Reduce stack usage in php_resolve_path()

tsrm_realpath() internally always allocates a string. If the out
parameter is provided it gets copied there and freed. What we
were doing here was to first copy the path from the allocated
string to a stack buffer, and then copy it from the stack buffer
to a zend_string. We might as well save one copy and one buffer.

main/fopen_wrappers.c

@@ -458,12 +458,22 @@ PHPAPI int php_fopen_primary_script(zend_file_handle *file_handle)
 }
 /* }}} */
 
+static zend_string *tsrm_realpath_str(const char *path) {
+	char *realpath = tsrm_realpath(path, NULL);
+	if (!realpath) {
+		return NULL;
+	}
+	zend_string *realpath_str = zend_string_init(realpath, strlen(realpath), 0);
+	efree(realpath);
+	return realpath_str;
+}
+
 /* {{{ php_resolve_path
  * Returns the realpath for given filename according to include path
  */
 PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_length, const char *path)
 {
-	char resolved_path[MAXPATHLEN];
+	zend_string *resolved_path;
 	char trypath[MAXPATHLEN];
 	const char *ptr, *end, *p;
 	const char *actual_path;
@@ -479,8 +489,8 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 	if ((*p == ':') && (p - filename > 1) && (p[1] == '/') && (p[2] == '/')) {
 		wrapper = php_stream_locate_url_wrapper(filename, &actual_path, STREAM_OPEN_FOR_INCLUDE);
 		if (wrapper == &php_plain_files_wrapper) {
-			if (tsrm_realpath(actual_path, resolved_path)) {
-				return zend_string_init(resolved_path, strlen(resolved_path), 0);
+			if ((resolved_path = tsrm_realpath_str(actual_path))) {
+				return resolved_path;
 			}
 		}
 		return NULL;
@@ -499,11 +509,7 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 #endif
 	    !path ||
 	    !*path) {
-		if (tsrm_realpath(filename, resolved_path)) {
-			return zend_string_init(resolved_path, strlen(resolved_path), 0);
-		} else {
-			return NULL;
-		}
+		return tsrm_realpath_str(filename);
 	}
 
 	ptr = path;
@@ -559,8 +565,8 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 				continue;
 			}
 		}
-		if (tsrm_realpath(actual_path, resolved_path)) {
-			return zend_string_init(resolved_path, strlen(resolved_path), 0);
+		if ((resolved_path = tsrm_realpath_str(actual_path))) {
+			return resolved_path;
 		}
 	} /* end provided path */
 
@@ -600,9 +606,7 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 				}
 			}
 
-			if (tsrm_realpath(actual_path, resolved_path)) {
-				return zend_string_init(resolved_path, strlen(resolved_path), 0);
-			}
+			return tsrm_realpath_str(actual_path);
 		}
 	}