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

[Kirill A. Shutemov]

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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