2001-12-17 18:20:47

by Aneesh Kumar KV

Subject: [Alpha/Linux ] Stack layout/and register values for ret_from_sys_call

Hi,

Can someone explain me what should be the stack layout and register
value( if there is any restriction ) before calling ret_from_syscall for
Alpha. Again in entry.S i find may places where we make current (
Register 8) as below

lda $8,0x3fff
bic $30,$8,$8

If someone can expain what happens in the above two assembly statement
it will be really helpful.

Thanks in advance.

-aneesh

2001-12-29 00:07:24

by Richard Henderson

Subject: Re: [Alpha/Linux ] Stack layout/and register values for ret_from_sys_call

On Mon, Dec 17, 2001 at 11:50:57PM +0530, Aneesh Kumar K.V wrote:
> Can someone explain me what should be the stack layout and register
> value( if there is any restriction ) before calling ret_from_syscall for
> Alpha.

Top of stack should contain a struct pt_regs. See asm/ptrace.h.

> lda $8,0x3fff
> bic $30,$8,$8
>
> If someone can expain what happens in the above two assembly statement
> it will be really helpful.

This computes the value for "current". The stack plus task structure
is aligned on a two-page boundary. See task_union in linux/sched.h.


r~