On 02/17/2017 12:21 PM, Alex Peshkoff wrote: > On 02/17/17 14:15, Stephan Bergmann wrote: >> On 02/17/2017 11:48 AM, Alex Peshkoff wrote: >>> On 02/16/17 15:52, Stephan Bergmann wrote: >>>> Forgive me if this has already been discussed or even fixed in later >>>> versions: At least the Firebird 3.0 we build as part of LibreOffice >>>> defines global operator new replacement functions in >>>> src/common/classes/alloc.h (forwarding to MemoryPool) that do not in >>>> general fulfil the alignment requirements for such functions. >>>> >>>> Came across this when Firebird compiled with a recent trunk Clang (with >>>> -O, and DEBUG_GDS_ALLOC being undefined) on x86_64-unknown-linux-gnu >>>> causes SEGV from misaligned MOVAPS instructions. >>>> >>> Yes - allocated memory is aligned at 8 bytes boundary now. >>> I've tried to set alignment to 16 but looks like that's far not 5 lines >>> patch - sometimes we were choosing between 4/8 bytes alignment, but last >>> years only 8 bytes alignment was used. >>> May be finding specific compiler flag to avoid this instruction is >>> simpler choice for today? >> (The way I work around this for now in LibreOffice is by always defining >> DEBUG_GDS_ALLOC when building with Clang on Linux X86-64, >> <https://cgit.freedesktop.org/libreoffice/core/commit/?id=8ea07101c1613d213fd7cea17f094a947b14cd00> >> "external/firebird: Work around operator new alignment violations". >> Since LibreOffice builds intended for widespread distribution are on >> Linux usually done with GCC not Clang, this shouldn't have a performance >> impact.) > > Afraid that this work around is not too stable (not to say more). > Certainly that macro does change details of memory allocation and may > provide 16-bit alignment in some particular case but be sure it's not > more than side effect and does not gurantee such alignment.
Note that I'm not relying on any 16-byte alignment there, but on the fact that Clang happens to make those aggressive alignment assumptions only for the replaceable global allocation functions. And with DEBUG_GDS_ALLOC defined, the global allocation functions defined in alloc.h are no longer replacements of such replaceable allocation functions. ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
