Making a Linux system call

I'm having trouble passing a variable (specifically an integer) from user mode to kernel mode. This is my code for my system call:

Code:

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#include <linux/linkage.h>
#include <linux/kernel.h>
#include <linux/sched.h>

asmlinkage int sys_processdisplay(int __user *procnum) {
              int procnumk = 0;
              copy_from_user(procnum, procnum, sizeof(int));
              printk(KERN_EMERG "procnumk is: %d\n", procnumk);
              return(1);
}

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The problem is procnumk stays at 0. When I compile I get a weird message anytime I try to use copy_from_user or get_user that says "modpost: 3 mismatches found"

I appreciate any help. Thanks!

You never pass procnumk to the function, you are passing the pointer to procnum each time. Try

Code:

---

#include <linux/linkage.h>
#include <linux/kernel.h>
#include <linux/sched.h>

asmlinkage int sys_processdisplay(int __user *procnum) {
              int procnumk = 0;
              copy_from_user(&procnumk, procnum, sizeof(int));
              printk(KERN_EMERG "procnumk is: %d\n", procnumk);
              return(1);
}

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Quote:

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Originally Posted by Shakti

You never pass procnumk to the function, you are passing the pointer to procnum each time. Try

Code:

---

#include <linux/linkage.h>
#include <linux/kernel.h>
#include <linux/sched.h>

asmlinkage int sys_processdisplay(int __user *procnum) {
              int procnumk = 0;
              copy_from_user(&procnumk, procnum, sizeof(int));
              printk(KERN_EMERG "procnumk is: %d\n", procnumk);
              return(1);
}

---

---

I still get the modpost warning and 0 for procnumk

Show the rest of the code. That isn't where the problem is.

That is all the code, could it be how I made the system call? This is how I called it:
retval = syscall(__NR_processdisplay, 1);

1) What do you think asmlinkage does?

2) Exactly how are you registering this as a system call?