1,885
edits
Changes
→Resources
[[Category:Computer Architecture]][[Category:Assembly Language]]''Assembly language'' is a [[Symbol|symbolic]] representation of [[Machine Language|machine language]]. It is therefore [[Portable|architecture-specific]].
Each instruction is represented by a short mnemonic word such as "LDR" for ''Load Register'', "MOV" for ''move'', or "MUL" for ''multiply'', followed by (optional) arguments. The [[Addressing Mode|addressing mode]] is implied by the format of the arguments. Different [[Assembler|assemblers]] use slightly different syntax.
== Examples ==
=== x86 ===
Here is a "Hello, World!" program in x86 assembler for a Linux system, using the [http://www.nasm.us/xdoc/2.11/html/nasmdoc1.html#section-1.1 Nasm] syntax:
global _start
_start:
mov edx,len ; message length(bytes) mov ecx,msg ; message location(memory address) mov ebx,1 ; file descriptor : 1 is stdout mov eax,4 ; kernel syscall number: 4 is sys_write int 0x80 ; invoke syscall
mov ebx,0 ; exit status: 0 (good) mov eax,1 ; kernel syscall number: 1 is sys_exit int 0x80 ; invoke syscall
section .rodata
msg db 'Hello, world!\n',0xa
len equ $ - msg
Here is the same program with [https://sourceware.org/binutils/docs/as/ GNU Assembler (gas/as)] syntax:
.text
.globl _start
_start:
mov $len, %edx /* file descriptor: 1 is stdout */
mov $msg, %ecx /* message location (memory address) */
mov $1, %ebx /* message length (bytes) */
mov $4, %eax /* write is syscall #4 */
int $0x80 /* invoke syscall */
mov $0, %ebx /* exit status: 0 (good) */
mov $1, %eax /* kernel syscall number: 1 is sys_exit */
int $0x80 /* invoke syscall */
.data
msg:
.ascii "Hello, World!\n"
len = . - msg
Notice that the order of the arguments in some lines is reversed between the two assemblers, and the prefixes to symbols and values also change.
=== ARM (32-bit) ===
This is written in [https://sourceware.org/binutils/docs/as/ GNU Assembler (gas/as)] syntax:
.text
.globl _start
_start:
mov %r0, $1 /* file descriptor: 1 is stdout */
ldr %r1, =msg /* message location (memory address) */
ldr %r2, =len /* message length (bytes) */
mov %r7, $4 /* write is syscall #4 */
swi $0 /* invoke syscall */
mov %r0, $0 /* exit status: 0 (good) */
mov %r7, $1 /* kernel syscall number: 1 is sys_exit */
swi $0 /* invoke syscall */
.data
msg:
.ascii "Hello, world!\n"
len = . - msg
== Resources ==
* [[Assembler Basics]]
* [http://leto.net/code/asm/hw_assembler.php "Hello World" in many different types of assembler]
* [[x86_64 Register and Instruction Quick Start]]
* [[aarch64 Register and Instruction Quick Start]]
