Modify pmtest1.asm to start and enter the protection mode as bootloader.

; ========================================================== =

; Pmtest1.asm

; Compilation Method: NASM pmtest1.asm-O pmtest1.com

The segment definition is removed to determine that the 55aa mark is added to the 512 byte

; ========================================================== =

 

% Include "PM. Inc"; constants, macros, and descriptions

 

Org07c00h

Jmplabel_begin

 

; Gdt

; Segment Base Address, segment boundaries, attributes

Label_gdt: descriptor 0, 0, 0; empty Descriptor

Label_desc_code32: descriptor 0, segcode32len-1, da_c + da_32; inconsistent code segment, 32

Label_desc_video: descriptor 0b8000h, 0 ffffh, da_drw; first video address

; Gdt ended

 

Gdtlenequ $-label_gdt; gdt Length

Gdtptrdwgdtlen-1; gdt Boundary

Dd0; gdt base address

 

; Gdt Select Sub-

Selectorcode32equlabel_desc_code32-label_gdt

Selectorvideoequlabel_desc_video-label_gdt

 

 

[Bits16]

Label_begin:

Movax, CS

Movds, ax

Moves, ax

Movss, ax

Movsp, 0100 H

 

; Initialize 32-bit code segment descriptor

Xoreax, eax

Movax, CS

Shleax, 4

Addeax, label_seg_code32

Movword [label_desc_code32 + 2], ax

Shreax, 16

Movbyte [label_desc_code32 + 4], Al

Movbyte [label_desc_code32 + 7], ah

 

Prepare for loading GDTR

Xoreax, eax

Movax, DS

Shleax, 4

Addeax, label_gdt; eax <-gdt base address

Movdword [gdtptr + 2], eax; [gdtptr + 2] <-gdt base address

 

; Load GDTR

Lgdt [gdtptr]

 

; Guanzhong disconnection

CLI

 

; Open address line A20

Inal, 92 h

Oral, 00000010b

Out92h, Al

 

; Prepare to switch to protection mode

Moveax, Cr0

Oreax, 1

Movcr0, eax

 

To enter the protection mode, modify the code here and try the redirection with an offset.

Jmpword selectorcode32: offset_32; execute this statement to load selectorcode32 into CS and jump to code32selector: 0

 

 

[Bits32]

 

Label_seg_code32:

 

Times 100 db 0; add meaningless code to test redirection with a low cost

Label_start:

Offset_32equlabel_start-label_seg_code32

Movax, selectorvideo

Movgs, ax; video segment Selection Sub-(Purpose)

 

Movedi, (80*10 + 0) * 2; screen 10th rows, 0th columns.

Movah, 0ch; 0000: Black Bottom 1100: Red Letter

Moval, 'P'

MoV [GS: EDI], ax

 

; Stop now

JMP $

 

Segcode32lenequ $-label_seg_code32

 

Times 510-($-$) db0; fill in the remaining space to make the generated binary code exactly 210 bytes

DW 0xaa55; End mark