Merge branch 'PHP-7.4' into PHP-8.0

* PHP-7.4:
  Fix symtable cache being used while cleaning symtable

Author: nikic

Zend/tests/symtable_cache_recursive_dtor.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Symtable cache slots may be acquired while cleaning symtable
+--FILE--
+<?php
+class A {
+    // Must be larger than the symtable cache.
+    static $max = 40;
+    function __destruct() {
+        if (self::$max-- < 0) return;
+        $x = 'y';
+        $$x = new a;
+    }
+}
+new A;
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/zend_execute.c

@@ -3396,12 +3396,13 @@ ZEND_API void execute_internal(zend_execute_data *execute_data, zval *return_val
 
 ZEND_API void zend_clean_and_cache_symbol_table(zend_array *symbol_table) /* {{{ */
 {
+	/* Clean before putting into the cache, since clean could call dtors,
+	 * which could use the cached hash. Also do this before the check for
+	 * available cache slots, as those may be used by a dtor as well. */
+	zend_symtable_clean(symbol_table);
 	if (EG(symtable_cache_ptr) >= EG(symtable_cache_limit)) {
 		zend_array_destroy(symbol_table);
 	} else {
-		/* clean before putting into the cache, since clean
-		   could call dtors, which could use cached hash */
-		zend_symtable_clean(symbol_table);
 		*(EG(symtable_cache_ptr)++) = symbol_table;
 	}
 }