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

[Artyom Tarasenko <atar4qemu@googlemail.com>]

2009/8/20 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?

Good idea! Don't know how to test it though.

And what about "ba" in the delay slot of "jmp"? Is the correct
behavior described somewhere? Would jump just be ignored? Whould it
execute one instruction on jump destination and then branch? Would
branch be ignored?