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

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Date:   Wed, 10 Apr 2019 10:08:41 -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 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,

Thanks,

- Arnaldo