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diff --git a/js/src/jit/AutoWritableJitCode.h b/js/src/jit/AutoWritableJitCode.h
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+++ b/js/src/jit/AutoWritableJitCode.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef jit_AutoWritableJitCode_h
+#define jit_AutoWritableJitCode_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/TimeStamp.h"
+
+#include <stddef.h>
+
+#include "jit/ExecutableAllocator.h"
+#include "jit/JitCode.h"
+#include "jit/ProcessExecutableMemory.h"
+#include "vm/JSContext.h"
+#include "vm/Realm.h"
+#include "vm/Runtime.h"
+
+namespace js::jit {
+
+// This class ensures JIT code is executable on its destruction. Creators
+// must call makeWritable(), and not attempt to write to the buffer if it fails.
+//
+// AutoWritableJitCodeFallible may only fail to make code writable; it cannot
+// fail to make JIT code executable (because the creating code has no chance to
+// recover from a failed destructor).
+class MOZ_RAII AutoWritableJitCodeFallible {
+  JSRuntime* rt_;
+  void* addr_;
+  size_t size_;
+
+ public:
+  AutoWritableJitCodeFallible(JSRuntime* rt, void* addr, size_t size)
+      : rt_(rt), addr_(addr), size_(size) {
+    rt_->toggleAutoWritableJitCodeActive(true);
+  }
+
+  AutoWritableJitCodeFallible(void* addr, size_t size)
+      : AutoWritableJitCodeFallible(TlsContext.get()->runtime(), addr, size) {}
+
+  explicit AutoWritableJitCodeFallible(JitCode* code)
+      : AutoWritableJitCodeFallible(code->runtimeFromMainThread(), code->raw(),
+                                    code->bufferSize()) {}
+
+  [[nodiscard]] bool makeWritable() {
+    return ExecutableAllocator::makeWritable(addr_, size_);
+  }
+
+  ~AutoWritableJitCodeFallible() {
+    mozilla::TimeStamp startTime = mozilla::TimeStamp::Now();
+    auto timer = mozilla::MakeScopeExit([&] {
+      if (Realm* realm = rt_->mainContextFromOwnThread()->realm()) {
+        realm->timers.protectTime += mozilla::TimeStamp::Now() - startTime;
+      }
+    });
+
+    if (!ExecutableAllocator::makeExecutableAndFlushICache(addr_, size_)) {
+      MOZ_CRASH();
+    }
+    rt_->toggleAutoWritableJitCodeActive(false);
+  }
+};
+
+// Infallible variant of AutoWritableJitCodeFallible, ensures writable during
+// construction
+class MOZ_RAII AutoWritableJitCode : private AutoWritableJitCodeFallible {
+ public:
+  AutoWritableJitCode(JSRuntime* rt, void* addr, size_t size)
+      : AutoWritableJitCodeFallible(rt, addr, size) {
+    MOZ_RELEASE_ASSERT(makeWritable());
+  }
+
+  AutoWritableJitCode(void* addr, size_t size)
+      : AutoWritableJitCode(TlsContext.get()->runtime(), addr, size) {}
+
+  explicit AutoWritableJitCode(JitCode* code)
+      : AutoWritableJitCode(code->runtimeFromMainThread(), code->raw(),
+                            code->bufferSize()) {}
+};
+
+}  // namespace js::jit
+
+#endif /* jit_AutoWritableJitCode_h */