Add a new Linux system call

The previous article explains the principles of Linux system invocation in detail, and then explains how to create a new Linux system call based on the principle of the previous article.

To add a new system call to the kernel, you need to perform 3 steps:
1. Add a new kernel function
2. Update the header file Unistd.h
3. Update the system call table calls for this new function. S

1. Add the function in KERNEL/SYS.C:
asmlinkage int Sysmul (int a, int b)
{
int C;
c = a*b;
return C;
}

2. Add the system call number in Arch/arm/include/asm/unistd.h: Add the following

#define __NR_PREADV(__nr_syscall_base+361)
#define __NR_PWRITEV (__nr_syscall_base+362)
#define __nr_rt_tgsigqueueinfo (__nr_syscall_base+363)
#define __nr_perf_event_open (__nr_syscall_base+364)
#define __NR_Sysmul(__nr_syscall_base+365)

Remarks: Add on last Side

3. In Arch/arm/kernel/calls. s to add code to the newly implemented system call function:

/* * */Call (SYS_INOTIFY_INIT1)
Call (SYS_PREADV)
Call (Sys_pwritev)
Call (Sys_rt_tgsigqueueinfo)
Call (Sys_perf_event_open)

Call (Sysmul)

Note: The system call number in the Unistd.h must be added to the last face

4. Recompile the kernel

Make Uimage arch=arm cross_compile=arm-linux-

5. Copy the kernel to the TFTP directory

CP arch/arm/boot/uimage/tftpboot/

Note: The 5th step can not be used to download to the Development Board via TFTP

6. Using System calls

#include <stdio.h>
#include <linux/unistd.h>
Main ()
{

int result;
result = Syscall (361,1, 2),//syscall procedure 1, the system calls MOV R7, #365 2, using the SVC command

Syscall (System call number, parameter 1, parameter 2) where parameter 1 and parameter 2 are two parameters of Sysmul
printf ("result =", result);
}

Add a new Linux system call