我正在修改一个在实模式之间切换以执行 BIOS 中断的例程，但遇到了分页问题。我之前没有分页，但现在我的操作系统使用分页，我需要在进入实模式之前禁用它（并在之后启用它）。
我的问题是，当执行远跳转导致页面禁用生效时，出现了严重错误，我重新启动。
下面显示的代码首先使用页表创建身份映射，该页表boot_page_table1只是身份映射前 4 MiB 的页表。这必须完成，因为我目前使用分页从更高的内存运行我的内核代码，并且所有内核代码都在0xC0100000从0x00100000. 然后我刷新 TLB 并跳转到附近的标签，但这次使用的是较低内存中的地址。我的指令指针现在应该指向标识映射代码，并且禁用分页应该是安全的。然后在 中禁用分页位cr3，TLB 再次刷新，因为我很偏执，并且切换模式的代码继续进行。
该代码通过将自身处理到 0x7c00 的 16 位内存中，然后跳转到该位置，以便它可以在 16 位实模式下工作。
如果我不禁用分页位并使其他所有内容保持不变，jmpw CODE16:REBASE(p_mode16)则进入跳转后的工作和无限循环让我认为这个问题是由于我禁用分页的方式而发生的。禁用分页时我错过了什么吗？我在其他帖子 上看到“因为您所做的事情非常不寻常，您可能会遇到模拟器的错误和兼容性问题”，但我不确定它是否只是我的代码错误。
该代码是使用带有 GAS 汇编器的 intel 语法编写的。
.intel_syntax noprefix
.code32
.global int32, _int32
#define regs16_t_size 13*2
#define INT32_BASE 0x00007C00
#define REBASE(x) (((x) - reloc) + INT32_BASE)
#define GDTENTRY(x) ((x) << 3)
#define CODE32 0x08
#define DATA32 0x10
#define CODE16 0x18
#define DATA16 0x20
#define STACK16 (INT32_BASE - regs16_t_size)
.global reloc
.global int32_end
.section .text
int32: .code32 # by Napalm
_int32:
cli # disable interrupts
pusha # save register state to 32bit stack
# Enable identity mapping the first MiB, jump, then disable paging
push [boot_page_directory] # Push first page directory entry to restore it after
mov eax, (offset boot_page_table1) - 0xC0000000 + 0x003
mov [boot_page_directory], eax
mov ecx, cr3 # Reload crc3 to force a TLB flush so the changes to take effect.
mov cr3, ecx
mov eax, (offset napalm_switch_disable_paging) - 0xC0000000
jmp eax
napalm_switch_disable_paging:
# Code is now running with the instruction pointer in lower memory,
# but the code is still assembled as though its in higher memory. Because
# of this, something like jmp INT32_BASE would fail since it would
# assemble as a relative jump from an address around 0xC0100000 to 0x7C00
# but will be running at an address around 0x00100000 causing it to jump to
# 0x40007C00.
# Disable paging bit
mov eax, cr0
and eax, ~0x80000000
mov cr0, eax
mov ecx, cr3 # Reload crc3 to force a TLB flush so the changes to take effect.
mov cr3, ecx
mov esi, (offset reloc) - 0xC0000000 # set source to code below
mov edi, INT32_BASE # set destination to new base address
mov ecx, int32_end - reloc # set copy size to our codes size
cld # clear direction flag (so we copy forward)
rep movsb # do the actual copy (relocate code to low 16bit space)
mov eax, INT32_BASE
jmp eax # jump to new code location
reloc: .code32 # by Napalm
mov [REBASE(stack32_ptr)], esp # save 32bit stack pointer
sidt [idt_ptr] # save 32bit idt pointer
sgdt [gdt_ptr] # save 32bit gdt pointer
lgdt [REBASE(gdt16_ptr)] # load 16bit gdt pointer
lea esi, [esp+0x24] # set position of intnum on 32bit stack
lodsd # read intnum into eax
mov [REBASE(ib)], al # set intrrupt immediate byte from our arguments
mov esi, [esi] # read regs pointer in esi as source
mov edi, STACK16 # set destination to 16bit stack
mov ecx, regs16_t_size # set copy size to our struct size
mov esp, edi # save destination to as 16bit stack offset
rep movsb # do the actual copy (32bit stack to 16bit stack)
jmpw CODE16:REBASE(p_mode16) # switch to 16bit selector (16bit protected mode)
p_mode16: .code16
jmp .-2
...
more of the routine thats not run due to the bug
...
stack32_ptr: # address in 32bit stack after we
.4byte 0x00000000 # save all general purpose registers
idt16_ptr: # IDT table pointer for 16bit access
.2byte 0x03FF # table limit (size)
.4byte 0x00000000 # table base address
gdt16_base: # GDT descriptor table
.null: # 0x00 - null segment descriptor
.4byte 0x00000000 # must be left zero'd
.4byte 0x00000000 # must be left zero'd
.code32: # 0x01 - 32bit code segment descriptor 0xFFFFFFFF
.2byte 0xFFFF # limit 0:15
.2byte 0x0000 # base 0:15
.byte 0x00 # base 16:23
.byte 0x9A # present, iopl/0, code, execute/read
.byte 0xCF # 4Kbyte granularity, 32bit selector; limit 16:19
.byte 0x00 # base 24:31
.data32: # 0x02 - 32bit data segment descriptor 0xFFFFFFFF
.2byte 0xFFFF # limit 0:15
.2byte 0x0000 # base 0:15
.byte 0x00 # base 16:23
.byte 0x92 # present, iopl/0, data, read/write
.byte 0xCF # 4Kbyte granularity, 32bit selector; limit 16:19
.byte 0x00 # base 24:31
.code16: # 0x03 - 16bit code segment descriptor 0x000FFFFF
.2byte 0xFFFF # limit 0:15
.2byte 0x0000 # base 0:15
.byte 0x00 # base 16:23
.byte 0x9A # present, iopl/0, code, execute/read
.byte 0x0F # 1Byte granularity, 16bit selector; limit 16:19
.byte 0x00 # base 24:31
.data16: # 0x04 - 16bit data segment descriptor 0x000FFFFF
.2byte 0xFFFF # limit 0:15
.2byte 0x0000 # base 0:15
.byte 0x00 # base 16:23
.byte 0x92 # present, iopl/0, data, read/write
.byte 0x0F # 1Byte granularity, 16bit selector; limit 16:19
.byte 0x00 # base 24:31
gdt16_ptr: # GDT table pointer for 16bit access
.2byte gdt16_ptr - gdt16_base - 1 # table limit (size)
.4byte gdt16_base # table base address
int32_end: # end marker (so we can copy the code)
.byte 0x00
永远不会到达带有jmp .-2atp_mode16标签的行，而是会重新启动。如果将jmp .-2放在 之前，jmpw则操作系统按预期进入无限循环。我在 QEMU 版本 2.11.1 上使用qemu-system-i386.