Effective Memory Checking Tools for Detecting Errors in C Programming

1. Object oriented analysis and design Memory Checking tools Itay levy

2. Introduction • While a programmer is writing a code for an application that he creates, he can sometimes make an error that will cause a malefaction in his program. • Syntax error • Memory access errors • Memory leaks • Logical errors • Etc..

3. Memory errors • Memory access errors and memory leaks are caused by various reasons like: • Using an unallocated variable • Double freeing • Not freeing at all • Etc..

4. Memory errors(1) • The programmer will not receive any error massages from the compiler if he makes a memory access error or memory leak , he will have to waste a lot of time on debugging.

5. The memory checking tools • The memory checking tools are a memory related errors detection tools that will help the programmer to find and fix the memory related error in a short time , Instead of wasting hours of debugging in order to find and fix the problems.

6. The memory checking tools • Existing tools are : • Valgrind • BoundsChecker • Rational purify • And many more

7. Example - ValGrind Here's an example C program with a memory error and a memory leak. #include <stdlib.h> void f(void) { int* x = malloc(10 * sizeof(int)); x[10] = 0; } int main(void) { f(); return 0; } // problem 1: heap block overrun // problem 2: memory leak -- x not freed

8. Example – Valgrind (1) • First compile the program. • Then use the Command: valgrind --leak-check=yes myprog arg1 arg2 in order to run the valgrind on your program.

9. Example – valgrind(2) • The error massages of our program will be: ==19182== Invalid write of size 4 ==19182== at 0x804838F: f (example.c:6) ==19182== by 0x80483AB: main (example.c:11) ==19182== Address 0x1BA45050 is 0 bytes after a block of size 40 alloc'd ==19182== at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130) ==19182== by 0x8048385: f (example.c:5) ==19182== by 0x80483AB: main (example.c:11) • The first line tells us what kind of error we got. • Below the first line is a stack trace telling you where the problem occurred • Some error messages have a second component which describes the memory address involved.

10. Example – valgrind(3) • Memory leak messages look like this: ==19182== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==19182== at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130) ==19182== by 0x8048385: f (a.c:5) ==19182== by 0x80483AB: main (a.c:11) • The stack trace tells you where the leaked memory was allocated. • He will not tell you why the memory was leaked.

11. A few things about valgrind • Valgrind works only on linux/unix. • Valgrind Can also be used as a cache profiler as well. • Valgrind can also be used to find data races in multithreaded programs.

12. Example – Rational Purify Lets run the Rational purify on the next HelloWorld program: #include <stdio.h> #Include <malloc.h> Static char *HelloWorld = “Hello, World”; Void main() { char *mystr = malloc(strlen(HelloWorld)); strncpy(mystr, HelloWorld,12); printf(“%s\n”,mystr); }

13. Example – Rational Purify (1) • Compile and link the program under Purify using the -g option to collect  debug data:purify cc -g <myprog>.o • Then Run the program : % a.out

14. Example – Rational Purify(2)

15. Example – Rational purify(3)