The Stack

With a colleague, sketch out how the following items would be arranged on the stack.

Assume the following:

• We are dealing with a 32-bit, little endian processor.
• int's are four bytes each

Code:

int w = 1;
int x = 2;
int y = 3;
int z = 4;
int int_array[4] = {5,6,7,8};

You can check your answer by looking at the following output from gcc on the above code.

        mov     DWORD PTR [rbp-4], 1
        mov     DWORD PTR [rbp-8], 2
        mov     DWORD PTR [rbp-12], 3
        mov     DWORD PTR [rbp-16], 4
        mov     DWORD PTR [rbp-32], 5
        mov     DWORD PTR [rbp-28], 6
        mov     DWORD PTR [rbp-24], 7
        mov     DWORD PTR [rbp-20], 8

Finally, if I executed the command, int_array[4] = 9;, which values change?

Answer:

Take a look at this output:

int_array[0] located at 0xffccb9b0
int_array[1] located at 0xffccb9b4
int_array[2] located at 0xffccb9b8
int_array[3] located at 0xffccb9bc
int_array[4] located at 0xffccb9c0
z located at 0xffccb9c0

Which is generated by running:

printf("int_array[0] located at %p\n", &int_array[0]);
printf("int_array[1] located at %p\n", &int_array[1]);
printf("int_array[2] located at %p\n", &int_array[2]);
printf("int_array[3] located at %p\n", &int_array[3]);
printf("int_array[4] located at %p\n", &int_array[4]);
printf("z located at %p\n", &z);