What are libtool's .la file for?

Question

What are libtool's .la files for? How are they used with a shared object?

Exorbitance

Also https://mcmap.net/q/74458/-what-39-s-the-difference-between-so-la-and-a-library-files/632951 – Sinkage

Answer 1

It is a textual file that includes a description of the library.

It allows libtool to create platform-independent names.

For example, libfoo goes to:

Under Linux:

/lib/libfoo.so       # Symlink to shared object
/lib/libfoo.so.1     # Symlink to shared object
/lib/libfoo.so.1.0.1 # Shared object
/lib/libfoo.a        # Static library
/lib/libfoo.la       # 'libtool' library

Under Cygwin:

/lib/libfoo.dll.a    # Import library
/lib/libfoo.a        # Static library
/lib/libfoo.la       # libtool library
/bin/cygfoo_1.dll    # DLL

Under Windows MinGW:

/lib/libfoo.dll.a    # Import library
/lib/libfoo.a        # Static library
/lib/libfoo.la       # 'libtool' library
/bin/foo_1.dll       # DLL

So libfoo.la is the only file that is preserved between platforms by libtool allowing to understand what happens with:

• Library dependencies
• Actual file names
• Library version and revision

Without depending on a specific platform implementation of libraries.

Mateya

so how to you turn the .la file to a platform specific shared lib file, like libfoo.la -> libfoo.so.* – Hodgkin

You can't libfoo.la holds only meta information, i.e. in libfoo.la (textual file) written where should you find libfoo.so.x.y.z – Mateya

Does it mean that in order to generate .la file, I need to use libtool (e.g. from automake)? One can rely on libtool to link the object files (gnu.org/software/libtool/manual/html_node/Using-Automake.html) but if I want to distribute a library without .la, does it mean it will be very difficult to link with it using Cygwin or mingw? – Bramante

In case that anyone want to disable this version stuff, you can use -avoid-version in your _la_LDFLAGS, instead of -version-info – Cribb

@Hodgkin as .la file holds metadata, it must have static library somewhere. To find that, You can run libtool --mode-link ${whatever_command_you_would_use_for_linking} -lfoo -L${where_libfoo.la_exists} and it will print the linking command as debug info. In my case the static files were in .libs/ folder containing *.la file – Circumjacent

Answer 2

According to http://blog.flameeyes.eu/2008/04/14/what-about-those-la-files, they're needed to handle dependencies. But using pkg-config may be a better option:

In a perfect world, every static library needing dependencies would have its own .pc file for pkg-config, and every package trying to statically link to that library would be using pkg-config --static to get the libraries to link to.

Sleigh

Answer 3

I found very good explanation about .la files here http://openbooks.sourceforge.net/books/wga/dealing-with-libraries.html

Summary (The way I understood): Because libtool deals with static and dynamic libraries internally (through --diable-shared or --disable-static) it creates a wrapper on the library files it builds. They are treated as binary library files with in libtool supported environment.

Didst