On Wed, Oct 26, 2016 at 4:01 PM, Martin Sebor <msebor@xxxxxxxxx> wrote: >> I believe -Wcast-align should be made to warn on x86/64 as well, in >> the light of the above, as now it is the most dangerous territory, >> where you only get crashes if the compiler decides to vectorize code >> AND you get unaligned memory (the crash I got was VERY hard to >> reproduce). >> >> The problem I see is a conflict between the C standard (accesses must >> be aligned for int, etc.) and the x86/64 machine (accesses need not be >> aligned for int, etc.), and GCC optimizations using the former, while >> the warning flag (-Wcast-align) taking the latter. >> >> I would like more comments, ideas on this in general as well. > > > -Wcast-align depends on the STRICT_ALIGNMENT GCC macro being > non-zero. The macro is set to zero for i386 which effectively > disables the warning. > > I agree that it would be useful to enable -Wcast-align even for > targets that tolerate unaligned accesses, not just for the reason > you mention but also to help detect invalid alignment assumptions > that may happen to be safe on the current target but not on others. -fsanitize=alignment ? https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html -- Mathieu
