On Thu, Nov 15, 2012 at 9:19 PM, Jakub Jelinek <ja...@redhat.com> wrote: > On Thu, Nov 15, 2012 at 09:05:13AM -0800, Konstantin Serebryany wrote: >> +dvyukov, +glider, +samsonov >> >> Sorry I am lagging behind e-mail, but I am sure Dmitry, Alexander or >> Alexey may submit the patch upstream. >> Please make sure to comment the reason for using a separate typedef. >> >> We need our custom unwinder based on frame pointers to remain the >> default choice on x86[_64] because this is a hotspot >> and replacing it with any library call (especially if that call does >> not use frame pointers but instead uses debug info) will slow down >> the tool significantly. >> The asan docs explicitly say that you need -fno-omit-frame-pointers to >> get reasonable bug reports. > > The backtrace at asan crash time definitely isn't a hotspot, so that IMHO is > a place which definitely should use a proper and accurrate library > unwinding.
Asan collects stack traces on every malloc/free call. > Frame pointers aren't emitted by default on either x86_64 or > i?86, system libraries likely won't have them, unless people rebuild > everything with -fsanitize=address -fno-omit-frame-pointer (unlikely to > happen) etc. So relying on frame pointers is definitely very risky. If a user has asan build where he adds -fsanitize=address, it seems trivial to add -fno-omit-frame-pointer as well. > Even > libasan itself is right now built with, even explicit, -fomit-frame-pointer. That's the right thing. Asan does not unwind itself and performance critical.
