> On Jul 22, 2020, at 8:40 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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
