[llvm] r318421 - [asan] Fix small X86_64 ShadowOffset for non-default shadow scale

[Walter Lee via llvm-commits]

Author: waltl
Date: Thu Nov 16 09:03:00 2017
New Revision: 318421

URL: http://llvm.org/viewvc/llvm-project?rev=318421&view=rev
Log:
[asan] Fix small X86_64 ShadowOffset for non-default shadow scale

The requirement is that shadow memory must be aligned to page
boundaries (4k in this case).  Use a closed form equation that always
satisfies this requirement.

Differential Revision: https://reviews.llvm.org/D39471

Modified:
    llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp

Modified: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp?rev=318421&r1=318420&r2=318421&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp Thu Nov 16 09:03:00 2017
@@ -97,7 +97,8 @@ static const uint64_t kDynamicShadowSent
 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 @@ static ShadowMapping getShadowMapping(Tr
 
   ShadowMapping Mapping;
 
+  Mapping.Scale = kDefaultShadowScale;
+  if (ClMappingScale.getNumOccurrences() > 0) {
+    Mapping.Scale = ClMappingScale;
+  }
+
   if (LongSize == 32) {
     if (IsAndroid)
       Mapping.Offset = kDynamicShadowSentinel;
@@ -528,7 +534,8 @@ static ShadowMapping getShadowMapping(Tr
       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 @@ static ShadowMapping getShadowMapping(Tr
     Mapping.Offset = kDynamicShadowSentinel;
   }
 
-  Mapping.Scale = kDefaultShadowScale;
-  if (ClMappingScale.getNumOccurrences() > 0) {
-    Mapping.Scale = ClMappingScale;
-  }
-
   if (ClMappingOffset.getNumOccurrences() > 0) {
     Mapping.Offset = ClMappingOffset;
   }