Alexander von Gluck IV <[email protected]> writes: > On Fri, 11 Oct 2013 09:50:08 -0700 > Francisco Jerez <[email protected]> wrote: > >> Kenneth Graunke <[email protected]> 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 fil >> 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. > > That would solve my issues. Do we need to do any kind of impact testing? I > haven't done much Mesa Linux development, so I'm not sure of the process. > Just send a git-send-email or git-format-patch formatted patch to the mailing list, and make sure to CC the original author of that commit so he can comment on that.
Thanks. > -- Alex
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