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libtool script contents
Since version 1.4, the
libtool script is generated by
configure (see section Configuring libtool). In earlier versions,
configure achieved this by calling a helper script called
‘ltconfig’. From libtool version 0.7 to 1.0, this script
simply set shell variables, then sourced the libtool backend,
ltconfig from libtool version 1.1 through 1.3
inlined the contents of
ltmain.sh into the generated
libtool, which improved performance on many systems. The tests
that ‘ltconfig’ used to perform are now kept in ‘libtool.m4’
where they can be written using Autoconf. This has the runtime
performance benefits of inlined
ltmain.sh, and improves
the build time a little while considerably easing the amount of raw
shell code that used to need maintaining.
The convention used for naming variables that hold shell commands for
delayed evaluation, is to use the suffix
_cmd where a single
line of valid shell script is needed, and the suffix
multiple lines of shell script may be delayed for later
evaluation. By convention,
_cmds variables delimit the
evaluation units with the
~ character where necessary.
Here is a listing of each of the configuration variables, and how they
are used within
ltmain.sh (see section Configuring libtool):
- Variable: CC
The name of the compiler used to configure libtool. This will always contain the compiler for the current language (see section Tags).
- Variable: ECHO
echoprogram that does not interpret backslashes as an escape character. It may be given only one argument, so due quoting is necessary.
- Variable: LD
The name of the linker that libtool should use internally for reloadable linking and possibly shared libraries.
- Variable: LTCC
- Variable: LTCFLAGS
The name of the C compiler and C compiler flags used to configure libtool.
- Variable: NM
The name of a BSD- or MS-compatible program that produces listings of global symbols. For BSD
nm, the symbols should be in one the following formats:
address C global-variable-name address D global-variable-name address T global-function-name
dumpbin, the symbols should be in one of the following formats:
counter size UNDEF notype External | global-var counter address section notype External | global-var counter address section notype () External | global-func
The size of the global variables are not zero and the section of the global functions are not "UNDEF". Symbols in "pick any" sections ("pick any" appears in the section header) are not global either.
- Variable: allow_undefined_flag
The flag that is used by ‘archive_cmds’ in order to declare that there will be unresolved symbols in the resulting shared library. Empty, if no such flag is required. Set to ‘unsupported’ if there is no way to generate a shared library with references to symbols that aren’t defined in that library.
- Variable: always_export_symbols
Whether libtool should automatically generate a list of exported symbols using
export_symbols_cmdsbefore linking an archive. Set to ‘yes’ or ‘no’. Default is ‘no’.
- Variable: archive_cmds
- Variable: archive_expsym_cmds
- Variable: old_archive_cmds
Commands used to create shared libraries, shared libraries with ‘-export-symbols’ and static libraries, respectively.
- Variable: old_archive_from_new_cmds
If the shared library depends on a static library, ‘old_archive_from_new_cmds’ contains the commands used to create that static library. If this variable is not empty, ‘old_archive_cmds’ is not used.
- Variable: old_archive_from_expsyms_cmds
If a static library must be created from the export symbol list in order to correctly link with a shared library, ‘old_archive_from_expsyms_cmds’ contains the commands needed to create that static library. When these commands are executed, the variable
sonamecontains the name of the shared library in question, and the ‘$objdir/$newlib’ contains the path of the static library these commands should build. After executing these commands, libtool will proceed to link against ‘$objdir/$newlib’ instead of
- Variable: lock_old_archive_extraction
Set to ‘yes’ if the extraction of a static library requires locking the library file. This is required on Darwin.
- Variable: build
- Variable: build_alias
- Variable: build_os
Set to the specified and canonical names of the system that libtool was built on.
- Variable: build_libtool_libs
Whether libtool should build shared libraries on this system. Set to ‘yes’ or ‘no’.
- Variable: build_old_libs
Whether libtool should build static libraries on this system. Set to ‘yes’ or ‘no’.
- Variable: compiler_c_o
Whether the compiler supports the ‘-c’ and ‘-o’ options simultaneously. Set to ‘yes’ or ‘no’.
- Variable: compiler_needs_object
Whether the compiler has to see an object listed on the command line in order to successfully invoke the linker. If ‘no’, then a set of convenience archives or a set of object file names can be passed via linker-specific options or linker scripts.
- Variable: dlopen_self_static
Whether it is possible to
dlopenthe executable itself, when it is linked statically (‘-all-static’). Set to ‘yes’ or ‘no’.
- Variable: export_dynamic_flag_spec
Compiler link flag that allows a dlopened shared library to reference symbols that are defined in the program.
- Variable: export_symbols_cmds
Commands to extract exported symbols from
libobjsto the file
- Variable: extract_expsyms_cmds
Commands to extract the exported symbols list from a shared library. These commands are executed if there is no file ‘$objdir/$soname-def’, and should write the names of the exported symbols to that file, for the use of ‘old_archive_from_expsyms_cmds’.
- Variable: fast_install
Determines whether libtool will privilege the installer or the developer. The assumption is that installers will seldom run programs in the build tree, and the developer will seldom install. This is only meaningful on platforms where
shlibpath_overrides_runpathis not ‘yes’, so
fast_installwill be set to ‘needless’ in this case. If
fast_installset to ‘yes’, libtool will create programs that search for installed libraries, and, if a program is run in the build tree, a new copy will be linked on-demand to use the yet-to-be-installed libraries. If set to ‘no’, libtool will create programs that use the yet-to-be-installed libraries, and will link a new copy of the program at install time. The default value is ‘yes’ or ‘needless’, depending on platform and configuration flags, and it can be turned from ‘yes’ to ‘no’ with the configure flag ‘--disable-fast-install’.
On some systems, the linker always hardcodes paths to dependent libraries into the output. In this case,
fast_installis never set to ‘yes’, and relinking at install time is triggered. This also means that
DESTDIRinstallation does not work as expected.
- Variable: file_magic_glob
How to find potential files when
sedexpression, and the
sedinstance is fed potential file names that are transformed by the
file_magic_globexpression. Useful when the shell does not support the shell option
want_nocaseglobinappropriate. Normally disabled (i.e.
- Variable: finish_cmds
Commands to tell the dynamic linker how to find shared libraries in a specific directory.
- Variable: global_symbol_pipe
A pipeline that takes the output of
NM, and produces a listing of raw symbols followed by their C names. For example:
$ eval "$NM progname | $global_symbol_pipe" D symbol1 C-symbol1 T symbol2 C-symbol2 C symbol3 C-symbol3 … $
The first column contains the symbol type (used to tell data from code) but its meaning is system dependent.
- Variable: global_symbol_to_cdecl
A pipeline that translates the output of
global_symbol_pipeinto proper C declarations. Since some platforms, such as HP/UX, have linkers that differentiate code from data, data symbols are declared as data, and code symbols are declared as functions.
- Variable: hardcode_action
Either ‘immediate’ or ‘relink’, depending on whether shared library paths can be hardcoded into executables before they are installed, or if they need to be relinked.
- Variable: hardcode_direct
Set to ‘yes’ or ‘no’, depending on whether the linker hardcodes directories if a library is directly specified on the command line (such as ‘dir/libname.a’) when
- Variable: hardcode_direct_absolute
Some architectures hardcode "absolute" library directories that can not be overridden by
hardcode_directis ‘yes’. In that case set
hardcode_direct_absoluteto ‘yes’, or otherwise ‘no’.
- Variable: hardcode_into_libs
Whether the platform supports hardcoding of run-paths into libraries. If enabled, linking of programs will be much simpler but libraries will need to be relinked during installation. Set to ‘yes’ or ‘no’.
- Variable: hardcode_libdir_flag_spec
Flag to hardcode a
libdirvariable into a binary, so that the dynamic linker searches
libdirfor shared libraries at runtime. If it is empty, libtool will try to use some other hardcoding mechanism.
- Variable: hardcode_libdir_separator
If the compiler only accepts a single
hardcode_libdir_flag, then this variable contains the string that should separate multiple arguments to that flag.
- Variable: hardcode_minus_L
Set to ‘yes’ or ‘no’, depending on whether the linker hardcodes directories specified by ‘-L’ flags into the resulting executable when
- Variable: hardcode_shlibpath_var
Set to ‘yes’ or ‘no’, depending on whether the linker hardcodes directories by writing the contents of ‘$shlibpath_var’ into the resulting executable when
hardcode_libdir_flag_specis specified. Set to ‘unsupported’ if directories specified by ‘$shlibpath_var’ are searched at run time, but not at link time.
- Variable: host
- Variable: host_alias
- Variable: host_os
Set to the specified and canonical names of the system that libtool was configured for.
- Variable: inherit_rpath
Whether the linker adds runtime paths of dependency libraries to the runtime path list, requiring libtool to relink the output when installing. Set to ‘yes’ or ‘no’. Default is ‘no’.
- Variable: install_override_mode
Permission mode override for installation of shared libraries. If the runtime linker fails to load libraries with wrong permissions, then it may fail to execute programs that are needed during installation, because these need the library that has just been installed. In this case, it is necessary to pass the mode to
installwith ‘-m install_override_mode’.
- Variable: libname_spec
The format of a library name prefix. On all Unix systems, static libraries are called ‘libname.a’, but on some systems (such as OS/2 or MS-DOS), the library is just called ‘name.a’.
- Variable: library_names_spec
A list of shared library names. The first is the name of the file, the rest are symbolic links to the file. The name in the list is the file name that the linker finds when given ‘-lname’.
- Variable: link_all_deplibs
Whether libtool must link a program against all its dependency libraries. Set to ‘yes’ or ‘no’. Default is ‘unknown’, which is a synonym for ‘yes’.
- Variable: link_static_flag
Linker flag (passed through the C compiler) used to prevent dynamic linking.
- Variable: macro_version
- Variable: macro_revision
The release and revision from which the libtool.m4 macros were taken. This is used to ensure that macros and
ltmain.shcorrespond to the same Libtool version.
- Variable: max_cmd_len
The approximate longest command line that can be passed to ‘$SHELL’ without being truncated, as computed by ‘LT_CMD_MAX_LEN’.
- Variable: need_lib_prefix
Whether we can
dlopenmodules without a ‘lib’ prefix. Set to ‘yes’ or ‘no’. By default, it is ‘unknown’, which means the same as ‘yes’, but documents that we are not really sure about it. ‘no’ means that it is possible to
dlopena module without the ‘lib’ prefix.
- Variable: need_version
Whether versioning is required for libraries, i.e. whether the dynamic linker requires a version suffix for all libraries. Set to ‘yes’ or ‘no’. By default, it is ‘unknown’, which means the same as ‘yes’, but documents that we are not really sure about it.
- Variable: need_locks
Whether files must be locked to prevent conflicts when compiling simultaneously. Set to ‘yes’ or ‘no’.
- Variable: no_builtin_flag
Compiler flag to disable builtin functions that conflict with declaring external global symbols as
- Variable: no_undefined_flag
The flag that is used by ‘archive_cmds’ in order to declare that there will be no unresolved symbols in the resulting shared library. Empty, if no such flag is required.
- Variable: postinstall_cmds
- Variable: old_postinstall_cmds
Commands run after installing a shared or static library, respectively.
- Variable: postuninstall_cmds
- Variable: old_postuninstall_cmds
Commands run after uninstalling a shared or static library, respectively.
- Variable: postlink_cmds
Commands necessary for finishing linking programs.
postlink_cmdsare executed immediately after the program is linked. Any occurrence of the string
postlink_cmdsis replaced by the name of the created executable (i.e. not the wrapper, if a wrapper is generated) prior to execution. Similarly,
@TOOL_OUTPUT@is replaced by the toolchain format of
@OUTPUT@. Normally disabled (i.e.
- Variable: reload_cmds
- Variable: reload_flag
Commands to create a reloadable object. Set
reload_cmdsto ‘false’ on systems that cannot create reloadable objects.
- Variable: runpath_var
The environment variable that tells the linker which directories to hardcode in the resulting executable.
- Variable: shlibpath_overrides_runpath
Indicates whether it is possible to override the hard-coded library search path of a program with an environment variable. If this is set to no, libtool may have to create two copies of a program in the build tree, one to be installed and one to be run in the build tree only. When each of these copies is created depends on the value of
fast_install. The default value is ‘unknown’, which is equivalent to ‘no’.
- Variable: shlibpath_var
The environment variable that tells the dynamic linker where to find shared libraries.
- Variable: soname_spec
The name coded into shared libraries, if different from the real name of the file.
- Variable: striplib
- Variable: old_striplib
Command to strip a shared (
striplib) or static (
old_striplib) library, respectively. If these variables are empty, the strip flag in the install mode will be ignored for libraries (see section Install mode).
- Variable: sys_lib_dlsearch_path_spec
Expression to get the run-time system library search path. Directories that appear in this list are never hard-coded into executables.
- Variable: sys_lib_search_path_spec
Expression to get the compile-time system library search path. This variable is used by libtool when it has to test whether a certain library is shared or static. The directories listed in
shlibpath_varare automatically appended to this list, every time libtool runs (i.e., not at configuration time), because some linkers use this variable to extend the library search path. Linker switches such as ‘-L’ also augment the search path.
- Variable: thread_safe_flag_spec
Linker flag (passed through the C compiler) used to generate thread-safe libraries.
- Variable: to_host_file_cmd
If the toolchain is not native to the build platform (e.g. if you are using MSYS to drive the scripting, but are using the MinGW native Windows compiler) this variable describes how to convert file names from the format used by the build platform to the format used by host platform. Normally set to ‘func_convert_file_noop’, libtool will autodetect most cases in which other values should be used. On rare occasions, it may be necessary to override the autodetected value (see section Cygwin to MinGW Cross).
- Variable: to_tool_file_cmd
If the toolchain is not native to the build platform (e.g. if you are using some Unix to drive the scripting together with a Windows toolchain running in Wine) this variable describes how to convert file names from the format used by the build platform to the format used by the toolchain. Normally set to ‘func_convert_file_noop’.
- Variable: version_type
The library version numbering type. One of ‘libtool’, ‘freebsd-aout’, ‘freebsd-elf’, ‘irix’, ‘linux’, ‘osf’, ‘sunos’, ‘windows’, or ‘none’.
- Variable: want_nocaseglob
Find potential files using the shell option
deplibs_check_methodis ‘file_magic’. Normally set to ‘no’. Set to ‘yes’ to enable the
nocaseglobshell option when looking for potential file names in a case-insensitive manner.
- Variable: whole_archive_flag_spec
Compiler flag to generate shared objects from convenience archives.
- Variable: wl
The C compiler flag that allows libtool to pass a flag directly to the linker. Used as:
Variables ending in ‘_cmds’ or ‘_eval’ contain a
‘~’-separated list of commands that are
evaled one after
another. If any of the commands return a nonzero exit status, libtool
generally exits with an error message.
Variables ending in ‘_spec’ are
evaled before being used by
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