[Valgrind-users] [Bug] There is the bug about valgrind decode armv8 thumb instruction

[Wuweijia <wuw...@hu...>]

Hi
                When the machine code is 0x4503,   the op is cmp,   but this is the T2 format , N bit(7-bit) is 0 ,  so   the thumb instrunction cmp-hi  is unhandled. And the decode action is failure .

                The 0x4503 machine code is generate by clang4.0\5.0\6.0, the machine  cpu can run this machine.


                The valgrind  source  is below ,  valgrind 3.12 , 3.13, 3.14 is the same:

                The guest_arm_toIR.c
                   case BITS8(0,1,0,0,0,1,0,1): {
      /* ---------------- CMP(HI) Rd, Rm ---------------- */
      UInt h1 = INSN0(7,7);
      UInt h2 = INSN0(6,6);
      UInt rM = (h2 << 3) | INSN0(5,3);
      UInt rN = (h1 << 3) | INSN0(2,0);
      if (h1 != 0 || h2 != 0) {   -------------------when h1 is zero, it mean cmp-hi instruction is not handle, and the decode is failured.,  and I comment this line ,the result is okay. Is it okay.
        IRTemp argL  = newTemp(Ity_I32);
         IRTemp argR  = newTemp(Ity_I32);
         assign( argL, getIRegT(rN) );
         assign( argR, getIRegT(rM) );
         /* Update flags regardless of whether in an IT block or not. */
         setFlags_D1_D2( ARMG_CC_OP_SUB, argL, argR, condT );
         DIP("cmphi r%u, r%u\n", rN, rM);
         goto decode_success;
      }
      break;
   }


                CMP T2 format:
T2
[cid:image001.png@01D3CC57.350C3590]

T2 variant
CMP{<c>}{<q>} <Rn>, <Rm> // <Rn> and <Rm> not both from R0-R7
Decode for this encoding
n = UInt(N:Rn); m = UInt(Rm);
(shift_t, shift_n) = (SRType_LSL, 0);
if n < 8 && m < 8 then UNPREDICTABLE;
if n == 15 || m == 15 then UNPREDICTABLE;

CONSTRAINED UNPREDICTABLE behavior
If n < 8 && m < 8, then one of the following behaviors must occur:
* The instruction is UNDEFINED.
* The instruction executes as NOP.
* The instruction executes as described, with no change to its behavior and no additional side effects.
* The condition flags become UNKNOWN.


BR
Owen