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

[Cyril Bur <cyrilbur@gmail.com>]

On Mon, 2017-07-31 at 10:58 +1000, Matt Brown wrote:
> This adds emulation for the isel instruction.
> Tested for correctness against the isel instruction and its extended
> mnemonics (lt, gt, eq) on ppc64le.
> 
> Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>

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

> ---
> v4:
> 	- simplify if statement to ternary op
> 	(same as isel emulation in kernel/traps.c)
> v2:
> 	- fixed opcode
> 	- fixed definition to include the 'if RA=0, a=0' clause
> 	- fixed ccr bitshifting error
> ---
>  arch/powerpc/lib/sstep.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index af4eef9..473bab5 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -1240,6 +1240,14 @@ int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
>  /*
>   * Logical instructions
>   */
> +		case 15:	/* isel */
> +			mb = (instr >> 6) & 0x1f; /* bc */
> +			val = (regs->ccr >> (31 - mb)) & 1;
> +			val2 = (ra) ? regs->gpr[ra] : 0;
> +
> +			regs->gpr[rd] = (val) ? val2 : regs->gpr[rb];
> +			goto logical_done;
> +
>  		case 26:	/* cntlzw */
>  			asm("cntlzw %0,%1" : "=r" (regs->gpr[ra]) :
>  			    "r" (regs->gpr[rd]));