为什么Bochs说“找不到启动设备”当我将内核与引导部门相连时？

Question

我正在关注这个< /a> 指南，以便尝试编写我自己的（非常基本的）操作系统。我已经让我的引导扇区与 Bochs 完美运行（我刚刚通过写入屏幕等进行了测试）。按照指南，我编写了一个非常基本的内核（一个仅在屏幕上打印 X 的 C 程序），并且（使用 gcc 将其编译为 .o 文件，然后使用 ld 将其链接到 .bin 后）我在我的引导扇区之后将其连接到整个内核映像文件中。我检查了文件的十六进制，它肯定是我的引导扇区，在 0x1fe 和 0x1ff 处包含“幻数”，然后是紧随幻数之后的内核。

当我运行 Bochs 而不在引导扇区后添加内核时（即，当映像文件只是我的引导扇区时），它运行得很好。当我运行 Bochs 并在引导扇区后连接内核时，Bochs 表示未找到可引导设备。为什么会出现这个问题？我也愿意提供所需的任何额外信息，但我不太确定与此问题相关的内容。

编辑：

我的 Bochs 配置文件：

floppya: 1_44="os-image", status=inserted
boot: a

我的 kernel.c：

extern void main() {
    char* video_memory = (char*) 0xb8000; // Pointer to the first text cell in video memory
    *video_memory = 'X'; // Sets the value of video_memory to an X.
}

我的引导扇区：

; A boot sector that boots a C kernel in a 32-bit protected mode

[org 0x7c00]    ; Tell the assembler where to load the boot sector
KERNEL_OFFSET equ 0x1000    ; Memory offset for kernel

mov [BOOT_DRIVE], dl

mov bp, 0x9000  ; Set up the stack
mov sp, bp

mov bx, MSG_REAL_MODE   ; Use BX as a parameter to the function call
call print_string   ; Tell the user that we have booted into 16-bit real mode

call load_kernel    ; Load the kernel

call switch_to_pm

jmp $   ; Hang indefinitely

%include "Printing/print_string.asm"
%include "Disk/diskload.asm"
%include "pm/gdt.asm"
%include "Printing/print_string_pm.asm"
%include "pm/switch_to_pm.asm"

[bits 16]

load_kernel:
    mov bx, MSG_LOAD_KERNEL ; Announce that we are loading the kernel
    call print_string

    mov bx, KERNEL_OFFSET
    mov dh, 15
    mov dl, [BOOT_DRIVE]
    call disk_load
    ret

[bits 32]

BEGIN_PM:
    mov ebx, MSG_PROT_MODE
    call print_string_pm

    call KERNEL_OFFSET  ; Move to where the kernel is and pray

    jmp $

; Data
BOOT_DRIVE db 0
MSG_REAL_MODE db "Started in 16-bit Real Mode", 0
MSG_PROT_MODE db "Successfully landed in 32-bit Protected Mode", 0
MSG_LOAD_KERNEL db "Loading kernel into memory", 0

times 510-($-$$) db 0   ; Padding
dw 0xaa55   ; Magic number to denote boot sector

我的最终映像二进制文件：

Starting at 0x0:
88 16 e5 7c bd 00 90 89 ec bb e6 7c e8 08 00 e8
af 00 e8 7d 00 eb fe 60 b4 0e eb 00 8a 07 3c 00
74 07 cd 10 83 c3 01 eb f3 61 c3 52 b4 02 88 f0
b5 00 b6 00 b1 02 cd 13 72 06 5a 38 c6 75 01 c3
bb 48 7c e8 d1 ff eb fe 44 69 73 6b 20 72 65 61
64 20 65 72 72 6f 72 21 00 00 00 00 00 00 00 00
00 ff ff 00 00 00 9a cf 00 ff ff 00 00 00 92 cf
00 17 00 59 7c 00 00 60 ba 00 80 0b 00 8a 03 b4
0f 3c 00 74 0b 66 89 02 83 c3 01 83 c2 02 eb ed
61 c3 fa 0f 01 16 71 7c 0f 20 c0 66 83 c8 01 0f
22 c0 ea a7 7c 08 00 66 b8 10 00 8e d8 8e d0 8e
c0 8e e0 8e e8 bd 00 00 09 00 89 ec e8 13 00 00
00 bb 2f 7d e8 50 ff bb 00 10 b6 0f 8a 16 e5 7c
e8 58 ff c3 bb 02 7d 00 00 e8 99 ff ff ff e8 1d
93 ff ff eb fe 00 53 74 61 72 74 65 64 20 69 6e
20 31 36 2d 62 69 74 20 52 65 61 6c 20 4d 6f 64
65 00 53 75 63 63 65 73 73 66 75 6c 6c 79 20 6c
61 6e 64 65 64 20 69 6e 20 33 32 2d 62 69 74 20
50 72 6f 74 65 63 74 65 64 20 4d 6f 64 65 00 4c
6f 61 64 69 6e 67 20 6b 65 72 6e 65 6c 20 69 6e
74 6f 20 6d 65 6d 6f 72 79 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa
e8 02 00 00 00 eb fe f3 0f 1e fb 55 89 e5 83 ec
10 c7 45 fc 00 80 0b 00 8b 45 fc c6 00 58 90 c9
c3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
...
Starting at 0x1000:
14 00 00 00 00 00 00 00 01 7a 52 00 01 7c 08 01
1b 0c 04 04 88 01 00 00 1c 00 00 00 1c 00 00 00
e7 ef ff ff 1a 00 00 00 00 45 0e 08 85 02 42 0d
05 52 c5 0c 04 04 00 00 00 00 00 00 00 00 00 00
...
Starting at 0x08047200:
04 00 00 00 0c 00 00 00 05 00 00 00 47 4e 55 00
02 00 00 c0 04 00 00 00 03 00 00 00

我之前没有注意到，也不知道为什么，在最后一个集合之前有一个巨大的零填充二进制末尾的非零十六进制代码。

我的 makefile：

all: os-image

os-image: boot_sect.bin kernel.bin
        cat $^ > os-image

kernel.bin: kernel_entry.o kernel.o
        ld -melf_i386 -o kernel.bin -Ttext 0x1000 $^ --oformat binary

kernel.o : kernel.c
        gcc -fno-pie -ffreestanding -m32 -c $< -o $@

kernel_entry.o : kernel_entry.asm
        nasm $< -f elf -o $@

boot_sect.bin : boot_sect.asm
        nasm $< -f bin -o $@

clean:
        rm -fr *.bin *.o os-image *.map

使用注释中建议的 Makefile 运行 objdump -Dx kernel.elf 的输出：

kernel.elf:     file format elf32-i386
kernel.elf
architecture: i386, flags 0x00000112:
EXEC_P, HAS_SYMS, D_PAGED
start address 0x00001000

Program Header:
    LOAD off    0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**12
         filesz 0x000000b4 memsz 0x000000b4 flags r--
    LOAD off    0x00001000 vaddr 0x00001000 paddr 0x00001000 align 2**12
         filesz 0x00000021 memsz 0x00000021 flags r-x
    LOAD off    0x00002000 vaddr 0x00002000 paddr 0x00002000 align 2**12
         filesz 0x00000038 memsz 0x00000038 flags r--
   STACK off    0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**4
         filesz 0x00000000 memsz 0x00000000 flags rwx

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000021  00001000  00001000  00001000  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .eh_frame     00000038  00002000  00002000  00002000  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  2 .comment      0000002b  00000000  00000000  00002038  2**0
                  CONTENTS, READONLY
SYMBOL TABLE:
00001000 l    d  .text  00000000 .text
00002000 l    d  .eh_frame      00000000 .eh_frame
00000000 l    d  .comment       00000000 .comment
00000000 l    df *ABS*  00000000 kernel_entry.asm
00000000 l    df *ABS*  00000000 kernel.c
00000000         *UND*  00000000 _start
00004000 g       .eh_frame      00000000 __bss_start
00001007 g     F .text  0000001a main
00004000 g       .eh_frame      00000000 _edata
00004000 g       .eh_frame      00000000 _end



Disassembly of section .text:

00001000 <main-0x7>:
    1000:       e8 02 00 00 00          call   1007 <main>
    1005:       eb fe                   jmp    1005 <main-0x2>

00001007 <main>:
    1007:       f3 0f 1e fb             endbr32
    100b:       55                      push   %ebp
    100c:       89 e5                   mov    %esp,%ebp
    100e:       83 ec 10                sub    $0x10,%esp
    1011:       c7 45 fc 00 80 0b 00    movl   $0xb8000,-0x4(%ebp)
    1018:       8b 45 fc                mov    -0x4(%ebp),%eax
    101b:       c6 00 58                movb   $0x58,(%eax)
    101e:       90                      nop
    101f:       c9                      leave
    1020:       c3                      ret

Disassembly of section .eh_frame:

00002000 <__bss_start-0x2000>:
    2000:       14 00                   adc    $0x0,%al
    2002:       00 00                   add    %al,(%eax)
    2004:       00 00                   add    %al,(%eax)
    2006:       00 00                   add    %al,(%eax)
    2008:       01 7a 52                add    %edi,0x52(%edx)
    200b:       00 01                   add    %al,(%ecx)
    200d:       7c 08                   jl     2017 <main+0x1010>
    200f:       01 1b                   add    %ebx,(%ebx)
    2011:       0c 04                   or     $0x4,%al
    2013:       04 88                   add    $0x88,%al
    2015:       01 00                   add    %eax,(%eax)
    2017:       00 1c 00                add    %bl,(%eax,%eax,1)
    201a:       00 00                   add    %al,(%eax)
    201c:       1c 00                   sbb    $0x0,%al
    201e:       00 00                   add    %al,(%eax)
    2020:       e7 ef                   out    %eax,$0xef
    2022:       ff                      (bad)
    2023:       ff 1a                   lcall  *(%edx)
    2025:       00 00                   add    %al,(%eax)
    2027:       00 00                   add    %al,(%eax)
    2029:       45                      inc    %ebp
    202a:       0e                      push   %cs
    202b:       08 85 02 42 0d 05       or     %al,0x50d4202(%ebp)
    2031:       52                      push   %edx
    2032:       c5 0c 04                lds    (%esp,%eax,1),%ecx
    2035:       04 00                   add    $0x0,%al
        ...

Disassembly of section .comment:

00000000 <.comment>:
   0:   47                      inc    %edi
   1:   43                      inc    %ebx
   2:   43                      inc    %ebx
   3:   3a 20                   cmp    (%eax),%ah
   5:   28 55 62                sub    %dl,0x62(%ebp)
   8:   75 6e                   jne    78 <main-0xf8f>
   a:   74 75                   je     81 <main-0xf86>
   c:   20 39                   and    %bh,(%ecx)
   e:   2e 34 2e                cs xor $0x2e,%al
  11:   30 2d 31 75 62 75       xor    %ch,0x75627531
  17:   6e                      outsb  %ds:(%esi),(%dx)
  18:   74 75                   je     8f <main-0xf78>
  1a:   31 7e 32                xor    %edi,0x32(%esi)
  1d:   30 2e                   xor    %ch,(%esi)
  1f:   30 34 2e                xor    %dh,(%esi,%ebp,1)
  22:   31 29                   xor    %ebp,(%ecx)
  24:   20 39                   and    %bh,(%ecx)
  26:   2e 34 2e                cs xor $0x2e,%al
  29:   30 00                   xor    %al,(%eax)