Messages in this thread | | | Date | Fri, 1 Nov 2019 11:06:11 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH RFC 1/6] perf/x86: Add perf text poke event |
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On Thu, Oct 31, 2019 at 12:29:15PM +0000, Mike Leach wrote: > On Thu, 31 Oct 2019 at 07:31, Leo Yan <leo.yan@linaro.org> wrote:
> > > Since all instructions (with the possible exception of RET) are > > > unconditional branch instructions: NOP, JMP, CALL. It makes no read > > > difference to the argument below. > > > > > > ( I'm thinking RET might be special in that it reads the return address > > > from the stack and therefore must emit the whole IP into the stream, as > > > we cannot know the stack state ) > > > > To be honest, I don't have knowledge what's the exactly format for 'ret' > > in CoreSight trace; so would like to leave this to Mike. > > > > For ETM trace we do not have to output the entire address into he stream if: > - address compression allows us to emit only the changed ls bit from the > last address. > - the address is identical to one of the last three addresses emitted ( we > just emit a ‘same address encoding’ > - we are using return stack compression and the address is top of the > return stack (we emit nothing and the decoder gets the address from its own > mode, of the return stack)
Cute. I don't actually know what PT does, but I figured there had to at least be the option to provide more information.
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