File: libtool.info, Node: LT_INIT, Next: Configure notes, Up: Configuring 5.4.1 The ‘LT_INIT’ macro ------------------------- If you are using GNU Autoconf (or Automake), you should add a call to ‘LT_INIT’ to your ‘configure.ac’ file. This macro adds many new tests to the ‘configure’ script so that the generated libtool script will understand the characteristics of the host. It's the most important of a number of macros defined by Libtool: -- Macro: LT_PREREQ (VERSION) Ensure that a recent enough version of Libtool is being used. If the version of Libtool used for ‘LT_INIT’ is earlier than VERSION, print an error message to the standard error output and exit with failure (exit status is 63). For example: LT_PREREQ([2.5.4]) -- Macro: LT_INIT (OPTIONS) -- Macro: AC_PROG_LIBTOOL -- Macro: AM_PROG_LIBTOOL Add support for the ‘--enable-shared’, ‘--disable-shared’, ‘--enable-static’, ‘--disable-static’, ‘--enable-pic’, and ‘--disable-pic’ ‘configure’ flags.(1) ‘AC_PROG_LIBTOOL’ and ‘AM_PROG_LIBTOOL’ are deprecated names for older versions of this macro; ‘autoupdate’ will upgrade your ‘configure.ac’ files. By default, this macro turns on shared libraries if they are available, and also enables static libraries if they don't conflict with the shared libraries. You can modify these defaults by passing either ‘disable-shared’ or ‘disable-static’ in the option list to ‘LT_INIT’, or using ‘AC_DISABLE_SHARED’ or ‘AC_DISABLE_STATIC’. # Turn off shared libraries during beta-testing, since they # make the build process take too long. LT_INIT([disable-shared]) The user may specify modified forms of the configure flags ‘--enable-shared’ and ‘--enable-static’ to choose whether shared or static libraries are built based on the name of the package. For example, to have shared ‘bfd’ and ‘gdb’ libraries built, but not shared ‘libg++’, you can run all three ‘configure’ scripts as follows: trick$ ./configure --enable-shared=bfd,gdb In general, specifying ‘--enable-shared=PKGS’ is the same as configuring with ‘--enable-shared’ every package named in the comma-separated PKGS list, and every other package with ‘--disable-shared’. The ‘--enable-static=PKGS’ flag behaves similarly, but it uses ‘--enable-static’ and ‘--disable-static’. The same applies to the ‘--enable-fast-install=PKGS’ flag, which uses ‘--enable-fast-install’ and ‘--disable-fast-install’. The package name ‘default’ matches any packages that have not set their name in the ‘PACKAGE’ environment variable. The ‘--enable-pic’ and ‘--disable-pic’ configure flags can be used to specify whether or not ‘libtool’ uses PIC objects. By default, ‘libtool’ uses PIC objects for shared libraries and non-PIC objects for static libraries. The ‘--enable-pic’ option also accepts a comma-separated list of package names. Specifying ‘--enable-pic=PKGS’ is the same as configuring every package in PKGS with ‘--enable-pic’ and every other package with the default configuration. The package name ‘default’ is treated the same as for ‘--enable-shared’ and ‘--enable-static’. This macro also sets the shell variable ‘LIBTOOL_DEPS’, that you can use to automatically update the libtool script if it becomes out-of-date. In order to do that, add to your ‘configure.ac’: LT_INIT AC_SUBST([LIBTOOL_DEPS]) and, to ‘Makefile.in’ or ‘Makefile.am’: LIBTOOL_DEPS = @LIBTOOL_DEPS@ libtool: $(LIBTOOL_DEPS) $(SHELL) ./config.status libtool If you are using GNU Automake, you can omit the assignment, as Automake will take care of it. You'll obviously have to create some dependency on ‘libtool’. Aside from ‘disable-static’ and ‘disable-shared’, there are other options that you can pass to ‘LT_INIT’ to modify its behaviour. Here is a full list: ‘dlopen’ Enable checking for dlopen support. This option should be used if the package makes use of the ‘-dlopen’ and ‘-dlpreopen’ libtool flags, otherwise libtool will assume that the system does not support dlopening. ‘win32-dll’ This option should be used if the package has been ported to build clean dlls on win32 platforms. Usually this means that any library data items are exported with ‘__declspec(dllexport)’ and imported with ‘__declspec(dllimport)’. If this option is not used, libtool will assume that the package libraries are not dll clean and will build only static libraries on win32 hosts. Provision must be made to pass ‘-no-undefined’ to ‘libtool’ in link mode from the package ‘Makefile’. Naturally, if you pass ‘-no-undefined’, you must ensure that all the library symbols *really are* defined at link time! ‘aix-soname=aix’ ‘aix-soname=svr4’ ‘aix-soname=both’ Enable the ‘--enable-aix-soname’ to ‘configure’, which the user can pass to override the given default. By default (and *always* in releases prior to 2.4.4), Libtool always behaves as if ‘aix-soname=aix’ is given, with no ‘configure’ option for the user to override. Specifically, when the ‘-brtl’ linker flag is seen in ‘LDFLAGS’ at build-time, static archives are built from static objects only, otherwise, traditional AIX shared library archives of shared objects using in-archive versioning are built (with the ‘.a’ file extension!). Similarly, with ‘-brtl’ in ‘LDFLAGS’, libtool shared archives are built from shared objects, without any filename-based versioning; and without ‘-brtl’ no shared archives are built at all. When ‘aix-soname=svr4’ option is given, or the ‘--enable-aix-soname=svr4’ ‘configure’ option is passed, static archives are always created from static objects, even without ‘-brtl’ in ‘LDFLAGS’. Shared archives are made from shared objects, and filename based versioning is enabled. When ‘aix-soname=both’ option is given, or the ‘--enable-aix-soname=svr4’ ‘configure’ option is passed, static archives are built traditionally (as ‘aix-soname=aix’), and both kinds of shared archives are built. The ‘.la’ pseudo-archive specifies one or the other depending on whether ‘-brtl’ is specified in ‘LDFLAGS’ when the library is built. ‘disable-fast-install’ Change the default behaviour for ‘LT_INIT’ to disable optimization for fast installation. The user may still override this default, depending on platform support, by specifying ‘--enable-fast-install’ to ‘configure’. ‘shared’ Change the default behaviour for ‘LT_INIT’ to enable shared libraries. This is the default on all systems where Libtool knows how to create shared libraries. The user may still override this default by specifying ‘--disable-shared’ to ‘configure’. ‘disable-shared’ Change the default behaviour for ‘LT_INIT’ to disable shared libraries. The user may still override this default by specifying ‘--enable-shared’ to ‘configure’. ‘static’ Change the default behaviour for ‘LT_INIT’ to enable static libraries. This is the default on all systems where shared libraries have been disabled for some reason, and on most systems where shared libraries have been enabled. If shared libraries are enabled, the user may still override this default by specifying ‘--disable-static’ to ‘configure’. ‘disable-static’ Change the default behaviour for ‘LT_INIT’ to disable static libraries. The user may still override this default by specifying ‘--enable-static’ to ‘configure’. ‘pic-only’ Change the default behaviour for ‘libtool’ to try to use only PIC objects. The user may still override this default by specifying ‘--disable-pic’ to ‘configure’. ‘no-pic’ Change the default behaviour of ‘libtool’ to try to use only non-PIC objects. The user may still override this default by specifying ‘--enable-pic’ to ‘configure’. -- Macro: LT_LANG (LANGUAGE) Enable ‘libtool’ support for the language given if it has not yet already been enabled. Languages accepted are "C++", "Fortran 77", "Java", "Go", and "Windows Resource". If Autoconf language support macros such as ‘AC_PROG_CXX’ are used in your ‘configure.ac’, Libtool language support will automatically be enabled. Conversely using ‘LT_LANG’ to enable language support for Libtool will automatically enable Autoconf language support as well. Both of the following examples are therefore valid ways of adding C++ language support to Libtool. LT_INIT LT_LANG([C++]) LT_INIT AC_PROG_CXX -- Macro: AC_LIBTOOL_DLOPEN This macro is deprecated, the ‘dlopen’ option to ‘LT_INIT’ should be used instead. -- Macro: AC_LIBTOOL_WIN32_DLL This macro is deprecated, the ‘win32-dll’ option to ‘LT_INIT’ should be used instead. -- Macro: AC_DISABLE_FAST_INSTALL This macro is deprecated, the ‘disable-fast-install’ option to ‘LT_INIT’ should be used instead. -- Macro: AC_DISABLE_SHARED -- Macro: AM_DISABLE_SHARED Change the default behaviour for ‘LT_INIT’ to disable shared libraries. The user may still override this default by specifying ‘--enable-shared’. The option ‘disable-shared’ to ‘LT_INIT’ is a shorthand for this. ‘AM_DISABLE_SHARED’ is a deprecated alias for ‘AC_DISABLE_SHARED’. -- Macro: AC_ENABLE_SHARED -- Macro: AM_ENABLE_SHARED Change the default behaviour for ‘LT_INIT’ to enable shared libraries. This is the default on all systems where Libtool knows how to create shared libraries. The user may still override this default by specifying ‘--disable-shared’. The option ‘shared’ to ‘LT_INIT’ is a shorthand for this. ‘AM_ENABLE_SHARED’ is a deprecated alias for ‘AC_ENABLE_SHARED’. -- Macro: AC_DISABLE_STATIC -- Macro: AM_DISABLE_STATIC Change the default behaviour for ‘LT_INIT’ to disable static libraries. The user may still override this default by specifying ‘--enable-static’. The option ‘disable-static’ to ‘LT_INIT’ is a shorthand for this. ‘AM_DISABLE_STATIC’ is a deprecated alias for ‘AC_DISABLE_STATIC’. -- Macro: AC_ENABLE_STATIC -- Macro: AM_ENABLE_STATIC Change the default behaviour for ‘LT_INIT’ to enable static libraries. This is the default on all systems where shared libraries have been disabled for some reason, and on most systems where shared libraries have been enabled. If shared libraries are enabled, the user may still override this default by specifying ‘--disable-static’. The option ‘static’ to ‘LT_INIT’ is a shorthand for this. ‘AM_ENABLE_STATIC’ is a deprecated alias for ‘AC_ENABLE_STATIC’. The tests in ‘LT_INIT’ also recognize the following environment variables: -- Variable: CC The C compiler that will be used by the generated ‘libtool’. If this is not set, ‘LT_INIT’ will look for ‘gcc’ or ‘cc’. -- Variable: CFLAGS Compiler flags used to generate standard object files. If this is not set, ‘LT_INIT’ will not use any such flags. It affects only the way ‘LT_INIT’ runs tests, not the produced ‘libtool’. -- Variable: CPPFLAGS C preprocessor flags. If this is not set, ‘LT_INIT’ will not use any such flags. It affects only the way ‘LT_INIT’ runs tests, not the produced ‘libtool’. -- Variable: LD The system linker to use (if the generated ‘libtool’ requires one). If this is not set, ‘LT_INIT’ will try to find out what is the linker used by ‘CC’. -- Variable: LDFLAGS The flags to be used by ‘libtool’ when it links a program. If this is not set, ‘LT_INIT’ will not use any such flags. It affects only the way ‘LT_INIT’ runs tests, not the produced ‘libtool’. -- Variable: LIBS The libraries to be used by ‘LT_INIT’ when it links a program. If this is not set, ‘LT_INIT’ will not use any such flags. It affects only the way ‘LT_INIT’ runs tests, not the produced ‘libtool’. -- Variable: NM Program to use rather than checking for ‘nm’. -- Variable: RANLIB Program to use rather than checking for ‘ranlib’. -- Variable: LN_S A command that creates a link of a program, a soft-link if possible, a hard-link otherwise. ‘LT_INIT’ will check for a suitable program if this variable is not set. -- Variable: DLLTOOL Program to use rather than checking for ‘dlltool’. Only meaningful for Cygwin/MS-Windows. -- Variable: OBJDUMP Program to use rather than checking for ‘objdump’. Only meaningful for Cygwin/MS-Windows. -- Variable: AS Program to use rather than checking for ‘as’. Only used on Cygwin/MS-Windows at the moment. -- Variable: MANIFEST_TOOL Program to use rather than checking for ‘mt’, the Manifest Tool. Only used on Cygwin/MS-Windows at the moment. -- Variable: LT_SYS_LIBRARY_PATH Libtool has heuristics for the system search path for runtime-loaded libraries. If the guessed default does not match the setup of the host system, this variable can be used to modify that path list, as follows (‘LT_SYS_LIBRARY_PATH’ is a colon-delimited list like ‘PATH’): • ‘path:’ The heuristically determined paths will be appended after the trailing colon; • ‘:path’ The heuristically determined paths will be prepended before the leading colon; • ‘path::path’ The heuristically determined paths will be inserted between the double colons; • ‘path’ With no dangling colons, the heuristically determined paths will be ignored entirely. With 1.3 era libtool, if you wanted to know any details of what libtool had discovered about your architecture and environment, you had to run the script with ‘--config’ and grep through the results. This idiom was supported up to and including 1.5.x era libtool, where it was possible to call the generated libtool script from ‘configure.ac’ as soon as ‘LT_INIT’ had completed. However, one of the features of libtool 1.4 was that the libtool configuration was migrated out of a separate ‘ltconfig’ file, and added to the ‘LT_INIT’ macro (nee ‘AC_PROG_LIBTOOL’), so the results of the configuration tests were available directly to code in ‘configure.ac’, rendering the call out to the generated libtool script obsolete. Starting with libtool 2.0, the multipass generation of the libtool script has been consolidated into a single ‘config.status’ pass, which happens after all the code in ‘configure.ac’ has completed. The implication of this is that the libtool script does not exist during execution of code from ‘configure.ac’, and so obviously it cannot be called for ‘--config’ details anymore. If you are upgrading projects that used this idiom to libtool 2.0 or newer, you should replace those calls with direct references to the equivalent Autoconf shell variables that are set by the configure time tests before being passed to ‘config.status’ for inclusion in the generated libtool script. -- Macro: LT_OUTPUT By default, the configured ‘libtool’ script is generated by the call to ‘AC_OUTPUT’ command, and there is rarely any need to use ‘libtool’ from ‘configure’. However, sometimes it is necessary to run configure time compile and link tests using ‘libtool’. You can add ‘LT_OUTPUT’ to your ‘configure.ac’ any time after ‘LT_INIT’ and any ‘LT_LANG’ calls; that done, ‘libtool’ will be created by a specially generated ‘config.lt’ file, and available for use in later tests. Also, when ‘LT_OUTPUT’ is used, for backwards compatibility with Automake regeneration rules, ‘config.status’ will call ‘config.lt’ to regenerate ‘libtool’, rather than generating the file itself. When you invoke the ‘libtoolize’ program (*note Invoking libtoolize::), it will tell you where to find a definition of ‘LT_INIT’. If you use Automake, the ‘aclocal’ program will automatically add ‘LT_INIT’ support to your ‘configure’ script when it sees the invocation of ‘LT_INIT’ in ‘configure.ac’. Because of these changes, and the runtime version compatibility checks Libtool now executes, we now advise *against* including a copy of ‘libtool.m4’ (and brethren) in ‘acinclude.m4’. Instead, you should set your project macro directory with ‘AC_CONFIG_MACRO_DIRS’. When you ‘libtoolize’ your project, a copy of the relevant macro definitions will be placed in your ‘AC_CONFIG_MACRO_DIRS’, where ‘aclocal’ can reference them directly from ‘aclocal.m4’. ---------- Footnotes ---------- (1) ‘LT_INIT’ requires that you define the ‘Makefile’ variable ‘top_builddir’ in your ‘Makefile.in’. Automake does this automatically, but Autoconf users should set it to the relative path to the top of your build directory (‘../..’, for example).
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