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

[Laurent Vivier]

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]

Laurent