The function address that is pushed by the individual fault handlers
before they call the common error_code path. It's a gross abuse of the
GS symbolic constant. :-)
Try running through one of the fault paths by hand, writing down the
stack state at each step...
HTH,
Keir
> I'm searching Xen's source code to understand exception handling. I've
> pasted a piece of code below.
>
> In arch/x86/x86_32/entry.S:
> error_code:
> pushl %fs
> pushl %es
> pushl %ds
> pushl %eax
> xorl %eax,%eax
> pushl %ebp
> pushl %edi
> pushl %esi
> pushl %edx
> decl %eax # eax = -1
> pushl %ecx
> pushl %ebx
> cld
> movl %gs,%ecx
> movl ORIG_EAX(%esp), %esi # get the error code
> movl GS(%esp), %edi # get the function address
> movl %eax, ORIG_EAX(%esp)
> movl %ecx, GS(%esp)
> movl $(__HYPERVISOR_DS),%edx
> movl %edx,%ds
> movl %edx,%es
> movl %edx,%fs
> movl %edx,%gs
> movl %esp,%edx
> pushl %esi # push the error code
> pushl %edx # push the pt_regs pointer
> GET_CURRENT(%ebx)
> call *%edi
> addl $8,%esp
> movb CS(%esp),%al
> testb $3,%al
> je restore_all_xen
> jmp process_guest_exception_and_events
>
> But I can not understand what function does following sentence refer to
> movl GS(%esp), %edi # get the function address
> Where does it come from?
>
> Thanks,
> Benjamin
>
>
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-=- MIME -=-
I'm searching Xen's source code to understand exception handling. I've
pasted a piece of code below.
In arch/x86/x86_32/entry.S:
error_code:
pushl %fs
pushl %es
pushl %ds
pushl %eax
xorl %eax,%eax
pushl %ebp
pushl %edi
pushl %esi
pushl %edx
decl %eax # eax =3D -1
pushl %ecx
pushl %ebx
cld
movl %gs,%ecx
movl ORIG_EAX(%esp), %esi # get the error code
movl GS(%esp), %edi # get the function address
movl %eax, ORIG_EAX(%esp)
movl %ecx, GS(%esp)
movl $(__HYPERVISOR_DS),%edx
movl %edx,%ds
movl %edx,%es
movl %edx,%fs
movl %edx,%gs
movl %esp,%edx
pushl %esi # push the error code
pushl %edx # push the pt_regs pointer
GET_CURRENT(%ebx)
call *%edi
addl $8,%esp
movb CS(%esp),%al
testb $3,%al
je restore_all_xen
jmp process_guest_exception_and_events
But I can not understand what function does following sentence refer to
movl GS(%esp), %edi # get the function address
Where does it come from?
Thanks,
Benjamin
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Use IT products in your business? Tell us what you think of them. Give us
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_______________________________________________
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Xen-devel@xxxxxxxxxxxxxxxxxxxxx
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Use IT products in your business? Tell us what you think of them. Give us
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