Re: Need help in understanding x86 syscall

linux-os (Dick Johnson)
2005-08-11T17:57:20Z

On Thu, 11 Aug 2005, Steven Rostedt wrote:

> On Thu, 2005-08-11 at 13:26 -0400, Steven Rostedt wrote:
>
>> 288fb seems to use "int 0x80" and so do all the other system calls that
>> I inspected.
>
> I expect that if I had a Gentoo system that I compiled for my machine,
> this would be different. But I suspect that Debian still wants to run on
> my old Pentium 75MHz laptop. How would libc know to use sysenter
> instead of int 0x80. It could do a test of the system, but would there
> be an if statement for every system call then? I guess that libc needs
> to be compiled either to use it or not. Since there are still several
> machines out there that don't have this feature, it would be safer to
> not use it.
>
> -- Steve
>

Well I have a small-C runtime library that I put together for
imbedded systems. Once somebody heard that I was using the
"obsolete" int 0x80, they insisted that I re-do everything to
use the new interface. Since I wasn't getting paid to think
on that project, I did what I was told. Bench-marks to 'getpid()'
showed the 0x80 interrupt faster by a few cycles so the "suits"
claimed that I must have done something wrong. So we had a
"code-review".

Finally it was decided; "The CPU must be handling things differently..."
i.e., go back to the simpler int 0x80 interface. It was obvious
to me that any difference in speed was simply noise. Both ways
are essentially the same for performance so I wouldn't lose
any sleep over an "older" 'C' runtime library.

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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