Stack Exploration (ITI8510)

Real-Time Operating Systems and Systems Programming

Basic Linux command-line and utilities for accessing it Standard Streams Stack Exploration Exploring Debugger Signals Threads Processes File Attributes Reading Binary Files LAB: Hufmann Encoder Network Sockets Optimization (mmap() helps here)

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In preparation for memory management, we shall investigate call stack contents.

Task

Write some small program for further exploration. The program should contain:

• function main() containing:
  • at least 3 integers, with some (different) default values
  • a string
• function void foo(int argument) containing:
  • at least 2 integers, with some default values

This base program can do practically anything (including nothing), as long as the function foo() runs.

1. Modify the program to print the memory addresses of all the variables. Use "%p" for printf() function. Use & operator on the variable to get the memory address as a value.
2. Within function foo(), use the memory address of the first declared variable to print out the value of address which precedes it and the memory address which follows it. (Use * operator to read memory from given location)
3. Can you go further? Can you read the variables of main() just by modifying the address of a variable in foo()? (Yes, but try it out)
4. Can you print the string from main()? Is it located in the stack?

 // note that there is a difference between the lines:
 char s[] = "foo:asdasdasd"; // is allocated on the stack
 char *s = "bar:dsadsadas";  // is not allocated on the stack

1. Comment some of the lines which print the addresses of variables in main() (from task 1), check that your program does not use them -- can you still print them by using an address from foo()?
2. Put the variables back to the stack. Write a function which tries to print out all the stack (4 bytes per line using printf() with "%08x\n". The program should crash at some point with a segmentation fault; this is the expected and desired result of the task and should be valued!

Note: For your convenience print the memory location address, then its contents as decimal, hexadecimal, and char.