Re: Question about signal syscalls !

[David Daney <ddaney@avtrex.com>]

Franck Bui-Huu wrote:
> David Daney wrote:
>> sys_sigreturn does not return to the caller in the conventional sense.
>
> I expect you're talking about this bite of code taken from 
> _sys_sigreturn():
>
>        /*
>         * Don't let your children do this ...
>         */
>        __asm__ __volatile__(
>                "move\t$29, %0\n\t"
>                "j\tsyscall_exit"
>                :/* no outputs */
>                :"r" (&regs));
>
>> The entire user context (i.e. the value of *all* registers) is replaced
>> with the values stored in the sigcontext structure on the caller's
>> stack.  If all registers are being restored from the sigcontext, then
>> there is no need to save the current values of the registers, because
>> they will never be used.
>>
>
> But I don't see where _all_ registers are saved. Only static registers
> are saved by save_static_function() right before calling
> _sys_sigreturn() and I agree I don't why we need to save those.
>
> And now I'm starting to think that we don't need to save static regs in
> setup_sigcontext() either...
>
All registers *must* be saved in the sigcontext.  That is part of the 
contract the kernel has with user code.

On return from an asynchronous signal, *all* registers must contain the 
same values they had before the process was interrupted.

David Daney

David Daney