How can I print the contents of stack in C program?

Question

I want to, as the title says, print the contents of the stack in my C program.

Here are the steps I took:

• I made a simple assembly (helper.s) file that included a function to return the address of my ebp register and a function to return the address of my esp register

  .globl get_esp
  
  get_esp:
      movl %esp, %eax
      ret
  # get_ebp is defined similarly, and included in the .globl section
  

• I called the get_esp () and get_ebp () functions from my C program ( fpC = get_esp (); where fpC is an int)
• I (successfully, I think) printed the address of my esp and ebp registers ( fprintf (stderr, "%x", fcP); )
• I tried, and failed to, print out the contents of my esp register. (I tried fprintf (sderr, "%d", *fcP); and fprintf (sderr, "%x", *((int *)fcP));, among other methods). My program hits a segmentation fault at runtime when this line is processed.

What am I doing wrong?

EDIT: This must be accomplished by calling these assembly functions to get the stack pointers. EDIT2: This is a homework assignment.

Answer 1

If your utilising a GNU system, you may be able to use GNU's extension to the C library for dealing backtraces, see here.

#include <execinfo.h>

int main(void)
{
     //call-a-lot-of-functions
}

void someReallyDeepFunction(void)
{
    int count;
    void *stack[50]; // can hold 50, adjust appropriately
    char **symbols;

    count = backtrace(stack, 50);
    symbols = backtrace_symbols(stack, count);

    for (int i = 0; i < count; i++)
        puts(symbols[i]);

    free(symbols);
}

Answer 2

get_esp returns esp as it is within the function. But this isn't the same as esp in the calling function, because the call operation changes esp.

I recommend replacing the function with a piece of inline assembly. This way esp won't change as you try to read it.

Also, printing to sderr wouldn't help. From my experience, stderr works much better.