Re: [PATCH 2/2] perf: use XSI-complaint version of strerror_r() instead of GNU-specific

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Mon, Jul 23, 2012 at 02:00:33PM -0400, Ulrich Drepper wrote:
> On Mon, Jul 23, 2012 at 11:00 AM, Kirill A. Shutemov
> <kirill@shutemov.name> wrote:
> > The right way to fix it is to switch to XSI-compliant version.
> 
> And why exactly would this be "the right way"?  Just fix the use of
> strerror_r or use strerror_l.

Okay. What about this:

>From 8b76ea28a09ebc72c7bdcc1d92e80a63a5cdaf1c Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Date: Mon, 23 Jul 2012 17:41:05 +0300
Subject: [PATCH] perf: fix strerror_r() usage
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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@shutemov.name>
---
 tools/perf/ui/browsers/hists.c | 4 ++--
 tools/perf/util/target.c       | 9 ++++++++-
 2 files changed, 10 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..45ab408 100644
--- a/tools/perf/util/target.c
+++ b/tools/perf/util/target.c
@@ -111,7 +111,14 @@ int perf_target__strerror(struct perf_target *target, int errnum,
 	const char *msg;
 
 	if (errnum >= 0) {
-		strerror_r(errnum, buf, buflen);
+		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';
+		}
+
 		return 0;
 	}
 
-- 
 Kirill A. Shutemov