Since my blog post about forced --as-needed yesterday, I started building the whole portage in a chroot to see how many packages break with the forced --as-needed at build time. While build-time failure are not the only problem here (for stuff like Python, Perl and Ruby packages, the failure may well be at runtime), build-time failure are probably the most common problem with --as-needed; if we also used --no-undefined, like Robert Wohlrab is trying (maybe a little too enthusiastically), most of the failures would be at build time by the way.
As usual, testing one case also adds tests for other side cases, this time I’ve added further checks to tell me if packages install files in /usr/man, /usr/info, /usr/locale, /usr/doc, /usr/X11R6, …and filed quite a few bugs about that already. But even without counting these problems, the run started telling me some interesting thing that I might add to the --as-needed fixing guide when I get back to work on it (maybe even this very evening).
I already knew that most of the failures I’d be receiving would be related to packages that lack a proper buildsystem and thus ignored LDFLAGS up to now (included --as-needed), but there are a few notes that really gets interested here: custom ./configure scripts seem to almost always ignore LDFLAGS and yet fail to properly link packages; a few glib-based packages fail to link to libgthread the main executable, failing to find g_thread_init(); and a lot of packages link the wrong OpenSSL library (they link libssl when they should link libcrypto).
This last note, about OpenSSL libraries, is also a very nice and useful example to show how --as-needed helps users in two main ways. Let’s go over a scenario where a package links in libssl instead of libcrypto (since libssl requires libcrypto, the symbols are satisfied, if the link is done without --as-needed).
First point: ABI changes: if libssl changed its ABI (happens sometimes, you know…), but libcrypto kept the same, the program would require an useless rebuild: it’s not affected by libssl ABI, but by libcrypto’s.
Second point, maybe even more useful at runtime: when executing the program, the libraries in NEEDED are loaded, recursively. While libssl is not too big, it would still require loading one further library that is unneeded to the program since libcrypto is the one that is actually needed. I sincerely don’t know if libssl has any constructor functions, but when this extra load happens with libraries that have many more dependencies, or constructor functions, it’s going to be a quite huge hit for no good reason.
At any rate, I wish to thank again all the people who contributed to pay for Yamato, as you can see the horsepower in it is being put to good use (although I’m still just at app-portage); and just so I don’t have to stress it to do the same work over and over again, I can tell you that some of the checks I add to my chroots for building are being added to portage, thanks to Zac, who’s always blazing fast to add deeper QA and repoman warnings, so that further mistakes don’t creep into the new code.. one hopes, at least.
Oh and before people start expecting cmake to be perfect with --as-needed, since no package using it has been reported as failing with --as-needed … well the truth is that I can’t build any package using cmake in that chroot since it fails to build because of xmlrpc-c. And don’t get me started again on why a build system has to use XML-RPC without a chance for the user to tell “not even in your dreams”.