Fix #79177: FFI doesn't handle well PHP exceptions within callback

When an FII callback function throws an unhandled exception, it makes
not much sense to return value to the C code.  Instead, we declare that
the return value is undefined in this case, and let userland deal with
that.

Author: cmb69

ext/ffi/ffi.c

@@ -886,6 +886,10 @@ static void zend_ffi_callback_trampoline(ffi_cif* cif, void* ret, void** args, v
 	}
 	free_alloca(fci.params, use_heap);
 
+	if (EG(exception)) {
+		return;
+	}
+
 	ret_type = ZEND_FFI_TYPE(callback_data->type->func.ret_type);
 	if (ret_type->kind != ZEND_FFI_TYPE_VOID) {
 		zend_ffi_zval_to_cdata(ret, ret_type, &retval);

ext/ffi/tests/bug79177.phpt

@@ -0,0 +1,40 @@
+--TEST--
+Bug #79177 (FFI doesn't handle well PHP exceptions within callback)
+--SKIPIF--
+<?php
+require_once('skipif.inc');
+require_once('utils.inc');
+try {
+    ffi_cdef("extern void *zend_printf;", ffi_get_php_dll_name());
+} catch (Throwable $e) {
+    die('skip PHP symbols not available');
+}
+?>
+--FILE--
+<?php
+require_once('utils.inc');
+$php = ffi_cdef("
+typedef char (*zend_write_func_t)(const char *str, size_t str_length);
+extern zend_write_func_t zend_write;
+", ffi_get_php_dll_name());
+
+echo "Before", PHP_EOL;
+
+$originalHandler = clone $php->zend_write;
+$php->zend_write = function($str, $len): string {
+    throw new \RuntimeException('Not allowed');
+};
+try { 
+    echo "After", PHP_EOL;
+} catch (\Throwable $exception) {
+    // Do not output anything here, as handler is overridden
+} finally {
+    $php->zend_write = $originalHandler;
+}
+if (isset($exception)) {
+    echo $exception->getMessage(), PHP_EOL;
+}
+?>
+--EXPECT--
+Before
+Not allowed