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October 31, 2010 22:16
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This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -1,3 +1,7 @@ ; vim:ts=8:sts=8:sw=8:filetype=nasm: ; This is the real bootstrap of the kernel, and ; it is this part that is loaded by the boot sector (boot.asm) org 0 bits 16 @@ -19,52 +23,159 @@ bits 16 RX_ACCESS equ 10011010b RW_ACCESS equ 10010010b code_seg equ 8 data_seg equ 16 start: mov ax,cs mov ds,ax mov ax,0x0e00+'A' mov bl,0x0f int 10h cli mov al,0xff out 0xa1, al mov al,0xfb out 0x21, al mov ax,0x0e00+'B' mov bl,0x0f int 10h ; Protect Enable -> 1 mov eax,cr0 or eax,1 mov cr0,eax lidt [idtr] lgdt [gdtr] ; Reset cs by far-jumping to the other side jmp code_seg:dword start32+0x8000 bits 32 start32: mov ax,data_seg mov ds,ax mov es,ax mov fs,ax mov gs,ax mov ss,ax mov ebx, 0xb8000 mov edi, ebx xor eax,eax mov ecx,2*80*25/4 ; 125 << 3 rep stosd mov word [ebx],0x0f00+'P' ; magic flag time: ; All entries have the same lower 4 bits (all set to 1 here): ; - present (bit 0) ; - Read-only/Writable (bit 1), 1 = Writable ; - User/Supervisor bit (bit 2), 1 = Accessible from user mode ; - Page-level writethrough (bit 3) ; For the final one, we set a couple more flags: ; - Global (bit 8), along with PGE, the page will remain in TLB after ; changing the page tables, we promise that the page has the same ; mapping in all tables. ; - Page Size (bit 7), this is the final page entry rather than a link ; to another table. In our case, this makes this a 2MB page since the ; bit is set already in the third level. ; Write PML4 (one entry, pointing to one PDP) mov edi, 0xa000 ; base address, where we put the PML4's mov eax, 0xb00f ; 0xb000 is where the PDP starts, 0xf is magic stosd xor eax,eax mov ecx, 0x03ff ; number of zero double-words in PML4 rep stosd ; Write PDP (one entry, pointing to one PD) mov eax, 0xc00f ; 0xc000 is the start of the PD stosd xor eax,eax mov ecx, 0x03ff ; number of zero double-words in PDP rep stosd ; Write PD (one entry mapped, address 0, plus flags) mov eax, 0x018f ; magic constant (see above) stosd xor eax,eax mov ecx, 0x03ff rep stosd ; Start mode-switching mov eax, 10100000b ; PAE and PGE mov cr4, eax mov edx, 0xa000 ; address of PML4 mov cr3, edx mov ecx, 0xc0000080 ; EFER MSR rdmsr or eax, 0x100 ; Set LME wrmsr mov eax,cr0 or eax,0x80000000 ; Enable paging mov cr0,eax ; Set code segment to L=1,D=0 xor eax,eax mov edi,gdt_start+0x8000+8 mov ecx,4 rep stosd mov word [gdt_start+8+5+0x8000], 0x2098 mov byte [gdt_start+16+5+0x8000], 0x90 jmp code_seg:dword start64+0x8000 bits 64 start64: mov ax,data_seg mov ds,ax mov edi,0xb8004 ; Just do something silly that should fail if we weren't in long mode shl rdi,32 test edi,edi jnz not_long shr rdi,32 ; Then proceed to write a message mov esi,message+0x8000 mov ecx,2 rep movsq mov rax,8 ; Random jmp $ not_long: ud2 message: dq 0x0747074e074f074c, 0x07450744074f074d gdt_start: define_descriptor 0,0,0,0,0,0 define_descriptor 0xffff,0,0,RX_ACCESS,0xcf,0 define_descriptor 0xffff,0,0,RW_ACCESS,0xcf,0 gdt_end: align 4 gdtr: dw gdt_end-gdt_start-1 ; Limit dd gdt_start+0x8000 ; Offset idtr: dw 0 dd 0 times 4096-($-$$) db 0 -
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This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -1,15 +1,6 @@ org 0 bits 16 %macro define_descriptor 6 ; 0-6 0,0,0,0,0,0 dw %1 ;seg_limit dw %2 ;addr_00_15 -
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This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -0,0 +1,79 @@ org 0 bits 16 struc Descriptor seg_limit: resw 1 addr_00_15: resw 1 addr_16_23: resb 1 access: resb 1 granularity: resb 1 addr_24_31: resb 1 endstruc %macro define_descriptor 6 ; 0-6 0,0,0,0,0,0 dw %1 ;seg_limit dw %2 ;addr_00_15 db %3 ;addr_16_23 db %4 ;flags db %5 ;access db %6 ;addr_24_31 %endmacro ; Bit Field ; 7 Present = 1 ; 6..5 Ring == 0 ; 4 Descriptor type == 1 ; 3..0 Type = cs: 1010, ds: 0010 RX_ACCESS equ 10011010b RW_ACCESS equ 10010010b jmp start align 4 init_gdt: define_descriptor 0,0,0,0,0,0 define_descriptor 0xffff,0,0,RX_ACCESS,0xcf,0 define_descriptor 0xffff,0,0,RW_ACCESS,0xcf,0 gdt_end: code_seg equ 8 data_seg equ 16 gdtr: dw gdt_end-init_gdt-1 ; Limit dd init_gdt+0x8000 ; Offset align 4 idtr: dw 0 dd 0 start: [...] ; Protect Enable -> 1 mov eax,cr0 or eax,1 mov cr0,eax lidt [ds:idtr] lgdt [ds:gdtr] ; Reset cs by far-jumping to the other side jmp code_seg:dword other_side+0x8000 bits 32 other_side: mov ax,data_seg mov ds,ax mov es,ax mov fs,ax mov gs,ax mov ss,ax start32: mov ebx,0xb8000 mov [ds:0xb8000], byte 0x43 inc ebx mov [ds:0xb8001], byte 0x0f hlt