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[[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.
=== x86 ===
Here is a "Hello, World!" program written for an x86_64 Linux system using 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):
.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 "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:
len equ $ - msg
=== ARM (32-bit) ===
.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:
.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]]:
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 ==