Fix PartitionAlloc randomization on 32-bit systems

third_party/WebKit/Source/wtf/AddressSpaceRandomization.cpp

Index: third_party/WebKit/Source/wtf/AddressSpaceRandomization.cpp
diff --git a/third_party/WebKit/Source/wtf/AddressSpaceRandomization.cpp b/third_party/WebKit/Source/wtf/AddressSpaceRandomization.cpp
index 2a363a33e306649fdf2dfc68a43e537f20a8d937..d0344457802bd75f7e2971ec877044f4b5b84432 100644
--- a/third_party/WebKit/Source/wtf/AddressSpaceRandomization.cpp
+++ b/third_party/WebKit/Source/wtf/AddressSpaceRandomization.cpp
@@ -86,6 +86,9 @@ static struct ranctx s_ranctx;
 // space too badly.
 void* getRandomPageBase()
 {
+#if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)

[Alexander Potapenko, 2015/10/13 16:02:42]

You also need "if !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)" around the anonymous
namespace above.

[jschuh, 2015/10/13 17:44:13]

I dropped this approach and just added a custom range as we discussed over chat.

+    return nullptr;
+#else
     uintptr_t random;
     random = static_cast<uintptr_t>(ranval(&s_ranctx));
 #if CPU(X86_64)
@@ -108,6 +111,17 @@ void* getRandomPageBase()
     random &= 0x3fffffffffUL;
     random += 0x1000000000UL;
 #else // !CPU(X86_64) && !CPU(ARM64)
+#if OS(WIN)
+    // On win32 host systems the randomization plus huge alignment causes
+    // excessive fragmentation. Plus most of these systems lack ASLR, so the
+    // randomization isn't buying anything. In that case we just skip it.
+    // TODO(jschuh): Just dump the randomization when HE-ASLR is present.
+    static BOOL isWow64 = -1;
+    if (isWow64 == -1 && !IsWow64Process(GetCurrentProcess(), &isWow64))
+        isWow64 = FALSE;
+    if (!isWow64)
+        return nullptr;
+#endif // OS(WIN)
     // This is a good range on Windows, Linux and Mac.
     // Allocates in the 0.5-1.5GB region.
     random &= 0x3fffffff;
@@ -115,6 +129,7 @@ void* getRandomPageBase()
 #endif // CPU(X86_64)
     random &= kPageAllocationGranularityBaseMask;
     return reinterpret_cast<void*>(random);
+#endif // !MEMORY_TOOL_REPLACES_ALLOCATOR
 }
 
 }