[Zend]: Fix unnecessary alignment in ZEND_CALL_FRAME_SLOT macro (php#10988)

Alignment is not necessary while calculating slots reserved for
zend_execute_data and _zend_vm_stack.

ZEND_STATIC_ASSERT ensures the correct alignment while code
compilation. Credit is to Ilija Tovilo.

PR: php#10988

Signed-off-by: Tony Su <[email protected]>
Reviewed-by  : Ilija Tovilo
Reviewed-by  : Dmitry Stogov
Reviewed-by  : Niels Dossche

Author: Tony Su

Zend/zend_compile.h

@@ -606,8 +606,12 @@ struct _zend_execute_data {
 #define ZEND_CALL_NUM_ARGS(call) \
 	(call)->This.u2.num_args
 
+/* Ensure the correct alignment before slots calculation */
+ZEND_STATIC_ASSERT(ZEND_MM_ALIGNED_SIZE(sizeof(zval)) == sizeof(zval),
+                   "zval must be aligned by ZEND_MM_ALIGNMENT");
+/* A number of call frame slots (zvals) reserved for zend_execute_data. */
 #define ZEND_CALL_FRAME_SLOT \
-	((int)((ZEND_MM_ALIGNED_SIZE(sizeof(zend_execute_data)) + ZEND_MM_ALIGNED_SIZE(sizeof(zval)) - 1) / ZEND_MM_ALIGNED_SIZE(sizeof(zval))))
+	((int)((sizeof(zend_execute_data) + sizeof(zval) - 1) / sizeof(zval)))
 
 #define ZEND_CALL_VAR(call, n) \
 	((zval*)(((char*)(call)) + ((int)(n))))

Zend/zend_execute.h

@@ -195,8 +195,12 @@ struct _zend_vm_stack {
 	zend_vm_stack prev;
 };
 
+/* Ensure the correct alignment before slots calculation */
+ZEND_STATIC_ASSERT(ZEND_MM_ALIGNED_SIZE(sizeof(zval)) == sizeof(zval),
+                   "zval must be aligned by ZEND_MM_ALIGNMENT");
+/* A number of call frame slots (zvals) reserved for _zend_vm_stack. */
 #define ZEND_VM_STACK_HEADER_SLOTS \
-	((ZEND_MM_ALIGNED_SIZE(sizeof(struct _zend_vm_stack)) + ZEND_MM_ALIGNED_SIZE(sizeof(zval)) - 1) / ZEND_MM_ALIGNED_SIZE(sizeof(zval)))
+	((sizeof(struct _zend_vm_stack) + sizeof(zval) - 1) / sizeof(zval))
 
 #define ZEND_VM_STACK_ELEMENTS(stack) \
 	(((zval*)(stack)) + ZEND_VM_STACK_HEADER_SLOTS)

Zend/zend_portability.h

@@ -750,4 +750,10 @@ extern "C++" {
 # define ZEND_CGG_DIAGNOSTIC_IGNORED_END
 #endif
 
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L) /* C11 */
+# define ZEND_STATIC_ASSERT(c, m) _Static_assert((c), m)
+#else
+# define ZEND_STATIC_ASSERT(c, m)
+#endif
+
 #endif /* ZEND_PORTABILITY_H */