linux-kernel - Re: [PATCH 1/2] perf expr: Force encapsulation on expr_id

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Message-ID: <CAP-5=fVT6wDwJPJFF30ttBeAcOxgkqiQgUPEKtwZWbPLJPqtBw@mail.gmail.com>
Date:   Wed, 26 Aug 2020 08:32:12 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Leo Yan <leo.yan@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/2] perf expr: Force encapsulation on expr_id_data

On Wed, Aug 26, 2020 at 4:34 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Tue, Aug 25, 2020 at 09:29:09PM -0700, Ian Rogers wrote:
> > This patch resolves some undefined behavior where variables in
> > expr_id_data were accessed (for debugging) without being defined. To
> > better enforce the tagged union behavior, the struct is moved into
> > expr.c and accessors provided. Tag values (kinds) are explicitly
> > identified.
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/perf/util/expr.c        | 64 ++++++++++++++++++++++++++++++-----
> >  tools/perf/util/expr.h        | 17 +++-------
> >  tools/perf/util/expr.y        |  2 +-
> >  tools/perf/util/metricgroup.c |  4 +--
> >  4 files changed, 62 insertions(+), 25 deletions(-)
> >
> > diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> > index 53482ef53c41..1ca0992db86b 100644
> > --- a/tools/perf/util/expr.c
> > +++ b/tools/perf/util/expr.c
> > @@ -17,6 +17,25 @@
> >  extern int expr_debug;
> >  #endif
> >
> > +struct expr_id_data {
> > +     union {
> > +             double val;
> > +             struct {
> > +                     double val;
> > +                     const char *metric_name;
> > +                     const char *metric_expr;
> > +             } ref;
> > +             struct expr_id  *parent;
> > +     };
> > +
> > +     enum {
> > +             EXPR_ID_DATA__VALUE,
> > +             EXPR_ID_DATA__REF,
> > +             EXPR_ID_DATA__REF_VALUE,
> > +             EXPR_ID_DATA__PARENT,
> > +     } kind;
>
> I like that, it's more clear than current state ;-)
>
> could you still put a small comment for each enum above,
> as a hint what it's used for?

Thanks, I had a go at this in v2:
https://lore.kernel.org/lkml/20200826153055.2067780-1-irogers@google.com/T/#u

Ian

> thanks,
> jirka
>