Fix GH-11715: opcache.interned_strings_buffer either has no effect or opcache_get_status() / phpinfo() is wrong

There are a couple of oddities.

1) The interned strings buffer comprises the whole hashtable
   datastructure.
   Therefore, it seems that the interned strings buffer size is the size of
   only said table. However, in the current code it also includes the size
   of the zend_accel_shared_globals.

2) ZCSG(interned_strings).end is computed starting from the accelerator
   globals struct itself. I would expect it to start from the part where
   the interned strings table starts.

3) When computing the used size, it is done using
   ZCSG(interned_strings).end - ZCSG(interned_strings).start. However,
   this does not include the uin32_t slots array because
   ZCSG(interned_strings).start pointers after that array.

This patch corrrects these 3 points.

Closes GH-11717.

Author: nielsdos

NEWS

@@ -5,6 +5,10 @@ PHP                                                                        NEWS
 - FFI:
   . Fix leaking definitions when using FFI::cdef()->new(...). (ilutov)
 
+- Opcache:
+  . Fixed bug GH-11715 (opcache.interned_strings_buffer either has no effect or
+    opcache_get_status() / phpinfo() is wrong). (nielsdos)
+
 03 Aug 2023, PHP 8.1.22
 
 - Build:

ext/opcache/ZendAccelerator.c

@@ -2856,7 +2856,7 @@ static int zend_accel_init_shm(void)
 	zend_shared_alloc_lock();
 
 	if (ZCG(accel_directives).interned_strings_buffer) {
-		accel_shared_globals = zend_shared_alloc((ZCG(accel_directives).interned_strings_buffer * 1024 * 1024));
+		accel_shared_globals = zend_shared_alloc(sizeof(zend_accel_shared_globals) + (ZCG(accel_directives).interned_strings_buffer * 1024 * 1024));
 	} else {
 		/* Make sure there is always at least one interned string hash slot,
 		 * so the table can be queried unconditionally. */
@@ -2893,7 +2893,7 @@ static int zend_accel_init_shm(void)
 		ZCSG(interned_strings).top =
 			ZCSG(interned_strings).start;
 		ZCSG(interned_strings).end =
-			(zend_string*)((char*)accel_shared_globals +
+			(zend_string*)((char*)(accel_shared_globals + 1) + /* table data is stored after accel_shared_globals */
 				ZCG(accel_directives).interned_strings_buffer * 1024 * 1024);
 		ZCSG(interned_strings).saved_top = NULL;
 

ext/opcache/tests/gh11715.phpt

@@ -0,0 +1,19 @@
+--TEST--
+GH-11715 (opcache.interned_strings_buffer either has no effect or opcache_get_status() / phpinfo() is wrong)
+--EXTENSIONS--
+opcache
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.interned_strings_buffer=16
+--FILE--
+<?php
+
+$info = opcache_get_status()['interned_strings_usage'];
+var_dump($info['used_memory'] + $info['free_memory']);
+var_dump($info['buffer_size']);
+
+?>
+--EXPECT--
+int(16777216)
+int(16777216)

ext/opcache/zend_accelerator_module.c

@@ -487,7 +487,7 @@ void zend_accel_info(ZEND_MODULE_INFO_FUNC_ARGS)
 			snprintf(buf, sizeof(buf), "%zu", ZSMMG(wasted_shared_memory));
 			php_info_print_table_row(2, "Wasted memory", buf);
 			if (ZCSG(interned_strings).start && ZCSG(interned_strings).end) {
-				snprintf(buf, sizeof(buf), "%zu", (size_t)((char*)ZCSG(interned_strings).top - (char*)ZCSG(interned_strings).start));
+				snprintf(buf, sizeof(buf), "%zu", (size_t)((char*)ZCSG(interned_strings).top - (char*)(accel_shared_globals + 1)));
 				php_info_print_table_row(2, "Interned Strings Used memory", buf);
 				snprintf(buf, sizeof(buf), "%zu", (size_t)((char*)ZCSG(interned_strings).end - (char*)ZCSG(interned_strings).top));
 				php_info_print_table_row(2, "Interned Strings Free memory", buf);
@@ -628,8 +628,8 @@ ZEND_FUNCTION(opcache_get_status)
 		zval interned_strings_usage;
 
 		array_init(&interned_strings_usage);
-		add_assoc_long(&interned_strings_usage, "buffer_size", (char*)ZCSG(interned_strings).end - (char*)ZCSG(interned_strings).start);
-		add_assoc_long(&interned_strings_usage, "used_memory", (char*)ZCSG(interned_strings).top - (char*)ZCSG(interned_strings).start);
+		add_assoc_long(&interned_strings_usage, "buffer_size", (char*)ZCSG(interned_strings).end - (char*)(accel_shared_globals + 1));
+		add_assoc_long(&interned_strings_usage, "used_memory", (char*)ZCSG(interned_strings).top - (char*)(accel_shared_globals + 1));
 		add_assoc_long(&interned_strings_usage, "free_memory", (char*)ZCSG(interned_strings).end - (char*)ZCSG(interned_strings).top);
 		add_assoc_long(&interned_strings_usage, "number_of_strings", ZCSG(interned_strings).nNumOfElements);
 		add_assoc_zval(return_value, "interned_strings_usage", &interned_strings_usage);