Make exit() unwind properly

exit() is now internally implemented by throwing an exception,
performing a normal stack unwind and a clean shutdown. This ensures
that no persistent resource leaks occur.

The exception is internal, cannot be caught and does not result in
the execution of finally blocks. This may be relaxed in the future.

Closes GH-5768.

1 files changed, 30 insertions, 1 deletions

diff --git a/Zend/zend_exceptions.c b/Zend/zend_exceptions.c
index 594186682b..63f994e580 100644
--- a/Zend/zend_exceptions.c
+++ b/Zend/zend_exceptions.c
@@ -41,6 +41,9 @@ ZEND_API zend_class_entry *zend_ce_value_error;
 ZEND_API zend_class_entry *zend_ce_arithmetic_error;
 ZEND_API zend_class_entry *zend_ce_division_by_zero_error;
 
+/* Internal pseudo-exception that is not exposed to userland. */
+static zend_class_entry zend_ce_unwind_exit;
+
 ZEND_API void (*zend_throw_exception_hook)(zval *ex);
 
 static zend_object_handlers default_exception_handlers;
@@ -81,6 +84,12 @@ void zend_exception_set_previous(zend_object *exception, zend_object *add_previo
 	if (exception == add_previous || !add_previous || !exception) {
 		return;
 	}
+
+	if (zend_is_unwind_exit(add_previous)) {
+		OBJ_RELEASE(add_previous);
+		return;
+	}
+
 	ZVAL_OBJ(&pv, add_previous);
 	if (!instanceof_function(Z_OBJCE(pv), zend_ce_throwable)) {
 		zend_error_noreturn(E_CORE_ERROR, "Previous exception must implement Throwable");
@@ -803,6 +812,8 @@ void zend_register_default_exception(void) /* {{{ */
 	INIT_CLASS_ENTRY(ce, "DivisionByZeroError", class_DivisionByZeroError_methods);
 	zend_ce_division_by_zero_error = zend_register_internal_class_ex(&ce, zend_ce_arithmetic_error);
 	zend_ce_division_by_zero_error->create_object = zend_default_exception_new;
+
+	INIT_CLASS_ENTRY(zend_ce_unwind_exit, "UnwindExit", NULL);
 }
 /* }}} */
 
@@ -898,10 +909,11 @@ static void zend_error_va(int type, const char *file, uint32_t lineno, const cha
 /* }}} */
 
 /* This function doesn't return if it uses E_ERROR */
-ZEND_API ZEND_COLD void zend_exception_error(zend_object *ex, int severity) /* {{{ */
+ZEND_API ZEND_COLD int zend_exception_error(zend_object *ex, int severity) /* {{{ */
 {
 	zval exception, rv;
 	zend_class_entry *ce_exception;
+	int result = FAILURE;
 
 	ZVAL_OBJ(&exception, ex);
 	ce_exception = ex->ce;
@@ -961,11 +973,15 @@ ZEND_API ZEND_COLD void zend_exception_error(zend_object *ex, int severity) /* {
 
 		zend_string_release_ex(str, 0);
 		zend_string_release_ex(file, 0);
+	} else if (ce_exception == &zend_ce_unwind_exit) {
+		/* We successfully unwound, nothing more to do */
+		result = SUCCESS;
 	} else {
 		zend_error(severity, "Uncaught exception '%s'", ZSTR_VAL(ce_exception->name));
 	}
 
 	OBJ_RELEASE(ex);
+	return result;
 }
 /* }}} */
 
@@ -987,3 +1003,16 @@ ZEND_API ZEND_COLD void zend_throw_exception_object(zval *exception) /* {{{ */
 	zend_throw_exception_internal(exception);
 }
 /* }}} */
+
+ZEND_API ZEND_COLD void zend_throw_unwind_exit()
+{
+	ZEND_ASSERT(!EG(exception));
+	EG(exception) = zend_objects_new(&zend_ce_unwind_exit);
+	EG(opline_before_exception) = EG(current_execute_data)->opline;
+	EG(current_execute_data)->opline = EG(exception_op);
+}
+
+ZEND_API zend_bool zend_is_unwind_exit(zend_object *ex)
+{
+	return ex->ce == &zend_ce_unwind_exit;
+}