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

[John R. <jr...@bi...>]

>                  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.
    <<snip>>

No, the hardware documentation says that the result is UNPREDICATBLE.

> */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;

When the instruction is 0x4503, then N:Rn (bits 7,2,1,0) is 3,
and Rm(bits 6,5,4,3) is 0.  Both effective register numbers
are less than 8, so this is an UNPREDICTABLE case.
The compiler/assembler made a mistake.