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fixed 2nd stage bootloader

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Gregory Kenneth Bowne 2024-03-15 15:21:51 -07:00
parent 5ff47dde28
commit 6c4ee8ed02
3 changed files with 27 additions and 3 deletions
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30
src/boot/boot2.asm
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@ -15,7 +15,7 @@ start:
switch_to_protected_mode: switch_to_protected_mode:
CLI ; Disable interrupts CLI ; Disable interrupts
LGDT [gdt_descriptor] ; Load the global descriptor table lgdt [gdt_descriptor] ; Load the global descriptor table
MOV EAX, CR0 MOV EAX, CR0
OR EAX, 0x1 ; Set the PE (Protection Enable) bit OR EAX, 0x1 ; Set the PE (Protection Enable) bit
MOV CR0, EAX MOV CR0, EAX
@ -23,7 +23,10 @@ start:
JMP CODE_SEG:init_pm ; CODE_SEG is the segment selector for code segment in GDT JMP CODE_SEG:init_pm ; CODE_SEG is the segment selector for code segment in GDT
init_pm: init_pm:
; Update segment registers here ; Update segment registers here
; ... ; Set code segment register (CS) to point to code segment descriptor (selector 1)
mov ax, 0x0001
mov ds, ax ; Set data segment register (DS) to point to data segment descriptor (selector 2)
mov es, ax ; Set other segment registers (ES, SS, etc.) as needed
RET RET
@ -62,7 +65,28 @@ start:
; Code to set up flat memory model for protected mode ; Code to set up flat memory model for protected mode
; This involves setting up the segment registers with selectors ; This involves setting up the segment registers with selectors
; that point to descriptors in the GDT that define a flat memory model ; that point to descriptors in the GDT that define a flat memory model
; ...
; Define GDT structure
gdt_struct:
; Null descriptor (ignored)
dq 0x0000000000000000h
dq 0x0000000000000000h
; Code segment descriptor (flat memory model)
; Base address 0, limit 0xffffffff (full 4GB)
; Present, Readable, Accessed, Code segment, 4KB granularity
; Flags: 0x9A (Bits explained below)
dq 0x0000000000000000h
dq 0x00CFFFFFFFh
db 0x9A
db 0xCF
; Data segment descriptor (flat memory model)
; Similar structure to code segment descriptor with Data segment flag set
dq 0x0000000000000000h
dq 0x00CFFFFFFFh
db 0x92
db 0xCF
; Jump to the kernel entry point ; Jump to the kernel entry point
JMP 0x1000:0x0000 ; Assuming the kernel is loaded at 0x1000:0x0000 JMP 0x1000:0x0000 ; Assuming the kernel is loaded at 0x1000:0x0000