Difference between revisions of "Assembly Language"
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[[Category:Computer Architecture]][[Category:Assembly Language]] | [[Category:Computer Architecture]][[Category:Assembly Language]] | ||
| − | ''Assembly language'' is a [[Symbol|symbolic]] representation of [[Machine Language|machine language]]. It is therefore [[Portable|architecture-specific]]. | + | ''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. | 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. | ||
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=== x86 === | === 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: | 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: | ||
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len equ $ - msg | len equ $ - msg | ||
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| − | + | 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. | |
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=== ARM (32-bit) === | === ARM (32-bit) === | ||
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.ascii "Hello, world!\n" | .ascii "Hello, world!\n" | ||
len = . - msg | 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 == | == Resources == | ||
Revision as of 12:00, 12 September 2022
Assembly language is a symbolic representation of machine language. It is therefore very 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 is implied by the format of the arguments. Different assemblers use slightly different syntax.
Examples
x86
Here is a "Hello, World!" program written for an x86_64 Linux system using the 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 Nasm syntax:
section .text
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'
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 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
ARM (64-bit) - AArch64
This is also in 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
