perf utils: Readlink /proc/self/exe to find the perf binary

Simplification: it is easier to open /proc/self/exe than /proc/$pid/exe.
Signed-off-by: NTommi Rantala <tommi.t.rantala@nokia.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170322130624.21881-7-tommi.t.rantala@nokia.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -370,15 +370,11 @@ static int write_cmdline(int fd, struct perf_header *h __maybe_unused,
 			 struct perf_evlist *evlist __maybe_unused)
 {
 	char buf[MAXPATHLEN];
-	char proc[32];
 	u32 n;
 	int i, ret;
 
-	/*
-	 * actual atual path to perf binary
-	 */
-	sprintf(proc, "/proc/%d/exe", getpid());
-	ret = readlink(proc, buf, sizeof(buf) - 1);
+	/* actual path to perf binary */
+	ret = readlink("/proc/self/exe", buf, sizeof(buf) - 1);
 	if (ret <= 0)
 		return -1;