10.7 Installing an Executable

Installing an executable uses exactly the same command line that I used to install the library earlier:

$ libtool cp hello /usr/local/bin gcc -o /tmp/libtool-28585/hello main.c /usr/local/lib/libhello.sl \ /usr/local/lib/libtrim.sl -Wl,+b -Wl,/usr/local/lib cp /tmp/libtool-28585/hello /usr/local/bin/hello $ /usr/local/bin/hello Hello, World!

As libtool said earlier, during the initial linking of the hello program in the build directory, hello must be rebuilt before installation. This is a peculiarity of HP-UX (and a few other architectures) which you won't see if you are following the examples on a GNU/Linux system. In the shell trace above, libtool has built an installable version of the hello program, saving me the trouble of remembering (or worse -- coding for) the particulars of HP-UX, which runs correctly from the installed location.

As a matter of interest, if you look at the attributes of the installed program using HP-UX's chatr command:

$ chatr /usr/local/bin/hello /usr/local/bin/hello: shared executable shared library dynamic path search: SHLIB_PATH disabled second embedded path enabled first /usr/local/lib internal name: /tmp/libtool-28585/hello shared library list: static /usr/local/lib/libhello.sl.0 static /usr/local/lib/libtrim.sl.0 dynamic /lib/libc.1 shared library binding: deferred ...

You can see that the runtime library search path for the installed hello program has been set to find the installed `libhello.sl.0' shared archive, preventing it from accidentally loading a different library (with the same name) from the default load path. This is a feature of libtool, and a very important one at that, and although it may not seem like the right way to do things initially, it saves a lot of trouble when you end up with several versions of a library installed in several locations, since each program will continue to use the version that it was linked with, subject to library versioning rules, see 11.4 Library Versioning.

Without the help of libtool, it is very difficult to prevent programs and libraries in the build tree from loading earlier (compatible) versions of a shared archive that were previously installed without an intimate knowledge of the build hosts architecture. Making it work portably would be nigh impossible! You should experiment with changes to the uninstalled library and satisfy yourself that the previously installed program continues to load the installed library at runtime, whereas the uninstalled program picks up the modifications in the uninstalled version of the library.

Equally importantly, the uninstalled hello program continues to load the uninstalled shared archive. This allows me to continue developing in the source directories and perform test builds in the knowledge that libtool has built all of my executables, including the uninstalled executables in the build tree, to load the correct version of the library. I can check wth HP-UX's chatr command, like this:

$ libtool --mode=execute chatr ./hello /tmp/hello/.libs/hello: shared executable shared library dynamic path search: SHLIB_PATH disabled second embedded path enabled first /tmp/intro-hello/.libs:\ /usr/local/lib internal name: .libs/hello shared library list: static /tmp/intro-hello/.libs/libhello.sl.0 static /tmp/intro-hello/.libs/libtrim.sl.0 dynamic /lib/libc.1 shared library binding: deferred ...

This example introduces the concept of Libtool modes. Most of the time libtool can infer a mode of operation from the contents of the command line, but sometimes (as in this example) it needs to be told. In 10.5 Executing Uninstalled Binaries we already used libtool in execute mode to run gdb against an uninstalled binary. In this example I am telling libtool that I want to pass the hello binary to the chatr command, particularly since I know that the `hello' file is a script to set the local execution environment before running the real binary.

The various modes that libtool has are described in the Libtool reference documentation, and are listed in the Libtool help text:

$ libtool --help ... MODE must be one of the following: clean remove files from the build directory compile compile a source file into a libtool object execute automatically set library path, then run a program finish complete the installation of libtool libraries install install libraries or executables link create a library or an executable uninstall remove libraries from an installed directory MODE-ARGS vary depending on the MODE. Try `libtool --help --mode=MODE' for a more detailed description of MODE.