info libtool

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15.4 ‘libtool’ script contents
==============================

Since version 1.4, the ‘libtool’ script is generated by ‘configure’
(*note Configuring::). 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, ‘ltmain.sh’. ‘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 ‘_cmds’ where 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’ (*note Configuring::):

-- Variable: AR
The name of the system library archiver.

-- Variable: CC
The name of the compiler used to configure libtool. This will
always contain the compiler for the current language (*note
Tags::).

-- Variable: ECHO
An ‘echo’ program 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

For MS ‘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: RANLIB
Set to the name of the ‘ranlib’ program, if any.

-- Variable: allow_undefined_flag
The flag that is used by ‘archive_cmds’ 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_cmds’ before 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: archiver_list_spec
Specify filename containing input files for ‘AR’.

-- 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 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 ‘soname’ contains 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 ‘soname’.

-- 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_support
Whether ‘dlopen’ is supported on the platform. Set to ‘yes’ or
‘no’.

-- Variable: dlopen_self
Whether it is possible to ‘dlopen’ the executable itself. Set to
‘yes’ or ‘no’.

-- Variable: dlopen_self_static
Whether it is possible to ‘dlopen’ the executable itself, when it
is linked statically (‘-all-static’). Set to ‘yes’ or ‘no’.

-- Variable: exclude_expsyms
List of symbols that should not be listed in the preloaded symbols.

-- 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 ‘libobjs’ to the file
‘export_symbols’.

-- 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_runpath’ is not ‘yes’, so ‘fast_install’ will
be set to ‘needless’ in this case. If ‘fast_install’ set 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_install’ is never
set to ‘yes’, and relinking at install time is triggered. This
also means that ‘DESTDIR’ installation does not work as expected.

-- Variable: file_magic_glob
How to find potential files when ‘deplibs_check_method’ is
‘file_magic’. ‘file_magic_glob’ is a ‘sed’ expression, and the
‘sed’ instance is fed potential file names that are transformed by
the ‘file_magic_glob’ expression. Useful when the shell does not
support the shell option ‘nocaseglob’, making ‘want_nocaseglob’
inappropriate. Normally disabled (i.e. ‘file_magic_glob’ is
empty).

-- Variable: finish_cmds
Commands to tell the dynamic linker how to find shared libraries in
a specific directory. These commands can be disabled during
testing local changes to shared libraries with ‘--no-finish’.

-- Variable: finish_eval
Same as ‘finish_cmds’, except the commands are not displayed.

-- 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_pipe’ into
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 ‘hardcode_libdir_flag_spec’ is
specified.

-- Variable: hardcode_direct_absolute
Some architectures hardcode "absolute" library directories that
cannot be overridden by ‘shlibpath_var’ when ‘hardcode_direct’ is
‘yes’. In that case set ‘hardcode_direct_absolute’ to ‘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 ‘libdir’ variable into a binary, so that the
dynamic linker searches ‘libdir’ for 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 ‘hardcode_libdir_flag_spec’ is specified.

-- Variable: hardcode_shlibpath_var
Set to ‘yes’ or ‘no’, depending on whether the linker hardcodes
directories by writing the contents of ‘$shlibpath_var’ into the
resulting executable when ‘hardcode_libdir_flag_spec’ is specified.
Set to ‘unsupported’ if directories specified by ‘$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: include_expsyms
List of symbols that must always be exported when using
‘export_symbols’.

-- 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
‘install’ with ‘-m INSTALL_OVERRIDE_MODE’.

-- Variable: libext
The standard old archive suffix (normally ‘a’).

-- 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.sh’
correspond 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 ‘dlopen’ modules 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 ‘dlopen’ a 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: nm_file_list_spec
Specify filename containing input files for ‘NM’.

-- Variable: no_builtin_flag
Compiler flag to disable builtin functions that conflict with
declaring external global symbols as ‘char’.

-- Variable: no_undefined_flag
The flag that is used by ‘archive_cmds’ to declare that there will
be no unresolved symbols in the resulting shared library. Empty,
if no such flag is required.

-- Variable: objdir
The name of the directory that contains temporary libtool files.

-- Variable: objext
The standard object file suffix (normally ‘o’).

-- Variable: pic_flag
Any additional compiler flags for building library object files.

-- 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_cmds’
are executed immediately after the program is linked. Any
occurrence of the string ‘@OUTPUT@’ in ‘postlink_cmds’ is 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. ‘postlink_cmds’ empty).

-- Variable: reload_cmds
-- Variable: reload_flag
Commands to create a reloadable object. Set ‘reload_cmds’ to
‘false’ on systems that cannot create reloadable objects.

-- Variable: runpath_var
The environment variable that tells the linker what 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 (*note
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_var’ are 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 where other values should be
used. On rare occasions, it may be necessary to override the
autodetected value (*note 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 ‘nocaseglob’, when
‘deplibs_check_method’ is ‘file_magic’. Normally set to ‘no’. Set
to ‘yes’ to enable the ‘nocaseglob’ shell 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: ‘${wl}SOME-FLAG’.

Variables ending in ‘_cmds’ or ‘_eval’ contain a ‘~’-separated list
of commands that are ‘eval’ed 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 ‘eval’ed before being used by
libtool.