On 6 May 2015 at 13:08, Carl Eugen Hoyos <ceho...@ag.or.at> wrote: > Nick Lewycky <nlewycky <at> google.com> writes: > > > On 6 May 2015 at 11:58, Carl Eugen Hoyos: > > > > > Nick Lewycky <nlewycky <at> google.com> writes: > > > > > > > This occurs when building ffmpeg with clang > > > > -fsanitize=address -O1 -fPIE. > > > > > > What is the usecase for -O1? > > > > It's very important for asan. ASan instruments > > every memory access (outside inline asm, for now) > > and if we don't run the optimizer then every local > > variable is a stack allocation with loads and > > stores, and all those loads and stores get > > instrumented leading to both crazy slowdown and > > binary size increase. > > What I meant was (and I believe I wasn't clear): > What is the usecase for -O1 as opposed to default > optimization? > Or in other words: Is the issue with clang also > reproducible with -O2 and -O3? >
Oh I see. Yes, it does. I happened to use clang -O1 because that's our normal "unoptimized" ASan configuration where I first found the bug. I assume it doesn't happen at -O0 but I haven't checked, it does happen at higher optimization levels too. > > Did you check performance with and without > > > your patch? > > > > No. > > I believe such a performance test is a precondition > for an asm patch (but I am not the maintainer). > I'm new here, I don't even know to test ffmpeg performance. I'm happy to run something if you have a suggestion? My two arguments are that correctness trumps performance (otherwise ffmpeg could be "return 0" -- don't tempt me, I'm already a compiler optimization engineer ;-) ), and that this is exactly what ffmpeg already did with PIC disabled. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel