Bfh-sts: Created page with "= Labels and Entry Point (_start) = This page explains how labels work in assembly programming and how the program’s entry point is defined. == What are labels == A label is a symbolic name for a memory address. It marks a location in code or data that can be referenced later. Syntax: LabelName: Example: SECTION .data EatMsg: db "Eat at Joe’s" SECTION .text mov rcx, EatMsg ; rcx ← address of the string mov rdx, [EatMsg] ; rdx ← first 8 bytes of the..."

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Created page with "= Labels and Entry Point (_start) = This page explains how labels work in assembly programming and how the program’s entry point is defined. == What are labels == A label is a symbolic name for a memory address. It marks a location in code or data that can be referenced later. Syntax: LabelName: Example: SECTION .data EatMsg: db "Eat at Joe’s" SECTION .text mov rcx, EatMsg ; rcx ← address of the string mov rdx, [EatMsg] ; rdx ← first 8 bytes of the..."

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= Labels and Entry Point (_start) =
This page explains how labels work in assembly programming and how the program’s entry point is defined.

== What are labels ==
A label is a symbolic name for a memory address.
It marks a location in code or data that can be referenced later.

Syntax:
LabelName:

Example:
SECTION .data
EatMsg: db "Eat at Joe’s"

SECTION .text
mov rcx, EatMsg ; rcx ← address of the string
mov rdx, [EatMsg] ; rdx ← first 8 bytes of the string

Here:
* EatMsg refers to the address of the string.
* [EatMsg] refers to the contents at that address.

== Why labels are needed ==
Labels replace hardcoded addresses and make programs relocatable:
* You don’t know where in memory your program will be loaded.
* The linker can adjust label references automatically.
* The code becomes modular and position-independent.

== Code labels ==
Labels can also be attached to code lines.
They mark destinations for jumps and branches, forming the basis for control flow.

Example:
mov eax, 5
loop_start:
dec eax
jnz loop_start ; jump back if eax ≠ 0

Here, loop_start marks the instruction to jump to.
Such code labels are essential for loops, branches, and function calls.

== The _start label ==
_start: defines the entry point of an assembly program on Linux.
It is the first instruction executed when the program runs.

Example:
global _start
_start:
mov rax, 60 ; system call for exit
xor rdi, rdi ; return code 0
syscall

* The keyword global makes _start visible to the linker.
* The operating system looks for this symbol to know where to begin execution.

Every NASM program for Linux must define exactly one entry point, usually called _start.

== Summary ==
* Labels are symbolic names for addresses.
* Data labels point to memory locations.
* Code labels mark positions for jumps.
* The _start label defines where execution begins.

[[Category:Assembly Programming]]

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