PROGRAMMING - Hacking: The Art of Exploitation

Graphics Programs Reference

In-Depth Information

Notice that the static_var retains its value between subsequent calls to

function() . This is because static variables retain their values, but also because

they are only initialized once. In addition, since the static variables are local

to a particular functional context, the static_var in the context of main()

retains its value of 1337 the entire time.

Once again, printing the addresses of these variables by dereferencing

them with the unary address operator will provide greater viability into what's

really going on. Take a look at static2.c for an example.

static2.c

#include <stdio.h>

void function() { // An example function, with its own context

int var = 5;

static int static_var = 5; // Static variable initialization

printf("\t[in function] var @ %p = %d\n", &var, var);

printf("\t[in function] static_var @ %p = %d\n", &static_var, static_var);

var++; // Add 1 to var.

static_var++; // Add 1 to static_var.

}

int main() { // The main function, with its own context

int i;

static int static_var = 1337; // Another static, in a different context

for(i=0; i < 5; i++) { // loop 5 times

printf("[in main] static_var @ %p = %d\n", &static_var, static_var);

function(); // Call the function.

}

The results of compiling and executing static2.c are as follows.

reader@hacking:~/booksrc $ gcc static2.c

reader@hacking:~/booksrc $ ./a.out

[in main] static_var @ 0x804968c = 1337