Re: Intel P6 vs P7 system call performance

Richard B. Johnson
2002-12-17T19:41:23Z

On 17 Dec 2002, Alan Cox wrote:

> On Tue, 2002-12-17 at 18:48, Ulrich Drepper wrote:
> > Alan Cox wrote:
> >
> > > Is there any reason you can't just keep the linker out of the entire
> > > mess by generating
> > >
> > > .byte whatever
> > > .dword 0xFFFF0000
> > >
> > > instead of call ?
> >
> > There is no such instruction. Unless you know about some secret
> > undocumented opcode...
>
> No I'd forgotten how broken x86 was
>

You can call intersegment with a full pointer. I don't know how
expensive that is. Since USER_CS is a fixed value in Linux, it
can be hard-coded

.byte 0x9a
.dword 0xfffff000
.word USER_CS

No. I didn't try this, I'm just looking at the manual. I don't know
what the USER_CS is (didn't look in the kernel) The book says the
pointer is 16:32 which means that it's a dword, followed by a word.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.