Re: [PATCH v2 07/18] perf env: Remove unnecessary NULL tests

[Ian Rogers]

On Sun, Oct 8, 2023 at 11:14 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Thu, Oct 5, 2023 at 4:09 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > clang-tidy was warning:
> > ```
> > util/env.c:334:23: warning: Access to field 'nr_pmu_mappings' results in a dereference of a null pointer (loaded from variable 'env') [clang-analyzer-core.NullDereference]
> >         env->nr_pmu_mappings = 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@xxxxxxxxxx>
> > ---
> >  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 = 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 = 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 = perf_env__read_pmu_mappings(env);
> >                 if (status)
> >                         return NULL;
> > --
> > 2.42.0.609.gbb76f46606-goog
> >