Don't use static (empty) strings as placeholder, but NULL instead

xdebug.c

@@ -415,9 +415,9 @@ static void php_xdebug_init_globals (zend_xdebug_globals *xg TSRMLS_DC)
 	xg->trace_context        = NULL;
 	xg->in_debug_info        = 0;
 	xg->coverage_enable      = 0;
-	xg->previous_filename    = "";
+	xg->previous_filename    = NULL;
 	xg->previous_file        = NULL;
-	xg->previous_mark_filename = "";
+	xg->previous_mark_filename = NULL;
 	xg->previous_mark_file     = NULL;
 	xg->paths_stack = NULL;
 	xg->branches.size        = 0;
@@ -1223,7 +1223,7 @@ PHP_RINIT_FUNCTION(xdebug)
 	XG(dead_code_analysis_tracker_offset) = zend_xdebug_cc_run_offset;
 	XG(dead_code_last_start_id) = 1;
 	XG(code_coverage_filter_offset) = zend_xdebug_filter_offset;
-	XG(previous_filename) = "";
+	XG(previous_filename) = NULL;
 	XG(previous_file) = NULL;
 	XG(gc_stats_file) = NULL;
 	XG(gc_stats_filename) = NULL;
@@ -1416,7 +1416,7 @@ ZEND_MODULE_POST_ZEND_DEACTIVATE_D(xdebug)
 		XG(branches).last_branch_nr = NULL;
 		XG(branches).size = 0;
 	}
-	XG(previous_mark_filename) = "";
+	XG(previous_mark_filename) = NULL;
 
 	return SUCCESS;
 }

xdebug_branch_info.c

@@ -339,7 +339,7 @@ void xdebug_branch_info_mark_reached(char *file_name, char *function_name, zend_
 	xdebug_coverage_function *function;
 	xdebug_branch_info *branch_info;
 
-	if (strcmp(XG(previous_mark_filename), file_name) == 0) {
+	if (XG(previous_mark_filename) && strcmp(XG(previous_mark_filename), file_name) == 0) {
 		file = XG(previous_mark_file);
 	} else {
 		if (!xdebug_hash_find(XG(code_coverage), file_name, strlen(file_name), (void *) &file)) {
@@ -401,7 +401,7 @@ void xdebug_branch_info_mark_end_of_function_reached(char *filename, char *funct
 	xdebug_branch_info *branch_info;
 	xdebug_path *path;
 
-	if (strcmp(XG(previous_mark_filename), filename) == 0) {
+	if (XG(previous_mark_filename) && strcmp(XG(previous_mark_filename), filename) == 0) {
 		file = XG(previous_mark_file);
 	} else {
 		if (!xdebug_hash_find(XG(code_coverage), filename, strlen(filename), (void *) &file)) {
@@ -434,7 +434,7 @@ void xdebug_branch_info_add_branches_and_paths(char *filename, char *function_na
 	xdebug_coverage_file *file;
 	xdebug_coverage_function *function;
 
-	if (strcmp(XG(previous_filename), filename) == 0) {
+	if (XG(previous_filename) && strcmp(XG(previous_filename), filename) == 0) {
 		file = XG(previous_file);
 	} else {
 		/* Check if the file already exists in the hash */

xdebug_code_coverage.c

@@ -471,7 +471,7 @@ void xdebug_count_line(char *filename, int lineno, int executable, int deadcode
 	xdebug_coverage_file *file;
 	xdebug_coverage_line *line;
 
-	if (strcmp(XG(previous_filename), filename) == 0) {
+	if (XG(previous_filename) && strcmp(XG(previous_filename), filename) == 0) {
 		file = XG(previous_file);
 	} else {
 		/* Check if the file already exists in the hash */
@@ -974,9 +974,9 @@ PHP_FUNCTION(xdebug_stop_code_coverage)
 	}
 	if (XG(do_code_coverage)) {
 		if (cleanup) {
-			XG(previous_filename) = "";
+			XG(previous_filename) = NULL;
 			XG(previous_file) = NULL;
-			XG(previous_mark_filename) = "";
+			XG(previous_mark_filename) = NULL;
 			XG(previous_mark_file) = NULL;
 			xdebug_hash_destroy(XG(code_coverage));
 			XG(code_coverage) = xdebug_hash_alloc(32, xdebug_coverage_file_dtor);