YongChul Kwon yongchul@cs CSE451 Section 1: Spring 2006 YongChul Kwon yongchul@cs

Reminders Sign up for mailing list Read the web site Start reading the book Homework due Monday Read & start project 0 Project 0 due Tuesday Check access to forkbomb.cs.washington.edu

More administrative infomation Office hour Prof. John Zahorjan Wed 3:30 – 4:20 @ CSE534 YongChul Kwon Mon & Thr 2:30-3:20 @ CSE216 By appointment Kurtis Heimerl Mon & Wed & Fri 12:30-1:20 @ CSExxx

CSE451 projects <=5 interesting & challenging projects Practice C & UNIX Shell & process control User-level threads Virtual memory trace analysis File systems Likely to be the same as past

Resources Use ‘forkbomb.cs.washington.edu’! VMware machines in 006 Well-managed(?) sandbox Do not disturb other students VMware machines in 006 Only for the final project Will distribute image for VMware player®

Advices Start early Read & code thoroughly Use tools It is HARD! Top-down From Big picture to details Use tools Editors, debuggers, compiler, shell, … Pencil & paper

Project 0 C programming warm-up

C Remember what you did in CSE303 Do you remember I know it is a painful memory… Do you remember Pointer & pointer arithmetic Stack & heap User defined data type Preprocessor String manipulation Standard C library

New in this course System call Union Function pointer % man 3 strcpy % man 3 fopen % man 2 open Union Function pointer What is a function? How is it stored in binary? How is it mapped into memory? What is a function pointer?

Example

Poll How do you “debug” your program? Print, print, print, print, print, … Stare & spot Ask friends Use debugger Other

GDB Most frequent GDB commands Execution: run, continue, step, next Browsing stack: up, down, backtrace Investigate data: display, print Break point: break, clear, condition Browsing source: list Don’t forget to specify ‘-g’ when you compile

Debugging relevant on later projects This slide is borrowed from section 1 in Winter 2006 In C99 #ifdef DEBUG # ifdef __KERNEL__ /* This one if debugging is on, and kernel space */ # define PDEBUG(...) printk(__VA_ARGS__) # else /* This one for user space */ # define PDEBUG(...) fprintf(stderr, __VA_ARGS__) # endif #else # define PDEBUG(...) /* not debugging: nothing */ #endif Usage PDEBUG(“Num1 : %d, Num2 : %do numbers: %d and %d\n”, num, num2); Don’t forget to declare DEBUG to enable

Write a safe code What is the problem of following code? char *buf = (char *)malloc(32); strcpy(buf, argv[1]); How can we fix it?

Probable errors Why do we get segmentation fault? Why do we get bus error? Do we have to write memory-leak-free program? Why? Operating system Web server Shell Homework