我无法从 x86 汇编中的 CD-ROM 读取扇区

Question

我正试图从我的ISOSYS引导加载程序加载OS32操作系统的第二阶段引导加载程序，但我似乎做不到。CF似乎总是被设置。这是从CD/DVD启动的，我使用Debian GNU/Linux 7.6 (Wheezy)

isosys.asm:

;===============================================================
;
;               ISOSYS v1.0 in isosys.asm
;
; Program for booting OS32 and OS32-based systems from CD/DVDs
; using the ElTorito boot standard.
;
; By Omar, 2014
;
; ===============================================================
; set up bios...
bits 16
org 0x7c00
; beginning of sector 1, byte 0:
; jump over functions block
jmp Start
;
; Print()
;      prints a string to standard output
; AL = 0 : terminate
;
Print:
   lodsb            ; grab a byte from SI and place it in AL
   cmp al, 0         ; is AL = 0?
   jc PrintDone         ; yep, we're done so return
   mov ah, 0eh
   int 0x10         ; nope, print the character
   jmp Print         ; loop until no more characters to be printed
PrintDone:
   ret            ; return to wherever we were!
;
; Start()
;      bootloader entry point
;
Start:
   mov si, creditmsg
   call Print         ; print the first message
   mov dh, 1         ; read 1 sector
.ReadSector:
   cli            ; disable interrupts
   push dx            ; push this stack value
   sti            ; re-enable interrupts
   mov ax, 0x1000         ; read sector into address 0x1000
   xor bx, bx         ; read sector into offset 0x0
   mov ah, 0x02         ; read sector function
   mov al, dh         ; read 1 sector
   mov ch, 0x0         ; must be 0x0 to read sector
   mov dh, 0         ; reading head 0
   mov cl, 0x02         ; start reading from sector 2 to load the second stage
   mov [CDDriveNumber], dl      ; store our drive number is variable CDDriveNumber
   cli            ; disable interrupts
   pusha            ; save the stack
   sti            ; enable interrupts
   int 0x13         ; INT 13h
   jc Error         ; handle error because Carry Flag is set
   pop dx            ; Restore DX
.ExecuteSector:
   ; now that our sector was loaded into address 0x1000:0x0, let's execute it!
   jmp 0x1000:0x0         ; jump to execute the sector
;
; Error()
;      handles errors when carry is set
;
Error:
   mov si, errmsg
   call Print         ; print an error message
   cli            ; disable interrupts to prevent problems
   hlt            ; halt the system... :(
; data section
creditmsg db "ISOSYS v1.0 by Omar Mohammad, Init...", 0
errmsg db "Cannot load the second stage. (File not found maybe?)", 0
CDDriveNumber db 0
times 2048 - ($-$$) db 0      ; fill in 2048 bytes with zeroes
; end of sector 1! :D Any more code here would take bytes 2048 and 2049 but we don't    need that...

这是开机。Asm，第二阶段:

bits 16
org 0x1000
Main:
   xor bx, bx
   mov ah, 0eh
   mov al, 'A'
   int 0x10
   cli
   hlt
times 2048 - ($-$$) db 0

我用nasm -f bin isosys.asm -o ISOSYS和nasm -f bin boot.asm -o BOOT编译然后我做了mkdir iso，然后cp ISOSYS iso/，然后cp BOOT iso/，然后生成ISO:genisoimage -no-emul-boot -boot-load-size 4 -eltorito-boot ISOSYS -o boot.iso iso/

我在VirtualBox中运行它，但它说的是无法加载第二阶段(文件没有找到也许?)这意味着携带标志被设置，但我似乎找不到错误。

谁来帮忙?帮助将非常感激!: *

Answer 1

您的堆栈处理完全关闭。你把dx(为什么?)放在cli…sti块中(为什么?)，然后是pusha，但不要把popa。

在mov ax, 0x1000之后，您还缺少mov es,ax来实际设置段寄存器到您希望加载代码的位置。

不能使用CHS函数(AH=02h)读取iso，必须使用带参数块的LBA函数(AH=42h)。有一个例子