Kenneth Graunke <kenn...@whitecape.org> writes: > On 10/10/2013 04:27 PM, Alexander von Gluck IV wrote: >> >> In llvm.py -fno-rtti is always a build flag if LLVM present >= 3.2 >> >> This breaks everything on our end (missing rtti related symbols) in our >> C++ libGL.so as Haiku uses dynamic casts. >> >> We build our LLVM packages with rtti (REQUIRES_RTTI=1). >> >> Not 100% sure why we're forcing no-rtti if LLVM >= 3.2. >> "llvm-config --cxxflags" should always show "-fno-rtti" if REQUIRES_RTTI=1 >> wasn't set at build time. If REQUIRES_RTTI was set, -fno-rtti is removed >> from the llvm-config cxxflags. >> >> It was originally added here: >> http://cgit.freedesktop.org/mesa/mesa/commit/scons/llvm.py?id=d37ae642034bcaca39492c1eb75b029fb27ceffb >> >> My solutions are either removing the forced -fno-rtti, or wrapping it >> with a platform != 'Haiku' >> >> Thoughts? >> >> -- Alex > > I would love to see us build with -fno-rtti for all Linux builds. I've > been meaning to try that and measure the impact. > The -fno-rtti option is evil, it changes the C++ ABI in an incompatible way. As you may have noticed from the build error, in some cases it's impossible to link normal C++ object files with -fno-rtti object files if the interface between them exposes polymorphic types.
That's the reason why some LLVM versions require us to build the interfacing module with -fno-rtti, and the same versions require us to build *without* -fno-rtti if RTTI was enabled in the LLVM build, as might be the case in Haiku and some Linux distributions. AFAICT the 'if' statement in scons/llvm.py:198 and the automake conditional in configure.ac:1953 are broken and should probably be removed. LLVM doesn't require -fno-rtti unless llvm-config says otherwise, and if it still does in some case it's an llvm-config bug that can probably be addressed differently. I don't think it's a good idea to enable -fno-rtti except for isolated modules that can be guaranteed not to expose or use any C++ API. There are legitimate uses of RTTI, and enabling -fno-rtti means that modules that use it cannot talk to modules that don't. Thanks. > --Ken > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
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