perf tools: use XSI-complaint version of strerror_r() instead of GNU-specific

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>
Acked-by: Ulrich Drepper <drepper@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ulrich Drepper <drepper@gmail.com>
Link: http://lkml.kernel.org/r/20120723210654.GA25248@shutemov.name
[ committer note: s/assert/BUG_ON/g ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 12 insertions, 3 deletions

diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
index 482f0517b61e..413bd62eedb1 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 1064d5b148ad..3f59c496e64c 100644
--- a/tools/perf/util/target.c
+++ b/tools/perf/util/target.c
@@ -110,8 +110,17 @@ int perf_target__strerror(struct perf_target *target, int errnum,
         int idx;
         const char *msg;
 
+        BUG_ON(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;
         }