Implement workaround for BETTER_BACKTRACES crash

When compiling with BETTER_BACKTRACES enabled, Asterisk will sometimes
crash when "core show locks" is run. This happens regularly in the
testsuite since several tests run "core show locks" to help with
debugging. This seems to be a fault with libraries on certain operating
systems (notably CentOS 6.2/6.3) running on virtual machines and
utilizing gcc 4.4.6.

(closes issue ASTERISK-20090)
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Merged revisions 371690 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371691 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@371692 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/utils.c

@@ -788,16 +788,20 @@ static const char *locktype2str(enum ast_lock_type type)
 static void append_backtrace_information(struct ast_str **str, struct ast_bt *bt)
 {
 	char **symbols;
+	int num_frames;
 
 	if (!bt) {
 		ast_str_append(str, 0, "\tNo backtrace to print\n");
 		return;
 	}
 
-	if ((symbols = ast_bt_get_symbols(bt->addresses, bt->num_frames))) {
+	/* store frame count locally to avoid the memory corruption that
+	 * sometimes happens on virtualized CentOS 6.x systems */
+	num_frames = bt->num_frames;
+	if ((symbols = ast_bt_get_symbols(bt->addresses, num_frames))) {
 		int frame_iterator;
 
-		for (frame_iterator = 0; frame_iterator < bt->num_frames; ++frame_iterator) {
+		for (frame_iterator = 0; frame_iterator < num_frames; ++frame_iterator) {
 			ast_str_append(str, 0, "\t%s\n", symbols[frame_iterator]);
 		}