Assembly x64 Intro - Register Usage

; testreg_64.asm   test what register names can be used
;
; compile: nasm -f elf64 -l testreg_64.lst  testasm_64.asm
; link: gcc -o testreg_64  testreg_64.o
; run: ./testreg  # may get segfault or other error
;
section .data  ; preset constants, writable
aa8: db 8 ; 8-bit
aa16: dw 16 ; 16-bit
aa32: dd 32 ; 32-bit
aa64: dq 64 ; 64-bit

section .bss
bb16: resw 16

section .rodata
cc16: db 8

section .text ; instructions, code segment
global main ; for gcc standard linking
main: ; label
push rbp ; set up stack

mov rax,[aa64] ; five registers in RAX
mov eax,[aa32] ; four registers in EAX
mov ax,[aa16]
mov ah,[aa8]
mov al,[aa8]

mov RAX,[aa64] ; upper case register names
mov EAX,[aa32]
mov AX,[aa16]
mov AH,[aa8]
mov AL,[aa8]

mov rbx,[aa64] ; five registers in RBX
mov ebx,[aa32] ; four registers in EBX
mov bx,[aa16]
mov bh,[aa8]
mov bl,[aa8]

mov rcx,[aa64] ; five registers in RCX
mov ecx,[aa32] ; four registers in ECX
mov cx,[aa16]
mov ch,[aa8]
mov cl,[aa8]

mov rdx,[aa64] ; five registers in RDX
mov edx,[aa32] ; four registers in EDX
mov dx,[aa16]
mov dh,[aa8]
mov dl,[aa8]

mov rsi,[aa64] ; three registers in RSI
mov esi,[aa32] ; two registers in ESI
mov si,[aa16]

mov rdi,[aa64] ; three registers in RDI
mov edi,[aa32] ; two registers in EDI
mov di,[aa16]

mov rbp,[aa64] ; three registers in RBP
mov ebp,[aa32] ; two registers in EBP
mov bp,[aa16]

mov r8,[aa64] ; just 64-bit r8 .. r15

movq xmm0, qword [aa64] ; xmm registers special

fld qword [aa64] ; floating point special

; POPF ; no "mov" on EFLAGS register
; PUSHF ; 32 bits on 386 and above

; mov rsp,[aa64] ; three registers in RSP
; mov esp,[aa32] ; two registers in ESP
; mov sp,[aa16] ; don't mess with stack

pop rbp
mov     rax,0           ; exit code, 0=normal
ret ; main returns to operating system

; end testreg_64.asm