[Qemu-devel] Re: target-sparc/TODO

[Blue Swirl <blauwirbel@gmail.com>]

On Thu, Aug 20, 2009 at 12:44 PM, Artyom
Tarasenko<atar4qemu@googlemail.com> wrote:
>>> Particularly I'm interested if
>>>
>>> jmp     %l1, %g4, %g0
>>>
>>> may behave other than on a real hw.
>>
>> No, if rd is %g0, the current PC will not be written anywhere (not by
>> real HW either).
>
> The reason I asked is the two following pieces of code work
> differently on a real and emulated SS-5. On a real one spacel! does an
> asi write, and spacel@ does an asi read, and under qemu  spacel! seems
> to do nothing, and spacel@ returns its second parameter multiplied by
> 4. Both of them don't even try to call an [unimplemented] asi
> operation, I've runned the tests with mmu and asi debug turned on.
>
> Real SS-5:
>
> ok 0 0 spacel@ .
> Data Access Error
> ok 0 20 spacel@ .
> 0
> ok 12345678 0 20 spacel!
> ok 0 20 spacel@ .
> 12345678
> ok
>
>
> qemu SS-5:
>
> ok 0 0 spacel@ .
> 0
> ok 0 20 spacel@ .
> 80
> ok 12345678 0 20 spacel!
> ok 0 20 spacel@ .
> 80
> ok
>
> I don't know sparc asm good enogh, but qemu behavior seems to be
> logical: in the first case I see no store op, and there are shifts
> which would multiply by 4:
>
> ok see spacel!
> code spacel!
> ffd26e0c     ld      [%g7], %l2
> ffd26e10     add     %g7, 4, %g7
> ffd26e14     ld      [%g7], %l0
> ffd26e18     add     %g7, 4, %g7
> ffd26e1c     sll     %g4, 2, %g4
> ffd26e20     call    ffd26e24
> ffd26e24     add     %g0, 14, %l1
>
> ok ffd26e24 dis
> ffd26e24     add     %g0, 14, %l1
> ffd26e28     add     %o7, %l1, %l1
> ffd26e2c     jmp     %l1, %g4, %g0
> ffd26e30     ba      ffd26f68
> ok
>
> ok see spacel@
> code spacel@
> ffd26830     ld      [%g7], %l0
> ffd26834     add     %g7, 4, %g7
> ffd26838     sll     %g4, 2, %g4
> ffd2683c     call    ffd26840
> ffd26840     add     %g0, 14, %l1
>
> ok ffd26840 dis
> ffd26840     add     %g0, 14, %l1
> ffd26844     add     %o7, %l1, %l1
> ffd26848     jmp     %l1, %g4, %g0
> ffd2684c     ba      ffd26984
>
>
> The code is identical on a real and emulated SS.
>
> It must be the jump, which jumps differently on a real hw and under
> qemu. Do you see from the code where the jump would jump to, or maybe
> you have a suggestion how to check where the jump jumps to on the real
> hw?

The target of the call instruction is also a delay slot instruction
for the call itself. Maybe this case is not handled correctly?