x86 Assembly Cheat Sheet

Key x86/x86-64 registers, NASM instruction syntax, control flow, and the stack/calling convention for low-level programming.

2 PagesAdvancedApr 2, 2026

General-Purpose Registers

The core x86-64 registers and their conventional uses.

EAX / RAX- 32-bit/64-bit accumulator, commonly holds return values
EBX / RBX- General-purpose base register
ECX / RCX- Counter register, used implicitly by loop instructions
EDX / RDX- Data register, paired with EAX for mul/div
ESP / RSP- Stack pointer, points to the top of the stack
EBP / RBP- Base pointer, frame reference for local variables
EIP / RIP- Instruction pointer, address of the next instruction

Basic Instructions

Data movement and arithmetic (NASM syntax).

asm

section .data    msg db "Hello, World!", 0xA   ; string with newlinesection .text    global _start_start:    mov eax, 5          ; move immediate value into eax    add eax, 3          ; eax = eax + 3    sub eax, 1          ; eax = eax - 1    mov ebx, eax        ; copy eax into ebx    inc ebx             ; ebx += 1    dec eax             ; eax -= 1    cmp eax, ebx        ; compare eax and ebx (sets flags)

Control Flow

Jumps and conditional branching.

asm

    mov ecx, 5loop_start:    cmp ecx, 0    je  loop_end        ; jump if equal (zero flag set)    dec ecx    jmp loop_startloop_end:    cmp eax, ebx    jg  greater         ; jump if eax > ebx    jl  less            ; jump if eax < ebx    jmp done

Stack & Calling Convention

Passing arguments and calling functions.

push eax- Decrements ESP/RSP, stores eax on the stack
pop eax- Loads the top of stack into eax, increments ESP/RSP
call func- Pushes the return address, jumps to func
ret- Pops the return address, jumps back to the caller
cdecl- Caller cleans the stack; arguments pushed right-to-left
System V AMD64 ABI- First 6 integer args passed in RDI, RSI, RDX, RCX, R8, R9

Linux Exit Syscall

Exiting a program on Linux x86-64.

asm

    mov rax, 60      ; syscall number for exit    xor rdi, rdi     ; exit code 0    syscall

Pro Tip

Remember that cmp and test only set CPU flags — always follow them with the matching conditional jump (je, jne, jg, jl…) to actually branch.

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