"Ye, Joey" <joey...@intel.com> writes: > Option 3: Define BIGGEST_ALIGNMENT as a fixed value 32 bytes, for > all x86 target, and extend to 64 or more bytes in future.
Assuming that code compiled with -mavx is intended to interoperate with code compiled without -mavx, I believe that this is the only viable long-term option. Unfortunately that would be a change in the ABI for any code which exposes a struct with an attribute((aligned)) field. BIGGEST_ALIGNMENT should always be a constant for code which can interoperate. I doubt that many ABIs expose a struct with a field with attribute((aligned)), but as far as I can see we are going to have to break those ABIs eventually. The question now is whether we should break them for 4.4, for 4.5, or for some later version. That said, I should also note that the glibc solution has been to fix the maximum alignment at 8, in that that is the alignment which malloc returns on the x86. I don't think that is a wise choice, but it is a choice that we could also make: we could simply fix the x86 BIGGEST_ALIGNMENT at 16 and never change it in the future. Ian
