Question

源码通常分成多个段（section）。标签（label）用于标示内存地址，区分大小写。注释（comment）以分号开始，持续到行尾。

除直接映射机器代码的命令外，还有语言定义的伪指令。伪指令（Pseudo Instruction）面向编译器，告知如何工作。

; hello.s

global _start

section .data
  hello : db `hello, world!\n`

section .text
  _start:
    mov   rax, 1    ; system call number should be stored in rax
    mov   rdi, 1    ; argument #1 in rdi: where to write (descriptor)?
    mov   rsi, hello  ; argument #2 in rsi: where does the string start?
    mov   rdx, 14   ; argument #3 in rdx: how many bytes to write?
    syscall       ; this instruction invokes a system call

    mov   rax, 60   ; 'exit' syscall number
    xor   rdi, rdi  ;
    syscall

$ nasm -g -F dwarf -f elf64 -o hello.o hello.s
$ ld -o test hello.o

# makefile

.PHONY: build clean

build:
  @nasm -g -F dwarf -f elf64 -o hello.o hello.s
  @ld -o hello hello.o

clean:
  -@rm -rf test hello a.out
  -@rm -rf *.o *.i *.a *.so

Linux Syscall Table for X64