Re: [Qemu-devel] [PATCH] target/m68k: fix V flag for CC_OP_SUBx

[Richard Henderson]

On 06/14/2017 01:39 PM, Laurent Vivier wrote:
> V flag for subtraction is:
>
>     v = (res ^ src1) & (src1 ^ src2)
>
> (see COMPUTE_CCR() in target/m68k/helper.c)
>
> But gen_flush_flags() uses:
>
>     v = (res ^ src2) & (src1 ^ src2)
>
> The problem has been found with the following program:
>
>          .global _start
> _start:
>          move.l  #-2147483648,%d0
>          subq.l  #1,%d0
>          jvc     1f
>          move.l #1,%d1
>          move.l #1,%d0
>          trap #0
> 1:
>          move.l #0,%d1
>          move.l #1,%d0
>          trap #0
>
> It works fine (exit(1)) on real hardware, and with "-singlestep".
>
> "-singlestep" uses gen_helper_flush_flags(), whereas
> without "-singlestep", V flag is computed directly in
> gen_flush_flags().
>
> This patch updates gen_flush_flags() to have the same result
> as with gen_helper_flush_flags().
>
> Signed-off-by: Laurent Vivier<address@hidden>
> ---
>   target/m68k/translate.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Richard Henderson <address@hidden>


r~