Re: cli()/sti() clarification

[george anzinger <george@mvista.com>]

irfan_hamid@softhome.net wrote:
> 
> Hi,
> 
> I added two system calls, blockintr() and unblockintr() to give cli()/sti()
> control to userland programs (yes I know its not advisable) but I only want
> to do it as a test. My test program looks like this:
> 
>         blockintr();
>         /* Some long calculations */
>         unblockintr();
> 
> The problem is that if I press Ctrl+C during the calculation, the program
> terminates. So I checked the _syscallN() and __syscall_return() macros to
> see if they explicitly call sti() before returning to userspace, but they
> dont.
> 
> Reading the lkml archives, I found that cli() disables only the interrupts,
> exceptions are allowed, so it makes sense that the SIGINT was delivered, but
> if thats the case, then how come the SIGINT was delivered from the Ctrl+C?
> Doesnt this mean that the SIGINT signal was generated as a result of the
> keyboard interrupt?
> 
> I know I am missing something here, would appreciate if someone could point
> me in the right direction.

Return from sys to user space is done by executing a "iret"
instruction.  In addition to picking up the return address
and segment it pick up EFLAGS which will contain the
interrupt flag as it was saved when the system call was
made...
> 
> Regards,
> Irfan Hamid.
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-- 
George Anzinger   george@mvista.com
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