Re: [PATCH v4 1/5] powerpc/lib/sstep: Add cmpb instruction emulation

[Cyril Bur <cyrilbur@gmail.com>]

On Mon, 2017-07-31 at 10:58 +1000, Matt Brown wrote:
> This patch adds emulation of the cmpb instruction, enabling xmon to
> emulate this instruction.
> Tested for correctness against the cmpb asm instruction on ppc64le.
> 
> Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>

Reviewed-by: Cyril Bur <cyrilbur@gmail.com>

> ---
> v2: 
> 	- fixed opcode
> 	- fixed mask typecasting
> ---
>  arch/powerpc/lib/sstep.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index 33117f8..87d277f 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -596,6 +596,22 @@ static nokprobe_inline void do_cmp_unsigned(struct pt_regs *regs, unsigned long
>  	regs->ccr = (regs->ccr & ~(0xf << shift)) | (crval << shift);
>  }
>  
> +static nokprobe_inline void do_cmpb(struct pt_regs *regs, unsigned long v1,
> +				unsigned long v2, int rd)
> +{
> +	unsigned long long out_val, mask;
> +	int i;
> +
> +	out_val = 0;
> +	for (i = 0; i < 8; i++) {
> +		mask = 0xffUL << (i * 8);
> +		if ((v1 & mask) == (v2 & mask))
> +			out_val |= mask;
> +	}
> +
> +	regs->gpr[rd] = out_val;
> +}
> +
>  static nokprobe_inline int trap_compare(long v1, long v2)
>  {
>  	int ret = 0;
> @@ -1049,6 +1065,10 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
>  			do_cmp_unsigned(regs, val, val2, rd >> 2);
>  			goto instr_done;
>  
> +		case 508: /* cmpb */
> +			do_cmpb(regs, regs->gpr[rd], regs->gpr[rb], ra);
> +			goto instr_done;
> +
>  /*
>   * Arithmetic instructions
>   */