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

[Laurent Vivier]

Le 03/11/2016 à 21:47, Richard Henderson a écrit :
> On 11/02/2016 03:15 PM, Laurent Vivier wrote:
>> +            for (i = 15; i >= 0; i--, mask >>= 1) {
>> +                if (mask & 1) {
>> +                    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);
>> +                    } else {
>> +                        gen_store(s, opsize, addr, mreg(i));
>> +                    }
>> +                    if (mask != 1) {
>> +                        tcg_gen_sub_i32(addr, addr, incr);
>> +                    }
>> +                }
> 
> One more thing: This is pre-decrement.  Why are you decrementing after
> the store?  Seems to me this should be
> 
>    if (mask & 1) {
>        tcg_gen_sub_i32(addr, addr, incr);
>        if (REG(insn, 0) + 8 == i ...)
>        ...
>    }
> 

Because it has already been decremented by gen_lea()... so this a
problem if we have page fault, except if we use your "areg writeback"
series, and we will.

Thanks,
Laurent