New MSan mapping layout (llvm part).

This is an implementation of
https://github.com/google/sanitizers/issues/579

It has a number of advantages over the current mapping:
* Works for non-PIE executables.
* Does not require ASLR; as a consequence, debugging MSan programs in
  gdb no longer requires "set disable-randomization off".
* Supports linux kernels >=4.1.2.
* The code is marginally faster and smaller.

This is an ABI break. We never really promised ABI stability, but
this patch includes a courtesy escape hatch: a compile-time macro
that reverts back to the old mapping layout.

llvm-svn: 249753

1 files changed, 15 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 9d4c7de729f..bc6da5acae1 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -232,10 +232,17 @@ static const MemoryMapParams Linux_I386_MemoryMapParams = {
 
 // x86_64 Linux
 static const MemoryMapParams Linux_X86_64_MemoryMapParams = {
+#ifdef MSAN_LINUX_X86_64_OLD_MAPPING
   0x400000000000,  // AndMask
   0,               // XorMask (not used)
   0,               // ShadowBase (not used)
   0x200000000000,  // OriginBase
+#else
+  0,               // AndMask (not used)
+  0x500000000000,  // XorMask
+  0,               // ShadowBase (not used)
+  0x100000000000,  // OriginBase
+#endif
 };
 
 // mips64 Linux
@@ -926,16 +933,17 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   ///
   /// Offset = (Addr & ~AndMask) ^ XorMask
   Value *getShadowPtrOffset(Value *Addr, IRBuilder<> &IRB) {
+    Value *OffsetLong = IRB.CreatePointerCast(Addr, MS.IntptrTy);
+
     uint64_t AndMask = MS.MapParams->AndMask;
-    assert(AndMask != 0 && "AndMask shall be specified");
-    Value *OffsetLong =
-      IRB.CreateAnd(IRB.CreatePointerCast(Addr, MS.IntptrTy),
-                    ConstantInt::get(MS.IntptrTy, ~AndMask));
+    if (AndMask)
+      OffsetLong =
+          IRB.CreateAnd(OffsetLong, ConstantInt::get(MS.IntptrTy, ~AndMask));
 
     uint64_t XorMask = MS.MapParams->XorMask;
-    if (XorMask != 0)
-      OffsetLong = IRB.CreateXor(OffsetLong,
-                                 ConstantInt::get(MS.IntptrTy, XorMask));
+    if (XorMask)
+      OffsetLong =
+          IRB.CreateXor(OffsetLong, ConstantInt::get(MS.IntptrTy, XorMask));
     return OffsetLong;
   }