如何在 NASM 程序集中使用 BIOS int 13h 从磁盘加载内核？
我已经被这个问题困扰了好几个星期了，不知道哪里出了问题，因为 NASM 没有给我任何错误。由于注释，该代码非常不言自明。
这是从 BIOS 加载的代码
;--------------------------------------------
; 'boot.asm'
; loaded from BIOS
[org 0x7C00]
[bits 16]
;--------------------------------------------
main:
mov ah, 0x0E ; print function
mov al, '.' ; ascii char
int 0x10 ; IO int
resetdisk:
mov ah, 0x00 ; reset function
mov dl, 0x00 ; drive
int 0x13 ; disk int
jc resetdisk
readdisk:
mov bx, 0x8000 ; segment
mov es, bx
mov bx, 0x0000 ; offset
mov ah, 0x02 ; read function
mov al, 0x03 ; sectors
mov ch, 0x00 ; cylinder
mov cl, 0x02 ; sector
mov dh, 0x00 ; head
mov dl, 0x00 ; drive
int 0x13 ; disk int
jc readdisk
jmp [es:bx] ; buffer
;--------------------------------------------
times 510 - ($ - $$) db 0x00
db 0x55, 0xAA
这是应该（但没有）加载的代码
;--------------------------------------------
; 'load.asm'
; loaded from 'boot.asm'
[org 0x8000]
[bits 16]
;--------------------------------------------
main:
mov ah, 0x0E ; print function
mov al, '.' ; ascii char
int 0x10 ; IO int
jmp $ ; hang
任何帮助将不胜感激。
帕特里克
I've been stuck with this for weeks now and have no idea where I'm going wrong because NASM hasn't given me any errors. The code is pretty self explanatory because of the comments.
this is the code that is loaded from the BIOS
;--------------------------------------------
; 'boot.asm'
; loaded from BIOS
[org 0x7C00]
[bits 16]
;--------------------------------------------
main:
mov ah, 0x0E ; print function
mov al, '.' ; ascii char
int 0x10 ; IO int
resetdisk:
mov ah, 0x00 ; reset function
mov dl, 0x00 ; drive
int 0x13 ; disk int
jc resetdisk
readdisk:
mov bx, 0x8000 ; segment
mov es, bx
mov bx, 0x0000 ; offset
mov ah, 0x02 ; read function
mov al, 0x03 ; sectors
mov ch, 0x00 ; cylinder
mov cl, 0x02 ; sector
mov dh, 0x00 ; head
mov dl, 0x00 ; drive
int 0x13 ; disk int
jc readdisk
jmp [es:bx] ; buffer
;--------------------------------------------
times 510 - ($ - $) db 0x00
db 0x55, 0xAA
This is the code that should be (but isn't) loaded
;--------------------------------------------
; 'load.asm'
; loaded from 'boot.asm'
[org 0x8000]
[bits 16]
;--------------------------------------------
main:
mov ah, 0x0E ; print function
mov al, '.' ; ascii char
int 0x10 ; IO int
jmp $ ; hang
Any help would be much appreciated.
Patrick
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jmp [es:bx]不会跳转到地址es:bx。此命令执行近跳转到存储在es:bx的字中的地址。这就是为什么许多旧的汇编器让你将这种指令拼写为jmp word ptr [es:bx]甚至jmp close ptr [es:bx]；这样会发生什么就更清楚了。您可能想要的是远跳转到固定位置：如果您确实想跳转到
es:bx，请使用retf：jmp [es:bx]doesn't jump to the addresses:bx. This command does a near jump to the address stored in the word ates:bx. This is why lots of older assemblers made you spell this kind of instruction asjmp word ptr [es:bx]or evenjmp near ptr [es:bx]; it's clearer this way what is going to happen. What you probably want here is a far jump to a fixed location:If you do want to jump to
es:bx, useretf:我不确定你想用代码实现什么，但如果我理解正确的话，你想从磁盘读取几个扇区到位置 0x8000 然后执行该代码？
如果是这种情况，那么您将必须明确地调用/跳转到该特定位置。 BIOS 不会为您调用该代码。启动时，一旦 BIOS 初始化，它将把指令指针 IP 设置为地址 0x7c00。然后CPU将开始按顺序执行代码，因此如果没有对0x8000的JMP/CALL，它将不会执行0x8000处的代码，直到它执行了0x7c00到0x8000之间的每个内存地址等。
所以解决方案是有一个jmp或调用jc readdisk 之后的指令。
如果我的理解不正确，那么我深表歉意。希望这有帮助。
I am not sure what you are trying to achieve with the code, but if I understand it correctly, You want to read a few sectors from the disk into the location 0x8000 and then execute that code?
If that is the case, then you will have to explictly make a CALL/JUMP to that particular location. The BIOS will not call that code for you. On boot, once the BIOS is initialized, it will set the Instruction Pointer IP to the address 0x7c00. The cpu will then start to execute the code sequentially, so without a JMP/CALL to 0x8000 it wont execute the code at 0x8000 until it has executed every memory address inbetween 0x7c00 to 0x8000 etc.
So the solution would be to have a jmp or call instruction after your jc readdisk.
If my understanding is incorrect then I apologize. Hope this helps.
INT13 的一个问题是磁头和磁道编号从 0 开始，但扇区编号由于某种原因从 1 开始。您可以检查扇区写入实用程序是否符合此编号方案。
问题：
One gotcha with INT13 is that head and track numbers start at 0, but sector numbers for some reason start at 1. You might check that your sector-writing utility conforms to this numbering scheme.
Questions:
我不知道你是否使用软盘来启动你的操作系统，但是如果你使用的话，我建议你在 ORG 和 Bits 声明之后声明一些东西，看一下（它们非常重要）：
这是一个很好的方法想法把这个。
问候。
I don't know if you're using a floppy to boot your OS, but if you are using, i suggest you to declare some things after the ORG and Bits declaration, take a look(they are very important):
It's a good idea to put this.
Regards.
我不确定为什么代码不起作用，因为我无法检查整个环境（磁盘、内存转储等）......但我可以说的是......代码是错误的。您正在加载第二个程序，不是在
0x8000处（这就是使用0rg 0x8000对吧？），而是在0x80000处。原因是，您以错误的方式使用段：偏移寻址，
地址
0x8000:0x0000被解析为线性地址0x80000，因为段值左移 4 位，然后添加到偏移量中。
要解决此问题，您应该查看内存转储并查看是否
该程序也按照您的预期工作......要么那样，要么您正在加载
磁盘的错误扇区。
I'm not sure why the code doesn't work, since I can't check the the whole environment (disk, memory dump, etc)...but what I can say is...the code is wrong. You are loading the second program, not at
0x8000(that was the point of using0rg 0x8000right?), but at0x80000.The reason being, you are using the segment:offset addressing in the wrong way,
the address
0x8000:0x0000is resolved to the linear address0x80000, sincethe segment value is shifted left by 4 bits an then added to the offset.
To resolve this problem, you should take a look at a memory dump and see if
the program works as you expect it too....either that or you're loading the
wrong sectors of the disk.