> On Jul 22, 2020, at 8:40 AM, Peter Zijlstra <pet...@infradead.org> wrote:
>
> On Tue, Jul 21, 2020 at 10:40:19PM +0000, Song Liu wrote:
>
>> We only need to block precise_ip >= 2. precise_ip == 1 is OK.
>
> Uuuh, how? Anything PEBS would have the same problem. Sure, precise_ip
> == 1 will not correct the IP, but the stack will not match regardless.
>
> You need IP,SP(,BP) to be a consistent set _AND_ have it match the
> current stack, PEBS simply cannot do that, because the regs get recorded
> (much) earlier than the PMI and the stack can have changed in the
> meantime.
>
By "OK", I meant unwinder will not report error (in my tests). For
accurate stack, we should do the same for precise_ip == 1.
Thanks,
Song
