Re: [Qemu-devel] [PATCH] improve emulation correctness

[Richard Henderson]

On 04/28/2014 06:05 AM, Dmitry Poletaev wrote:
> -        env->cc_src = (eflags & ~(CC_C | CC_O)) |
> -            (lshift(src ^ t0, 11 - (DATA_BITS - 1)) & CC_O) |
> +        env->cc_src = (eflags & ~CC_C) |
>              ((src >> (DATA_BITS - count)) & CC_C);
> +        if (count == 1) {
> +            env->cc_src |= (lshift(src ^ t0, 11 - (DATA_BITS - 1)) & CC_O);
> +        }

This isn't what you described either, since you fail to clear the old value of
the O flag before oring in the new one.  You wanted

    if (count == 1) {
        env->cc_src = (env->cc_src & ~CC_O)
                    | (lshift(src ^ t0, 11 - (DATA_BITS - 1)) & CC_O);
    }

First off, do more testing before submitting patches.

Second, you've gotten an adequate description of why we're not going to take
patches to choose one particular undefined behaviour over another.


r~