Fix JIT stub veneers being reused after an OPcache restart on AArch64

ext/opcache/jit/zend_jit.c

@@ -3702,8 +3702,8 @@ void zend_jit_startup(void *buf, size_t size, bool reattached)
 		*dasm_ptr = (void**)*dasm_ptr + sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0]);
 #elif defined(IR_TARGET_AARCH64)
 		zend_jit_stub_handlers = dasm_buf;
-		*dasm_ptr = (void**)*dasm_ptr + (sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0])) * 2;
-		memset(zend_jit_stub_handlers, 0, (sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0])) * 2 * sizeof(void*));
+		*dasm_ptr = (void**)*dasm_ptr + (sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0])) * 3;
+		memset(zend_jit_stub_handlers, 0, (sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0])) * 3 * sizeof(void*));
 #endif
 		*dasm_ptr = (void*)ZEND_MM_ALIGNED_SIZE_EX(((size_t)(*dasm_ptr)), 16);
 		zend_jit_protect();
@@ -3889,6 +3889,9 @@ void zend_jit_restart(void)
 
 		/* restore JIT buffer pos */
 		dasm_ptr[0] = dasm_ptr[1];
+#if defined(IR_TARGET_AARCH64)
+		zend_jit_restore_stub_handlers();
+#endif
 
 		zend_jit_trace_restart();
 

ext/opcache/jit/zend_jit_ir.c

@@ -449,6 +449,24 @@ static void zend_jit_commit_veneers(void)
 		}
 	}
 }
+
+/* zend_jit_commit_veneers() replaces the address of a stub by the address of a veneer emitted
+ * after it. zend_jit_restart() rewinds the buffer below such veneers, so it restores the
+ * original addresses, kept after the pending veneers. */
+static void zend_jit_save_stub_handlers(void)
+{
+	int count = sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0]);
+
+	memcpy(zend_jit_stub_handlers + count * 2, zend_jit_stub_handlers, count * sizeof(void*));
+}
+
+static void zend_jit_restore_stub_handlers(void)
+{
+	int count = sizeof(zend_jit_stubs) / sizeof(zend_jit_stubs[0]);
+
+	memcpy(zend_jit_stub_handlers, zend_jit_stub_handlers + count * 2, count * sizeof(void*));
+	memset(zend_jit_stub_handlers + count, 0, count * sizeof(void*));
+}
 #endif
 
 static bool zend_jit_prefer_const_addr_load(zend_jit_ctx *jit, uintptr_t addr)
@@ -2969,6 +2987,9 @@ static void zend_jit_setup_stubs(void)
 		}
 		zend_jit_free_ctx(&jit);
 	}
+#if defined(IR_TARGET_AARCH64)
+	zend_jit_save_stub_handlers();
+#endif
 }
 
 #define REGISTER_HELPER(n)  \

ext/opcache/tests/jit/restart_stub_veneers.phpt

@@ -0,0 +1,117 @@
+--TEST--
+JIT stub handlers must not point to veneers discarded by an OPcache restart
+--DESCRIPTION--
+On AArch64, traces that are out of branch range of a stub get a veneer, and the address of the
+stub in zend_jit_stub_handlers[] is replaced by the address of that veneer. Code compiled after a
+restart must not branch to veneers in the discarded part of the JIT buffer. Needs more than 1 MB
+of JIT code, and different code after the restart than before it.
+--EXTENSIONS--
+opcache
+--SKIPIF--
+<?php
+if (ini_get('opcache.jit') === false) die('skip PHP is compiled without JIT');
+if (getenv('SKIP_SLOW_TESTS')) die('skip slow test');
+?>
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.jit=disable
+opcache.jit_buffer_size=16M
+--CONFLICTS--
+server
+--FILE--
+<?php
+$dir = __DIR__ . '/restart_stub_veneers';
+@mkdir($dir);
+@mkdir("$dir/a");
+@mkdir("$dir/b");
+
+/* Workload A: classes with hot loops */
+for ($i = 0; $i < 200; $i++) {
+    $src = "<?php\nclass C$i {\n";
+    for ($m = 0; $m < 6; $m++) {
+        $src .= "  public static function m$m(array \$a, int \$k): int {\n"
+            . "    \$s = $i;\n"
+            . "    foreach (\$a as \$j => \$v) { if ((\$v + \$k) % " . ($m + 2) . " === 0) { \$s += \$v * $m; } else { \$s ^= \$j; } \$s .= ''; \$s = (int)\$s; }\n"
+            . "    \$str = str_repeat('x', \$k % 7); \$s += strlen(\$str);\n"
+            . "    return \$s;\n  }\n";
+    }
+    file_put_contents("$dir/a/C$i.php", $src . "}\n");
+}
+
+/* Workload B: polymorphic branches, closures and caught exceptions */
+for ($i = 0; $i < 400; $i++) {
+    $src = "<?php\nclass P$i implements ArrayAccess {\n  private array \$d = [];\n"
+        . "  public function offsetExists(mixed \$o): bool { return isset(\$this->d[\$o]); }\n"
+        . "  public function offsetGet(mixed \$o): mixed { return \$this->d[\$o] ?? null; }\n"
+        . "  public function offsetSet(mixed \$o, mixed \$v): void { \$this->d[\$o] = \$v; }\n"
+        . "  public function offsetUnset(mixed \$o): void { unset(\$this->d[\$o]); }\n"
+        . "  public function run(array \$a): mixed { \$r = 0; foreach (\$a as \$k => \$v) {\n"
+        . "    if (is_int(\$v)) { \$r += \$v * $i; } elseif (is_string(\$v)) { \$r .= substr(\$v, 0, 2); } elseif (is_array(\$v)) { \$r = count(\$v) + (int)\$r; } else { \$r = \$v ?? \$r; }\n"
+        . "    \$this[\$k % 17] = \$r; \$x = fn(\$y) => \$y . \$k; \$r = is_string(\$r) ? strlen(\$x(\$r)) : \$r; }\n"
+        . "    try { if (\$r % " . (($i % 9) + 2) . " === 0) { throw new RuntimeException('x'); } } catch (Throwable \$e) { \$r++; }\n"
+        . "    return \$r; }\n}\n";
+    file_put_contents("$dir/b/P$i.php", $src);
+}
+
+file_put_contents("$dir/a.inc", <<<'PHP'
+<?php
+$a = range(1, 200);
+for ($i = 0; $i < 200; $i++) {
+    require_once __DIR__ . "/a/C$i.php";
+    $c = "C$i";
+    for ($r = 0; $r < 4; $r++) {
+        for ($m = 0; $m < 6; $m++) { $c::{"m$m"}($a, $r + $m); }
+    }
+}
+PHP);
+file_put_contents("$dir/b.inc", <<<'PHP'
+<?php
+$mix = [];
+for ($j = 0; $j < 120; $j++) { $mix[] = [$j, "s$j", [$j], null, 1.5][$j % 5]; }
+for ($i = 0; $i < 400; $i++) {
+    require_once __DIR__ . "/b/P$i.php";
+    $c = "P$i";
+    (new $c())->run($mix);
+}
+PHP);
+file_put_contents("$dir/b.php", "<?php\nrequire __DIR__ . '/b.inc';\necho \"b ok\\n\";\n");
+file_put_contents("$dir/ab.php", "<?php\nrequire __DIR__ . '/a.inc';\nrequire __DIR__ . '/b.inc';\necho \"ab ok\\n\";\n");
+file_put_contents("$dir/reset.php", "<?php\nvar_dump(opcache_reset());\n");
+
+include __DIR__ . '/../php_cli_server.inc';
+
+$ini = '-d opcache.enable=1 -d opcache.enable_cli=1 -d opcache.jit=tracing -d opcache.jit_buffer_size=64M'
+    . ' -d opcache.jit_max_root_traces=100000 -d opcache.jit_max_side_traces=100000'
+    . ' -d opcache.jit_max_exit_counters=65536 -d opcache.validate_timestamps=0'
+    . ' -d opcache.file_update_protection=0 -d error_reporting=' . (E_ALL & ~E_DEPRECATED);
+$ext = ini_get('extension_dir');
+if (file_exists($ext . DIRECTORY_SEPARATOR . (PHP_OS_FAMILY === 'Windows' ? 'php_opcache.dll' : 'opcache.so'))) {
+    $ini .= ' -d extension_dir=' . $ext . ' -d zend_extension=opcache';
+}
+php_cli_server_start($ini);
+
+$base = 'http://' . PHP_CLI_SERVER_ADDRESS . '/jit/restart_stub_veneers/';
+foreach (['b', 'b', 'reset', 'ab', 'ab'] as $script) {
+    echo @file_get_contents($base . $script . '.php') ?: "no response\n";
+}
+?>
+--CLEAN--
+<?php
+$dir = __DIR__ . '/restart_stub_veneers';
+foreach (array_merge(glob("$dir/a/*.php"), glob("$dir/b/*.php")) as $file) {
+    @unlink($file);
+}
+@rmdir("$dir/a");
+@rmdir("$dir/b");
+foreach (['a.inc', 'b.inc', 'b.php', 'ab.php', 'reset.php'] as $file) {
+    @unlink("$dir/$file");
+}
+@rmdir($dir);
+?>
+--EXPECT--
+b ok
+b ok
+bool(true)
+ab ok
+ab ok