MIPS: Fix unaligned read/write operations in wasm.

src/utils.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_UTILS_H_
 #define V8_UTILS_H_
 
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
@@ skipping 1697 matching lines @@
 
 // Returns current value of top of the stack. Works correctly with ASAN.
 DISABLE_ASAN
 inline uintptr_t GetCurrentStackPosition() {
   // Takes the address of the limit variable in order to find out where
   // the top of stack is right now.
   uintptr_t limit = reinterpret_cast<uintptr_t>(&limit);
   return limit;
 }
 
+
+template <typename V>
+static inline V ReadUnalignedValue(const void* p) {
+#if !(V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64)

[titzer, 2016/01/23 15:45:21]

Actually now that I think about it, a memmove() on all architectures is probably
going to generate exactly the same code (though I didn't check with LLVM),
except also handle alignment on ARM. Maybe we should have an #ifdef for
endianness, since I think we need to flip the byte order on big endian here as
well.

+  return *reinterpret_cast<const V*>(p);
+#else
+  V r;
+  memmove(&r, p, sizeof(V));
+  return r;
+#endif  // V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+}
+
+
+template <typename V>
+static inline void WriteUnalignedValue(void* p, V value) {
+#if !(V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64)
+  *(reinterpret_cast<V*>(p)) = value;
+#else   // V8_TARGET_ARCH_MIPS
+  memmove(p, &value, sizeof(V));
+#endif  // V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+}
+
+
 static inline double ReadDoubleValue(const void* p) {
-#ifndef V8_TARGET_ARCH_MIPS
-  return *reinterpret_cast<const double*>(p);
-#else   // V8_TARGET_ARCH_MIPS
-  // Prevent compiler from using load-double (mips ldc1) on (possibly)
-  // non-64-bit aligned address.
-  union conversion {
-    double d;
-    uint32_t u[2];
-  } c;
-  const uint32_t* ptr = reinterpret_cast<const uint32_t*>(p);
-  c.u[0] = *ptr;
-  c.u[1] = *(ptr + 1);
-  return c.d;
-#endif  // V8_TARGET_ARCH_MIPS
+  return ReadUnalignedValue<double>(p);
 }
 
 
 static inline void WriteDoubleValue(void* p, double value) {
-#ifndef V8_TARGET_ARCH_MIPS
-  *(reinterpret_cast<double*>(p)) = value;
-#else   // V8_TARGET_ARCH_MIPS
-  // Prevent compiler from using load-double (mips sdc1) on (possibly)
-  // non-64-bit aligned address.
-  union conversion {
-    double d;
-    uint32_t u[2];
-  } c;
-  c.d = value;
-  uint32_t* ptr = reinterpret_cast<uint32_t*>(p);
-  *ptr = c.u[0];
-  *(ptr + 1) = c.u[1];
-#endif  // V8_TARGET_ARCH_MIPS
+  WriteUnalignedValue(p, value);
 }
 
 
 static inline uint16_t ReadUnalignedUInt16(const void* p) {
-#if !(V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64)
-  return *reinterpret_cast<const uint16_t*>(p);
-#else   // V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
-  // Prevent compiler from using load-half (mips lh) on (possibly)
-  // non-16-bit aligned address.
-  union conversion {
-    uint16_t h;
-    uint8_t b[2];
-  } c;
-  const uint8_t* ptr = reinterpret_cast<const uint8_t*>(p);
-  c.b[0] = *ptr;
-  c.b[1] = *(ptr + 1);
-  return c.h;
-#endif  // V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+  return ReadUnalignedValue<uint16_t>(p);
 }
 
 
 static inline void WriteUnalignedUInt16(void* p, uint16_t value) {
-#if !(V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64)
-  *(reinterpret_cast<uint16_t*>(p)) = value;
-#else   // V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
-  // Prevent compiler from using store-half (mips sh) on (possibly)
-  // non-16-bit aligned address.
-  union conversion {
-    uint16_t h;
-    uint8_t b[2];
-  } c;
-  c.h = value;
-  uint8_t* ptr = reinterpret_cast<uint8_t*>(p);
-  *ptr = c.b[0];
-  *(ptr + 1) = c.b[1];
-#endif  // V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+  WriteUnalignedValue(p, value);
 }
 
+
+static inline void WriteUnalignedUInt32(void* p, uint32_t value) {
+  WriteUnalignedValue(p, value);
+}
+
+
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_UTILS_H_