[RFC PATCH] perf util: asprintf helper for leak sanitizer

[Ian Rogers <irogers@google.com>]

asprintf is a source of memory leaks but produces bad stack traces on
my Debian linux. This patch adds a simple asprintf implementation to
util.c that works around it.

Before output:
```
==1541752==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 10 byte(s) in 1 object(s) allocated from:
    #0 0x7f90c76b89cf in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69
    #1 0x7f90c649d2c7 in __vasprintf_internal libio/vasprintf.c:71
    #2 0x55ad9b79afbf  (/tmp/perf/perf+0x850fbf)

SUMMARY: AddressSanitizer: 10 byte(s) leaked in 1 allocation(s).
```

After output:
```
==1545918==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 10 byte(s) in 1 object(s) allocated from:
    #0 0x7f2755a7077b in __interceptor_strdup ../../../../src/libsanitizer/asan/asan_interceptors.cpp:439
    #1 0x564986a8df31 in asprintf util/util.c:566
    #2 0x5649869b5901 in metricgroup__lookup_default_metricgroup util/metricgroup.c:1520
    #3 0x5649869b5e57 in metricgroup__lookup_create util/metricgroup.c:1579
    #4 0x5649869b6ddc in parse_groups util/metricgroup.c:1698
    #5 0x5649869b7714 in metricgroup__parse_groups util/metricgroup.c:1771
    #6 0x5649867da9d5 in add_default_attributes tools/perf/builtin-stat.c:2164
    #7 0x5649867ddbfb in cmd_stat tools/perf/builtin-stat.c:2707
    #8 0x5649868fa5a2 in run_builtin tools/perf/perf.c:323
    #9 0x5649868fab13 in handle_internal_command tools/perf/perf.c:377
    #10 0x5649868faedb in run_argv tools/perf/perf.c:421
    #11 0x5649868fb443 in main tools/perf/perf.c:537
    #12 0x7f2754846189 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

SUMMARY: AddressSanitizer: 10 byte(s) leaked in 1 allocation(s).
```

RFC: is this useful for others? Should we have a build flag for it?
---
 tools/perf/util/util.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index c1fd9ba6d697..57eb528c5fed 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -552,3 +552,22 @@ int sched_getcpu(void)
 	return -1;
 }
 #endif
+
+int asprintf(char **restrict strp, const char *restrict fmt, ...)
+{
+	char buf[1024];
+	va_list ap;
+	int size;
+	char *result;
+
+	va_start(ap, fmt);
+	size = vsnprintf(buf, sizeof(buf), fmt, ap);
+	if (size < (int)sizeof(buf))
+		result = strdup(buf);
+	else
+		size = vasprintf(&result, fmt, ap);
+
+	*strp = result;
+	va_end(ap);
+	return size;
+}
-- 
2.41.0.162.gfafddb0af9-goog