https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77330
--- Comment #13 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- On Wed, 24 Aug 2016, bernd.edlinger at hotmail dot de wrote: > It is only necessary if __float128 is declared a base type. > But __m512 is no base type, right? It's clear that __m512 should not be considered a basic type - such types are a large part of the point of having aligned_alloc and other such aligned allocation interfaces. __float128 is now (GCC 7) an alias for _Float128, which is defined by TS 18661-3 to be a basic type (and _Decimal128 met the relevant requirements long before that). > Then MALLOC_ABI_ALIGNMENT should be changed to 128 at least for the i386. I think that would risk breaking applications that do not use any 16-byte-aligned types, without obvious benefits (only those programs that do use those types are affected by the present issue with malloc providing insufficient alignment). MALLOC_ABI_ALIGNMENT is indeed unnecessarily conservative. For glibc targets it could reflect the actual glibc logic, depending on the glibc version determined at GCC configure time - except that this might break things for applications that replace malloc with a version that yields lower alignment (possibly only for small allocations - if there is a 16-byte-aligned basic type, ISO C requires malloc (1) to return a 16-byte-aligned address, but some replacements may be for contexts where that is unnecessary), knowing the higher alignment is irrelevant to their application, so there would need to be some way to address that breakage.
