On 07/31/2017 05:15 PM, Jeff Law wrote: > It's supposed to. My concern would be that most of the time a > mis-aligned stack just works -- it's only when we see those key SSE2 > instructions that it'll fault. So bugs in this support could stay > latent for a long time. Exactly. I think GCC 6 was the first release were we saw GCC exploiting struct alignment for SSE2 to heap objects (because the *other* tcmalloc, in tchsh, did not follow ABI), and GCC 7 is the first release where we saw SSE2 stack stores in the rather non-vectorizable malloc code in glibc. I'm pretty sure all hell would break lose if we shipped the i686 compat userland with SSE2 optimization due to these issues, and I'm concerned that all things considered, turning on SSE2 optimizations is probably not worth the effort. Thanks, Florian
