127 lines
2.9 KiB
NASM
127 lines
2.9 KiB
NASM
[BITS 16]
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global entry
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entry:
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cli ; no interrupts
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xor ax,ax
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mov ds, ax
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lgdt [gdt_desc] ; load gdt register
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mov eax, cr0 ; set pmode bit
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or al, 1
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mov cr0, eax
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jmp 08h:Pmodecode
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[BITS 32]
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Pmodecode:
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mov ax, 0x10 ; set up segments
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov ebp, 0x400000
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mov esp, ebp
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mov eax, 0x1f001f00
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mov ecx, (80*25)/2
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mov edi, 0xb8000
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rep stosd ; clear screen
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call start
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hlt_loop:
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hlt
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jmp hlt_loop
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extern start
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; currently unused first 8MB identity paging
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; taken from Linux 0.01
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setup_paging:
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mov ecx, 1024*3 ; 3K?
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xor eax, eax
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mov edi, 0x1000
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rep stosd ; zero first 3K for some reason
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mov edi, 0x4000
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mov eax, 0x800007 ; 8MB + 7
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std ; fill backwards
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.fill:
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stosd
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sub eax, 0x1000
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jge .fill
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cld ; fix direction
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mov dword [0x0000], 0x2000 + 7
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mov dword [0x0004], 0x3000 + 7
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mov eax, 0x1000
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mov cr3, eax ; page dir start 0x1000
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mov eax, cr0
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or eax, 0x80000000
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mov cr0, eax ; set paging bit
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ret ; flushes pre-fetch queue
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user_test:
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mov dword [0xb8000], 0x0f000f00 | 'U' | 's' << 16
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mov dword [0xb8004], 0x0f000f00 | 'e' | 'r' << 16
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mov dword [0xb8008], 0x0f000f00 | 'm' | 'o' << 16
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mov dword [0xb800C], 0x0f000f00 | 'd' | 'e' << 16
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mov word [0xb8010], 0x0f00 | '!'
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mov edi, 0xA0000
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xor eax, eax
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.loop:
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mov cx, 320
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rep stosb
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inc al
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cmp eax, 200
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jl .loop
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xor ebx, ebx
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div bl
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global jmp_usermode_test
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jmp_usermode_test:
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mov ax, 0x20 | 3
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov eax, esp
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push 0x20 | 3
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push eax
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pushfd
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push 0x18 | 3
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push user_test
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iret
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global flushTSS
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flushTSS:
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mov ax, 0x28
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ltr ax
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ret
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extern tss_data
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gdt_desc:
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dw gdt_end - gdt
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dd gdt
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gdt:
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gdt_null: dq 0
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gdt_code: dw 0xFFFF, 0 ; bits 0-15 limit (4GB), bits 0-15 base address
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db 0 ; bits 16-23 base address
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db 10011010b ; access byte
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db 11001111b ; bits 16-19 limit (4GB), 4 bits flags
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db 0 ; bits 24-31 base address
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gdt_data: dw 0xFFFF, 0 ; bits 0-15 limit (4GB), bits 0-15 base address
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db 0 ; bits 16-23 base address
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db 10010010b ; access byte
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db 11001111b ; bits 16-19 limit (4GB), 4 bits flags
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db 0 ; bits 24-31 base address
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gdt_r3code: dw 0xFFFF, 0 ; bits 0-15 limit (4GB), bits 0-15 base address
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db 0 ; bits 16-23 base address
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db 0xFA ; access byte
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db 11001111b ; bits 16-19 limit (4GB), 4 bits flags
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db 0 ; bits 24-31 base address
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gdt_r3data: dw 0xFFFF, 0 ; bits 0-15 limit (4GB), bits 0-15 base address
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db 0 ; bits 16-23 base address
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db 0xF2 ; access byte
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db 11001111b ; bits 16-19 limit (4GB), 4 bits flags
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db 0 ; bits 24-31 base address
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gdt_tss: dw 0x2080, 0x0000;26*4, tss_data ; bits 0-15 limit (4GB), bits 0-15 base address
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db 0x2 ; bits 16-23 base address
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db 0x89 ; access byte
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db 00000000b ; bits 16-19 limit (4GB), 4 bits flags
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db 0 ; bits 24-31 base address
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gdt_end:
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