IRQ vector assignment for system call exception

IRQ vector assignment for system call exception

[yen]

Hi:
   I have a quwstion. Why the number 128 is reserver for system call exception in 
interrupt vectors? Why not other numbers? Are there any historical reasons?
thanks.
                  
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Open WebMail Project (http://openwebmail.org)

Re: IRQ vector assignment for system call exception

[Coywolf Qi Hunt]

2005/12/8, yen <yen@eos.cs.nthu.edu.tw>:
> Hi:
>    I have a quwstion. Why the number 128 is reserver for system call exception in
> interrupt vectors? Why not other numbers? Are there any historical reasons?
> thanks.
>

0x80 stands in the middle of [0..0xff].
--
Coywolf Qi Hunt
http://sosdg.org/~coywolf/

Re: IRQ vector assignment for system call exception

[linux-os (Dick Johnson)]

On Thu, 8 Dec 2005, Coywolf Qi Hunt wrote:

> 2005/12/8, yen <yen@eos.cs.nthu.edu.tw>:
>> Hi:
>>    I have a quwstion. Why the number 128 is reserver for system call exception in
>> interrupt vectors? Why not other numbers? Are there any historical reasons?
>> thanks.
>>
>
> 0x80 stands in the middle of [0..0xff].
> --
> Coywolf Qi Hunt
> http://sosdg.org/~coywolf/

If he's looking for 'secret codes' in the kernel, he might look
at:
 	LINUX_REBOOT_MAGIC2
 	LINUX_REBOOT_MAGIC2B
 	LINUX_REBOOT_MAGIC2C

... in linux-`uname -r`/include/linux/reboot.h Hint: Cvt dec to hex.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.
.

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Thank you.

Re: IRQ vector assignment for system call exception

[Gaurav Dhiman]

yes, definetely a historical reason. System libraries need to know
this vector to invoke system call.

-Gaurav


On 12/8/05, yen <yen@eos.cs.nthu.edu.tw> wrote:
> Hi:
>    I have a quwstion. Why the number 128 is reserver for system call exception in
> interrupt vectors? Why not other numbers? Are there any historical reasons?
> thanks.
>
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--
- Gaurav
my blog: http://lkdp.blogspot.com/
--

Re: IRQ vector assignment for system call exception

[Arjan van de Ven]

On Sat, 2005-12-10 at 18:50 +0530, Gaurav Dhiman wrote:
> yes, definetely a historical reason. System libraries need to know
> this vector to invoke system call.

nowadays it's also mostly unused; sysenter and friends are used instead
and they don't use this entry point.

Re: IRQ vector assignment for system call exception

[Ingo Molnar]

* Arjan van de Ven <arjan@infradead.org> wrote:

> On Sat, 2005-12-10 at 18:50 +0530, Gaurav Dhiman wrote:
> > yes, definetely a historical reason. System libraries need to know
> > this vector to invoke system call.
> 
> nowadays it's also mostly unused; sysenter and friends are used 
> instead and they don't use this entry point.

note that some system-calls are still invoked via int80 by glibc, such 
as fork() - even on sysenter/syscall capable CPUs.

	Ingo

Re: IRQ vector assignment for system call exception

[Jan Engelhardt]

>> On Sat, 2005-12-10 at 18:50 +0530, Gaurav Dhiman wrote:
>> > yes, definetely a historical reason. System libraries need to know
>> > this vector to invoke system call.
>> 
>> nowadays it's also mostly unused; sysenter and friends are used 
>> instead and they don't use this entry point.
>
>note that some system-calls are still invoked via int80 by glibc, such 
>as fork() - even on sysenter/syscall capable CPUs.

OT: Any idea when glibc moves to use sysenter on capable CPUs?



Jan Engelhardt
-- 

Re: IRQ vector assignment for system call exception

[Arjan van de Ven]

On Thu, 2005-12-15 at 23:50 +0100, Jan Engelhardt wrote:
> >> On Sat, 2005-12-10 at 18:50 +0530, Gaurav Dhiman wrote:
> >> > yes, definetely a historical reason. System libraries need to know
> >> > this vector to invoke system call.
> >> 
> >> nowadays it's also mostly unused; sysenter and friends are used 
> >> instead and they don't use this entry point.
> >
> >note that some system-calls are still invoked via int80 by glibc, such 
> >as fork() - even on sysenter/syscall capable CPUs.
> 
> OT: Any idea when glibc moves to use sysenter on capable CPUs?

it has been doing that for a LOOOONG time
exception are syscalls that sysenter can't do (iirc 6 argument ones, and
I suspect fork() because it's just "special", but all normal ones are
done via sysenter already from even before 2.6.0 got released.