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From:   Ian Rogers <irogers@google.com>
Date:   Mon, 9 Oct 2023 09:33:32 -0700
Message-ID: <CAP-5=fX1f022Z052mOxgJODg_jOPCqHScjZam2_3YwUXqriO4A@mail.gmail.com>
Subject: Re: [PATCH v2 07/18] perf env: Remove unnecessary NULL tests
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Yicong Yang <yangyicong@hisilicon.com>,
        Jonathan Cameron <jonathan.cameron@huawei.com>,
        Yang Jihong <yangjihong1@huawei.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Ming Wang <wangming01@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Yanteng Si <siyanteng@loongson.cn>,
        Yuan Can <yuancan@huawei.com>,
        Ravi Bangoria <ravi.bangoria@amd.com>,
        James Clark <james.clark@arm.com>, llvm@lists.linux.dev,
        linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        bpf@vger.kernel.org
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On Sun, Oct 8, 2023 at 11:14=E2=80=AFPM Namhyung Kim <namhyung@kernel.org> =
wrote:
>
> On Thu, Oct 5, 2023 at 4:09=E2=80=AFPM Ian Rogers <irogers@google.com> wr=
ote:
> >
> > clang-tidy was warning:
> > ```
> > util/env.c:334:23: warning: Access to field 'nr_pmu_mappings' results i=
n a dereference of a null pointer (loaded from variable 'env') [clang-analy=
zer-core.NullDereference]
> >         env->nr_pmu_mappings =3D pmu_num;
> > ```
> >
> > As functions are called potentially when !env was true. This condition
> > could never be true as it would produce a segv, so remove the
> > unnecessary NULL tests and silence clang-tidy.
>
> IIRC !env was to handle live sessions like perf top
> or when it doesn't have a perf data file.  Anyway,
> it doesn't seem to work anymore.

I trust the analyzer here and it would be better to crash earlier,
from env being NULL, than in a particular conditional branch. Like
you, I wasn't able to find a failure from removing the checks.

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/util/env.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/perf/util/env.c b/tools/perf/util/env.c
> > index a164164001fb..44140b7f596a 100644
> > --- a/tools/perf/util/env.c
> > +++ b/tools/perf/util/env.c
> > @@ -457,7 +457,7 @@ const char *perf_env__cpuid(struct perf_env *env)
> >  {
> >         int status;
> >
> > -       if (!env || !env->cpuid) { /* Assume local operation */
> > +       if (!env->cpuid) { /* Assume local operation */
> >                 status =3D perf_env__read_cpuid(env);
> >                 if (status)
> >                         return NULL;
> > @@ -470,7 +470,7 @@ int perf_env__nr_pmu_mappings(struct perf_env *env)
> >  {
> >         int status;
> >
> > -       if (!env || !env->nr_pmu_mappings) { /* Assume local operation =
*/
> > +       if (!env->nr_pmu_mappings) { /* Assume local operation */
> >                 status =3D perf_env__read_pmu_mappings(env);
> >                 if (status)
> >                         return 0;
> > @@ -483,7 +483,7 @@ const char *perf_env__pmu_mappings(struct perf_env =
*env)
> >  {
> >         int status;
> >
> > -       if (!env || !env->pmu_mappings) { /* Assume local operation */
> > +       if (!env->pmu_mappings) { /* Assume local operation */
> >                 status =3D perf_env__read_pmu_mappings(env);
> >                 if (status)
> >                         return NULL;
> > --
> > 2.42.0.609.gbb76f46606-goog
> >