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[Qemu-devel] Re: target-sparc/TODO
From: |
Blue Swirl |
Subject: |
[Qemu-devel] Re: target-sparc/TODO |
Date: |
Fri, 21 Aug 2009 22:45:52 +0300 |
On Fri, Aug 21, 2009 at 3:40 PM, Artyom
Tarasenko<address@hidden> wrote:
> 2009/8/21 Artyom Tarasenko <address@hidden>:
>> 2009/8/20 Blue Swirl <address@hidden>:
>>> On Thu, Aug 20, 2009 at 12:44 PM, Artyom
>>> Tarasenko<address@hidden> 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?
>
> Page 55 of The SPARC v8 Architecture Manual
> (http://www.sparc.org/standards/V8.pdf) describes this case
> explicitly:
> cpu should execute one instruction on the jump target and then branch.
> Is it what qemu currently does?
I may be blind, I don't see the description of this case in that page.
However, I made a small Linux test program to test it:
.global _start
.type _start, function
_start:
mov 1, %o0
call 1f
#ifdef NOP
nop
#endif
1: inc %o0
mov 1, %g1
ta 0x10
(and a BSD version:
#include <sys/syscall.h>
.globl _start
_start:
mov 1, %o0
call 1f
#ifdef NOP
nop
#endif
1: inc %o0
mov SYS_exit, %g1
ta 0
)
Both QEMU and real (Sparc64) hardware exit with return value of 3, so
the inc is re-executed. If I add a nop in the call delay slot, the
return value is 2.
- [Qemu-devel] target-sparc/TODO, Artyom Tarasenko, 2009/08/17
- [Qemu-devel] Re: target-sparc/TODO, Blue Swirl, 2009/08/17
- [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/19
- [Qemu-devel] Re: target-sparc/TODO, Blue Swirl, 2009/08/19
- [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/20
- [Qemu-devel] Re: target-sparc/TODO, Blue Swirl, 2009/08/20
- [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/21
- [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/21
- [Qemu-devel] Re: target-sparc/TODO,
Blue Swirl <=
- [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/21
- Re: [Qemu-devel] Re: target-sparc/TODO, Igor Kovalenko, 2009/08/21
- Re: [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/21
- [Qemu-devel] Re: target-sparc/TODO, Blue Swirl, 2009/08/22
- [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/22
- Re: [Qemu-devel] Re: target-sparc/TODO, Robert Reif, 2009/08/22
- Re: [Qemu-devel] Re: target-sparc/TODO, Artyom Tarasenko, 2009/08/22
- Re: [Qemu-devel] Re: target-sparc/TODO, Robert Reif, 2009/08/22