handle_sys question

handle_sys question

[Songmao Tian]

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Hello all:
   In handle_sys there's a
50<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/kernel/scall32-o32.S;h=a632bc144efa1b9ca977a582864530e33ee039cb;hb=72c04af9a2d57b7945cf3de8e71461bd80695d50#l50>
       sw      a3, PT_R26(sp)          # save a3 for syscall
restarting

I woner why it need to save  a3 in R26(k0) slot in the stack?

Thanks,
songmao

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Re: handle_sys question

[David Daney]

On 05/22/2012 02:40 AM, Songmao Tian wrote:
> Hello all:
>     In handle_sys there's a
> 50
> <http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/kernel/scall32-o32.S;h=a632bc144efa1b9ca977a582864530e33ee039cb;hb=72c04af9a2d57b7945cf3de8e71461bd80695d50#l50>
>          sw      a3, PT_R26(sp)          # save a3 for syscall restarting
>
> I woner why it need to save  a3 in R26(k0) slot in the stack?
>

It has to go somewhere.  The K0 and K1 slots aren't used to save other 
things.

David Daney

Re: handle_sys question

[Songmao Tian]

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OK, I find the usage. continue to read the code:-), thanks.

587 static int handle_signal(unsigned long sig, siginfo_t *info,
588     struct k_sigaction *ka, sigset_t *oldset, struct pt_regs *regs)
589 {
590     int ret;
……
602     /* fallthrough */
603     case ERESTARTNOINTR:        /* Userland will reload $v0.  */
604         regs->regs[7] = regs->regs[26];
605         regs->cp0_epc -= 8;
606     }



2012/5/23 David Daney <david.daney@cavium.com>

> On 05/22/2012 02:40 AM, Songmao Tian wrote:
>
>> Hello all:
>>    In handle_sys there's a
>> 50
>> <http://git.kernel.org/?p=**linux/kernel/git/torvalds/**
>> linux-2.6.git;a=blob;f=arch/**mips/kernel/scall32-o32.S;h=**
>> a632bc144efa1b9ca977a582864530**e33ee039cb;hb=**
>> 72c04af9a2d57b7945cf3de8e71461**bd80695d50#l50<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/kernel/scall32-o32.S;h=a632bc144efa1b9ca977a582864530e33ee039cb;hb=72c04af9a2d57b7945cf3de8e71461bd80695d50#l50>
>> >
>>
>>         sw      a3, PT_R26(sp)          # save a3 for syscall restarting
>>
>> I woner why it need to save  a3 in R26(k0) slot in the stack?
>>
>>
> It has to go somewhere.  The K0 and K1 slots aren't used to save other
> things.
>
> David Daney
>

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