[PATCH 2/2] perf: fix strerror_r() usage

From: Kirill A. Shutemov
Date: Mon Jul 23 2012 - 10:41:05 EST


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 âperf_target__strerrorâ:
util/target.c:114:13: error: ignoring return value of âstrerror_râ, declared with attribute warn_unused_result [-Werror=unused-result]
ui/browsers/hists.c: In function âhist_browser__dumpâ:
ui/browsers/hists.c:981:13: error: ignoring return value of âstrerror_râ, 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@xxxxxxxxxxxxx>
---
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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