Re: Need help in understanding x86 syscall

Bodo Eggert
2005-08-11T23:26:07Z

On Thu, 11 Aug 2005, Steven Rostedt wrote:
> On Thu, 2005-08-11 at 15:41 +0200, Bodo Eggert wrote:

> > According to my documentation it isn't. A software interrupt is a far call
> > with an extra pushf, and a hardware interrupt is protected against recursion
> > by the PIC, not by an interrupt flag.
>
> I disagree with your definition of a system call. The "int 0x80"
> changes from user mode to kernel mode so it is much more powerful than a
> "far call".

Far calls and jumps can change to a inner ring. This is done by a special
segment selector containing the segment _and_ the offset to jump to (the
offset from the call instruction is ignored).

> Also the CPU does protect against recursion and more than
> one interrupt coming in at the same time. The PIC also works with the
> CPU in this regard, but as I shown in my previous email, the interrupt
> flag _does_ protect against it.

Showing == claiming? However, my documentation was wrong.

http://www.baldwin.cx/386htm/INT.htm
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