NASM with Bochs - 组装 - 打印字符串

Question

我想打印一个字符串，并且正在使用 NASM Assembly、Bochs 来运行程序，并且有两个简单的文件。我正在制作一个非常简单的引导扇区来开始学习汇编。我正在尝试自学，并且正在使用此 PDF： https://www.cs.bham.ac.uk/~exr/lectures/opsys/10_11/lectures/os-dev.pdf 我正在尝试创建自己的字符串打印函数。

问题：

; Question 4
; Put together all of the ideas in this section to make a self-contained function for printing
; null-terminated strings, that can be used as follows:
;
; A boot sector that prints a string using our function.
;
[org 0x7c00] ; Tell the assembler where this code will be loaded
mov bx, HELLO_MSG ; Use BX as a parameter to our function , so
call print_string ; we can specify the address of a string.
mov bx, GOODBYE_MSG
call print_string
jmp $ ; Hang
%include "print_string.asm"
; Data
HELLO_MSG:
db ’Hello , World!’, 0 ; <-- The zero on the end tells our routine
; when to stop printing characters.
GOODBYE_MSG:
db ’Goodbye!’, 0
; Padding and magic number.
times 510-($-$$) db 0
dw 0xaa55
; For good marks, make sure the function is careful when modifying registers and that
; you fully comment the code to demonstrate your understanding.

我的代码：

bootsect.asm

    org 0x7c00 ; Start at boot sector. Allows us to add offset for labels efficiently


    mov bx, loading_sys_msg
    calltest:
    call str_out
    ;jmp calltest

    jmp $ ; Jump forever. Because end of program lol

; Includes
    %include "str_out.asm"

; Database Resources

    loading_sys_msg:
    db 'Loading OIK v0.0.1', 0

; Padding and magic BIOS number.

times 510-($-$$) db 0
dw 0xaa55
`

str_out.asm

;
; String-printing function
;
str_out:
pusha
pop bx
;add bx, 0x7c00 ; Adds current address if boot sect and no org called (not used)
mov ah, 0x0e    ; BIOS teletyping for 0x10 interrupt
mov ax, 0x00    ;prep counter
mov al, [bx]    ; character to print placed in al (bx address contents)
prnt:                   ; printing loop
int 0x10            ; interrupt print
add ax, 0x01    ; add to counter for removal afterwards
add bx, 0x01    ; move bx address forward by 1
mov al, [bx]    ; character to print placed in al (bx address contents)
cmp al, 0           ; Compare [al -?- 0]
jg prnt             ; If greater, jump to print
sub bx, ax      ;remove the counter amount
;sub bx, 0x7c00 ;remove address addition if used earlier (not used)
push bx
popa

Bochs 配置：

# Tell bochs to use our boot sector code as though it were
# a floppy disk inserted into a computer at boot time.
floppya: 1_44=boot_sect.bin, status=inserted
boot: a

当 Bochs 启动时，屏幕清空，没有任何反应。我做错了什么？

（感谢 Jester 告诉我我没有说明问题。我还是 Stack Overflow 的新手。）

Answer 1

str_out少了一条RET指令，但是少了显示是因为你垃圾啊

mov ah, 0x0e    ; BIOS teletyping for 0x10 interrupt
mov ax, 0x00    ;prep counter

通常我不会给出练习的例子，但在这种情况下，你已经做出了合理的努力，并且可以理解你的逻辑。

            org     0x7c00

            mov     bx, Msg
            call    str_out
            hlt
            jmp     $ - 1

str_out:    mov     ah, 0x0e
prnt:       mov     al, [bx]
            int     0x10
            add     bx, 0x01
            cmp     al, 0
            jg      prnt
            ret

  Msg:      db      'Loading OIK v0.0.1', 0

    times 510-($-$$) db 0
        dw  0xaa55

不完全确定在修改寄存器时确保函数小心是什么意思，但这个例子确实有效。由于这本质上是您的代码的副本，您需要做的就是记录它，但您可能会被问到两个特质。你为什么使用这些指令，为什么它们是按这个顺序排列的。