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.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 Here is a similar program for a 32-bit x86 system using the [http://www.nasm.us/xdoc/2.11/html/nasmdoc1.html#section-1.1 Nasm] syntax: section .text
arm64 section format fix
[[Category:Computer Architecture]][[Category:Assembly Language]]''Assembly language'' is a [[Symbol|symbolic]] representation of [[Machine Language|machine language]]. It is therefore very [[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 written for a an x86_64 Linux systemusing the [https://sourceware.org/binutils/docs/as/ GNU Assembler (gas/as)] syntax (which is the main assembler used in open source projects such as the Linux kernel, as well as the [[SPO600]] course), using Linux [[Syscalls]]:
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
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 using Linux [[Syscalls]]:
.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
=== ARM (64-bit) - AArch64 ===
This is also in [https://sourceware.org/binutils/docs/as/ GNU Assembler (gas/as)] syntax using Linux [[Syscalls]]:
.text
.globl _start
_start:
mov x0, 1 /* file descriptor: 1 is stdout */
adr x1, msg /* message location (memory address) */
mov x2, len /* message length (bytes) */
mov x8, 64 /* write is syscall #64 */
svc 0 /* invoke syscall */
mov x0, 0 /* status -> 0 */
mov x8, 93 /* exit is syscall #93 */
svc 0 /* invoke syscall */
.data
msg: .ascii "Hello, world!\n"
len= . - msg
=== 6502 ===
Here is the same "Hello World" program in [[6502]] assembler as used in the [[6502 Emulator]], using the [[6502_Emulator#ROM_Routines|ROM routines]] for output:
define SCINIT $ff81 ; initialize/clear screen
define CHROUT $ffd2 ; output character to screen
JSR SCINIT ; clear screen
LDY #$00 ; set Y index to zero
loop: LDA msg,Y ; get a character
BEQ done ; quit if character is null
JSR CHROUT ; output the character
INY ; increment index
JMP loop ; get next character
done: BRK ; break (stop program)
msg:
DCB "H","e","l","l","o",$2C,$20
DCB "W","o","r","l","d","!",$0d, $00
== 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]]