OS Project 0 & 1

National Taiwan University

OS Project 0 & 1

Advisor: Dr. Chih-Wen Hsueh

Student: Tang-Hsun Tu

台灣大學網媒所 / 資工所

Wireless Networking and Embedded Systems Laboratory Real-Time System Software Group

April 21, 2023

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Linux Installation Linux Kernel Compilation System Call

Outline

National Taiwan University

Linux Installation

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Including shells, libraries, tools, compiler, servers, applications.

Ubuntu, Redhat, Fedora, Mandrake, SuSE, Debian, Ubuntu, Gentoo…

Live CDs You can make your own Linux distribution This slide is based on Ubuntu 10.04 LTS

Linux Distribution

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Modify the boot sequence to boot your computer from CD-ROM

Make sure your hardware and device A clear head and relaxed mind Some drinks and food

Before Installation

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/dev/hda, /dev/hdb, /dev/hdc, … /dev/hda1, /dev/hda2, …

/dev/sda, /dev/scd0, … Mount Points

/ /swap …

Disks and Partitions

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Swap partition is usually twice as RAM when it is less than 1GB

No more than four primary partition including root partition and swap partition

If four isn’t enough, use extend partition Make sure all your mount points are correct

Partition Division

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After dividing partitions, you only need to click your mouse.

After installation, reboot and enjoy your Linux!

Installation by text mode is the same as graphic mode

End of Installation

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鳥哥的私房菜 http://linux.vbird.org/

Ubuntu 正體中文站 http://www.ubuntu-tw.org/

Ubuntu Homepage http://www.ubuntu.com/

Reference

National Taiwan University

Linux Kernel Compilation

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Kernel is the core of an operating system. Scheduler, task management, memory

management, … You need to compile kernel source code to

binary in order to run.

What is Linux Kernel?

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You can configure your Linux by compiling a new kernel. Add new features, ex. patch kernel. Support new hardware. Disable functions you don’t need. Develop your own kernel. ...

When Should We Compile Kernel?

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Kernel Website, http://www.kernel.org

You also can download the source from Ubuntu.

Where to D/L Linux Kernel?

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You need to be root to compile kernel sudo -i

Download the necessary tools apt-get update apt-get install kernel-package gcc libncurses5-dev

automake gcc libc6-dev build-essential Go to System/Administration/synaptic

package Manager or http://www.kernel.org/ Get the kernel source code e.g. 2.6.35.5

Prepare Your Kernel Source Code

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Unzip kernel source code. cd /usr/src tar jxvf linux-source-2.6.X.tar.bz2

You may have many versions of Linux source codes.

Prepare Your Kernel Source Code (Cont)

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There are many ways to configure. make config make menuconfig make xconfig ...

If you do not know how to configure, you can copy the old config file from /boot. make mrproper cp /boot/config-`uname -r` .config make menuconfig

Configure your Kernel

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Configure your Kernel (Cont)

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If you meet some problems (SATA) Device Drivers --->

SCSI device support ---> <*> SCSI device support <*> SCSI disk support

Device Drivers ---> SCSI device support --->

SCSI low-level drivers ---> [*] Serial ATA (SATA) support

Configure your Kernel (Cont)

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#make clean #make bzImage #make modules #make modules_install #make install #mkinitramfs –o /boot/initrd.img-2.6.x 2.6.x

Kernel Compilation

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See how many cores/hyperthreading on your machine cat /proc/cpuinfo | grep processor | wc –l e.g. 8

Compile with the number of jobs make –j8 bzImage make –j8 modules ...

Speed up Kernel Compilation

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Setup your boot manager. vim /boot/grub/menu.lst

Add the following section (Grub1): title Ubuntu 10.04 LTS, kernel 2.6.35.5 uuid xxxx kernel /boot/vmlinuz-2.6.35.5 root=UUID=xxxx

ro splash initrd /boot/initrd.img-2.6.35.5

Configure your Boot Menu

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Setup your boot manager. vim /boot/grub/grub.cfg

Add the following section (Grub2):

Configure your Boot Menu (Cont)

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Install ssh server apt-get install ssh

A ssh client on Windows. http://ntu.csie.org/~piaip/pietty/

Some Useful Tools

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鳥哥的私房菜 http://linux.vbird.org/

Google http://www.google.com/

Reference

National Taiwan University

System Call

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System call is the mechanism used by an application program to request service from the OS.

Users can use it to communicate with kernel. Here are two approaches developing our own

system calls Using kernel module Modify the source code of linux directly

Introduction

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Building system calls in kernel module is more flexible than modifying kernel. When we want to use our system call, just install our kernel modules; and if we don’t need it right away, just remove modules. Modifying kernel is not necessary. (But you still

need to modify your kernel for O.S. project one.)

Using Kernel Module

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For sys_call_table, your should extern it in a file such as <top directory to the kernel sources>/arch/x86/kernel/i386_ksyms_32.c.

Export sys_call_table

extern void* sys_call_table[];/*variable should be exported. */ EXPORT_SYMBOL(sys_call_table);

010203

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sys_call_table is read-only after kernel version 2.6.23.

If you really want to try this method using kernel version which is higher than 2.6.23, you will have to modify your current kernel source and recompile it.

Export sys_call_table (Cont)

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Firstly, check your compiled kernel version uname –a

In x86 32bit vim /usr/src/linux-2.6.x/arch/x86/kernel/ entry_32.S .section .rodata, “a” .section .data, “aw”

Export sys_call_table (Cont)

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In x86 64bit vim /usr/src/linux-2.6.x/arch/x86/kernel/syscall_64.c line 22: delete the “const”

Export sys_call_table (Cont)

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Add to export symbol vim /usr/src/linux-2.6.x/kernel/kallsyms.c extern void *sys_call_table; EXPORT_SYMBOL(sys_call_table);

Export sys_call_table (Cont)

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vim makefile vim myservice.c

Write Your Makefile

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Include and Define

Extern the “sys_call_table”

Write your own system call

Write Kernel Module

#include <linux/kernel.h> /* We're doing kernel work */ #include <linux/module.h> #define __NR_mysyscall 200 /* define the number of our system call */

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typedef void (*sys_call_ptr_t)(void);extern sys_call_ptr_t sys_call_table[];sys_call_ptr_t orig_sys_call;

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/* Our system call */ asmlinkage int mysyscall(int n) { printk("enter mysyscall()\n"); return 2*n; }

0102030405

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Initialize the kernel module

Extern the “sys_call_table”

Write Kernel Module (Cont)

/* Initialize the module - replace the system call */ int init_module() { printk("Insert mysyscall module\n"); orig_sys_call = sys_call_table[__NR_mysyscall]; sys_call_table[__NR_mysyscall] = mysyscall; return 0; }

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/* Cleanup - unregister the appropriate file from /proc */void cleanup_module() { printk("Remove mysyscall module\n"); sys_call_table[__NR_mysyscall] = orig_sys_call; }

0102030405

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Compile make

Insert the module to kernel insmod ./myservice.ko

Remove the module from kernel rmmod myservice

List the modules in kernel lsmod

Use Kernel Module

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Write an application to use your system call vim ap.c

Compile and execute gcc ap.c –o ap ./ap 10

User Application

#include <stdlib.h>#include <stdio.h>#define _GNU_SOURCE #include <unistd.h>#include <sys/syscall.h>

#define __NR_mysyscall 200

int main(int argc,char *argv[]){ printf("%d\n", syscall(__NR_mysyscall, atoi(argv[1]))); return 0;}

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Here are two approaches developing our own system calls Using kernel module Modify the source code of Linux directly

Build Your Own System Calls

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Create a new file in /usr/src/linux-2.6.x/kernel/ vim myservice.c

Add your system call

Write Your System Call

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

asmlinkage int sys_myservice(int arg1){ printk("my service is invoked!\n"); return arg1 * 10;}

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In x86 32bit /usr/src/linux-2.6.x/arch/x86/include/asm/unistd_32.h

The index must be the last in the list e.g. #define __NR_myservice 338

Write Your System Call (Cont) - x86_32

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Create an entry (function name) in system call table /usr/src/linux-2.6.x/arch/x86/kernel/syscall_table_32.S .long sys_myservice

Write Your System Call (Cont) - x86_32

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In x86 64bit /usr/src/linux-2.6.x/arch/x86/include/asm/unistd_64.h

The index must be the last in the list #define __NR_myservice 300 __SYSCALL(__NR_myservice, sys_myservice)

Write Your System Call (Cont) - x86_64

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Define the prototype /usr/src/linux-2.6.x/include/linux/syscalls.h #define asmlinkage int sys_myservice(int arg1);

Write Your System Call (Cont)

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Add to makefile to compile vim /usr/linux-2.6.x/kernel/Makefile obj-y += myservice.o

Now, you can recompile your kernel

Write Your System Call (Cont)

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Write an application to use your system call vim ap.c

Compile and execute gcc ap.c –o ap ./ap 10

User Application

#include <stdlib.h>#include <stdio.h>#define _GNU_SOURCE#include <unistd.h>#include <sys/syscall.h>

#define __NR_myservice 300

int main(int argc,char *argv[]){ printf("%d\n", syscall(__NR_myservice, atoi(argv[1]))); return 0;}

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Since we want measure the number of sent signals and called sys_kill(), we might need to add a counter to system call “kill()” in /usr/src/Linux-2.6.x/kernel/signal.c. e.g. int nr_kills;

If you want to use this variable in your system call or kernel module, you have to export it. EXPORT_SYMBOL(nr_kills);

printk can print messages in kernel, use dmesg to check.

Hints

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Results

Hints (Cont)

1.

2.

3.

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LXR, http://rswiki.csie.org/lxr/http/source

Some Useful Tool

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Manpages apt-get install manpages-dev

Some Useful Tool (Cont)

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Kernel Website http://www.kernel.org

LXR http://rswiki.csie.org/lxr/http/source http://lxr.linux.no/linux/

Google http://www.google.com/

Reference

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Q & A