Re: [Qemu-devel] [PATCH v2 1/2] target-m68k: add 64bit mull

[Richard Henderson]

On 10/28/2016 04:01 PM, Laurent Vivier wrote:
> +    if (ext & 0x400) {
> +        if (!m68k_feature(s->env, M68K_FEATURE_QUAD_MULDIV)) {
> +            gen_exception(s, s->pc - 4, EXCP_UNSUPPORTED);
> +            return;
> +        }
> +
> +        SRC_EA(env, src1, OS_LONG, 0, NULL);
> +
> +        if (sign) {
> +            tcg_gen_muls2_i32(DREG(ext, 12), DREG(ext, 0), src1, DREG(ext, 
> 12));
> +        } else {
> +            tcg_gen_mulu2_i32(DREG(ext, 12), DREG(ext, 0), src1, DREG(ext, 
> 12));
> +        }

TCG will react badly if Dl == Dh, and thus the two outputs are the same.

This is undefined in the spec, but guests violating the spec shouldn't cause 
qemu to crash.

I think you should compute this into N and Z and move the results (perhaps in 
an order matching real hw?) to the data registers afterward.


r~