Re: [Qemu-devel] [PATCH v2 2/3] target-m68k: implement 680x0 movem

[Richard Henderson <rth@twiddle.net>]

On 11/02/2016 03:15 PM, Laurent Vivier wrote:
> +                    if ((insn & 7) + 8 == i &&
> +                        m68k_feature(s->env, M68K_FEATURE_EXT_FULL)) {
> +                        /* M68020+: if the addressing register is the
> +                         * register moved to memory, the value written
> +                         * is the initial value decremented by the size of
> +                         * the operation
> +                         * M68000/M68010: the value is the initial value
> +                         */
> +                        TCGv tmp = tcg_temp_new();
> +                        tcg_gen_sub_i32(tmp, mreg(i), incr);
> +                        gen_store(s, opsize, addr, tmp);
> +                        tcg_temp_free(tmp);

This doesn't look right.  Is the value stored the intermediate value of the 
decremented register, or the final value?  What you're storing is reg-4, which 
is neither of these things.

I could see, maybe, that reg-4 might well turn out to be the right value for

	movem	{a0-a7}, (sp)-

since sp == a7, and therefore stored first.  But I question that's the correct 
result for

	movem	{a0-a7}, (a1)-

If it's the incremental value, then you can just store "addr" and you don't 
need a temp.  If it's the final value, then you can compute

	tcg_gen_subi_i32(tmp, AREG(insn, 0), ctpop32(mask) * 4);



r~