Talk about which aspects or parts of linux embody the characteristics of protected mode, and explain that you need to choose a piece of linux source code (optional).

This code puts the CPU in protected mode.

Cli /* Turn off all interrupts */

mov ax，#0x0000

Cld /*DF is cleared, which increases the string operation by */

Do_move: mov es, ax /* Address of the target segment to be moved, that is, to the 0 th segment */

Add ax, #0x 1000.

Cmax, #0x9000 /* Move 9 segments * * *

Jz end_move /*** End of move * * * * * * *

Mobile ds, ax

sub di，di

sub si，si

Movcx, # 0x8000/* * The size of one move is 32K words, that is, 64K bytes * * */

Represents movsw

jmp do_move

/* * * * * * * * The above code is to move the core code from 000 1H:0000H to 0000h * */

End_move: move axis, cs

Mov ds, ax /** Because ds is used in front, it needs to be reset, otherwise it will be wrong */

Lidt idt_48 /*** * * Load interrupt descriptor table, 3 words long and 48 bits */

LGDTGDT _ 48/* * Load global descriptor table, 3 words and 48 bits */

Call empty _8042

mov al，#0xD 1

Output #0x64, al

Call empty _8042

Move al, #0xDF

Out # 0x60, Al/* * * * * * Open A20 address line * * * * * * *

Call empty _8042

Output #0x20, al

. Words 0x00eb, 0x00eb | jmp $+2, jmp $+2

2.out #0xA0, al | and to 8259A-2

. Words 0x00eb, 0x00eb

3.mov al, #0x20 | Write ICW2 to host 8259A.

Out #0x2 1, al | hardware interrupt entry address 0x20 and ICW 1

| Know interrupt vector length = 8 bytes.

. Words 0x00eb, 0x00eb

4.mov al, #0x28 | Start of hardware integer 2 (0x28)

Out #0xA 1, al | The interrupt entry of the second block 8259A is 0x28.

. Words 0x00eb, 0x00eb

5.mov al, #0x04 | 8259- 1 is the master device.

Out # 0x2 1, Al | interrupt request 2 has cascade processing.

. Words 0x00eb, 0x00eb

Mov al, #0x02 | 8259-2 is the slave.

Out #0xA 1 and al | correspond to the above. Tell everyone that I am a colleague of IR2.

| Cascading processors.

. Words 0x00eb, 0x00eb

6. mov al, #0x0 1 | 8086 mode of both.

out #0x2 1，al

. Words 0x00eb, 0x00eb

out #0xA 1，al

. Words 0x00eb, 0x00eb

Mov al, #0xFF | Temporarily mask all interrupts.

out #0x2 1，al

. Words 0x00eb, 0x00eb

out #0xA 1，al

Mov ax, #0x000 1 | protection mode (PE) bit

Lmsw ax | That's it!

JmpI 0,8 | JMP offset 0(cs) of segment 8

/* * * * * This function ensures that the keyboard command queue is empty * * * * * * *

empty_8042:

. Words 0x00eb, 0x00eb

In aluminum, #0x64

Test aluminum #2

jnz empty_8042

Soak in water to soften