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

[Richard Henderson <rth@twiddle.net>]

On 11/03/2016 02:11 PM, Laurent Vivier wrote:
> Le 03/11/2016 à 20:47, Richard Henderson a écrit :
>> 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);
>>
>
> As it was not clear for me, I have written a test to see what was the
> good value.
>
> my test program is:
>
> top:
>         .space 64,0
> stack:
>         .text
>         .globl _start
> _start:
>         lea stack,%a4
>         lea 1,%a0
>         lea 2,%a1
>         lea 3,%a2
>         lea 4,%a3
>         lea 5,%a5
>         lea 6,%a6
>         moveq.l #8, %d0
>         moveq.l #9, %d1
>         moveq.l #10, %d2
>         moveq.l #11, %d3
>         moveq.l #12, %d4
>         moveq.l #13, %d5
>         moveq.l #14, %d6
>         moveq.l #15, %d7
>         movem.l %a0-%a7/%d0-%d7,-(%a4)
>
> on a real 68040:
>
> initial value of A4 is 0x800020ec
> final value of A4 is   0x800020ac
>
> (gdb) x/15x 0x800020ac
> 0x800020ac: 0x00000008	0x00000009	0x0000000a	0x0000000b
> 0x800020bc: 0x0000000c	0x0000000d	0x0000000e	0x0000000f
> 0x800020cc: 0x00000001	0x00000002	0x00000003	0x00000004
> 0x800020dc: 0x800020e8	0x00000005	0x00000006
>
> Stored value is thus 0x800020e8 so this is initial value - 4.
> [I have tried the same test with a1, for the same result]

Weird.  But, ok.


r~