[PATCH] 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       | 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
--
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