1. Build A New Kernel and Add New System Calls in A Linux OS
C.L. Chou

2. Goals Learn how to build a new Linux kernel
Learn how to add new system calls

3. Build A New Linux Kernel

4. Reference Refer to relative documents on Internet
Use “how to build a linux kernel” as key words for search engine.
E.g.

5. Note for Kernel Configuration
File system support
RAM disk support may need to be checked when configuring the kernel.
Device Drivers  Block devices  RAM disk support
Network devices’ drivers have to be checked according to what kinds of network devices equipped on your PC.

6. Note for Kernel Compilation and Installation
Basic installation steps:
%make xconfig/menuconfig
%make dep
%make clean
%make bzImage
%make modules
%make modules_install
%make install
Automatically copy kernel image, copy system.map, create initial ramdisk, modify grub.conf, etc.

7. Add New System Calls

8. Reference Refer to relative documents on Internet
Use “how to add a system call” as key words for search engine.
E.g.

9. Added or Modified Kernel Files
The version of example kernel is
Files added or modified in the kernel:
arch/i386/kernel/syscall_table.S (split from entry.S)
include/asm/unistd.h
include/linux/myservice.h
include/net/myvariable.h
net/ipv4/myservice.c
init/main.c
net/ipv4/tcp.c

10. Functionalities of added system calls
mysetflag()
Turn on/off a kernel flag to start/stop counting the number of invoking tcp_sendmsg() in the kernel.
mygetdata()
Obtain the number of invoking tcp_sendmsg() recorded in the kernel.

11. arch/i386/kernel/syscall_table.S
Modified file
Search key words:
sys_mysetflag
sys_mygetdata

12. include/asm/unistd.h Modified file Search key words: mysetflag
mygetdata
#define NR_syscalls 313
313 is the total number of system calls.

13. include/linux/myservice.h
Added file
The header file of net/ipv4/myservice.c

14. include/net/myvariable.h
Added file
Declaration of two global variables and one data structure which are used in kernel.

15. net/ipv4/myservice.c Added file
Define two system call functions and one initialization function.
sys_mysetflag()
sys_mygetdata()
myvariable_init()

16. init/main.c
Modified file
Search key word:
myvariable_init (twice)

17. net/ipv4/tcp.c Modified file Search key words: myflag (twice)
tcp_sendmsg_call_count (twice)

18. User-level Example Program Files
myservice_user.h
myservice_user.c
Compiling myservice_user.c
gcc –o myservice_user myservice_user.c

19. Demo Date: 4/24 (Mon.), 4/25(Tues.) at EC215 Steps:
Run the user-level program.
Run any application that creates a TCP connection to send data packets.
ssh
ftp
http

20. Downloading FTP Site IP: 140.113.214.77 Port: 21 Login: homework
Password: homework
Files:
Build A New Kernel and Add New System Calls.ptt
linux tar.gz
myservice_user.tar.gz