linux-kernel - Re: [PATCH 15/19] perf tools: use XSI-complaint version of strerror

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Date:	Thu, 26 Jul 2012 09:39:59 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ulrich Drepper <drepper@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 15/19] perf tools: use XSI-complaint version of strerror_r() instead of GNU-specific

On Wed, 25 Jul 2012 14:41:30 -0300, Arnaldo Carvalho de Melo wrote:
> From: Kirill A. Shutemov <kirill@...temov.name>
>
> Perf uses GNU-specific version of strerror_r(). The GNU-specific strerror_r()
> returns a pointer to a string containing the error message.  This may be either
> a pointer to a string that the function stores in buf, or a pointer to some
> (immutable) static string (in which case buf is unused).
>
> In glibc-2.16 GNU version was marked with attribute warn_unused_result.  It
> triggers few warnings in perf:
>
> util/target.c: In function ‘perf_target__strerror’:
> util/target.c:114:13: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
> ui/browsers/hists.c: In function ‘hist_browser__dump’:
> ui/browsers/hists.c:981:13: error: ignoring return value of ‘strerror_r’, declared with attribute warn_unused_result [-Werror=unused-result]
>
> They are bugs.
>
> Let's fix strerror_r() usage.
>
> Signed-off-by: Kirill A. Shutemov <kirill@...temov.name>
> Acked-by: Ulrich Drepper <drepper@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Ulrich Drepper <drepper@...il.com>
> Link: http://lkml.kernel.org/r/20120723210654.GA25248@shutemov.name
> [ committer note: s/assert/BUG_ON/g ]
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/ui/browsers/hists.c |    4 ++--
>  tools/perf/util/target.c       |   11 ++++++++++-
>  2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
> index 482f051..413bd62 100644
> --- a/tools/perf/ui/browsers/hists.c
> +++ b/tools/perf/ui/browsers/hists.c
> @@ -978,8 +978,8 @@ static int hist_browser__dump(struct hist_browser *browser)
>  	fp = fopen(filename, "w");
>  	if (fp == NULL) {
>  		char bf[64];
> -		strerror_r(errno, bf, sizeof(bf));
> -		ui_helpline__fpush("Couldn't write to %s: %s", filename, bf);
> +		const char *err = strerror_r(errno, bf, sizeof(bf));
> +		ui_helpline__fpush("Couldn't write to %s: %s", filename, err);
>  		return -1;
>  	}
>  
> diff --git a/tools/perf/util/target.c b/tools/perf/util/target.c
> index 1064d5b..3f59c49 100644
> --- a/tools/perf/util/target.c
> +++ b/tools/perf/util/target.c
> @@ -110,8 +110,17 @@ int perf_target__strerror(struct perf_target *target, int errnum,
>  	int idx;
>  	const char *msg;
>  
> +	BUG_ON(buflen > 0);
> +

No! It should be

  	BUG_ON(buflen == 0);

Thanks,
Namhyung


>  	if (errnum >= 0) {
> -		strerror_r(errnum, buf, buflen);
> +		const char *err = strerror_r(errnum, buf, buflen);
> +
> +		if (err != buf) {
> +			size_t len = strlen(err);
> +			char *c = mempcpy(buf, err, min(buflen - 1, len));
> +			*c = '\0';
> +		}
> +
>  		return 0;
>  	}
--
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