articles/assembly.md: update article

articles/assembly.md

@@ -4,7 +4,11 @@ Assembly, also known as assembler, is family of low-level [programming languages
 Assembly is also OS-specific, since it depends on [syscalls](syscall.md) to do anything useful and things like the program
 entrypoint differ between operating systems.
 
-## Examples (x86-64 assembly, Linux)
+An assembler program is then converted into machine code by an *assembler*. Some assemblers are gas, the assembler of the [GNU](gnu.md)
+project which supports multiple architecures and [NASM](https://www.nasm.us/), a popular x86-only assembler.
+
+## Examples
+### Hello world (x86-64, Linux)
 ```nasm
 default rel                 ; tell the assembler to use RIP-relative addressing
                             ; instead of absolute memory addresses
@@ -33,4 +37,36 @@ nasm -felf64 -o hello.o hello.asm             # assemble, generates an object fi
 cc -static-pie -nostdlib -o hello hello.o     # now link to get an executable
 ```
 
+### Hello world (ARM64, Linux)
+```asm
+.global _start
+.section .text
+
+_start:
+	mov x0, #1			// stdout file descriptor
+	adr x1, msg 		// address of buffer, pc relative
+	mov x2, msg_len 	// length of buffer
+	mov w8, #0x40		// service number
+	svc #0				// do syscall
+
+	mov x0, #39			// return number
+	mov w8, #0x5d		// exit syscall
+	svc #0
+
+.section .rodata
+msg: .ascii "Hello, world!\n"
+.equ msg_len, . - msg
+```
+
+For this we use the gas (GNU assembler):
+```sh
+as -o hello.o hello.asm
+cc -nostdlib -o hello hello.o
+```
+
+### Factorial (x86-64, Linux)
+```nasm
+```
+TODO
+
 TODO examples for other architectures