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make unreal mode unreal again

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This commit is contained in:
Elaina Claus
2025-09-05 11:45:46 -04:00
parent 2e2b4f991d
commit 01ec6da0cc
1 changed files with 22 additions and 48 deletions
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64
src/stage2/stage2.nasm
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@@ -149,7 +149,7 @@ main:
add sp, 0x6
call SetTextMode
call disable_cursor
call disable_cursor_bios
print_string HelloPrompt_info
; enable A20 gate
@@ -185,14 +185,6 @@ main:
hcf:
ERROR STEVIA_DEBUG_OK
; ##############################
;
; SYSTEM CONFIGURATION FUNCTIONS
;
; ##############################
; ##############################
;
; SYSTEM CONFIGURATION FUNCTIONS
@@ -201,56 +193,38 @@ hcf:
ALIGN 4, db 0x90
EnterUnrealMode:
__CDECL16_ENTRY
cli ; no interrupts
.func:
cli ; no interrupts
push ds ; save real mode data/stack selectors
push es
push fs
push gs
push ss
push cs ; save real mode code selector
xor ax, ax ;
pop ax ; save cs to ax to setup far jump
mov word [__UNREAL_SEGMENT], ax
lgdt [((__STAGE2_SEGMENT << 4) + unreal_gdt_info)] ; load unreal gdt
mov eax, cr0
or al,1 ; set pmode bit
mov cr0, eax ; switch to pmode
jmp short $+2
jmp short $+2 ; i-cache flush
;jmp far 0x0008:EnterUnrealMode.load_cs
; set cs to a pm code segment (0x8) w/ the following
;jmp far 0x0008:EnterUnrealMode.set_segs
db 0xEA ; jmp far imm16:imm16
dw EnterUnrealMode.load_cs ; error_far_ptr
dw EnterUnrealMode.set_segs ; error_far_ptr
dw 0x0008 ; error_far_seg
.load_cs:
mov bx, 0x10 ; select descriptor 2
mov ds, bx ; 10h = 0001_0000b
mov ss, bx
mov es, bx
mov fs, bx
mov gs, bx ; other data/stack to index 2 (off 0x10)
.set_segs:
mov ax, 0x10 ; select descriptor 2
mov ds, ax ; 10h = 0001_0000b
mov es, ax ; es to big data
mov ss, ax ; big stack
mov fs, ax
mov gs, ax ; extra segments to big data as well
.pm_start:
; code here is running in protected mode
.pm_end:
mov eax, cr0
and al,0xFE ; toggle bit 1 of cr0
mov cr0, eax ; back to realmode
jmp short $+2
jmp short $+2 ; i-cache flush
;jmp far 0x0008:EnterUnrealMode.unload_cs
db 0xEA ; jmp far imm16:imm16
dw EnterUnrealMode.unload_cs ; error_far_ptr
__UNREAL_SEGMENT:
dw 0x0000 ; error_far_seg
EnterUnrealMode.unload_cs:
pop ss
pop gs
pop fs
pop es
pop ds ; get back old segments
sti
.endp:
sti ; re-enable interupts
__CDECL16_EXIT
ret
end_text: