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Date:   Wed, 18 Nov 2020 10:35:45 +0100
From:   Jiri Olsa <jolsa@redhat.com>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
Cc:     Ian Rogers <irogers@google.com>, Jiri Olsa <jolsa@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Michael Petlan <mpetlan@redhat.com>,
        Song Liu <songliubraving@fb.com>,
        Stephane Eranian <eranian@google.com>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH 06/24] perf tools: Add build_id__is_defined function
Message-ID: <20201118093545.GB1414446@krava>
References: <20201117110053.1303113-1-jolsa@kernel.org>
 <20201117110053.1303113-7-jolsa@kernel.org>
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 <20201117205359.GJ1216482@krava>
 <20201117233313.GD657351@kernel.org>
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On Tue, Nov 17, 2020 at 08:33:13PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Nov 17, 2020 at 09:53:59PM +0100, Jiri Olsa escreveu:
> > On Tue, Nov 17, 2020 at 11:00:37AM -0800, Ian Rogers wrote:
> > > On Tue, Nov 17, 2020 at 3:01 AM Jiri Olsa <jolsa@kernel.org> wrote:
> > > 
> > > > Adding build_id__is_defined helper to check build id
> > > > is defined and is != zero build id.
> > > >
> > > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > > > ---
> > > >  tools/perf/util/build-id.c | 7 +++++++
> > > >  tools/perf/util/build-id.h | 1 +
> > > >  2 files changed, 8 insertions(+)
> > > >
> > > > diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
> > > > index 6b410c3d52dc..7d9ecc37849c 100644
> > > > --- a/tools/perf/util/build-id.c
> > > > +++ b/tools/perf/util/build-id.c
> > > > @@ -912,3 +912,10 @@ void build_id__init(struct build_id *bid, const u8
> > > > *data, size_t size)
> > > >         memcpy(bid->data, data, size);
> > > >         bid->size = size;
> > > >  }
> > > > +
> > > > +bool build_id__is_defined(const struct build_id *bid)
> > > > +{
> > > > +       static u8 zero[BUILD_ID_SIZE];
> > > > +
> > > > +       return bid && bid->size ? memcmp(bid->data, &zero, bid->size) :
> > > > false;
> 
> > > Fwiw, I find this method to test for zero a little hard to parse - I'm
> > 
> > heh, it's controversial one, Namhyung commented
> > on this one in previous version, so I changed it ;-)
> >   https://lore.kernel.org/lkml/CAM9d7cjjGjTN8sDgLZ1PoQZ-sUXWjnVaNdyOVE1yHxq46PrPkw@mail.gmail.com/
> 
> So, the kernel has an idiom for this in lib/string.c:
> 
> /**
>  * memchr_inv - Find an unmatching character in an area of memory.
>  * @start: The memory area
>  * @c: Find a character other than c
>  * @bytes: The size of the area.
>  *
>  * returns the address of the first character other than @c, or %NULL
>  * if the whole buffer contains just @c.
>  */
> void *memchr_inv(const void *start, int c, size_t bytes)
> 
> No need for any array of some particular size :-)

ok, will check

thanks,
jirka