[Support] fix the ULEB128 decoding bug.

[arphaman]

Summary

This patch fixes the ULEB128 decoding which currently overflows when evaluating (*p & 0x7f) << Shift were *p = 0x10 and Shift is 28.

[dexonsmith]

Ouch. LGTM!

[arphaman]

Closed by commit rL216268 (authored by @arphaman).

llvm/trunk/include/llvm/Support/LEB128.h

 
 
 /// Utility function to decode a ULEB128 value.
 inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr) {
   const uint8_t *orig_p = p;
   uint64_t Value = 0;
   unsigned Shift = 0;
   do {
-    Value += (*p & 0x7f) << Shift;
+    Value += uint64_t(*p & 0x7f) << Shift;
     Shift += 7;
   } while (*p++ >= 128);
   if (n)
     *n = (unsigned)(p - orig_p);
   return Value;
 }
 
 /// Utility function to get the size of the ULEB128-encoded value.
 extern unsigned getULEB128Size(uint64_t Value);
 
 /// Utility function to get the size of the SLEB128-encoded value.
 extern unsigned getSLEB128Size(int64_t Value);
 
 }  // namespace llvm
 
 #endif  // LLVM_SYSTEM_LEB128_H

llvm/trunk/unittests/Support/LEB128Test.cpp

#define EXPECT_DECODE_ULEB128_EQ(EXPECTED, VALUE) \
   EXPECT_DECODE_ULEB128_EQ(64u, "\x40");
   EXPECT_DECODE_ULEB128_EQ(0x7fu, "\x7f");
   EXPECT_DECODE_ULEB128_EQ(0x80u, "\x80\x01");
   EXPECT_DECODE_ULEB128_EQ(0x81u, "\x81\x01");
   EXPECT_DECODE_ULEB128_EQ(0x90u, "\x90\x01");
   EXPECT_DECODE_ULEB128_EQ(0xffu, "\xff\x01");
   EXPECT_DECODE_ULEB128_EQ(0x100u, "\x80\x02");
   EXPECT_DECODE_ULEB128_EQ(0x101u, "\x81\x02");
+  EXPECT_DECODE_ULEB128_EQ(4294975616ULL, "\x80\xc1\x80\x80\x10");
 
   // Decode ULEB128 with extra padding bytes
   EXPECT_DECODE_ULEB128_EQ(0u, "\x80\x00");
   EXPECT_DECODE_ULEB128_EQ(0u, "\x80\x80\x00");
   EXPECT_DECODE_ULEB128_EQ(0x7fu, "\xff\x00");
   EXPECT_DECODE_ULEB128_EQ(0x7fu, "\xff\x80\x00");
   EXPECT_DECODE_ULEB128_EQ(0x80u, "\x80\x81\x00");
   EXPECT_DECODE_ULEB128_EQ(0x80u, "\x80\x81\x80\x00");