linux-kernel - Re: [PATCH 2/2] perf: use XSI-complaint version of strerror

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Message-ID: <87zk6q564l.fsf@sejong.aot.lge.com>
Date:	Tue, 24 Jul 2012 09:56:26 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Ulrich Drepper <drepper@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf: use XSI-complaint version of strerror_r() instead of GNU-specific

On Tue, 24 Jul 2012 00:06:54 +0300, Kirill A. Shutemov wrote:
> From 11d62205ee3c534aa9b0e9a24a312438ac726ffb Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill@...temov.name>
> Date: Mon, 23 Jul 2012 17:41:05 +0300
> Subject: [PATCH 2/2] perf: fix strerror_r() usage
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> 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.
>

Thanks for fixing this. Just a minor nitpick below..


> Signed-off-by: Kirill A. Shutemov <kirill@...temov.name>
> ---
>  tools/perf/ui/browsers/hists.c |  4 ++--
>  tools/perf/util/target.c       | 12 +++++++++++-
>  2 files changed, 13 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..5c4b3b1 100644
> --- a/tools/perf/util/target.c
> +++ b/tools/perf/util/target.c
> @@ -9,6 +9,7 @@
>  #include "target.h"
>  #include "debug.h"
>  
> +#include <assert.h>
>  #include <pwd.h>
>  #include <string.h>
>  
> @@ -110,8 +111,17 @@ int perf_target__strerror(struct perf_target *target, int errnum,
>  	int idx;
>  	const char *msg;
>  
> +	assert(buflen > 0);
> +

It seems perf (and me too) prefers BUG_ON than assert:

  namhyung@...ong:perf$ git grep BUG_ON\( | wc -l
  55
  namhyung@...ong:perf$ git grep assert\( | wc -l
  16
  
It's not a big deal, though. I'm ok if others are happy with it.

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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