Re: [PATCH] perf scripts python arm-cs-trace-disasm.py: Skip disasm if address continuity is broken

[James Clark]

On 23/08/2024 10:57 am, Ganapatrao Kulkarni wrote:
> Hi James/Mike,
>
> On 23-08-2024 02:33 pm, James Clark wrote:
> > On 19/08/2024 11:59 am, Mike Leach wrote:
> > > Hi,
> > >
> > > A new branch of OpenCSD is available - ocsd-consistency-checks-1.5.4-rc1
> > >
> > > Testing I managed to do confirms the N atom on unconditional branches
> > > appear to work. I do not have a test case for the range
> > > discontinuities.
> > >
> > > The checks are enabled using operation flags on decoder creation. See
> > > the docs for details.
> > >
> > > Mike
> >
> > Hi Mike,
> >
> > I tested the new OpenCSD and I don't see the error anymore in the
> > disassembly script. I'm not sure if we need to go any further and add
> > the backwards check, it looks like just a later symptom and the checks
> > that you've added already prevent it.
> >
> > If you release a new version I can send the perf patch. I was going to
> > use these flags if that looks right to you? As far as I know that's the
> > set that can be always on and won't fail on bad hardware?
> >
> > I also assumed that ETM4_OPFLG_PKTDEC_AA64_OPCODE_CHK can be given even
> > for etmv3 and it's just a nop?
> >
> > diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c 
> > b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> > index e917985bbbe6..90967fd807e6 100644
> > --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> > +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> > @@ -685,9 +685,14 @@ cs_etm_decoder__create_etm_decoder(struct 
> > cs_etm_decoder_params *d_params,
> >                  return 0;
> >
> >          if (d_params->operation == CS_ETM_OPERATION_DECODE) {
> > +               int decode_flags = OCSD_CREATE_FLG_FULL_DECODER;
> > +#ifdef OCSD_OPFLG_N_UNCOND_DIR_BR_CHK
> > +               decode_flags |= OCSD_OPFLG_N_UNCOND_DIR_BR_CHK | 
> > OCSD_OPFLG_CHK_RANGE_CONTINUE |
> > +                               ETM4_OPFLG_PKTDEC_AA64_OPCODE_CHK;
> > +#endif
> >                  if (ocsd_dt_create_decoder(decoder->dcd_tree,
> >                                             decoder->decoder_name,
> > -                                          OCSD_CREATE_FLG_FULL_DECODER,
> > +                                          decode_flags,
> >                                             trace_config, &csid))
> >                          return -1;
>
> I tried Mike's branch with above James's patch and still the segfault is 
> happening to us.

Looks like the Perf bug is only on the timestamped decode path, you can 
force timeless as a workaround. Timestamps aren't used by the 
disassembly script anyway:

  --itrace=Zb

Full command:

  perf script -i ./kcore -s python:tools/perf/scripts/python/arm-cs-\
     trace-disasm.py --itrace=Zb -- -k ./kcore/kcore_dir/kcore

You can also disable timestamps when recording then you don't need the 
itrace option. This will save you a lot of data anyway.

But I'm still working on the proper fix.