perf srcline: Do not consider empty files as valid srclines

Sometimes we get a non-null, but empty, string for the filename from
bfd. This then results in srclines of the form ":0", which is different
from the canonical SRCLINE_UNKNOWN in the form "??:0".  Set the file to
NULL if it is empty to fix this.
Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yao Jin <yao.jin@linux.intel.com>
Link: http://lkml.kernel.org/r/20170806212446.24925-14-milian.wolff@kdab.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/srcline.c

@@ -155,6 +155,9 @@ static void find_address_in_section(bfd *abfd, asection *section, void *data)
 	a2l->found = bfd_find_nearest_line(abfd, section, a2l->syms, pc - vma,
 					   &a2l->filename, &a2l->funcname,
 					   &a2l->line);
+
+	if (a2l->filename && !strlen(a2l->filename))
+		a2l->filename = NULL;
 }
 
 static struct a2l_data *addr2line_init(const char *path)
@@ -248,6 +251,9 @@ static int addr2line(const char *dso_name, u64 addr,
 					     &a2l->funcname, &a2l->line) &&
 		       cnt++ < MAX_INLINE_NEST) {
 
+			if (a2l->filename && !strlen(a2l->filename))
+				a2l->filename = NULL;
+
 			if (node != NULL) {
 				if (inline_list__append_dso_a2l(dso, node))
 					return 0;