syscall numbers larger than 255?

syscall numbers larger than 255?

[Chris Friesen]

Just a quick and simple question for someone that knows the answer.

Stock 2.4.20 for i386 uses syscalls up to 252.  I want to add about a 
half-dozen new syscalls (forward porting stuff that we've got on 2.4.18).

Does x86 support syscall numbers > 255?  If yes, do I have to do 
anything special to use them? If not, what are my options?

Thanks,

Chris

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Re: syscall numbers larger than 255?

[Richard B. Johnson]

On Mon, 10 Nov 2003, Chris Friesen wrote:

>
> Just a quick and simple question for someone that knows the answer.
>
> Stock 2.4.20 for i386 uses syscalls up to 252.  I want to add about a
> half-dozen new syscalls (forward porting stuff that we've got on 2.4.18).
>
> Does x86 support syscall numbers > 255?  If yes, do I have to do
> anything special to use them? If not, what are my options?
>
> Thanks,
>
> Chris

Sure. With the old int 0x80 calling convention, the syscall number
is just put into the EAX register which can contain 32 bits. There
may be some mask on the kernel side to limit 'damage', but you
can change this if you are adding system-calls. The newer calling
convention also has just the 32 bit limitation.


Cheers,
Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips).
            Note 96.31% of all statistics are fiction.

Re: syscall numbers larger than 255?

[Davide Libenzi]

On Mon, 10 Nov 2003, Chris Friesen wrote:

> 
> Just a quick and simple question for someone that knows the answer.
> 
> Stock 2.4.20 for i386 uses syscalls up to 252.  I want to add about a 
> half-dozen new syscalls (forward porting stuff that we've got on 2.4.18).
> 
> Does x86 support syscall numbers > 255?  If yes, do I have to do 
> anything special to use them? If not, what are my options?

Currently there's a discrepancy between include/asm-i386/unistd.h and 
arch/i386/kernel/entry.S. While the first define function numbers up to 
252, the entry.S file fill up the table up to 258 (epoll crosses the 255 
boundary :).



- Davide

Re: syscall numbers larger than 255?

[Andi Kleen]

Chris Friesen <cfriesen@nortelnetworks.com> writes:

> Just a quick and simple question for someone that knows the answer.
> 
> Stock 2.4.20 for i386 uses syscalls up to 252.  I want to add about a
> half-dozen new syscalls (forward porting stuff that we've got on
> 2.4.18).
> 
> Does x86 support syscall numbers > 255?  If yes, do I have to do
> anything special to use them? If not, what are my options?

They should work fine on x86.

-Andi