Steps
- modify arch/x86/kernel/syscall_table_32.S
- modify arch/x86/include/asm/unistd_32.h
- modify arch/x86/include/asm/syscalls.h
- modify arch/x86/kernel/Makefile
- add and implement arch/x86/kernel/hello.c
- make && sudo make modules_install && sudo make install && sudo reboot (Compile Kernel)
modify arch/x86/kernel/syscall_table_32.S
this file contains all the syscall names, so add a new line for our new system call at the end of the file
add .long sys_mycall at the end
modify arch/x86/include/asm/unistd_32.h
add #define __NR_mycall 338 before #ifdef __KERNEL__
modify #define NR_syscalls <number of system calls + 1>
modify arch/x86/include/asm/syscalls.h
the interface (declaration) of the system calls
add asm_linkage int mycall(void); after asmlinkage long sys_mmap(...);
modify arch/x86/kernel/Makefile
make sure the new system call will be compiledadd obj-y += mycall.o after obj-y := process...
add and implement arch/x86/kernel/hello.c
#include <linux/kernel.h>
#include <linux/linkage.h>
asmlinkage int sys_mycall(void) {
printk("Hello, how are you?\n");
return 0;
}
Test
- modify /usr/include/asm/unistd_32.h
- modify /usr/include/bits/syscall.h
- write a program to test it
- see the output in dmesg
add #define __NR_mycall 341 at the end, before #endifmodify /usr/include/bits/syscall.h
add #define SYS_mycall __NR_mycall at the end of the filewrite a program to test it
#include <syscall.h>#include <stdio.h>
int main() {
int r;
r = syscall(__NR_mycall);
printf("return value = %d\n", r);
return 0;
}
see the output in dmesg
simply type "dmesg" to check if the output is there
