Cross-compilation and pkg-config

As it happens – and as I noted yesterday – one of my current gigs involves cross-compilation of Gentoo packages; this should also be obvious for those monitoring my commits. This sometimes involves simply fixing the ebuilds; and other times it needs to move up the stream and fix the buildsystem of the original project. Lately, I hit a number of the latter cases.

In the previous post, I noted that I fixed upower’s build system to not choose the backend based on the presence of files in the build’s machine. Somehow, checking for presence of files in the system to choose whether to enable stuff, or to install stuff, seems to be the thing to do for build system; a similar situation happened with SystemTap, that tries to identify the prefix of NSS and Avahi headers by checking for the /usr/include/nss and /usr/include/avahi-common directories, among others. Or, I should have said, tried, since luckily my two patches to solve those issues have also been merged today.

Another package I had to fix for cross-compilation recently was ecryptfs-utils, and again NSS is involved. This time rather than testing the presence of files, the build system did almost the right thing, and used the nss-config script that ships with the package to identify which flags and libraries to use. While it is a step in the right direction, compared to SystemTap’s, it is not yet the real right thing to do.

What is the problem? When you’re cross-compiling, simply calling nss-config will not do: the build machine’s script would be used, which will report the library paths of that system and not your target, which is what you really want. How do you solve this trouble then? Simple, you use the freedesktop-developed pkg-config utility, that can be easily rigged to handle cross-compilation nicely, even though it is not as immediate as you’d like, and if you ever tried using it in a cross-compilation environment, you probably remember the problems.

It is for this reason that I started writing cross-compile documentation for pkg-config in my Autotools Mythbuster quasi-book. Speaking about which, I’d like to find some time to spend focusing on writing more sections of it. To do so, though, my only chance is likely going to be if I get to take some vacation, and book a hotel room while I work on it: the former part is needed as right now my gigs tend to occupy my whole day leaving me with scarce to no free time, and the latter because at home I have too many things to take care of to actually focus on writing when I’m not working.

At any rate, please people, make sure you support pkg-config rather than rely on custom scripts that are not really cross-compilable.. it is the best thing you can do, trust me on this please.

One thought on “Cross-compilation and pkg-config

  1. “Too many ‘irons’ and not enough ‘fires'” I know the scenario well. I have the same issues to a degree. Much I want to accomplish but lack the time to allocate due to the ‘home’ environment. As well bringing up the skill level to something more widely productive is an added burden here.Be glad you don’t have a child as well. Those moments when you can concentrate on what you want to instead of ‘need’ to; become even fewer.Though there are a lot of nice rewards that go along with parenting I usually am not aware of them ;-PI’ll try real hard to review those last two sections before Monday and push any suggestions.


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