Skip to content

Quick Reference: x86 64 Assembly & GDB

Jump to bottom
Tony Oreglia edited this page Jan 4, 2019 · 5 revisions

Registers

General-purpose registers - there are 16 general-purpose registers - rax, rbx, rcx, rdx, rbp, rsp, rsi, rdi, r8, r9, r10, r11, r12, r13, r14, r15

  • data- section is used for declaring initialized data or constants

  • bss- section is used for declaring non initialized variables

  • text- section is used for code

  • rdi- first argument

  • rsi- second argument

  • rdx- third argument

  • rcx- fourth argument

  • r8- fifth argument

  • r9- sixth

The first six integer or pointer arguments are passed in registers RDI, RSI, RDX, RCX, R8, R9 (R10 is used as a static chain pointer in case of nested functions.

RAX is used as the return value from a funtion.

Preserved registers RBX, RBP, and R12–R15

All other registers must be saved by the caller if it wishes to preserve their values

Operations

  • ADD- integer add
  • SUB- substract
  • MUL- unsigned multiply
  • IMUL- signed multiply
  • DIV- unsigned divide
  • IDIV- signed divide
  • INC- increment
  • DEC- decrement
  • NEG- negate

The initial number must be stored in rax. rax can be multiplied by a value in any of the other registers. The result will be stored in rdx:rax.

Control Flow

JE - if equal JZ - if zero JNE - if not equal JNZ - if not zero JG - if first operand is greater than second JGE - if first operand is greater or equal to second JA - the same that JG, but performs unsigned comparison JAE - the same that JGE, but performs unsigned comparison

Data Types

The fundamental data types are bytes, words, doublewords, quadwords, and double quadwords.

  • byte is eight bits
  • word is 2 bytes
  • doubleword is 4 bytes
  • quadword is 8 bytes
  • double quadword is 16 bytes (128 bits).

.data section

syntax

[variable-name] define-directive initial-value

There are five basic forms of the define directive −

Directive Purpose Storage Space
DB Define Byte allocates 1 byte
DW Define Word allocates 2 bytes
DD Define Doubleword allocates 4 bytes
DQ Define Quadword allocates 8 bytes
DT Define Ten Bytes allocates 10 bytes

e.g choice DB 'y' number DW 12345

GDB

display (char *) $ecx undisplay 2

Clone this wiki locally