Add API to exempt function from being traced in JIT (#15559)

Internally accessible via zend_jit_blacklist_function / externally via opcache_jit_blacklist.
The functionality currently only affects tracing JIT, but may be extended to other JIT modes in future.

Author: bwoebi

NEWS

@@ -27,6 +27,7 @@ PHP                                                                        NEWS
 
 - Opcache:
   . Fixed bug GH-15657 (Segmentation fault in dasm_x86.h). (nielsdos)
+  . Added opcache_jit_blacklist() function. (Bob)
 
 - PHPDBG:
   . Fixed bug GH-15901 (phpdbg: Assertion failure on i funcs). (cmb)

UPGRADING

@@ -820,6 +820,10 @@ PHP 8.4 UPGRADE NOTES
   . Added mb_ucfirst and mb_lcfirst functions.
     RFC: https://wiki.php.net/rfc/mb_ucfirst
 
+- OPCache:
+  . Added opcache_jit_blacklist function. It allows skipping the tracing JIT
+    execution of select functions.
+
 - PCNTL:
   . Added pcntl_setns allowing a process to be reassociated with a namespace in order
     to share resources with other processes within this context.

ext/opcache/jit/zend_jit.c

@@ -706,7 +706,7 @@ static bool zend_may_be_dynamic_property(zend_class_entry *ce, zend_string *memb
 # endif
 #endif
 
-void zend_jit_status(zval *ret)
+ZEND_EXT_API void zend_jit_status(zval *ret)
 {
 	zval stats;
 	array_init(&stats);

ext/opcache/jit/zend_jit.h

@@ -162,7 +162,8 @@ void zend_jit_startup(void *jit_buffer, size_t size, bool reattached);
 void zend_jit_shutdown(void);
 void zend_jit_activate(void);
 void zend_jit_deactivate(void);
-void zend_jit_status(zval *ret);
+ZEND_EXT_API void zend_jit_status(zval *ret);
+ZEND_EXT_API void zend_jit_blacklist_function(zend_op_array *op_array);
 void zend_jit_restart(void);
 
 #define ZREG_LOAD           (1<<0)

ext/opcache/jit/zend_jit_ir.c

@@ -10102,6 +10102,20 @@ static int zend_jit_do_fcall(zend_jit_ctx *jit, const zend_op *opline, const zen
 				ir_STORE(jit_EX(opline), jit_IP(jit));
 			}
 			jit_observer_fcall_begin(jit, rx, observer_handler);
+
+			if (trace) {
+				int32_t exit_point = zend_jit_trace_get_exit_point(opline, ZEND_JIT_EXIT_TO_VM);
+
+				exit_addr = zend_jit_trace_get_exit_addr(exit_point);
+				if (!exit_addr) {
+					return 0;
+				}
+			} else {
+				exit_addr = NULL;
+			}
+
+			zend_jit_check_timeout(jit, NULL /* we're inside the called function */, exit_addr);
+
 			jit_observer_fcall_is_unobserved_end(jit, &unobserved_data);
 		}
 

ext/opcache/jit/zend_jit_trace.c

@@ -7656,6 +7656,24 @@ static void zend_jit_blacklist_root_trace(const zend_op *opline, size_t offset)
 	zend_shared_alloc_unlock();
 }
 
+ZEND_EXT_API void zend_jit_blacklist_function(zend_op_array *op_array) {
+	zend_jit_op_array_trace_extension *jit_extension = (zend_jit_op_array_trace_extension *)ZEND_FUNC_INFO(op_array);
+	if (!jit_extension || !(jit_extension->func_info.flags & ZEND_FUNC_JIT_ON_HOT_TRACE)) {
+		return;
+	}
+
+	zend_shared_alloc_lock();
+	SHM_UNPROTECT();
+	zend_jit_unprotect();
+
+	zend_jit_stop_persistent_op_array(op_array);
+	jit_extension->func_info.flags &= ~ZEND_FUNC_JIT_ON_HOT_TRACE;
+
+	zend_jit_protect();
+	SHM_PROTECT();
+	zend_shared_alloc_unlock();
+}
+
 static bool zend_jit_trace_is_bad_root(const zend_op *opline, zend_jit_trace_stop stop, size_t offset)
 {
 	const zend_op **cache_opline = JIT_G(bad_root_cache_opline);

ext/opcache/jit/zend_jit_vm_helpers.c

@@ -521,16 +521,17 @@ static int zend_jit_trace_record_fake_init_call_ex(zend_execute_data *call, zend
 		 && (func->op_array.fn_flags & (ZEND_ACC_CLOSURE|ZEND_ACC_FAKE_CLOSURE))) {
 			return -1;
 		}
-		if (func->type == ZEND_USER_FUNCTION
-		 && (func->op_array.fn_flags & ZEND_ACC_CLOSURE)) {
+		if (func->type == ZEND_USER_FUNCTION) {
 			jit_extension =
 				(zend_jit_op_array_trace_extension*)ZEND_FUNC_INFO(&func->op_array);
-			if (UNEXPECTED(!jit_extension
-			 || !(jit_extension->func_info.flags & ZEND_FUNC_JIT_ON_HOT_TRACE)
-			 || (func->op_array.fn_flags & ZEND_ACC_FAKE_CLOSURE))) {
+            if (UNEXPECTED(!jit_extension && (func->op_array.fn_flags & ZEND_ACC_CLOSURE))
+			 || (jit_extension && !(jit_extension->func_info.flags & ZEND_FUNC_JIT_ON_HOT_TRACE))
+			 || (func->op_array.fn_flags & ZEND_ACC_FAKE_CLOSURE)) {
 				return -1;
 			}
-			func = (zend_function*)jit_extension->op_array;
+			if (func->op_array.fn_flags & ZEND_ACC_CLOSURE) {
+				func = (zend_function*)jit_extension->op_array;
+			}
 		}
 		if (is_megamorphic == ZEND_JIT_EXIT_POLYMORPHISM
 		 /* TODO: use more accurate check ??? */
@@ -1100,17 +1101,18 @@ zend_jit_trace_stop ZEND_FASTCALL zend_jit_trace_execute(zend_execute_data *ex,
 					stop = ZEND_JIT_TRACE_STOP_BAD_FUNC;
 					break;
 				}
-				if (func->type == ZEND_USER_FUNCTION
-				 && (func->op_array.fn_flags & ZEND_ACC_CLOSURE)) {
+				if (func->type == ZEND_USER_FUNCTION) {
 					jit_extension =
 						(zend_jit_op_array_trace_extension*)ZEND_FUNC_INFO(&func->op_array);
-					if (UNEXPECTED(!jit_extension)
-					 || !(jit_extension->func_info.flags & ZEND_FUNC_JIT_ON_HOT_TRACE)
+					if (UNEXPECTED(!jit_extension && (func->op_array.fn_flags & ZEND_ACC_CLOSURE))
+					 || (jit_extension && !(jit_extension->func_info.flags & ZEND_FUNC_JIT_ON_HOT_TRACE))
 					 || (func->op_array.fn_flags & ZEND_ACC_FAKE_CLOSURE)) {
 						stop = ZEND_JIT_TRACE_STOP_INTERPRETER;
 						break;
 					}
-					func = (zend_function*)jit_extension->op_array;
+					if (func->op_array.fn_flags & ZEND_ACC_CLOSURE) {
+						func = (zend_function*)jit_extension->op_array;
+					}
 				}
 
 #ifndef HAVE_GCC_GLOBAL_REGS

ext/opcache/opcache.stub.php

@@ -14,6 +14,8 @@ function opcache_compile_file(string $filename): bool {}
 
 function opcache_invalidate(string $filename, bool $force = false): bool {}
 
+function opcache_jit_blacklist(Closure $closure): void {}
+
 /**
  * @return array<string, mixed>|false
  * @refcount 1

ext/opcache/opcache_arginfo.h

@@ -0,0 +1,23 @@
+--TEST--
+Basic usage of opcache_jit_blacklist()
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.file_update_protection=0
+opcache.protect_memory=1
+opcache.jit=tracing
+--EXTENSIONS--
+opcache
+--FILE--
+<?php
+function foo() {
+    $x = 1;
+    $x += 0;
+    ++$x;
+    var_dump($x);
+}
+opcache_jit_blacklist(foo(...));
+foo();
+?>
+--EXPECT--
+int(2)

ext/opcache/tests/jit/opcache_jit_blacklist.phpt

@@ -24,6 +24,7 @@
 #include "php.h"
 #include "ZendAccelerator.h"
 #include "zend_API.h"
+#include "zend_closures.h"
 #include "zend_shared_alloc.h"
 #include "zend_accelerator_blacklist.h"
 #include "php_ini.h"
@@ -924,6 +925,21 @@ ZEND_FUNCTION(opcache_invalidate)
 	}
 }
 
+/* {{{ Prevents JIT on function. Call it before the first invocation of the given function. */
+ZEND_FUNCTION(opcache_jit_blacklist)
+{
+	zval *closure;
+
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "O", &closure, zend_ce_closure) == FAILURE) {
+		RETURN_THROWS();
+	}
+
+	const zend_function *func = zend_get_closure_method_def(Z_OBJ_P(closure));
+	if (ZEND_USER_CODE(func->type)) {
+		zend_jit_blacklist_function((zend_op_array *)&func->op_array);
+	}
+}
+
 ZEND_FUNCTION(opcache_compile_file)
 {
 	zend_string *script_name;