[PATCH] [UBSan][MIPS]

[Sagar Thakur]

Hi rsmith, kcc, samsonov, dsanders,

On MIPS, shift operation on signed types give unpredictable results. Therefore we use unsigned value while shifting and after shifting is done we convert it back to signed value.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D9247

Files:
  lib/ubsan/ubsan_value.cc

Index: lib/ubsan/ubsan_value.cc
===================================================================
--- lib/ubsan/ubsan_value.cc
+++ lib/ubsan/ubsan_value.cc
@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <endian.h>
 #include "ubsan_platform.h"
 #if CAN_SANITIZE_UB
 #include "ubsan_value.h"
@@ -27,7 +28,24 @@
     // to SIntMax.
     const unsigned ExtraBits =
       sizeof(SIntMax) * 8 - getType().getIntegerBitWidth();
+#if defined(__mips__)
+    UIntMax Value = UIntMax(Val) << ExtraBits >> ExtraBits;;
+    uptr ExtraBytes= ExtraBits / 8;
+#if BYTE_ORDER == LITTLE_ENDIAN
+    u8 * ValuePtr = (u8 *) &Value + (sizeof(UIntMax) - ExtraBytes);
+#else
+    u8 * ValuePtr = (u8 *) &Value;
+#endif
+    uptr Mask = 1UL << (getType().getIntegerBitWidth() - 1);
+    if(Val & Mask) {
+      for (uptr i = 0 ; i < ExtraBytes ; i++) {
+        *(ValuePtr + i) |= 0xff;
+      }
+    }
+    return SIntMax(Value);
+#else
     return SIntMax(Val) << ExtraBits >> ExtraBits;
+#endif
   }
   if (getType().getIntegerBitWidth() == 64)
     return *reinterpret_cast<s64*>(Val);

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