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Re: PATCH: PR other/55333: libsanitizer StackTrace::FastUnwindStack wrong x32
On Thu, Nov 15, 2012 at 9:19 PM, Jakub Jelinek <jakub@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.