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Old 11-01-2003, 07:28 AM   #1
LQ Newbie
Registered: Nov 2003
Location: VietNam
Distribution: Linux RedHat 9.0
Posts: 1

Rep: Reputation: 0
Question Error when add a new system call in RH9.0.

Hi all,
I need your help !
I am a newbie of Linux, I use Linux Redhat 9.0, kernel 2.4.20-8.
I want to add a new systam call in kernel but i got an error
This is what i have done:
I add a new entry in /arch/i386/kernel/entry.S :
................................./*kernel system call*/
.long SYMBOL(sys_demo_write)
before this line:
.rept (..)
Then, I add in /include/i-386/linux/unistd.h
..................../*kernel systemcall*/
#define __NR_demo_write 259
the last system call in my kernel is 258

And i add add function in /kernel/sys.c like this:
asmlinkage int sys_demo_write()
printk("This is a systemcall");
return 0;
After i compile kernel and run it.
I creat a program to test my new system call like this:
#include <stdio.h>
#include <stdlib.h>
#include <linux/unistd.h>

int main ()
return 0;

But when i compile this program with gcc, i got an error:
"In function demo_write,
__NR_demo_write undeclared.
I do not know what happen, can you please help me correct this error.
Thank you very much.
Old 11-01-2003, 01:31 PM   #2
Registered: Oct 2003
Distribution: Slackware
Posts: 112

Rep: Reputation: 15
Well, firstly, you are in the wrong place for such a question. You probably should subscribe to the linux kernel mailing list. Go to and scroll down a bit. You will find instructions for subscribing.

Second, when you change the arch includes in your linux kernel source tree, this does not change the includes in your /usr/include tree - nor should it. Nor can you casually change those files, or you potentially break any other build that doesn't know about your changes to the ABI.

Just curious, why do you want to add a syscall?
Old 11-01-2003, 01:52 PM   #3
Senior Member
Registered: Apr 2003
Location: Lancaster, England
Distribution: Debian Etch, OS X 10.4
Posts: 1,263

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moderators please delete

Last edited by kev82; 11-01-2003 at 03:07 PM.


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