Index: compiler-rt/trunk/lib/asan/asan_mapping.h
===================================================================
--- compiler-rt/trunk/lib/asan/asan_mapping.h
+++ compiler-rt/trunk/lib/asan/asan_mapping.h
@@ -139,7 +139,8 @@
 static const u64 kDefaultShadowSentinel = ~(uptr)0;
 static const u64 kDefaultShadowOffset32 = 1ULL << 29;  // 0x20000000
 static const u64 kDefaultShadowOffset64 = 1ULL << 44;
-static const u64 kDefaultShort64bitShadowOffset = 0x7FFF8000;  // < 2G.
+static const u64 kDefaultShort64bitShadowOffset =
+    0x7FFFFFFF & (~0xFFFULL << kDefaultShadowScale);  // < 2G.
 static const u64 kIosShadowOffset32 = 1ULL << 30;  // 0x40000000
 static const u64 kIosShadowOffset64 = 0x120200000;
 static const u64 kIosSimShadowOffset32 = 1ULL << 30;
Index: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -97,7 +97,8 @@
 static const uint64_t kIOSShadowOffset32 = 1ULL << 30;
 static const uint64_t kIOSSimShadowOffset32 = 1ULL << 30;
 static const uint64_t kIOSSimShadowOffset64 = kDefaultShadowOffset64;
-static const uint64_t kSmallX86_64ShadowOffset = 0x7FFF8000;  // < 2G.
+static const uint64_t kSmallX86_64ShadowOffsetBase = 0x7FFFFFFF;  // < 2G.
+static const uint64_t kSmallX86_64ShadowOffsetAlignMask = ~0xFFFULL;
 static const uint64_t kLinuxKasan_ShadowOffset64 = 0xdffffc0000000000;
 static const uint64_t kPPC64_ShadowOffset64 = 1ULL << 41;
 static const uint64_t kSystemZ_ShadowOffset64 = 1ULL << 52;
@@ -495,6 +496,11 @@
 
   ShadowMapping Mapping;
 
+  Mapping.Scale = kDefaultShadowScale;
+  if (ClMappingScale.getNumOccurrences() > 0) {
+    Mapping.Scale = ClMappingScale;
+  }
+
   if (LongSize == 32) {
     if (IsAndroid)
       Mapping.Offset = kDynamicShadowSentinel;
@@ -528,7 +534,8 @@
       if (IsKasan)
         Mapping.Offset = kLinuxKasan_ShadowOffset64;
       else
-        Mapping.Offset = kSmallX86_64ShadowOffset;
+        Mapping.Offset = (kSmallX86_64ShadowOffsetBase &
+                          (kSmallX86_64ShadowOffsetAlignMask << Mapping.Scale));
     } else if (IsWindows && IsX86_64) {
       Mapping.Offset = kWindowsShadowOffset64;
     } else if (IsMIPS64)
@@ -548,11 +555,6 @@
     Mapping.Offset = kDynamicShadowSentinel;
   }
 
-  Mapping.Scale = kDefaultShadowScale;
-  if (ClMappingScale.getNumOccurrences() > 0) {
-    Mapping.Scale = ClMappingScale;
-  }
-
   if (ClMappingOffset.getNumOccurrences() > 0) {
     Mapping.Offset = ClMappingOffset;
   }