Question

我正在尝试从我的OSOS操作系统的ISOSYS引导加载程序加载第二阶段引导加载程序，但我似乎无法做到这一点。 CF似乎总是被设定。这是从CD / DVD启动的，我使用的是Debian GNU / Linux 7.6（Wheezy）

这是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boot.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

我使用nasm -f bin isosys.asm -o ISOSYS和nasm -f bin boot.asm -o BOOT进行了编译然后我做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（可能没找到文件？）这意味着Carry Flag已设置但我似乎无法找到错误。

有人帮忙吗？非常感谢帮助！：*

Answer 1

你的筹码处理完全没了。你在dx‥cli区块内推送sti（为什么？）（为什么？），然后是pusha，但不是popa。

在mov es,ax之后你还错过了一个mov ax, 0x1000来实际设置段寄存器到你想要加载代码的位置。

您无法使用CHS功能（AH = 02h）读取ISO，您必须使用带参数块的LBA功能（AH = 42h）。 Have an example.

我无法从x86汇编中的CD-ROM中读取扇区

1 个答案: