Reset Z_EXTRA_P(op2) of ZEND_INIT_FCALL for opcache file cache

The offset becomes stale if the environment changes. We're currently relying on
other factors in the environment staying constant, e.g. send types. But this
seems to be the worst offender.

Partially addresses phpGH-17733
Closes phpGH-20328

Author: iluuu1994

NEWS

@@ -55,6 +55,8 @@ PHP                                                                        NEWS
   . Fixed bug GH-19875 (JIT 1205 segfault on large file compiled in subprocess).
     (Arnaud)
   . Fixed bug GH-20012 (heap buffer overflow in jit). (Arnaud)
+  . Partially fixed bug GH-17733 (Avoid calling wrong function when reusing file
+    caches across differing environments). (ilutov)
 
 - PgSql:
   . Fix memory leak when first string conversion fails. (nielsdos)

ext/opcache/zend_file_cache.c

@@ -535,13 +535,32 @@ static void zend_file_cache_serialize_op_array(zend_op_array            *op_arra
 			}
 			if (opline->op2_type == IS_CONST) {
 				SERIALIZE_PTR(opline->op2.zv);
+
+				/* See GH-17733. Reset Z_EXTRA_P(op2) of ZEND_INIT_FCALL, which
+				 * is an offset into the global function table, to avoid calling
+				 * incorrect functions when environment changes. This, and the
+				 * equivalent code below, can be removed once proper system ID
+				 * validation is implemented. */
+				if (opline->opcode == ZEND_INIT_FCALL) {
+					zval *op2 = opline->op2.zv;
+					UNSERIALIZE_PTR(op2);
+					Z_EXTRA_P(op2) = 0;
+					ZEND_VM_SET_OPCODE_HANDLER(opline);
+				}
 			}
 #else
 			if (opline->op1_type == IS_CONST) {
 				opline->op1.constant = RT_CONSTANT(opline, opline->op1) - literals;
 			}
 			if (opline->op2_type == IS_CONST) {
-				opline->op2.constant = RT_CONSTANT(opline, opline->op2) - literals;
+				zval *op2 = RT_CONSTANT(opline, opline->op2);
+				opline->op2.constant = op2 - literals;
+
+				/* See GH-17733 and comment above. */
+				if (opline->opcode == ZEND_INIT_FCALL) {
+					Z_EXTRA_P(op2) = 0;
+					ZEND_VM_SET_OPCODE_HANDLER(opline);
+				}
 			}
 #endif
 #if ZEND_USE_ABS_JMP_ADDR