File: libtool.info,  Node: Autoconf macros,  Next: Makefile rules,  Up: Integrating libtool

5.1 Autoconf macros exported by libtool
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Libtool uses a number of macros to interrogate the host system when it
is being built, and you can use some of them yourself too.  Although
there are a great many other macros in the libtool installed m4 files,
these do not form part of the published interface, and are subject to
change between releases.

Macros in the ‘LT_CMD_’ namespace check for various shell commands:

 -- Macro: LT_CMD_MAX_LEN
     Finds the longest command line that can be safely passed to
     ‘$SHELL’ without being truncated, and store in the shell variable
     ‘$max_cmd_len’.  It is only an approximate value, but command lines
     of this length or shorter are guaranteed not to be truncated.

Macros in the ‘LT_FUNC_’ namespace check characteristics of library
functions:

 -- Macro: LT_FUNC_DLSYM_USCORE
     ‘AC_DEFINE’ the preprocessor symbol ‘DLSYM_USCORE’ if we have to
     add an underscore to symbol-names passed in to ‘dlsym’.

Macros in the ‘LT_LIB_’ namespace check characteristics of system
libraries:

 -- Macro: LT_LIB_M
     Set ‘LIBM’ to the math library or libraries required on this
     machine, if any.

 -- Macro: LT_LIB_DLLOAD
     This is the macro used by ‘libltdl’ to determine what dlloaders to
     use on this machine, if any.  Several shell variables are set (and
     ‘AC_SUBST’ed) depending on the dlload interfaces are available on
     this machine.  ‘LT_DLLOADERS’ contains a list of libtool libraries
     that can be used, and if necessary also sets ‘LIBADD_DLOPEN’ if
     additional system libraries are required by the ‘dlopen’ loader,
     and ‘LIBADD_SHL_LOAD’ if additional system libraries are required
     by the ‘shl_load’ loader, respectively.  Finally some symbols are
     set in ‘config.h’ depending on the loaders that are found to work:
     ‘HAVE_LIBDL’, ‘HAVE_SHL_LOAD’, ‘HAVE_DYLD’, ‘HAVE_DLD’.

Macros in the ‘LT_PATH_’ namespace search the system for the full path
to particular system commands:

 -- Macro: LT_PATH_LD
     Add a ‘--with-gnu-ld’ option to ‘configure’.  Try to find the path
     to the linker used by ‘$CC’, and whether it is the GNU linker.  The
     result is stored in the shell variable ‘$LD’, which is
     ‘AC_SUBST’ed.

 -- Macro: LT_PATH_NM
     Try to find a BSD-compatible ‘nm’ or a MS-compatible ‘dumpbin’
     command on this machine.  The result is stored in the shell
     variable ‘$NM’, which is ‘AC_SUBST’ed.

Macros in the ‘LT_SYS_’ namespace probe for system characteristics:

 -- Macro: LT_SYS_DLOPEN_SELF
     Tests whether a program can dlopen itself, and then also whether
     the same program can still dlopen itself when statically linked.
     Results are stored in the shell variables ‘$enable_dlopen_self’ and
     ‘enable_dlopen_self_static’ respectively.

 -- Macro: LT_SYS_DLOPEN_DEPLIBS
     Define the preprocessor symbol ‘LTDL_DLOPEN_DEPLIBS’ if the OS
     needs help to load dependent libraries for ‘dlopen’ (or
     equivalent).

 -- Macro: LT_SYS_DLSEARCH_PATH
     Define the preprocessor symbol ‘LT_DLSEARCH_PATH’ to the system
     default library search path.

 -- Macro: LT_SYS_MODULE_EXT
     Define the preprocessor symbol ‘LT_MODULE_EXT’ to the extension
     used for runtime loadable modules.  If you use libltdl to open
     modules, then you can simply use the libtool library extension,
     ‘.la’.

 -- Macro: LT_SYS_MODULE_PATH
     Define the preprocessor symbol ‘LT_MODULE_PATH_VAR’ to the name of
     the shell environment variable that determines the run-time module
     search path.

 -- Macro: LT_SYS_SYMBOL_USCORE
     Set the shell variable ‘sys_symbol_underscore’ to ‘no’ unless the
     compiler prefixes global symbols with an underscore.