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

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Date:	Tue, 24 Jul 2012 00:06:54 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Ulrich Drepper <drepper@...il.com>
Cc:	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 Mon, Jul 23, 2012 at 04:48:22PM -0400, Ulrich Drepper wrote:
> On Mon, Jul 23, 2012 at 4:31 PM, Kirill A. Shutemov
> <kirill@...temov.name> wrote:
> > +               const char *err = strerror_r(errnum, buf, buflen);
> > +
> > +               if (err != buf && buflen > 0) {
> > +                       size_t len = strlen(err);
> > +                       char *c = mempcpy(buf, err, min(buflen - 1, len));
> > +                       *c = '\0';
> > +               }
> 
> No need to check for err == NULL.

There's no such check.

> buflen == 0 is a possibility given
> the interface but I'd say this is an error and should be tested for at
> the beginning of the function and the call should fail or even abort
> the program.

>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.

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);
+
 	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;
 	}
 
-- 
 Kirill A. Shutemov
--
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