为什么我们在引导加载程序的开头需要 ORG 0x7c00？
Why do we need ORG 0x7c00 at the beginning of a bootloader?
在我见过的每个引导加载程序代码中，文件开头都有“ORG 0x7c00”这一行。据我所知，BIOS 会将这段代码放在地址 0x7c00.
那么做“org 0x7c00”的原因是什么？如果第一条指令加载到0x7c00，计数器会自动从那里开始吗？每条指令的地址不都是0x7c00+offset吗？
如果您有以下代码：
org 0x7c00
bits 16
jmp somefunction
somefunction:
xor ax, ax
mov ds, ax
cli
lgdt[gdtr]
mov eax, cr0
or al, 1
mov cr0, eax
jmp 0x08:protectedMode
bits 32
protectedMode:
mov ax, 0x10
mov ds, ax
hlt
gdt_start:
dq 0x0
gdt_code:
dw 0xFFFF ;limit 0-15
dw 0x0 ;base 0-15
db 0x0 ;base 16-23
db 10011010b ;pr, privi (2), s, ex, dc, rw, ac
db 11001111b ;gr, sz, limit 16-19
db 0x0 ;base 24-31
gdt_data:
dw 0xFFFF
dw 0x0
db 0x0
db 10010010b
db 11001111b
db 0x0
gdtr:
dw 24
dd gdt_start
times 510 - ($-$$) db 0
dw 0xAA55
Assemble 与 nasm -fbin boot.s -oboot.bin。您可以使用 ndisasm 轻松反汇编 boot.bin 的第一部分（16 位部分），看看会发生什么。 运行 命令 ndisasm -b16 boot.bin 并查看结果：
00000000 EB00 jmp short 0x2
00000002 31C0 xor ax,ax
00000004 8ED8 mov ds,ax
00000006 FA cli
00000007 0F0116387C lgdt [0x7c38]
0000000C 0F20C0 mov eax,cr0
0000000F 0C01 or al,0x1
00000011 0F22C0 mov cr0,eax
00000014 EA197C0800 jmp 0x8:0x7c19
00000019 66B810008ED8 mov eax,0xd88e0010
0000001F F4 hlt
00000020 0000 add [bx+si],al
00000022 0000 add [bx+si],al
00000024 0000 add [bx+si],al
00000026 0000 add [bx+si],al
00000028 FF db 0xff
00000029 FF00 inc word [bx+si]
0000002B 0000 add [bx+si],al
0000002D 9ACF00FFFF call 0xffff:0xcf
00000032 0000 add [bx+si],al
00000034 0092CF00 add [bp+si+0xcf],dl
00000038 1800 sbb [bx+si],al
0000003A 207C00 and [si+0x0],bh
0000003D 0000 add [bx+si],al
0000003F 0000 add [bx+si],al
00000041 0000 add [bx+si],al
00000043 0000 add [bx+si],al
00000045 0000 add [bx+si],al
00000047 0000 add [bx+si],al
00000049 0000 add [bx+si],al
0000004B 0000 add [bx+si],al
0000004D 0000 add [bx+si],al
0000004F 0000 add [bx+si],al
00000051 0000 add [bx+si],al
00000053 0000 add [bx+si],al
00000055 0000 add [bx+si],al
00000057 0000 add [bx+si],al
00000059 0000 add [bx+si],al
0000005B 0000 add [bx+si],al
0000005D 0000 add [bx+si],al
0000005F 0000 add [bx+si],al
00000061 0000 add [bx+si],al
00000063 0000 add [bx+si],al
00000065 0000 add [bx+si],al
00000067 0000 add [bx+si],al
00000069 0000 add [bx+si],al
0000006B 0000 add [bx+si],al
0000006D 0000 add [bx+si],al
0000006F 0000 add [bx+si],al
00000071 0000 add [bx+si],al
00000073 0000 add [bx+si],al
00000075 0000 add [bx+si],al
00000077 0000 add [bx+si],al
00000079 0000 add [bx+si],al
0000007B 0000 add [bx+si],al
0000007D 0000 add [bx+si],al
0000007F 0000 add [bx+si],al
00000081 0000 add [bx+si],al
00000083 0000 add [bx+si],al
00000085 0000 add [bx+si],al
00000087 0000 add [bx+si],al
00000089 0000 add [bx+si],al
0000008B 0000 add [bx+si],al
0000008D 0000 add [bx+si],al
0000008F 0000 add [bx+si],al
00000091 0000 add [bx+si],al
00000093 0000 add [bx+si],al
00000095 0000 add [bx+si],al
00000097 0000 add [bx+si],al
00000099 0000 add [bx+si],al
0000009B 0000 add [bx+si],al
0000009D 0000 add [bx+si],al
0000009F 0000 add [bx+si],al
000000A1 0000 add [bx+si],al
000000A3 0000 add [bx+si],al
000000A5 0000 add [bx+si],al
000000A7 0000 add [bx+si],al
000000A9 0000 add [bx+si],al
000000AB 0000 add [bx+si],al
000000AD 0000 add [bx+si],al
000000AF 0000 add [bx+si],al
000000B1 0000 add [bx+si],al
000000B3 0000 add [bx+si],al
000000B5 0000 add [bx+si],al
000000B7 0000 add [bx+si],al
000000B9 0000 add [bx+si],al
000000BB 0000 add [bx+si],al
000000BD 0000 add [bx+si],al
000000BF 0000 add [bx+si],al
000000C1 0000 add [bx+si],al
000000C3 0000 add [bx+si],al
000000C5 0000 add [bx+si],al
000000C7 0000 add [bx+si],al
000000C9 0000 add [bx+si],al
000000CB 0000 add [bx+si],al
000000CD 0000 add [bx+si],al
000000CF 0000 add [bx+si],al
000000D1 0000 add [bx+si],al
000000D3 0000 add [bx+si],al
000000D5 0000 add [bx+si],al
000000D7 0000 add [bx+si],al
000000D9 0000 add [bx+si],al
000000DB 0000 add [bx+si],al
000000DD 0000 add [bx+si],al
000000DF 0000 add [bx+si],al
000000E1 0000 add [bx+si],al
000000E3 0000 add [bx+si],al
000000E5 0000 add [bx+si],al
000000E7 0000 add [bx+si],al
000000E9 0000 add [bx+si],al
000000EB 0000 add [bx+si],al
000000ED 0000 add [bx+si],al
000000EF 0000 add [bx+si],al
000000F1 0000 add [bx+si],al
000000F3 0000 add [bx+si],al
000000F5 0000 add [bx+si],al
000000F7 0000 add [bx+si],al
000000F9 0000 add [bx+si],al
000000FB 0000 add [bx+si],al
000000FD 0000 add [bx+si],al
000000FF 0000 add [bx+si],al
00000101 0000 add [bx+si],al
00000103 0000 add [bx+si],al
00000105 0000 add [bx+si],al
00000107 0000 add [bx+si],al
00000109 0000 add [bx+si],al
0000010B 0000 add [bx+si],al
0000010D 0000 add [bx+si],al
0000010F 0000 add [bx+si],al
00000111 0000 add [bx+si],al
00000113 0000 add [bx+si],al
00000115 0000 add [bx+si],al
00000117 0000 add [bx+si],al
00000119 0000 add [bx+si],al
0000011B 0000 add [bx+si],al
0000011D 0000 add [bx+si],al
0000011F 0000 add [bx+si],al
00000121 0000 add [bx+si],al
00000123 0000 add [bx+si],al
00000125 0000 add [bx+si],al
00000127 0000 add [bx+si],al
00000129 0000 add [bx+si],al
0000012B 0000 add [bx+si],al
0000012D 0000 add [bx+si],al
0000012F 0000 add [bx+si],al
00000131 0000 add [bx+si],al
00000133 0000 add [bx+si],al
00000135 0000 add [bx+si],al
00000137 0000 add [bx+si],al
00000139 0000 add [bx+si],al
0000013B 0000 add [bx+si],al
0000013D 0000 add [bx+si],al
0000013F 0000 add [bx+si],al
00000141 0000 add [bx+si],al
00000143 0000 add [bx+si],al
00000145 0000 add [bx+si],al
00000147 0000 add [bx+si],al
00000149 0000 add [bx+si],al
0000014B 0000 add [bx+si],al
0000014D 0000 add [bx+si],al
0000014F 0000 add [bx+si],al
00000151 0000 add [bx+si],al
00000153 0000 add [bx+si],al
00000155 0000 add [bx+si],al
00000157 0000 add [bx+si],al
00000159 0000 add [bx+si],al
0000015B 0000 add [bx+si],al
0000015D 0000 add [bx+si],al
0000015F 0000 add [bx+si],al
00000161 0000 add [bx+si],al
00000163 0000 add [bx+si],al
00000165 0000 add [bx+si],al
00000167 0000 add [bx+si],al
00000169 0000 add [bx+si],al
0000016B 0000 add [bx+si],al
0000016D 0000 add [bx+si],al
0000016F 0000 add [bx+si],al
00000171 0000 add [bx+si],al
00000173 0000 add [bx+si],al
00000175 0000 add [bx+si],al
00000177 0000 add [bx+si],al
00000179 0000 add [bx+si],al
0000017B 0000 add [bx+si],al
0000017D 0000 add [bx+si],al
0000017F 0000 add [bx+si],al
00000181 0000 add [bx+si],al
00000183 0000 add [bx+si],al
00000185 0000 add [bx+si],al
00000187 0000 add [bx+si],al
00000189 0000 add [bx+si],al
0000018B 0000 add [bx+si],al
0000018D 0000 add [bx+si],al
0000018F 0000 add [bx+si],al
00000191 0000 add [bx+si],al
00000193 0000 add [bx+si],al
00000195 0000 add [bx+si],al
00000197 0000 add [bx+si],al
00000199 0000 add [bx+si],al
0000019B 0000 add [bx+si],al
0000019D 0000 add [bx+si],al
0000019F 0000 add [bx+si],al
000001A1 0000 add [bx+si],al
000001A3 0000 add [bx+si],al
000001A5 0000 add [bx+si],al
000001A7 0000 add [bx+si],al
000001A9 0000 add [bx+si],al
000001AB 0000 add [bx+si],al
000001AD 0000 add [bx+si],al
000001AF 0000 add [bx+si],al
000001B1 0000 add [bx+si],al
000001B3 0000 add [bx+si],al
000001B5 0000 add [bx+si],al
000001B7 0000 add [bx+si],al
000001B9 0000 add [bx+si],al
000001BB 0000 add [bx+si],al
000001BD 0000 add [bx+si],al
000001BF 0000 add [bx+si],al
000001C1 0000 add [bx+si],al
000001C3 0000 add [bx+si],al
000001C5 0000 add [bx+si],al
000001C7 0000 add [bx+si],al
000001C9 0000 add [bx+si],al
000001CB 0000 add [bx+si],al
000001CD 0000 add [bx+si],al
000001CF 0000 add [bx+si],al
000001D1 0000 add [bx+si],al
000001D3 0000 add [bx+si],al
000001D5 0000 add [bx+si],al
000001D7 0000 add [bx+si],al
000001D9 0000 add [bx+si],al
000001DB 0000 add [bx+si],al
000001DD 0000 add [bx+si],al
000001DF 0000 add [bx+si],al
000001E1 0000 add [bx+si],al
000001E3 0000 add [bx+si],al
000001E5 0000 add [bx+si],al
000001E7 0000 add [bx+si],al
000001E9 0000 add [bx+si],al
000001EB 0000 add [bx+si],al
000001ED 0000 add [bx+si],al
000001EF 0000 add [bx+si],al
000001F1 0000 add [bx+si],al
000001F3 0000 add [bx+si],al
000001F5 0000 add [bx+si],al
000001F7 0000 add [bx+si],al
000001F9 0000 add [bx+si],al
000001FB 0000 add [bx+si],al
000001FD 0055AA add [di-0x56],dl
像跳转到标签这样的短跳转是相对的。这意味着即使您没有 org 指令，跳转也会起作用。同时，跳远是绝对的。它跳转到指定为 segment:offset 对的地址。 org 伪指令告诉汇编程序将 org（原始）值添加到偏移量。这允许当你远跳到一个位置未知的标签时（而不是硬编码标签的位置），汇编器将根据代码在 RAM 中的实际位置正确计算偏移量。
对于上面的示例，org 指令仅对远跳转到保护模式和 lgdt 指令有用。你看到远跳被反汇编到00000014 EA197C0800 jmp 0x8:0x7c19行。远跳转的地址是绝对地址，即直接计算地址。如果您没有 org 指令，反汇编的远跳转将改为 jmp 0x8:0x19。这不是正确的地址。它会跳转到地址 0x19，这与您的引导加载程序代码将加载到 0x7c00 的事实无关。您需要告诉汇编程序将 0x7c00 添加到所有绝对地址（主要是远跳转和 lgdt 指令）。
在我见过的每个引导加载程序代码中，文件开头都有“ORG 0x7c00”这一行。据我所知，BIOS 会将这段代码放在地址 0x7c00.
那么做“org 0x7c00”的原因是什么？如果第一条指令加载到0x7c00，计数器会自动从那里开始吗？每条指令的地址不都是0x7c00+offset吗？
如果您有以下代码：
org 0x7c00
bits 16
jmp somefunction
somefunction:
xor ax, ax
mov ds, ax
cli
lgdt[gdtr]
mov eax, cr0
or al, 1
mov cr0, eax
jmp 0x08:protectedMode
bits 32
protectedMode:
mov ax, 0x10
mov ds, ax
hlt
gdt_start:
dq 0x0
gdt_code:
dw 0xFFFF ;limit 0-15
dw 0x0 ;base 0-15
db 0x0 ;base 16-23
db 10011010b ;pr, privi (2), s, ex, dc, rw, ac
db 11001111b ;gr, sz, limit 16-19
db 0x0 ;base 24-31
gdt_data:
dw 0xFFFF
dw 0x0
db 0x0
db 10010010b
db 11001111b
db 0x0
gdtr:
dw 24
dd gdt_start
times 510 - ($-$$) db 0
dw 0xAA55
Assemble 与 nasm -fbin boot.s -oboot.bin。您可以使用 ndisasm 轻松反汇编 boot.bin 的第一部分（16 位部分），看看会发生什么。 运行 命令 ndisasm -b16 boot.bin 并查看结果：
00000000 EB00 jmp short 0x2
00000002 31C0 xor ax,ax
00000004 8ED8 mov ds,ax
00000006 FA cli
00000007 0F0116387C lgdt [0x7c38]
0000000C 0F20C0 mov eax,cr0
0000000F 0C01 or al,0x1
00000011 0F22C0 mov cr0,eax
00000014 EA197C0800 jmp 0x8:0x7c19
00000019 66B810008ED8 mov eax,0xd88e0010
0000001F F4 hlt
00000020 0000 add [bx+si],al
00000022 0000 add [bx+si],al
00000024 0000 add [bx+si],al
00000026 0000 add [bx+si],al
00000028 FF db 0xff
00000029 FF00 inc word [bx+si]
0000002B 0000 add [bx+si],al
0000002D 9ACF00FFFF call 0xffff:0xcf
00000032 0000 add [bx+si],al
00000034 0092CF00 add [bp+si+0xcf],dl
00000038 1800 sbb [bx+si],al
0000003A 207C00 and [si+0x0],bh
0000003D 0000 add [bx+si],al
0000003F 0000 add [bx+si],al
00000041 0000 add [bx+si],al
00000043 0000 add [bx+si],al
00000045 0000 add [bx+si],al
00000047 0000 add [bx+si],al
00000049 0000 add [bx+si],al
0000004B 0000 add [bx+si],al
0000004D 0000 add [bx+si],al
0000004F 0000 add [bx+si],al
00000051 0000 add [bx+si],al
00000053 0000 add [bx+si],al
00000055 0000 add [bx+si],al
00000057 0000 add [bx+si],al
00000059 0000 add [bx+si],al
0000005B 0000 add [bx+si],al
0000005D 0000 add [bx+si],al
0000005F 0000 add [bx+si],al
00000061 0000 add [bx+si],al
00000063 0000 add [bx+si],al
00000065 0000 add [bx+si],al
00000067 0000 add [bx+si],al
00000069 0000 add [bx+si],al
0000006B 0000 add [bx+si],al
0000006D 0000 add [bx+si],al
0000006F 0000 add [bx+si],al
00000071 0000 add [bx+si],al
00000073 0000 add [bx+si],al
00000075 0000 add [bx+si],al
00000077 0000 add [bx+si],al
00000079 0000 add [bx+si],al
0000007B 0000 add [bx+si],al
0000007D 0000 add [bx+si],al
0000007F 0000 add [bx+si],al
00000081 0000 add [bx+si],al
00000083 0000 add [bx+si],al
00000085 0000 add [bx+si],al
00000087 0000 add [bx+si],al
00000089 0000 add [bx+si],al
0000008B 0000 add [bx+si],al
0000008D 0000 add [bx+si],al
0000008F 0000 add [bx+si],al
00000091 0000 add [bx+si],al
00000093 0000 add [bx+si],al
00000095 0000 add [bx+si],al
00000097 0000 add [bx+si],al
00000099 0000 add [bx+si],al
0000009B 0000 add [bx+si],al
0000009D 0000 add [bx+si],al
0000009F 0000 add [bx+si],al
000000A1 0000 add [bx+si],al
000000A3 0000 add [bx+si],al
000000A5 0000 add [bx+si],al
000000A7 0000 add [bx+si],al
000000A9 0000 add [bx+si],al
000000AB 0000 add [bx+si],al
000000AD 0000 add [bx+si],al
000000AF 0000 add [bx+si],al
000000B1 0000 add [bx+si],al
000000B3 0000 add [bx+si],al
000000B5 0000 add [bx+si],al
000000B7 0000 add [bx+si],al
000000B9 0000 add [bx+si],al
000000BB 0000 add [bx+si],al
000000BD 0000 add [bx+si],al
000000BF 0000 add [bx+si],al
000000C1 0000 add [bx+si],al
000000C3 0000 add [bx+si],al
000000C5 0000 add [bx+si],al
000000C7 0000 add [bx+si],al
000000C9 0000 add [bx+si],al
000000CB 0000 add [bx+si],al
000000CD 0000 add [bx+si],al
000000CF 0000 add [bx+si],al
000000D1 0000 add [bx+si],al
000000D3 0000 add [bx+si],al
000000D5 0000 add [bx+si],al
000000D7 0000 add [bx+si],al
000000D9 0000 add [bx+si],al
000000DB 0000 add [bx+si],al
000000DD 0000 add [bx+si],al
000000DF 0000 add [bx+si],al
000000E1 0000 add [bx+si],al
000000E3 0000 add [bx+si],al
000000E5 0000 add [bx+si],al
000000E7 0000 add [bx+si],al
000000E9 0000 add [bx+si],al
000000EB 0000 add [bx+si],al
000000ED 0000 add [bx+si],al
000000EF 0000 add [bx+si],al
000000F1 0000 add [bx+si],al
000000F3 0000 add [bx+si],al
000000F5 0000 add [bx+si],al
000000F7 0000 add [bx+si],al
000000F9 0000 add [bx+si],al
000000FB 0000 add [bx+si],al
000000FD 0000 add [bx+si],al
000000FF 0000 add [bx+si],al
00000101 0000 add [bx+si],al
00000103 0000 add [bx+si],al
00000105 0000 add [bx+si],al
00000107 0000 add [bx+si],al
00000109 0000 add [bx+si],al
0000010B 0000 add [bx+si],al
0000010D 0000 add [bx+si],al
0000010F 0000 add [bx+si],al
00000111 0000 add [bx+si],al
00000113 0000 add [bx+si],al
00000115 0000 add [bx+si],al
00000117 0000 add [bx+si],al
00000119 0000 add [bx+si],al
0000011B 0000 add [bx+si],al
0000011D 0000 add [bx+si],al
0000011F 0000 add [bx+si],al
00000121 0000 add [bx+si],al
00000123 0000 add [bx+si],al
00000125 0000 add [bx+si],al
00000127 0000 add [bx+si],al
00000129 0000 add [bx+si],al
0000012B 0000 add [bx+si],al
0000012D 0000 add [bx+si],al
0000012F 0000 add [bx+si],al
00000131 0000 add [bx+si],al
00000133 0000 add [bx+si],al
00000135 0000 add [bx+si],al
00000137 0000 add [bx+si],al
00000139 0000 add [bx+si],al
0000013B 0000 add [bx+si],al
0000013D 0000 add [bx+si],al
0000013F 0000 add [bx+si],al
00000141 0000 add [bx+si],al
00000143 0000 add [bx+si],al
00000145 0000 add [bx+si],al
00000147 0000 add [bx+si],al
00000149 0000 add [bx+si],al
0000014B 0000 add [bx+si],al
0000014D 0000 add [bx+si],al
0000014F 0000 add [bx+si],al
00000151 0000 add [bx+si],al
00000153 0000 add [bx+si],al
00000155 0000 add [bx+si],al
00000157 0000 add [bx+si],al
00000159 0000 add [bx+si],al
0000015B 0000 add [bx+si],al
0000015D 0000 add [bx+si],al
0000015F 0000 add [bx+si],al
00000161 0000 add [bx+si],al
00000163 0000 add [bx+si],al
00000165 0000 add [bx+si],al
00000167 0000 add [bx+si],al
00000169 0000 add [bx+si],al
0000016B 0000 add [bx+si],al
0000016D 0000 add [bx+si],al
0000016F 0000 add [bx+si],al
00000171 0000 add [bx+si],al
00000173 0000 add [bx+si],al
00000175 0000 add [bx+si],al
00000177 0000 add [bx+si],al
00000179 0000 add [bx+si],al
0000017B 0000 add [bx+si],al
0000017D 0000 add [bx+si],al
0000017F 0000 add [bx+si],al
00000181 0000 add [bx+si],al
00000183 0000 add [bx+si],al
00000185 0000 add [bx+si],al
00000187 0000 add [bx+si],al
00000189 0000 add [bx+si],al
0000018B 0000 add [bx+si],al
0000018D 0000 add [bx+si],al
0000018F 0000 add [bx+si],al
00000191 0000 add [bx+si],al
00000193 0000 add [bx+si],al
00000195 0000 add [bx+si],al
00000197 0000 add [bx+si],al
00000199 0000 add [bx+si],al
0000019B 0000 add [bx+si],al
0000019D 0000 add [bx+si],al
0000019F 0000 add [bx+si],al
000001A1 0000 add [bx+si],al
000001A3 0000 add [bx+si],al
000001A5 0000 add [bx+si],al
000001A7 0000 add [bx+si],al
000001A9 0000 add [bx+si],al
000001AB 0000 add [bx+si],al
000001AD 0000 add [bx+si],al
000001AF 0000 add [bx+si],al
000001B1 0000 add [bx+si],al
000001B3 0000 add [bx+si],al
000001B5 0000 add [bx+si],al
000001B7 0000 add [bx+si],al
000001B9 0000 add [bx+si],al
000001BB 0000 add [bx+si],al
000001BD 0000 add [bx+si],al
000001BF 0000 add [bx+si],al
000001C1 0000 add [bx+si],al
000001C3 0000 add [bx+si],al
000001C5 0000 add [bx+si],al
000001C7 0000 add [bx+si],al
000001C9 0000 add [bx+si],al
000001CB 0000 add [bx+si],al
000001CD 0000 add [bx+si],al
000001CF 0000 add [bx+si],al
000001D1 0000 add [bx+si],al
000001D3 0000 add [bx+si],al
000001D5 0000 add [bx+si],al
000001D7 0000 add [bx+si],al
000001D9 0000 add [bx+si],al
000001DB 0000 add [bx+si],al
000001DD 0000 add [bx+si],al
000001DF 0000 add [bx+si],al
000001E1 0000 add [bx+si],al
000001E3 0000 add [bx+si],al
000001E5 0000 add [bx+si],al
000001E7 0000 add [bx+si],al
000001E9 0000 add [bx+si],al
000001EB 0000 add [bx+si],al
000001ED 0000 add [bx+si],al
000001EF 0000 add [bx+si],al
000001F1 0000 add [bx+si],al
000001F3 0000 add [bx+si],al
000001F5 0000 add [bx+si],al
000001F7 0000 add [bx+si],al
000001F9 0000 add [bx+si],al
000001FB 0000 add [bx+si],al
000001FD 0055AA add [di-0x56],dl
像跳转到标签这样的短跳转是相对的。这意味着即使您没有 org 指令，跳转也会起作用。同时，跳远是绝对的。它跳转到指定为 segment:offset 对的地址。 org 伪指令告诉汇编程序将 org（原始）值添加到偏移量。这允许当你远跳到一个位置未知的标签时（而不是硬编码标签的位置），汇编器将根据代码在 RAM 中的实际位置正确计算偏移量。
对于上面的示例，org 指令仅对远跳转到保护模式和 lgdt 指令有用。你看到远跳被反汇编到00000014 EA197C0800 jmp 0x8:0x7c19行。远跳转的地址是绝对地址，即直接计算地址。如果您没有 org 指令，反汇编的远跳转将改为 jmp 0x8:0x19。这不是正确的地址。它会跳转到地址 0x19，这与您的引导加载程序代码将加载到 0x7c00 的事实无关。您需要告诉汇编程序将 0x7c00 添加到所有绝对地址（主要是远跳转和 lgdt 指令）。