On 13/03/15 22:10, Francisco Jerez wrote: > Emil Velikov <emil.l.veli...@gmail.com> writes: > >> Hi all, >> >> Allow me to sum all that is said here, plus elaborate on some of the >> myths and alternative solutions proposed. >> >> Considering that this is a never ending and somewhat emotional topic, I >> would kindly ask people to read this while in their happy place. >> >> >> Myths >> ----- >> >> * "The LLVM-enabled variants of Mesa are the only implementations where >> this is an issue" >> >> Up-to recently all mesa drivers (not limited to LLVM) were using >> __builtin_clrsb if supported. IIRC that symbol was introduced with GCC >> 4.7 and was also causing problems until the Steam runtime was updated. >> >> >> * "... they use a subset of C++ that prevents them from needing to link >> with libstc++. Use of LLVM prevents much of Mesa from using that option." >> >> Based on reading the documentation and a quick test I did some ~3months >> ago, using C++'s "new" leads to dependency of the C++ runtime. >> >> >> >> The problem >> ----------- >> * Binary program X, ships it's own version of libgcc_s/libstdc++/foo. >> This problem is not new, afaict it existed for over 10 years, and there >> was never a single/simple/robust solution. >> >> >> The solutions >> ------------- >> * Allow people to static link against libgcc/libstdc++. >> >> Imho this should be option, disabled by default provided at configure >> time. This way builders/distributions can op-in if they choose to do so. >> >> >> * Always use the libraries provided by the distribution. >> * Use PackageKit-like solution to check/manage dependencies. >> >> In a open-source only environment this might work out but not for a >> binary only program/library. The people behind the latter have limited >> resources, thus it's virtually impossible to test it every distribution >> out there for each update of the said dependency. Some libraries have >> compatibility policies, some don't. Also distributions occasionally >> patch the library, which might cause additional issues. >> >> >> * Use bundled library if newer (check the SONAME). >> >> For libgcc_s at least, the library does not seems to be forward compatible. >> > > That belongs to your list of myths, see: > https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html > Well spotted! As I've checked this (experimentally) some months ago, but I wasn't 100% sure about it - thus the "seems" rather than "is".
Considering I cannot test atm (gcc 4.6 & gcc 4.7 fails to build), we'll say that I was delusional and add it to the myths list :P -Emil _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
