diff -r 000000000000 -r 6474c204b198 js/src/assembler/jit/ExecutableAllocatorWin.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/assembler/jit/ExecutableAllocatorWin.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,134 @@
+/*
+ * Copyright (C) 2008 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "assembler/jit/ExecutableAllocator.h"
+
+#if ENABLE_ASSEMBLER && WTF_OS_WINDOWS
+
+#include "jswin.h"
+#include "mozilla/WindowsVersion.h"
+
+extern uint64_t random_next(uint64_t *, int);
+
+namespace JSC {
+
+uint64_t ExecutableAllocator::rngSeed;
+
+size_t ExecutableAllocator::determinePageSize()
+{
+    SYSTEM_INFO system_info;
+    GetSystemInfo(&system_info);
+    return system_info.dwPageSize;
+}
+
+void *ExecutableAllocator::computeRandomAllocationAddress()
+{
+    /*
+     * Inspiration is V8's OS::Allocate in platform-win32.cc.
+     *
+     * VirtualAlloc takes 64K chunks out of the virtual address space, so we
+     * keep 16b alignment.
+     *
+     * x86: V8 comments say that keeping addresses in the [64MiB, 1GiB) range
+     * tries to avoid system default DLL mapping space. In the end, we get 13
+     * bits of randomness in our selection.
+     * x64: [2GiB, 4TiB), with 25 bits of randomness.
+     */
+    static const unsigned chunkBits = 16;
+#if WTF_CPU_X86_64
+    static const uintptr_t base = 0x0000000080000000;
+    static const uintptr_t mask = 0x000003ffffff0000;
+#elif WTF_CPU_X86
+    static const uintptr_t base = 0x04000000;
+    static const uintptr_t mask = 0x3fff0000;
+#else
+# error "Unsupported architecture"
+#endif
+    uint64_t rand = random_next(&rngSeed, 32) << chunkBits;
+    return (void *) (base | rand & mask);
+}
+
+static bool
+RandomizeIsBrokenImpl()
+{
+    // We disable everything before Vista, for now.
+    return !mozilla::IsVistaOrLater();
+}
+
+static bool
+RandomizeIsBroken()
+{
+    // Use the compiler's intrinsic guards for |static type value = expr| to avoid some potential
+    // races if runtimes are created from multiple threads.
+    static int result = RandomizeIsBrokenImpl();
+    return !!result;
+}
+
+ExecutablePool::Allocation ExecutableAllocator::systemAlloc(size_t n)
+{
+    void *allocation = NULL;
+    // Randomization disabled to avoid a performance fault on x64 builds.
+    // See bug 728623.
+#ifndef JS_CPU_X64
+    if (!RandomizeIsBroken()) {
+        void *randomAddress = computeRandomAllocationAddress();
+        allocation = VirtualAlloc(randomAddress, n, MEM_COMMIT | MEM_RESERVE,
+                                  PAGE_EXECUTE_READWRITE);
+    }
+#endif
+    if (!allocation)
+        allocation = VirtualAlloc(0, n, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
+    ExecutablePool::Allocation alloc = { reinterpret_cast<char*>(allocation), n };
+    return alloc;
+}
+
+void ExecutableAllocator::systemRelease(const ExecutablePool::Allocation& alloc)
+{
+    VirtualFree(alloc.pages, 0, MEM_RELEASE);
+}
+
+void
+ExecutablePool::toggleAllCodeAsAccessible(bool accessible)
+{
+    char* begin = m_allocation.pages;
+    size_t size = m_freePtr - begin;
+
+    if (size) {
+        // N.B. DEP is not on automatically in Windows XP, so be sure to use
+        // PAGE_NOACCESS instead of PAGE_READWRITE when making inaccessible.
+        DWORD oldProtect;
+        int flags = accessible ? PAGE_EXECUTE_READWRITE : PAGE_NOACCESS;
+        if (!VirtualProtect(begin, size, flags, &oldProtect))
+            MOZ_CRASH();
+    }
+}
+
+#if ENABLE_ASSEMBLER_WX_EXCLUSIVE
+#error "ASSEMBLER_WX_EXCLUSIVE not yet suported on this platform."
+#endif
+
+}
+
+#endif // HAVE(ASSEMBLER)