On Thu, 2014-07-17 at 15:10 +0200, Armin Rigo wrote:
>
> Thanks for the explanations! And, just to be complete, may I ask how
> PyPy finds the other libraries it needs,
Excellent question for a PyPy developer; to be honest, I actually have
very little idea :-)
I guess it just adds the -l / -L / -I flags (discovered either by
checking a pre-defined set of paths, or by running pkg-config) and hopes
that all the right libraries are installed and headers are at the
correct place, and blows up otherwise.
It seems from a cursory grep that the Makefile writing logic is here:
pypy/pypy/rpython/translator/platform
Specifically, see posix.py and linux.py.
> and how in general project X finds library Y that it depends on?
The build systems usually try pkg-config, then a list of pre-defined
locations and flags. Then a dummy executable is compiled, linked and
run. If it works, everything is great, if not, it complains and/or
disables the dependency.
Now, this has to do with building, but as we've established, the
buildpacks don't actually build anything, but rather unpack pre-compiled
binaries. In this case, it's a dynamic linker thing. In brief, it looks
for libraries in RPATH / LD_LIBRARY_PATH and standard locations.
Does this make sense to you?
> I still fail to see why we're discussing libffi specifically here...
Actually, I'm not sure about that either :-)
Maybe the machines provided by Heroku already have all other libraries
that the binaries of PyPy that you provide via the buildbot are
dynamically linked against, and so libffi is the only problematic one...
--
Sincerely yours,
Yury V. Zaytsev
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