DOC PREVIEW
CMU CS 15213 - lecture

This preview shows page 1-2-3-4-25-26-27-52-53-54-55 out of 55 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 55 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Carnegie MellonIntroduction to Computer Systems15-213/18-243, spring 200921stLecture, Apr. 2ndInstructors:Gregory Kesden and Markus PüschelCarnegie MellonAnnouncements Exam Next Tuesday Covers: Ch 5–8, 10.1–10.8 Next recitations: answering your questions Malloclab Due April 16th 150 points Can be done in teams of 2 (recommended to reduce workload) Has a check pointCarnegie MellonToday Memory related bugs System level I/O Unix I/O Standard I/O RIO (robust I/O) package Conclusions and examplesCarnegie MellonMemory-Related Perils and Pitfalls Dereferencing bad pointers Reading uninitialized memory Overwriting memory Referencing nonexistent variables Freeing blocks multiple times Referencing freed blocks Failing to free blocksCarnegie MellonDereferencing Bad Pointers The classic scanf bugint val;...scanf(“%d”, val);Carnegie MellonReading Uninitialized Memory Assuming that heap data is initialized to zero/* return y = Ax */int *matvec(int **A, int *x) { int *y = malloc(N*sizeof(int));int i, j;for (i=0; i<N; i++)for (j=0; j<N; j++)y[i] += A[i][j]*x[j];return y;}Carnegie MellonOverwriting Memory Allocating the (possibly) wrong sized objectint **p;p = malloc(N*sizeof(int));for (i=0; i<N; i++) {p[i] = malloc(M*sizeof(int));}Carnegie MellonOverwriting Memory Not checking the max string size Basis for classic buffer overflow attacks 1988 Internet worm Modern attacks on Web servers AOL/Microsoft IM warchar s[8];int i;gets(s); /* reads “123456789” from stdin */Carnegie MellonOverwriting Memory Misunderstanding pointer arithmeticint *search(int *p, int val) {while (*p && *p != val)p += sizeof(int);return p;}Carnegie MellonReferencing Nonexistent Variables Forgetting that local variables disappear when a function returnsint *foo () {int val;return &val;}Carnegie MellonFreeing Blocks Multiple Times Nasty!x = malloc(N*sizeof(int));<manipulate x>free(x);y = malloc(M*sizeof(int));<manipulate y>free(x);Carnegie MellonReferencing Freed Blocks Evil! x = malloc(N*sizeof(int));<manipulate x>free(x);...y = malloc(M*sizeof(int));for (i=0; i<M; i++)y[i] = x[i]++;Carnegie MellonFailing to Free Blocks (Memory Leaks) Slow, long-term killer! foo() {int *x = malloc(N*sizeof(int));...return;}Carnegie MellonFailing to Free Blocks (Memory Leaks) Freeing only part of a data structurestruct list {int val;struct list *next;};foo() {struct list *head = malloc(sizeof(struct list));head->val = 0;head->next = NULL;<create and manipulate the rest of the list>...free(head);return;}Carnegie MellonDealing With Memory Bugs Conventional debugger (gdb) Good for finding bad pointer dereferences Hard to detect the other memory bugs Debugging malloc (UToronto CSRI malloc) Wrapper around conventional malloc Detects memory bugs at malloc and free boundaries Memory overwrites that corrupt heap structures Some instances of freeing blocks multiple times Memory leaks Cannot detect all memory bugs Overwrites into the middle of allocated blocks Freeing block twice that has been reallocated in the interim Referencing freed blocksCarnegie MellonDealing With Memory Bugs (cont.) Some malloc implementations contain checking code Linux glibc malloc: setenv MALLOC_CHECK_ 2 FreeBSD: setenv MALLOC_OPTIONS AJR Binary translator: valgrind (Linux), Purify Powerful debugging and analysis technique Rewrites text section of executable object file Can detect all errors as debugging malloc Can also check each individual reference at runtime Bad pointers Overwriting Referencing outside of allocated block Garbage collection (Boehm-Weiser Conservative GC) Let the system free blocks instead of the programmer.Carnegie MellonOverwriting Memory Referencing a pointer instead of the object it points toint *BinheapDelete(int **binheap, int *size) {int *packet;packet = binheap[0];binheap[0] = binheap[*size - 1];*size--;Heapify(binheap, *size, 0);return(packet);}Carnegie MellonToday Memory related bugs System level I/O Unix I/O Standard I/O RIO (robust I/O) package Conclusions and examplesCarnegie MellonUnix Files A Unix file is a sequence of m bytes: B0, B1, .... , Bk, .... , Bm-1 All I/O devices are represented as files: /dev/sda2 (/usr disk partition) /dev/tty2 (terminal) Even the kernel is represented as a file: /dev/kmem (kernel memory image)  /proc (kernel data structures)Carnegie MellonUnix File Types Regular file File containing user/app data (binary, text, whatever) OS does not know anything about the format other than “sequence of bytes”, akin to main memory Directory file A file that contains the names and locations of other files Character special and block special files Terminals (character special) and disks (block special) FIFO (named pipe) A file type used for inter-process communication Socket A file type used for network communication between processesCarnegie MellonUnix I/O Key Features Elegant mapping of files to devices allows kernel to export simple interface called Unix I/O Important idea: All input and output is handled in a consistent and uniform way Basic Unix I/O operations (system calls):  Opening and closing files open()and close() Reading and writing a file read() and write() Changing the current file position (seek) indicates next offset into file to read or write lseek()B0B1• • • Bk-1BkBk+1• • •Current file position = kCarnegie MellonOpening Files Opening a file informs the kernel that you are getting ready to access that file Returns a small identifying integer file descriptor fd == -1 indicates that an error occurred Each process created by a Unix shell begins life with three open files associated with a terminal: 0: standard input 1: standard output 2: standard errorint fd; /* file descriptor */if ((fd = open("/etc/hosts", O_RDONLY)) < 0) {perror("open");exit(1);}Carnegie MellonClosing Files Closing a file informs the kernel that you are finished accessing that file Closing an already closed file is a recipe for disaster in threaded programs (more on this later) Moral: Always check return codes, even for seemingly benign functions such as close()int fd; /* file descriptor */int retval; /* return value */if ((retval = close(fd)) < 0) {perror("close");exit(1);}Carnegie


View Full Document

CMU CS 15213 - lecture

Documents in this Course
lecture

lecture

14 pages

lecture

lecture

46 pages

Caches

Caches

9 pages

lecture

lecture

39 pages

Lecture

Lecture

36 pages

Lecture

Lecture

45 pages

Lecture

Lecture

56 pages

lecture

lecture

11 pages

lecture

lecture

9 pages

Lecture

Lecture

36 pages

Lecture

Lecture

37 pages

Exam

Exam

16 pages

Lecture

Lecture

10 pages

Lecture

Lecture

43 pages

Lecture

Lecture

8 pages

Lecture

Lecture

8 pages

Lecture

Lecture

36 pages

Lecture

Lecture

43 pages

Lecture

Lecture

12 pages

Lecture

Lecture

37 pages

Lecture

Lecture

6 pages

Lecture

Lecture

40 pages

coding

coding

2 pages

Exam

Exam

17 pages

Exam

Exam

14 pages

Lecture

Lecture

29 pages

Lecture

Lecture

34 pages

Exam

Exam

11 pages

Lecture

Lecture

9 pages

Lecture

Lecture

37 pages

Lecture

Lecture

36 pages

lecture

lecture

46 pages

Lecture

Lecture

33 pages

Lecture

Lecture

57 pages

Lecture

Lecture

32 pages

Lecture

Lecture

46 pages

Lecture

Lecture

40 pages

Lecture

Lecture

11 pages

Lecture

Lecture

6 pages

Lecture

Lecture

43 pages

Lecture

Lecture

12 pages

Lecture

Lecture

18 pages

Exam

Exam

10 pages

Lecture

Lecture

45 pages

Lecture

Lecture

37 pages

Exam

Exam

24 pages

class09

class09

21 pages

class22

class22

37 pages

class20

class20

30 pages

class27

class27

33 pages

class25

class25

21 pages

class04

class04

31 pages

Lecture

Lecture

59 pages

class01a

class01a

14 pages

class12

class12

45 pages

class29

class29

33 pages

Lecture

Lecture

39 pages

Lecture

Lecture

6 pages

class03

class03

34 pages

lecture

lecture

42 pages

Lecture

Lecture

40 pages

Lecture

Lecture

47 pages

Exam

Exam

19 pages

R06-B

R06-B

25 pages

class17

class17

37 pages

class25

class25

31 pages

Lecture

Lecture

15 pages

final-f06

final-f06

17 pages

Lecture

Lecture

9 pages

lecture

lecture

9 pages

Exam

Exam

15 pages

Lecture

Lecture

22 pages

class11

class11

45 pages

lecture

lecture

50 pages

Linking

Linking

37 pages

Lecture

Lecture

64 pages

Integers

Integers

40 pages

Exam

Exam

11 pages

Lecture

Lecture

37 pages

Lecture

Lecture

44 pages

Lecture

Lecture

37 pages

Lecture

Lecture

9 pages

Lecture

Lecture

37 pages

Lecture

Lecture

45 pages

Final

Final

25 pages

lecture

lecture

9 pages

Lecture

Lecture

30 pages

Lecture

Lecture

16 pages

Final

Final

17 pages

Lecture

Lecture

8 pages

Exam

Exam

11 pages

Lecture

Lecture

47 pages

Lecture

Lecture

9 pages

lecture

lecture

39 pages

Exam

Exam

11 pages

lecture

lecture

41 pages

lecture

lecture

37 pages

Lecture

Lecture

59 pages

Lecture

Lecture

45 pages

Exam 1

Exam 1

18 pages

Lecture

Lecture

41 pages

Lecture

Lecture

32 pages

Lecture

Lecture

30 pages

Lecture

Lecture

9 pages

Lecture

Lecture

9 pages

Lecture

Lecture

15 pages

Lecture

Lecture

11 pages

Lecture

Lecture

9 pages

Lecture

Lecture

34 pages

Lecture

Lecture

40 pages

Lecture

Lecture

4 pages

Lecture

Lecture

46 pages

Lecture

Lecture

8 pages

Lecture

Lecture

65 pages

Lecture

Lecture

38 pages

Lecture

Lecture

35 pages

Lecture

Lecture

8 pages

Lecture

Lecture

34 pages

Lecture

Lecture

8 pages

Exam

Exam

13 pages

Lecture

Lecture

43 pages

Lecture

Lecture

9 pages

Lecture

Lecture

12 pages

Lecture

Lecture

9 pages

Lecture

Lecture

34 pages

Lecture

Lecture

43 pages

Lecture

Lecture

7 pages

Lecture

Lecture

45 pages

Lecture

Lecture

24 pages

Lecture

Lecture

47 pages

Lecture

Lecture

12 pages

Lecture

Lecture

20 pages

Lecture

Lecture

9 pages

Exam

Exam

11 pages

Lecture

Lecture

52 pages

Lecture

Lecture

20 pages

Exam

Exam

11 pages

Lecture

Lecture

35 pages

Lecture

Lecture

47 pages

Lecture

Lecture

18 pages

Lecture

Lecture

30 pages

Lecture

Lecture

59 pages

Lecture

Lecture

37 pages

Lecture

Lecture

22 pages

Lecture

Lecture

35 pages

Exam

Exam

23 pages

Lecture

Lecture

9 pages

Lecture

Lecture

22 pages

class12

class12

32 pages

Lecture

Lecture

8 pages

Lecture

Lecture

39 pages

Lecture

Lecture

44 pages

Lecture

Lecture

38 pages

Lecture

Lecture

69 pages

Lecture

Lecture

41 pages

Lecture

Lecture

12 pages

Lecture

Lecture

52 pages

Lecture

Lecture

59 pages

Lecture

Lecture

39 pages

Lecture

Lecture

83 pages

Lecture

Lecture

59 pages

class01b

class01b

17 pages

Exam

Exam

21 pages

class07

class07

47 pages

Lecture

Lecture

11 pages

Odyssey

Odyssey

18 pages

multicore

multicore

66 pages

Lecture

Lecture

6 pages

lecture

lecture

41 pages

lecture

lecture

55 pages

lecture

lecture

52 pages

lecture

lecture

33 pages

lecture

lecture

46 pages

lecture

lecture

17 pages

lecture

lecture

49 pages

Exam

Exam

17 pages

lecture

lecture

56 pages

Exam 2

Exam 2

16 pages

Exam 2

Exam 2

16 pages

Notes

Notes

37 pages

Lecture

Lecture

40 pages

Lecture

Lecture

36 pages

Lecture

Lecture

43 pages

Lecture

Lecture

25 pages

Exam

Exam

13 pages

Lecture

Lecture

32 pages

Lecture

Lecture

12 pages

Lecture

Lecture

58 pages

Lecture

Lecture

29 pages

Lecture

Lecture

59 pages

Lecture

Lecture

41 pages

Lecture

Lecture

50 pages

Exam

Exam

17 pages

Lecture

Lecture

29 pages

Lecture

Lecture

44 pages

Lecture

Lecture

41 pages

Lecture

Lecture

52 pages

Lecture

Lecture

40 pages

Lecture

Lecture

33 pages

lecture

lecture

10 pages

Lecture

Lecture

27 pages

Lecture

Lecture

29 pages

Lecture

Lecture

39 pages

Lecture

Lecture

9 pages

Lecture

Lecture

29 pages

Lecture

Lecture

8 pages

Lecture

Lecture

43 pages

Lecture

Lecture

43 pages

Lecture

Lecture

75 pages

Lecture

Lecture

55 pages

Exam

Exam

12 pages

Lecture

Lecture

43 pages

Lecture

Lecture

35 pages

lecture

lecture

36 pages

Exam

Exam

33 pages

lecture

lecture

56 pages

lecture

lecture

64 pages

lecture

lecture

8 pages

Exam

Exam

14 pages

Lecture

Lecture

43 pages

Lecture

Lecture

36 pages

lecture

lecture

56 pages

lecture

lecture

75 pages

lecture

lecture

36 pages

Lecture

Lecture

50 pages

Lecture

Lecture

45 pages

Lecture

Lecture

13 pages

Exam

Exam

23 pages

Lecture

Lecture

10 pages

Lecture

Lecture

48 pages

Lecture

Lecture

83 pages

lecture

lecture

57 pages

Lecture

Lecture

33 pages

Lecture

Lecture

39 pages

Lecture

Lecture

33 pages

lecture

lecture

54 pages

Lecture

Lecture

30 pages

Exam

Exam

13 pages

Lecture

Lecture

36 pages

Lecture

Lecture

40 pages

Exam

Exam

17 pages

Lecture

Lecture

9 pages

Exam

Exam

15 pages

Lecture

Lecture

44 pages

Lecture

Lecture

34 pages

Lecture

Lecture

24 pages

Lecture

Lecture

29 pages

class12

class12

43 pages

lecture

lecture

43 pages

class22

class22

22 pages

R06-B

R06-B

25 pages

class01b

class01b

19 pages

lecture

lecture

29 pages

lab1

lab1

8 pages

Caches

Caches

36 pages

lecture

lecture

55 pages

Lecture,

Lecture,

37 pages

Integers

Integers

40 pages

Linking

Linking

38 pages

lecture

lecture

45 pages

Lecture

Lecture

61 pages

Linking

Linking

33 pages

lecture

lecture

40 pages

lecture

lecture

40 pages

Lecture

Lecture

32 pages

lecture

lecture

48 pages

lecture

lecture

44 pages

Exam

Exam

11 pages

Lecture

Lecture

31 pages

Lecture

Lecture

46 pages

Lecture

Lecture

40 pages

Lecture

Lecture

40 pages

Exam

Exam

12 pages

Lecture

Lecture

42 pages

Lecture

Lecture

36 pages

Lecture

Lecture

45 pages

Lecture

Lecture

41 pages

Lecture

Lecture

13 pages

Lecture

Lecture

35 pages

Lecture

Lecture

20 pages

Final

Final

19 pages

Lecture

Lecture

33 pages

Lecture

Lecture

50 pages

Lecture

Lecture

33 pages

Lecture

Lecture

27 pages

Lecture

Lecture

6 pages

Exam

Exam

15 pages

Lecture

Lecture

24 pages

Lecture

Lecture

23 pages

Lecture

Lecture

43 pages

Lecture

Lecture

32 pages

Lecture

Lecture

52 pages

Lecture

Lecture

37 pages

Lecture

Lecture

36 pages

Lecture

Lecture

34 pages

Lecture

Lecture

40 pages

Lecture

Lecture

15 pages

lecture

lecture

21 pages

Lecture

Lecture

58 pages

Lecture

Lecture

49 pages

Lecture

Lecture

36 pages

Lecture

Lecture

11 pages

Lecture

Lecture

12 pages

Lecture

Lecture

58 pages

Lecture

Lecture

33 pages

Exam

Exam

15 pages

Lecture

Lecture

35 pages

Lecture

Lecture

10 pages

Lecture

Lecture

25 pages

Lecture

Lecture

31 pages

Lecture

Lecture

24 pages

Lecture

Lecture

34 pages

Lecture

Lecture

50 pages

lecture

lecture

35 pages

Lecture

Lecture

11 pages

Lecture

Lecture

39 pages

Lecture

Lecture

45 pages

Lecture

Lecture

41 pages

exam1-f05

exam1-f05

11 pages

Lecture

Lecture

4 pages

Lecture

Lecture

17 pages

Exam

Exam

17 pages

malloc()

malloc()

12 pages

Lecture

Lecture

57 pages

Lecture

Lecture

30 pages

Lecture

Lecture

30 pages

Lecture

Lecture

47 pages

Lecture

Lecture

33 pages

Exam

Exam

12 pages

Lecture

Lecture

43 pages

Lectures

Lectures

33 pages

Lecture

Lecture

36 pages

lecture

lecture

33 pages

Exam

Exam

14 pages

Lecture

Lecture

43 pages

Lecture

Lecture

25 pages

Load more
Download lecture
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view lecture and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view lecture 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?