perf tools: Use the DWARF unwind info only if loaded

Use the info only if it has been found in the .debug_frame section of
the ELF binary.

Signed-off-by: Jean Pihet <jean.pihet@linaro.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linaro-kernel@lists.linaro.org
Cc: patches@linaro.org
Link: http://lkml.kernel.org/r/1387212194-8028-1-git-send-email-jean.pihet@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/unwind.c

@@ -340,10 +340,10 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
 	/* Check the .debug_frame section for unwinding info */
 	if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
 		memset(&di, 0, sizeof(di));
-		dwarf_find_debug_frame(0, &di, ip, 0, map->dso->name,
-				       map->start, map->end);
-		return dwarf_search_unwind_table(as, ip, &di, pi,
-						 need_unwind_info, arg);
+		if (dwarf_find_debug_frame(0, &di, ip, 0, map->dso->name,
+					   map->start, map->end))
+			return dwarf_search_unwind_table(as, ip, &di, pi,
+							 need_unwind_info, arg);
 	}
 #endif