pkg-config vs. Cross Compile and Multi-arch

One of the areas where pkg-config can cause some problems is when trying to cross compile some code, or when working with multi-arch systems (such as bi-arch AMD64 Linux distros). While it is possible to use pkg-config in such systems by manipulating $PKG_CONFIG_PATH and/or $PKG_CONFIG_LIBDIR, users can't just follow the instructions given for the single-arch case.

After some discussion with Wolfgang Wieser, we came up with a proposal for better supporting cross-compile and multi-arch uses. The main changes would be:

  • Add a new --host option pkg-config. This would allow pkg-config to use different default search paths based on the host type, and search for .pc files in host type specific subdirs on the search path.
  • If an unknown host type is given, then no default search path is disabled altogether.
  • The autoconf macro would pass this argument whenever it detected that pkg-config supported it.

For the common case, this should allow most packages to be built for the non default architecture on a bi-arch system, or cross compiled, by just passing --host=foo to configure and (you might still need to set $CC or $CFLAGS, depending on the compiler setup).

For packages that install .pc files, they should continue to work. However it will be worth updating them to install their .pc file into a host type specific sub directory (the autoconf macros will make this easy to do).

If this code is likely to affect you, send comments to the pkg-config mailing list (or leave comments here).

Comments:

Ian Campbell -

I like the look of what you are doing, but thought you might be interested in how we have solved this problem for cross compiling.

We have a cross tool chain (e.g. arm-linux-gcc) which is installed into prefix /opt/arcom/. We then build pkg-config with --libdir=/opt/arcom/arm-linux/lib --program-prefix=arm-linux-

Now when we cross compile libraries we put their .pc into the arm-linux pkgconfig directory and when we build something using pkg-config we pass in $PKGCONFIG (or whatever it is called) as arm-linux-pkgconfig -- which has nice symmetry with overriding $CC etc. If --host=arm-linux would cause configure to search for arm-linux-pkgconfig automatically like it does with gcc then that would be even cooler.

This scheme probably doesn't help at all with bi-arch though.

Ian.

James Henstridge -

Ian: with these changes, you should be able to use the system's default pkg-config binary. It will just skip the system configured search paths, and only look in the directories you set in $PKG_CONFIG_PATH (which is the instructions most packages give you if installed packages can't be found).

Having multiple pkg-config binaries would be another option, but the only difference between them would be about 3 strings inside the binaries, which seems a bit wasteful. It also removes the need to recompile pkg-config when you want to target a new host type.