

--dll

Create a DLL instead of a regular executable. You may also use  -shared or specify a  LIBRARY in a given  .def file. [This option is specific to the i386 PE targeted port of the linker]

--enable-long-section-names --disable-long-section-names

The PE variants of the Coff object format add an extension that permits the use of section names longer than eight characters, the normal limit for Coff. By default, these names are only allowed in object files, as fully-linked executable images do not carry the Coff string table required to support the longer names. As a GNU extension, it is possible to allow their use in executable images as well, or to (probably pointlessly!) disallow it in object files, by using these two options. Executable images generated with these long section names are slightly non-standard, carrying as they do a string table, and may generate confusing output when examined with non-GNU PE-aware tools, such as file viewers and dumpers. However, GDB relies on the use of PE long section names to find Dwarf-2 debug information sections in an executable image at runtime, and so if neither option is specified on the command-line,  ld will enable long section names, overriding the default and technically correct behaviour, when it finds the presence of debug information while linking an executable image and not stripping symbols. [This option is valid for all PE targeted ports of the linker]

--enable-stdcall-fixup --disable-stdcall-fixup

If the link finds a symbol that it cannot resolve, it will attempt to do “fuzzy linking” by looking for another defined symbol that differs only in the format of the symbol name (cdecl vs stdcall) and will resolve that symbol by linking to the match. For example, the undefined symbol  _foo might be linked to the function  _foo@12, or the undefined symbol  _bar@16 might be linked to the function  _bar. When the linker does this, it prints a warning, since it normally should have failed to link, but sometimes import libraries generated from third-party dlls may need this feature to be usable. If you specify  --enable-stdcall-fixup, this feature is fully enabled and warnings are not printed. If you specify  --disable-stdcall-fixup, this feature is disabled and such mismatches are considered to be errors. [This option is specific to the i386 PE targeted port of the linker]

--leading-underscore --no-leading-underscore

For most targets default symbol-prefix is an underscore and is defined in target's description. By this option it is possible to disable/enable the default underscore symbol-prefix.

--export-all-symbols

If given, all global symbols in the objects used to build a DLL will be exported by the DLL. Note that this is the default if there otherwise wouldn't be any exported symbols. When symbols are explicitly exported via DEF files or implicitly exported via function attributes, the default is to not export anything else unless this option is given. Note that the symbols  DllMain@12,  DllEntryPoint@0,  DllMainCRTStartup@12, and  impure_ptr will not be automatically exported. Also, symbols imported from other DLLs will not be re-exported, nor will symbols specifying the DLL's internal layout such as those beginning with  _head_ or ending with  _iname. In addition, no symbols from  libgcc,  libstd++,  libmingw32, or  crtX.o will be exported. Symbols whose names begin with  __rtti_ or  __builtin_ will not be exported, to help with C++ DLLs. Finally, there is an extensive list of cygwin-private symbols that are not exported (obviously, this applies on when building DLLs for cygwin targets). These cygwin-excludes are:  _cygwin_dll_entry@12,  _cygwin_crt0_common@8,  _cygwin_noncygwin_dll_entry@12,  _fmode,  _impure_ptr,  cygwin_attach_dll,  cygwin_premain0,  cygwin_premain1,  cygwin_premain2,  cygwin_premain3, and  environ. [This option is specific to the i386 PE targeted port of the linker]

--exclude-symbols  symbol , symbol ,...

Specifies a list of symbols which should not be automatically exported. The symbol names may be delimited by commas or colons. [This option is specific to the i386 PE targeted port of the linker]

--exclude-all-symbols

Specifies no symbols should be automatically exported. [This option is specific to the i386 PE targeted port of the linker]

--file-alignment

Specify the file alignment. Sections in the file will always begin at file offsets which are multiples of this number. This defaults to 512. [This option is specific to the i386 PE targeted port of the linker]

--heap  reserve --heap  reserve , commit

Specify the number of bytes of memory to reserve (and optionally commit) to be used as heap for this program. The default is 1Mb reserved, 4K committed. [This option is specific to the i386 PE targeted port of the linker]

--image-base  value

Use  value as the base address of your program or dll. This is the lowest memory location that will be used when your program or dll is loaded. To reduce the need to relocate and improve performance of your dlls, each should have a unique base address and not overlap any other dlls. The default is 0x400000 for executables, and 0x10000000 for dlls. [This option is specific to the i386 PE targeted port of the linker]

--kill-at

If given, the stdcall suffixes (@ nn) will be stripped from symbols before they are exported. [This option is specific to the i386 PE targeted port of the linker]

--large-address-aware

If given, the appropriate bit in the “Characteristics” field of the COFF header is set to indicate that this executable supports virtual addresses greater than 2 gigabytes. This should be used in conjunction with the /3GB or /USERVA= valuemegabytes switch in the “[operating systems]” section of the BOOT.INI. Otherwise, this bit has no effect. [This option is specific to PE targeted ports of the linker]

--major-image-version  value

Sets the major number of the “image version”. Defaults to 1. [This option is specific to the i386 PE targeted port of the linker]

--major-os-version  value

Sets the major number of the “os version”. Defaults to 4. [This option is specific to the i386 PE targeted port of the linker]

--major-subsystem-version  value

Sets the major number of the “subsystem version”. Defaults to 4. [This option is specific to the i386 PE targeted port of the linker]

--minor-image-version  value

Sets the minor number of the “image version”. Defaults to 0. [This option is specific to the i386 PE targeted port of the linker]

--minor-os-version  value

Sets the minor number of the “os version”. Defaults to 0. [This option is specific to the i386 PE targeted port of the linker]

--minor-subsystem-version  value

Sets the minor number of the “subsystem version”. Defaults to 0. [This option is specific to the i386 PE targeted port of the linker]

--output-def  file

The linker will create the file  file which will contain a DEF file corresponding to the DLL the linker is generating. This DEF file (which should be called  *.def) may be used to create an import library with  dlltool or may be used as a reference to automatically or implicitly exported symbols. [This option is specific to the i386 PE targeted port of the linker]

--out-implib  file

The linker will create the file  file which will contain an import lib corresponding to the DLL the linker is generating. This import lib (which should be called  *.dll.a or  *.a may be used to link clients against the generated DLL; this behaviour makes it possible to skip a separate  dlltool import library creation step. [This option is specific to the i386 PE targeted port of the linker]

--enable-auto-image-base

Automatically choose the image base for DLLs, unless one is specified using the  --image-base argument. By using a hash generated from the dllname to create unique image bases for each DLL, in-memory collisions and relocations which can delay program execution are avoided. [This option is specific to the i386 PE targeted port of the linker]

--disable-auto-image-base

Do not automatically generate a unique image base. If there is no user-specified image base ( --image-base) then use the platform default. [This option is specific to the i386 PE targeted port of the linker]

--dll-search-prefix  string

When linking dynamically to a dll without an import library, search for  <string><basename>.dll in preference to  lib<basename>.dll. This behaviour allows easy distinction between DLLs built for the various "subplatforms": native, cygwin, uwin, pw, etc. For instance, cygwin DLLs typically use  --dll-search-prefix=cyg. [This option is specific to the i386 PE targeted port of the linker]

--enable-auto-import

Do sophisticated linking of  _symbol to  __imp__symbol for DATA imports from DLLs, and create the necessary thunking symbols when building the import libraries with those DATA exports. Note: Use of the 'auto-import' extension will cause the text section of the image file to be made writable. This does not conform to the PE-COFF format specification published by Microsoft.

Note - use of the 'auto-import' extension will also cause read only data which would normally be placed into the .rdata section to be placed into the .data section instead. This is in order to work around a problem with consts that is described here: http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html

Using 'auto-import' generally will 'just work' – but sometimes you may see this message:

"variable '<var>' can't be auto-imported. Please read the documentation for ld's --enable-auto-import for details."

This message occurs when some (sub)expression accesses an address ultimately given by the sum of two constants (Win32 import tables only allow one). Instances where this may occur include accesses to member fields of struct variables imported from a DLL, as well as using a constant index into an array variable imported from a DLL. Any multiword variable (arrays, structs, long long, etc) may trigger this error condition. However, regardless of the exact data type of the offending exported variable, ld will always detect it, issue the warning, and exit.

There are several ways to address this difficulty, regardless of the data type of the exported variable:

One way is to use –enable-runtime-pseudo-reloc switch. This leaves the task of adjusting references in your client code for runtime environment, so this method works only when runtime environment supports this feature.

A second solution is to force one of the 'constants' to be a variable – that is, unknown and un-optimizable at compile time. For arrays, there are two possibilities: a) make the indexee (the array's address) a variable, or b) make the 'constant' index a variable. Thus:

          extern type extern_array[];
          extern_array[1] -->
             { volatile type *t=extern_array; t[1] }
     

or

          extern type extern_array[];
          extern_array[1] -->
             { volatile int t=1; extern_array[t] }
     

For structs (and most other multiword data types) the only option is to make the struct itself (or the long long, or the ...) variable:

          extern struct s extern_struct;
          extern_struct.field -->
             { volatile struct s *t=&extern_struct; t->field }
     

or

          extern long long extern_ll;
          extern_ll -->
            { volatile long long * local_ll=&extern_ll; *local_ll }
     

A third method of dealing with this difficulty is to abandon 'auto-import' for the offending symbol and mark it with __declspec(dllimport). However, in practise that requires using compile-time #defines to indicate whether you are building a DLL, building client code that will link to the DLL, or merely building/linking to a static library. In making the choice between the various methods of resolving the 'direct address with constant offset' problem, you should consider typical real-world usage:

Original:

          --foo.h
          extern int arr[];
          --foo.c
          #include "foo.h"
          void main(int argc, char **argv){
            printf("%d\n",arr[1]);
          }
     

Solution 1:

          --foo.h
          extern int arr[];
          --foo.c
          #include "foo.h"
          void main(int argc, char **argv){
            /* This workaround is for win32 and cygwin; do not "optimize" */
            volatile int *parr = arr;
            printf("%d\n",parr[1]);
          }
     

Solution 2:

          --foo.h
          /* Note: auto-export is assumed (no __declspec(dllexport)) */
          #if (defined(_WIN32) || defined(__CYGWIN__)) && \
            !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
          #define FOO_IMPORT __declspec(dllimport)
          #else
          #define FOO_IMPORT
          #endif
          extern FOO_IMPORT int arr[];
          --foo.c
          #include "foo.h"
          void main(int argc, char **argv){
            printf("%d\n",arr[1]);
          }
     

A fourth way to avoid this problem is to re-code your library to use a functional interface rather than a data interface for the offending variables (e.g. set_foo() and get_foo() accessor functions). [This option is specific to the i386 PE targeted port of the linker]

--disable-auto-import

Do not attempt to do sophisticated linking of  _symbol to  __imp__symbol for DATA imports from DLLs. [This option is specific to the i386 PE targeted port of the linker]

--enable-runtime-pseudo-reloc

If your code contains expressions described in –enable-auto-import section, that is, DATA imports from DLL with non-zero offset, this switch will create a vector of 'runtime pseudo relocations' which can be used by runtime environment to adjust references to such data in your client code. [This option is specific to the i386 PE targeted port of the linker]

--disable-runtime-pseudo-reloc

Do not create pseudo relocations for non-zero offset DATA imports from DLLs. This is the default. [This option is specific to the i386 PE targeted port of the linker]

--enable-extra-pe-debug

Show additional debug info related to auto-import symbol thunking. [This option is specific to the i386 PE targeted port of the linker]

--section-alignment

Sets the section alignment. Sections in memory will always begin at addresses which are a multiple of this number. Defaults to 0x1000. [This option is specific to the i386 PE targeted port of the linker]

--stack  reserve --stack  reserve , commit

Specify the number of bytes of memory to reserve (and optionally commit) to be used as stack for this program. The default is 2Mb reserved, 4K committed. [This option is specific to the i386 PE targeted port of the linker]

--subsystem  which --subsystem  which : major --subsystem  which : major . minor

Specifies the subsystem under which your program will execute. The legal values for  which are  native,  windows,  console,  posix, and  xbox. You may optionally set the subsystem version also. Numeric values are also accepted for  which. [This option is specific to the i386 PE targeted port of the linker]

The following options set flags in the DllCharacteristics field of the PE file header: [These options are specific to PE targeted ports of the linker]

--dynamicbase

The image base address may be relocated using address space layout randomization (ASLR). This feature was introduced with MS Windows Vista for i386 PE targets.

--forceinteg

Code integrity checks are enforced.

--nxcompat

The image is compatible with the Data Execution Prevention. This feature was introduced with MS Windows XP SP2 for i386 PE targets.

--no-isolation

Although the image understands isolation, do not isolate the image.

--no-seh

The image does not use SEH. No SE handler may be called from this image.

--no-bind

Do not bind this image.

--wdmdriver

The driver uses the MS Windows Driver Model.

--tsaware

The image is Terminal Server aware.

2.1.2 Options specific to C6X uClinux targets

The C6X uClinux target uses a binary format called DSBT to support shared libraries. Each shared library in the system needs to have a unique index; all executables use an index of 0.

--dsbt-size  size

This option sets the number of entires in the DSBT of the current executable or shared library to  size. The default is to create a table with 64 entries.

--dsbt-index  index

This option sets the DSBT index of the current executable or shared library to  index. The default is 0, which is appropriate for generating executables. If a shared library is generated with a DSBT index of 0, the  R_C6000_DSBT_INDEX relocs are copied into the output file.

The `--no-merge-exidx-entries' switch disables the merging of adjacent exidx entries in frame unwind info.

2.1.3 Options specific to Motorola 68HC11 and 68HC12 targets

The 68HC11 and 68HC12 linkers support specific options to control the memory bank switching mapping and trampoline code generation.

--no-trampoline

This option disables the generation of trampoline. By default a trampoline is generated for each far function which is called using a  jsr instruction (this happens when a pointer to a far function is taken).

--bank-window  name

This option indicates to the linker the name of the memory region in the ` MEMORY' specification that describes the memory bank window. The definition of such region is then used by the linker to compute paging and addresses within the memory window.

2.1.4 Options specific to Motorola 68K target

The following options are supported to control handling of GOT generation when linking for 68K targets.

--got= type

This option tells the linker which GOT generation scheme to use.  type should be one of ` single', ` negative', ` multigot' or ` target'. For more information refer to the Info entry for  ld.