Data Management

DATA MANAGEMENT

Data Section Declaration

Declare variables and allocate memory in the data section. The data section is used to define variables and constants, specifying their data type and initial values.

section .data
    variable_name data_type initial_value
    num dd 10

Variable Name - Provide a name for the data variable;
Data Type - Specify the size of the data, determining the number of bytes allocated;
Initial Value - Assign an initial value to the variable;

Data Types and Sizes

In assembly language, data is represented in binary form. There’s no inherent distinction between data types like integers, characters, or strings. Instead, data is distinguished by its memory allocation size.

The data types commonly used in assembly language include:

Data Type	Description	Size (Bytes)	Size (Bits)
`DB`	Byte	1	8
`DW`	Word	2	16
`DD`	Double Word	4	32
`DQ`	Quad Word	8	64
`DT`	Ten Bytes	10	80

Accessing Data Addresses

When referencing data variables, it’s essential to understand that the variable name represents the address of the data rather than the actual value. Attempting to load the value of a variable num directly into a register like ebx will load its address, not its value.

.section data
    num DD 5

section .text
    global _start

_start:
    MOV eax,1
    MOV ebx,[num] ; if i used num directly, it would be the address and not the value
    INT 80h

When using num, the destination register would contain something akin to $0x08048000, representing the memory address where the variable num is stored;
On the other hand, when using [num], the destination register would hold 0x08048000 (without the $ sign), denoting the value stored in the variable num, which in this case is 5;

In GDB, I can inspect registers with info registers [register_name] and analyze memory content with commands like x/x [address].