linux-kernel - Re: [PATCH] perf: Support for Openembedded/Yocto -dbg packages

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Message-ID: <20131002061335.GD31122@gmail.com>
Date:	Wed, 2 Oct 2013 08:13:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Waiman Long <Waiman.Long@...com>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf: Support for Openembedded/Yocto -dbg packages


* Namhyung Kim <namhyung@...nel.org> wrote:

> Hi Ingo and Arnaldo,
> 
> On Wed, 18 Sep 2013 15:29:03 +0200, Ingo Molnar wrote:
> > * Arnaldo Carvalho de Melo <acme@...stprotocols.net> wrote:
> >
> >> Em Wed, Sep 18, 2013 at 12:18:01PM +0200, Peter Zijlstra escreveu:
> >> > On Wed, Sep 18, 2013 at 12:02:12PM +0200, Ricardo Ribalda Delgado wrote:
> >> > > Perhaps this is even more clear than v2:
> >> 
> >> > > len = snprintf(file, size, "%s", symbol_conf.symfs);
> >> > > size -= len;
> >> > > file += len;
> >> > > len = snprintf(file, MIN(size,(last_slash - dso->long_name) + 2),
> >> > > "%s",  dso->long_name);
> >> > > size -= len;
> >> > > file += len;
> >> > > len = snprintf(file, size, ".debug%s",  last_slash);
> >> 
> >> > len = 0;
> >> 
> >> > len += snprintf(str + len, size - len, ...);
> >> > len += snprintf(str + len, size - len, ...);
> >> 
> >> And avoid snprintf like the plague, use scnprintf instead...  See
> >> e7f01d1e3d8d501deb8abeaa269d5d48a703b8b0 for details :-)
> >
> > Hm, could we do:
> >
> > 	#define snprintf scnprintf
> >
> > or:
> >
> > 	#define snprintf(x...) BUILD_BUG()
> >
> > ?
> >
> > I don't think there's any valid code, except printf wrappers (which we 
> > don't have in perf), where the semantics of snprintf() would be needed.
> 
> There are some places that use snprintf() to query the actual length:
> 
> tools/perf/util/srcline.c:245:	size = snprintf(NULL, 0, "%s:%u", file, line) + 1;
> tools/perf/util/values.c:147:		width = snprintf(NULL, 0, "%d", values->pid[i]);
> tools/perf/util/values.c:150:		width = snprintf(NULL, 0, "%d", values->tid[i]);
> tools/perf/util/values.c:154:			width = snprintf(NULL, 0, "%" PRIu64, values->value[i][j]);
> tools/perf/util/values.c:189:		width = snprintf(NULL, 0, "%d", values->pid[i]);
> tools/perf/util/values.c:192:		width = snprintf(NULL, 0, "%d", values->tid[i]);
> tools/perf/util/values.c:200:		width = snprintf(NULL, 0, "%" PRIx64, values->counterrawid[j]);
> tools/perf/util/values.c:206:			width = snprintf(NULL, 0, "%" PRIu64, values->value[i][j]);

I think that should be a separate, more obviously named helper inline 
instead, something like:

static inline printf_width(const char *fmt, ...)
{
        va_list args;
        int width;

        va_start(args, fmt);
        width = vsnprintf(NULL, 0, fmt, args);
        va_end(args);

        return width;
}

#define snprintf(fmt...) BUILD_BUG_ON(1, "Use scnprintf() instead of snprintf()")

or so? Then we could use it like this:

> tools/perf/util/values.c:147:		width = printf_width("%d", values->pid[i]);

and naked snprintf use would provoke a build bug.

Various printf wrappers can still use vsnprintf() - it's the routine use 
of snprintf() instead of scnprintf() that should be inhibited.

Thanks,

	Ingo
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