[Buildroot] On the usefulness of .la files and .pc files
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Wed Mar 18 16:44:50 UTC 2009
Hi,
My question is slightly out of topic because it doesn't concern
Buildroot specifically, but as it concerns the autotools build system,
I thought I could share it with the list.
When compiling libraries using libtool, a .la file gets installed
in /usr/lib. It defines several informations such as :
* The names of the library ;
* The dependencies of the library ;
* The directory where the library is installed ;
* A few other informations.
Many libraries also install a .pc file in /usr/lib/pkgconfig/. It also
describe the dependencies, the library name, the flags to compile new
applications/libraries on top of the library, etc.
I can't figure out why there are two different mechanisms. From my
understanding, both of these files serve the same purpose : describe
how new applications/libraries can be built against the library. Am I
wrong ?
Let's take the example of libpng. It installs :
* /usr/lib/libpng12.la, with things like
dlname='libpng12.so.0'
dependency_libs='-L/home/thomas/thirdparty/staging/usr/lib/ -lz -lm'
libdir='/usr/lib'
* /usr/lib/pkgconfig/libpng12.pc, with :
prefix=/usr
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include/libpng12
Name: libpng
Description: Loads and saves PNG files
Version: 1.2.35
Libs: -L${libdir} -lpng12
Libs.private: -lz -lm
Cflags: -I${includedir}
* /usr/bin/libpng12-config, which is a shell script that also
basically gives the same information.
While I understand that /usr/bin/libpng12-config is a legacy script
that predates the widespread usage of pkg-config, I can't figure out
why both the .pc file and .la file are needed.
Any insight ?
Thanks a lot!
Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com
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