Improve seeding of AddressSpaceRandomization randomness.

Source/wtf/AddressSpaceRandomization.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "wtf/AddressSpaceRandomization.h"
 
 #include "wtf/PageAllocator.h"
-#include "wtf/ProcessID.h"
 #include "wtf/SpinLock.h"
 
+#if OS(WIN)
+#include <windows.h>
+#else
+#include <sys/time.h>
+#include <unistd.h>
+#endif
+
 namespace WTF {
 
 namespace {
 
 // This is the same PRNG as used by tcmalloc for mapping address randomness;
 // see http://burtleburtle.net/bob/rand/smallprng.html
 struct ranctx {
     int lock;
     bool initialized;
     uint32_t a;
@@ skipping 16 matching lines @@
 
 #undef rot
 
 uint32_t ranval(ranctx* x)
 {
     spinLockLock(&x->lock);
     if (UNLIKELY(!x->initialized)) {
         x->initialized = true;
         char c;
         uint32_t seed = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(&c));
-        seed ^= static_cast<uint32_t>(getCurrentProcessID());
+        uint32_t pid;
+        uint32_t usec;
+#if OS(WIN)
+        pid = GetCurrentProcessId();
+        SYSTEMTIME st;
+        GetSystemTime(&st);
+        usec = static_cast<uint32_t>(st.wMilliseconds * 1000);
+#else
+        pid = static_cast<uint32_t>(getpid());
+        struct timeval tv;
+        gettimeofday(&tv, 0);
+        usec = static_cast<uint32_t>(tv.tv_usec);
+#endif
+        seed ^= pid;
+        seed ^= usec;
         x->a = 0xf1ea5eed;
         x->b = x->c = x->d = seed;
         for (int i = 0; i < 20; ++i) {
             (void) ranvalInternal(x);
         }
     }
     uint32_t ret = ranvalInternal(x);
     spinLockUnlock(&x->lock);
     return ret;
 }
@@ skipping 10 matching lines @@
     uintptr_t random;
     random = static_cast<uintptr_t>(ranval(&s_ranctx));
 #if CPU(X86_64)
     random <<= 32UL;
     random |= static_cast<uintptr_t>(ranval(&s_ranctx));
     // This address mask gives a low liklihood of address space collisions.
     // We handle the situation gracefully if there is a collision.
 #if OS(WIN)
     // 64-bit Windows has a bizarrely small 8TB user address space.
     // Allocates in the 1-5TB region.
+    // TODO(cevans): I think Win 8.1 has 47-bits like Linux.
     random &= 0x3ffffffffffUL;
     random += 0x10000000000UL;
 #else
     // Linux and OS X support the full 47-bit user space of x64 processors.
     random &= 0x3fffffffffffUL;
 #endif
 #elif CPU(ARM64)
     // ARM64 on Linux has 39-bit user space.
     random &= 0x3fffffffffUL;
     random += 0x1000000000UL;
 #else // !CPU(X86_64) && !CPU(ARM64)
     // This is a good range on Windows, Linux and Mac.
     // Allocates in the 0.5-1.5GB region.
     random &= 0x3fffffff;
     random += 0x20000000;
 #endif // CPU(X86_64)
     random &= kPageAllocationGranularityBaseMask;
     return reinterpret_cast<void*>(random);
 }
 
 }