Re: [PATCH v1] perf intel-pt: pkt-decoder: Fix alignment issues

[Ian Rogers]

On Thu, Oct 5, 2023 at 12:06 PM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 5/10/23 18:48, Ian Rogers wrote:
> > On Mon, Oct 2, 2023 at 3:19 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >>
> >> The byte aligned buffer is cast to large types and dereferenced
> >> causing misaligned pointer warnings from undefined behavior sanitizer.
> >> Fix the alignment issues with memcpy which may require the
> >> introduction of temporaries.
> >>
> >> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> >> ---
> >
> > This is a relatively small change that fixes building with
> > -fsanitize=alignment -fsanitize-undefined-trap-on-error. Adrian, as
> > this is Intel-PT could you take a look?
>
> Thanks! This has been down my list of things to do for ages,
> but using get_unaligned_le16() etc seems nicer.  I sent a patch
> set for that.

Thanks Adrian! Your patch set looks good and I think after Arnaldo's
comment is addressed we should go with it.

Ian

> >
> > Thanks,
> > Ian
> >
> >>  .../intel-pt-decoder/intel-pt-pkt-decoder.c   | 21 ++++++++++++-------
> >>  1 file changed, 14 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c b/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
> >> index af9710622a1f..28659874d84e 100644
> >> --- a/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
> >> +++ b/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
> >> @@ -83,7 +83,7 @@ static int intel_pt_get_long_tnt(const unsigned char *buf, size_t len,
> >>         if (len < 8)
> >>                 return INTEL_PT_NEED_MORE_BYTES;
> >>
> >> -       payload = le64_to_cpu(*(uint64_t *)buf);
> >> +       memcpy_le64(&payload, buf, sizeof(payload));
> >>
> >>         for (count = 47; count; count--) {
> >>                 if (payload & BIT63)
> >> @@ -220,6 +220,8 @@ static int intel_pt_get_3byte(const unsigned char *buf, size_t len,
> >>  static int intel_pt_get_ptwrite(const unsigned char *buf, size_t len,
> >>                                 struct intel_pt_pkt *packet)
> >>  {
> >> +       uint32_t tmp;
> >> +
> >>         packet->count = (buf[1] >> 5) & 0x3;
> >>         packet->type = buf[1] & BIT(7) ? INTEL_PT_PTWRITE_IP :
> >>                                          INTEL_PT_PTWRITE;
> >> @@ -228,12 +230,13 @@ static int intel_pt_get_ptwrite(const unsigned char *buf, size_t len,
> >>         case 0:
> >>                 if (len < 6)
> >>                         return INTEL_PT_NEED_MORE_BYTES;
> >> -               packet->payload = le32_to_cpu(*(uint32_t *)(buf + 2));
> >> +               memcpy(&tmp, buf + 2, sizeof(tmp));
> >> +               packet->payload = le32_to_cpu(tmp);
> >>                 return 6;
> >>         case 1:
> >>                 if (len < 10)
> >>                         return INTEL_PT_NEED_MORE_BYTES;
> >> -               packet->payload = le64_to_cpu(*(uint64_t *)(buf + 2));
> >> +               memcpy_le64(&packet->payload, buf + 2, sizeof(packet->payload));
> >>                 return 10;
> >>         default:
> >>                 return INTEL_PT_BAD_PACKET;
> >> @@ -258,7 +261,7 @@ static int intel_pt_get_mwait(const unsigned char *buf, size_t len,
> >>         if (len < 10)
> >>                 return INTEL_PT_NEED_MORE_BYTES;
> >>         packet->type = INTEL_PT_MWAIT;
> >> -       packet->payload = le64_to_cpu(*(uint64_t *)(buf + 2));
> >> +       memcpy_le64(&packet->payload, buf + 2, sizeof(packet->payload));
> >>         return 10;
> >>  }
> >>
> >> @@ -454,6 +457,8 @@ static int intel_pt_get_ip(enum intel_pt_pkt_type type, unsigned int byte,
> >>                            struct intel_pt_pkt *packet)
> >>  {
> >>         int ip_len;
> >> +       uint16_t tmp16;
> >> +       uint32_t tmp32;
> >>
> >>         packet->count = byte >> 5;
> >>
> >> @@ -465,13 +470,15 @@ static int intel_pt_get_ip(enum intel_pt_pkt_type type, unsigned int byte,
> >>                 if (len < 3)
> >>                         return INTEL_PT_NEED_MORE_BYTES;
> >>                 ip_len = 2;
> >> -               packet->payload = le16_to_cpu(*(uint16_t *)(buf + 1));
> >> +               memcpy(&tmp16, buf + 1, sizeof(tmp16));
> >> +               packet->payload = le16_to_cpu(tmp16);
> >>                 break;
> >>         case 2:
> >>                 if (len < 5)
> >>                         return INTEL_PT_NEED_MORE_BYTES;
> >>                 ip_len = 4;
> >> -               packet->payload = le32_to_cpu(*(uint32_t *)(buf + 1));
> >> +               memcpy(&tmp32, buf + 1, sizeof(tmp32));
> >> +               packet->payload = le32_to_cpu(tmp32);
> >>                 break;
> >>         case 3:
> >>         case 4:
> >> @@ -484,7 +491,7 @@ static int intel_pt_get_ip(enum intel_pt_pkt_type type, unsigned int byte,
> >>                 if (len < 9)
> >>                         return INTEL_PT_NEED_MORE_BYTES;
> >>                 ip_len = 8;
> >> -               packet->payload = le64_to_cpu(*(uint64_t *)(buf + 1));
> >> +               memcpy_le64(&packet->payload, buf + 1, sizeof(packet->payload));
> >>                 break;
> >>         default:
> >>                 return INTEL_PT_BAD_PACKET;
> >> --
> >> 2.42.0.582.g8ccd20d70d-goog
> >>
>