Search⌘ K
Home/
Courses/
Debugging, Disassembly & Reversing in Linux for x64 Architecture

Assigning Numbers to Memory Cells Using Pointers

Learn how to assign numbers to memory locations using pointers.

We'll cover the following...

Pointers to assign numbers

The following sequence of pseudocode is a set of instructions to interpret the contents of the %RAX register as the address of a memory cell and then assign a value to that memory cell:

address a -> rax
1 -> (rax)

Assigning numbers in C and C++

In C and C++, assigning a number is called dereferencing a pointer, and we write:

C++
int a;
int *pa = &a;      // declaration and definition of a pointer
*pa = 1;           // get a memory cell (dereference a pointer) and assign a value to it

Assigning numbers in assembly language

In assembly language, we write:

Assembly (GAS x86)
lea  a,  %rax       # load the address “a” into %rax
movl $1, (%rax)     # use %rax as a pointer

The lea (load effective address) instruction is a method of obtaining an address from one of the Intel processors’ memory addressing modes. It moves the contents of the specified memory address to the destination register. Again, we see movl instead of mov because integers occupy 3232-bit memory cells, and we want to address only a 3232-bit memory cell. When it comes to x64 Linux, memory cells that contain integers are half the size ( ...