Re: Need help in understanding x86 syscall

linux-os (Dick Johnson)
2005-08-11T18:22:13Z

On Thu, 11 Aug 2005, Steven Rostedt wrote:

> On Thu, 2005-08-11 at 13:46 -0400, linux-os (Dick Johnson) wrote:
>
>>
>> I was talking about the one who had the glibc support to use
>> the newer system-call entry (who's name can confuse).
>>
>> You are looking at code that uses int 0x80. It's an interrupt,
>> therefore, in the kernel, once the stack is set up, interrupts
>> need to be (re)enabled.
>
> int is a call to either an interrupt or exception procedure. 0x80 is
> setup in Linux to be a trap and not an interrupt vector. So it does
> _not_ turn off interrupts.
>

I'm not sure you can stop the CPU from clearing the interrupt
bit in EFLAGS if you execute an interrupt. The interrupt handler
may be supported by a trap-gate, but the event has already
occurred. The documentation I have isn't clear on this at all.

> I'm looking at the sysenter code which is suppose to be the fast entry
> into the system, and it looks like it is suppose to call the
> sysenter_entry when used. I'm trying to write something to test this
> out, since I still have the ud2 op in my sysentry code. So if I do get
> this to work, I can cause a bug.
>
> -- Steve
>

Cheers,
Dick Johnson
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
Warning : 98.36% of all statistics are fiction.
.
I apologize for the following. I tried to kill it with the above dot :

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