linux-kernel - Re: [PATCH v3 1/3] perf: use hweight64 instead of hweight

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Date:   Wed, 10 Apr 2019 10:10:42 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Mao Han <han_mao@...ky.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v3 1/3] perf: use hweight64 instead of hweight_long

Em Wed, Apr 10, 2019 at 10:08:41AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Wed, Apr 10, 2019 at 04:16:43PM +0800, Mao Han escreveu:
> > On 32-bits platform with more than 32 registers, the 64 bits mask is
> > truncate to the lower 32 bits and the return value of hweight_long will
> > always smaller than 32. When kernel outputs more than 32 registers, but
> > the user perf program only counts 32, there will be a data mismatch
> > result to overflow check fail.
> > 
> > CC: Peter Zijlstra <peterz@...radead.org>
> > CC: Ingo Molnar <mingo@...hat.com>
> > CC: Arnaldo Carvalho de Melo <acme@...nel.org>
> > CC: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > CC: Jiri Olsa <jolsa@...hat.com>
> > CC: Namhyung Kim <namhyung@...nel.org>
> > 
> > Signed-off-by: Mao Han <han_mao@...ky.com>
> > ---
> >  tools/perf/util/evsel.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > index 7835e05..73c78be 100644
> > --- a/tools/perf/util/evsel.c
> > +++ b/tools/perf/util/evsel.c
> > @@ -2322,7 +2322,7 @@ int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
> >  		if (data->user_regs.abi) {
> >  			u64 mask = evsel->attr.sample_regs_user;
> >  
> > -			sz = hweight_long(mask) * sizeof(u64);
> > +			sz = hweight64(mask) * sizeof(u64);
> >  			OVERFLOW_CHECK(array, sz, max_size);
> >  			data->user_regs.mask = mask;
> >  			data->user_regs.regs = (u64 *)array;
> 
> Later on, in the same function, perf_evsel__parse_sample() we have:
> 
>         data->intr_regs.abi = PERF_SAMPLE_REGS_ABI_NONE;
>         if (type & PERF_SAMPLE_REGS_INTR) {
>                 OVERFLOW_CHECK_u64(array);
>                 data->intr_regs.abi = *array;
>                 array++;
> 
>                 if (data->intr_regs.abi != PERF_SAMPLE_REGS_ABI_NONE) {
>                         u64 mask = evsel->attr.sample_regs_intr;
> 
>                         sz = hweight_long(mask) * sizeof(u64);
>                         OVERFLOW_CHECK(array, sz, max_size);
>                         data->intr_regs.mask = mask;
>                         data->intr_regs.regs = (u64 *)array;
>                         array = (void *)array + sz;
>                 }
>         }
> 
> You forgot to convert that one, doing it for you,

Also in perf_event__sample_event_size() we need to do the same thing,
right?

- Arnaldo