Xen devel - Oct 2012 - The entry of Xen's exception handler

Hi, I am trying to understand the exception handler of Xen. In
xen/arch/x86/x86_64/entry.S, the entry of the page fault handler is :

ENTRY(page_fault)
        movl  $TRAP_page_fault,4(%rsp)
        jmp   handle_exception

Here I did not get why to put the exception vector ($TRAP_page_fault) to
stack before calling handle_exception?

Thanks,

-- 
Xinxin


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel

On 02/10/2012 21:51, Xinxin Jin wrote:
> Hi, I am trying to understand the exception handler of Xen. In
> xen/arch/x86/x86_64/entry.S, the entry of the page fault handler is :
>
> ENTRY(page_fault)
>         movl  $TRAP_page_fault,4(%rsp)
>         jmp   handle_exception
>
> Here I did not get why to put the exception vector ($TRAP_page_fault)
> to stack before calling handle_exception?
This is so every single exception fills in its cpu_user_regs with the
correct trap, so the C code an distinguish if its needs to.  (See
current.h for the structures which get filled in)

~Andrew
>
> Thanks,
>
> -- 
> Xinxin
>

On 02/10/2012 21:51, "Xinxin Jin" <xinxinjin89@gmail.com> wrote:
> Hi, I am trying to understand the exception handler of Xen. In
> xen/arch/x86/x86_64/entry.S, the entry of the page fault handler is :
> 
> ENTRY(page_fault)
>         movl  $TRAP_page_fault,4(%rsp)
>         jmp   handle_exception
> 
> Here I did not get why to put the exception vector ($TRAP_page_fault) to
stack
> before calling handle_exception?
Otherwise handle_exception would not know which type of exception it was
handling, would it.

 -- Keir
> Thanks,