Introduce ZEND_OPCACHE_SHM_REATTACHMENT macro

Makes the code more self-documenting, avoiding a comment in all places. Also
makes testing easier on platforms that do not support shm reattachment.

Author: iluuu1994

Zend/zend_compile.c

@@ -8576,7 +8576,7 @@ static void zend_compile_property_hooks(
 	ce->num_hooked_props++;
 
 	/* See zend_link_hooked_object_iter(). */
-#ifndef ZEND_WIN32
+#ifndef ZEND_OPCACHE_SHM_REATTACHMENT
 	if (!ce->get_iterator) {
 		/* Will be removed again, in case of Iterator or IteratorAggregate. */
 		ce->get_iterator = zend_hooked_object_get_iterator;
@@ -9107,7 +9107,7 @@ static void zend_compile_class_decl(znode *result, zend_ast *ast, bool toplevel)
 
 	/* We currently don't early-bind classes that implement interfaces or use traits */
 	if (!ce->num_interfaces && !ce->num_traits && !ce->num_hooked_prop_variance_checks
-#ifdef ZEND_WIN32
+#ifdef ZEND_OPCACHE_SHM_REATTACHMENT
 	 /* See zend_link_hooked_object_iter(). */
 	 && !ce->num_hooked_props
 #endif

Zend/zend_inheritance.c

@@ -1746,15 +1746,10 @@ ZEND_API inheritance_status zend_verify_property_hook_variance(const zend_proper
 	return zend_perform_covariant_type_check(ce, prop_info->type, ce, value_arg_info->type);
 }
 
-#ifdef ZEND_WIN32
-/* Hooked properties set get_iterator, which causes issues on Windows. Windows
- * attaches multiple processes to the same shm, with each process potentially
- * having different addresses to the corresponding get_iterator function due to
- * ASLR. This prevents us from caching the class.
- *
- * To at least cache the unlinked class, avoid early-binding on Windows, and set
- * get_iterator during inheritance. The linked class may not use inheritance
- * cache. */
+#ifdef ZEND_OPCACHE_SHM_REATTACHMENT
+/* Hooked properties set get_iterator, which causes issues on for shm
+ * reattachment. Avoid early-binding on Windows and set get_iterator during
+ * inheritance. The linked class may not use inheritance cache. */
 static void zend_link_hooked_object_iter(zend_class_entry *ce) {
 	if (!ce->get_iterator && ce->num_hooked_props) {
 		ce->get_iterator = zend_hooked_object_get_iterator;
@@ -3431,7 +3426,7 @@ static zend_class_entry *zend_lazy_class_load(zend_class_entry *pce)
 	return ce;
 }
 
-#ifndef ZEND_WIN32
+#ifndef ZEND_OPCACHE_SHM_REATTACHMENT
 # define UPDATE_IS_CACHEABLE(ce) do { \
 			if ((ce)->type == ZEND_USER_CLASS) { \
 				is_cacheable &= (ce)->ce_flags; \
@@ -3576,7 +3571,7 @@ ZEND_API zend_class_entry *zend_do_link_class(zend_class_entry *ce, zend_string
 			zend_enum_register_funcs(ce);
 		}
 
-#ifdef ZEND_WIN32
+#ifdef ZEND_OPCACHE_SHM_REATTACHMENT
 		zend_link_hooked_object_iter(ce);
 #endif
 
@@ -3868,7 +3863,7 @@ ZEND_API zend_class_entry *zend_try_early_bind(zend_class_entry *ce, zend_class_
 				zend_begin_record_errors();
 			}
 
-#ifdef ZEND_WIN32
+#ifdef ZEND_OPCACHE_SHM_REATTACHMENT
 			zend_link_hooked_object_iter(ce);
 #endif
 

Zend/zend_portability.h

@@ -863,4 +863,11 @@ static zend_always_inline uint64_t ZEND_BYTES_SWAP64(uint64_t u)
 }
 #endif
 
+#ifdef ZEND_WIN32
+/* Whether it's allowed to reattach to a shm segment from different processes on
+ * this platform. This prevents pointing to internal structures from shm due to
+ * ASLR. Currently only possible on Windows. */
+# define ZEND_OPCACHE_SHM_REATTACHMENT 1
+#endif
+
 #endif /* ZEND_PORTABILITY_H */