我想打印一个字符串,我正在使用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Assembly。我正在尝试自学,并使用此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功能。
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靴子时,屏幕清除,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。我仍然是Stack Overflow的新手。)
答案 0 :(得分:0)
str_out
缺少RET指令,但缺少显示是因为你丢弃了AH
mov ah, 0x0e ; BIOS teletyping for 0x10 interrupt
mov ax, 0x00 ;prep counter
通常我不会举例说明练习,但在这种情况下,你已经做出了合理的努力,而且可以让你的逻辑变得更好。
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
不完全确定的含义是确保修改寄存器时功能小心,但此示例确实有效。因为这基本上是代码的副本,所以您需要做的就是记录它,但是有两个特性可能会被问到。你为什么使用这些指令,为什么它们按照这个顺序排列。