perf tools: Fix errors under optimization level '-Og'

Optimization level '-Og' offers a reasonable level of optimization while
maintaining fast compilation and a good debugging experience. This patch
tries to make it work.

  $ make DEBUG=1 EXTRA_CFLAGS='-Og'
  bench/epoll-ctl.c: In function ‘do_threads’:
  bench/epoll-ctl.c:274:9: error: ‘ret’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
    return ret;
           ^~~
  ...

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20190316080556.3075-4-changbin.du@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: changbindu

tools/lib/bpf/libbpf.c

@@ -622,7 +622,7 @@ bpf_object__init_maps(struct bpf_object *obj, int flags)
 	bool strict = !(flags & MAPS_RELAX_COMPAT);
 	int i, map_idx, map_def_sz, nr_maps = 0;
 	Elf_Scn *scn;
-	Elf_Data *data;
+	Elf_Data *data = NULL;
 	Elf_Data *symbols = obj->efile.symbols;
 
 	if (obj->efile.maps_shndx < 0)

tools/perf/bench/epoll-ctl.c

@@ -224,7 +224,7 @@ static int do_threads(struct worker *worker, struct cpu_map *cpu)
 	pthread_attr_t thread_attr, *attrp = NULL;
 	cpu_set_t cpuset;
 	unsigned int i, j;
-	int ret;
+	int ret = 0;
 
 	if (!noaffinity)
 		pthread_attr_init(&thread_attr);

tools/perf/bench/epoll-wait.c

@@ -293,7 +293,7 @@ static int do_threads(struct worker *worker, struct cpu_map *cpu)
 	pthread_attr_t thread_attr, *attrp = NULL;
 	cpu_set_t cpuset;
 	unsigned int i, j;
-	int ret, events = EPOLLIN;
+	int ret = 0, events = EPOLLIN;
 
 	if (oneshot)
 		events |= EPOLLONESHOT;

tools/perf/tests/backward-ring-buffer.c

@@ -18,7 +18,7 @@ static void testcase(void)
 	int i;
 
 	for (i = 0; i < NR_ITERS; i++) {
-		char proc_name[10];
+		char proc_name[15];
 
 		snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);
 		prctl(PR_SET_NAME, proc_name);