1. Add a New System Call to Linux

2. Hw1 Add a New System Call to Linux and Compile Kernel
Add a New System Call to Linux by Kernel Module

3. Compile your own Linux kernel
Get the source
The Linux Kernel Archives
ftp://linux.cis.nctu.edu.tw/kernel/(交大資科)
(中山大學)

4. Compile your own Linux kernel
Steps:
Get the kernel source from ftp
Installing the kernel source code - kernel source is put in /usr/src - #cd /usr/src - #tar xvzf linux-2.4.x.tar.gz
make mroproper (Cleanup /usr/src/linux/目錄所有.o的object file , dependencies and kernel’s .config)

5. Compile your own Linux kernel
Steps:
Setup the kernel configuration make config or menuconfig or xconfig
#make dep
#make clean
#make bzImage
#make modules
#make modules_install (Modules will be installed in /lib/modules/2.4.x)
#make install

6. Compile your own Linux kernel
Edit Bootloader Configuration File -- /etc/lilo.conf
# lilo (完成)

7. Add a New System Call
Edit : /usr/src/linux/include/asm/unistd.h #define __NR_exit 1
#define __NR_fork 2 ……
#define __NR_lremovexattr 236
#define __NR_fremovexattr 237
#define __NR_hello 239
add #defines for you new system calls at the end

8. Add a New System Call Edit the file :
/usr/src/linux/arch/i386/kernel/entry.S
.data
ENTRY(sys_call_table)
.long SYMBOL_NAME(sys_ni_syscall) /* 0
.long SYMBOL_NAME(sys_exit)
.long SYMBOL_NAME(sys_fork) …
.long SYMBOL_NAME(sys_ni_syscall)
.long SYMBOL_NAME(sys_hello)
.rept NR_syscalls-(.-sys_call_table)/4
.endr

9. Add a New System Call Implement system call in kernel/sys.c
Modify the Makefile in the directory you placed your .c file so that your code gets compiled and linked in properly
Modify the Makefile line to have a .o of your source code
For example . Adding hello.o
O_OBJS += …. Hello.o

10. The Simple Kernel Module
A Kernel Module must have at least two functions：
“start” (initialization) function called init_module() which is called when the module is insmoded into kernel.
“end” (cleanup) function called clean_module() which is called just before it is rmmoded.

11. Compiling Kernel Modules
A kernel module should be compiled with the –c flag.
A kernel modules must be compiled with the optimization flag, -O because the kernel make extensive use of inline function
Define symbols using gcc’s –D option：
__KERNEL__：tells the header files that the code will be run in kernel mode.
MODULE: tells the header files to give the appropriate definitions for a kernel module.

12. Adding System Call by Module
KERNELDIR=/usr/src/linux-2.4
Include $(KERNELDIR)/.config
CFLAGS=-c –D__KERNEL__ -DMODULE –I$(KERNELDIR)/include –O2 –Wall
Ifdef CONFIG_SMP
CFLAGS += -D__SMP__ -DSMP
Endif
All: test2.o
Clean:
rm –f test2.o
Install:
/sbin/insmod test2.o
Remove:
/sbin/rmmod test2

13. Adding System Call by Module
#include <linux/kernel.h> /* for kernel function */
#include <linux/module.h> /* for module */
#include <linux/unistd.h> /* for system calls */
#include “hello.h“
extern void *sys_call_table[];
void (*orig_sys_call)(void);
/* my system call */
int hello(unsignedlong arg) {
printk( KERN_EMERG "Hello System Call: %d\n", arg);
return 0; }

14. Adding System Call by Module
/* init function, called when loaded */
int init_module(void) {
printk(KERN_EMERG“hello module installed\n");
orig_sys_call= sys_call_table[SYS_hello]; /* backup the original system call*/
sys_call_table[SYS_hello] = hello ; /* replace with my system call */
return 0; }
void cleanup_module(void)
printk(KERN_EMERG“hello module uninstalled\n");
sys_call_table[SYS_hello] = orig_sys_call; /* restore the original system call */
/* try to remove thieline */
MODULE_LICENSE("GPL");

15. Reference http://fossil.wpi.edu/docs/howto_add_systemcall.html
The Linux Kernel Module Programming Guide
鳥哥的 Linux 私房菜