linux-kernel - Re: [PATCH 2/4] perf tools: Introduce cpu_map__snprint

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Date:   Sat, 25 Feb 2017 13:27:34 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        Steven Rostedt <rostedt@...dmis.org>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 2/4] perf tools: Introduce cpu_map__snprint_mask()

Hi Arnaldo,

On Fri, Feb 24, 2017 at 06:08:53PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Feb 24, 2017 at 10:12:49AM +0900, Namhyung Kim escreveu:
> > The cpu_map__snprint_mask() is to generate string representation of
> > cpumask bitmap.  For cpu 0 to 11, it'll return "fff".
> > 
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> >  tools/perf/util/cpumap.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> >  tools/perf/util/cpumap.h |  1 +
> >  2 files changed, 47 insertions(+)
> > 
> > diff --git a/tools/perf/util/cpumap.c b/tools/perf/util/cpumap.c
> > index 8c7504939113..08540ab2a891 100644
> > --- a/tools/perf/util/cpumap.c
> > +++ b/tools/perf/util/cpumap.c
> > @@ -673,3 +673,49 @@ size_t cpu_map__snprint(struct cpu_map *map, char *buf, size_t size)
> >  	pr_debug("cpumask list: %s\n", buf);
> >  	return ret;
> >  }
> > +
> > +static char hex_char(char val)
> 
> Why do you use 'char' above and...

My bad.  The argument should be unsigned.  The semantics is that it
converts a bitmap value into a character (string).

> 
> > +{
> > +	if (0 <= val && val <= 9)
> > +		return val + '0';
> > +	if (10 <= val && val < 16)
> > +		return val - 10 + 'a';
> > +	return '?';
> > +}
> > +size_t cpu_map__snprint_mask(struct cpu_map *map, char *buf, size_t size)
> <SNIP>
> > +	for (cpu = last_cpu / 4 * 4; cpu >= 0; cpu -= 4) {
> > +		unsigned char bits = bitmap[cpu / 8];
> 
> 'unsigned char' here?
> 
> Some compilers don't like it, for instance:
> 
>   19 fedora:24-x-ARC-uClibc: FAIL
> 
>   CC       /tmp/build/perf/util/cpumap.o
> util/cpumap.c: In function 'hex_char':
> util/cpumap.c:679:2: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (0 <= val && val <= 9)
>   ^
> cc1: all warnings being treated as errors
> 
> And:
> 
>   10 debian:experimental-x-arm64: FAIL
> 
>   CC       /tmp/build/perf/util/cpumap.o
> util/cpumap.c: In function 'hex_char':
> util/cpumap.c:679:8: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>   if (0 <= val && val <= 9)
>         ^~
> 
> Are you ok with the patch below?

I'd rather change hex_char() instead.  How about this?

diff --git a/tools/perf/util/cpumap.c b/tools/perf/util/cpumap.c
index 6ab8699f0233..061018b42393 100644
--- a/tools/perf/util/cpumap.c
+++ b/tools/perf/util/cpumap.c
@@ -674,11 +674,11 @@ size_t cpu_map__snprint(struct cpu_map *map, char *buf, size_t size)
        return ret;
 }
 
-static char hex_char(char val)
+static char hex_char(unsigned char val)
 {
-       if (0 <= val && val <= 9)
+       if (val < 10)
                return val + '0';
-       if (10 <= val && val < 16)
+       if (val < 16)
                return val - 10 + 'a';
        return '?';
 }