Assembly Tutorial – The Data Section

So far we have only used the data section of our programs to define data and to read that data at runtime. However, we can also write to the data section! Try running the following code through the debugger:

.section .data
var:
.byte 5

.section .text

.globl _start
_start:

movq $10, var

movq $60, %rax
movq $0, %rdi
syscall

Using the techniques we learned in a previous post, you will see that the line

movq $10, var

changes the value of the byte of memory named var from 5 to 10.

If you want to define read only data in your binary, you can do so with the .rodata section. This works just like the data section. However, if you try to write to the memory here, you will get a seg-fault.