startup.asm

一个类linux的dos下开发的操作系统.

	popa			; pop GP registers
	pop ds			; pop segment registers
	pop es
	pop fs
	pop gs
	add esp,8		; drop exception number and error code
	iret

; the stack is always 32 bits wide in 32-bit pmode
; the push will zero-extend (sign-extend?) the byte to 32 bits
isr0:
	push byte 0
	push byte 0
	jmp fault1		; zero divide (fault)
isr1:
	push byte 0
	push byte 1
	jmp fault1		; debug/single step
isr2:
	push byte 0
	push byte 2
	jmp fault1		; non-maskable interrupt (trap)
isr3:
	push byte 0
	push byte 3
	jmp fault1		; INT3 (trap)
isr4:
	push byte 0
	push byte 4
	jmp fault1		; INTO (trap)
isr5:
	push byte 0
	push byte 5
	jmp fault1		; BOUND (fault)
isr6:
	push byte 0
	push byte 6
	jmp fault1		; invalid opcode (fault)
isr7:
	push byte 0
	push byte 7
	jmp fault1		; coprocessor not available (fault)
isr8:
	nop
	nop
	push byte 8
	jmp fault1		; double fault (abort w/ error code)
isr9:
	push byte 0
	push byte 9
	jmp fault1		; coproc segment overrun (abort; 386/486SX only)
isr0A:
	nop
	nop
	push byte 0Ah
	jmp fault1		; bad TSS (fault w/ error code)
isr0B:
	nop
	nop
	push byte 0Bh
	jmp fault1		; segment not present (fault w/ error code)
isr0C:
	nop
	nop
	push byte 0Ch
	jmp fault1		; stack fault (fault w/ error code)
isr0D:
	nop
	nop
	push byte 0Dh
	jmp fault1		; GPF (fault w/ error code)
isr0E:
	nop
	nop
	push byte 0Eh
	jmp fault1		; page fault
isr0F:
	push byte 0
	push byte 0Fh
	jmp fault1		; reserved
isr10:
	push byte 0
	push byte 10h
	jmp fault1		; FP exception/coprocessor error (trap)
isr11:
	push byte 0
	push byte 11h
	jmp fault1		; alignment check (trap; 486+ only)
isr12:
	push byte 0
	push byte 12h
	jmp fault1		; machine check (Pentium+ only)
isr13:
	push byte 0
	push byte 13h
	jmp fault1
isr14:
	push byte 0
	push byte 14h
	jmp fault1
isr15:
	push byte 0
	push byte 15h
	jmp fault1
isr16:
	push byte 0
	push byte 16h
	jmp fault1
isr17:
	push byte 0
	push byte 17h
	jmp fault1
isr18:
	push byte 0
	push byte 18h
	jmp fault1
isr19:
	push byte 0
	push byte 19h
	jmp fault1
isr1A:
	push byte 0
	push byte 1Ah
	jmp fault1
isr1B:
	push byte 0
	push byte 1Bh
	jmp fault1
isr1C:
	push byte 0
	push byte 1Ch
	jmp fault1
isr1D:
	push byte 0
	push byte 1Dh
	jmp fault1
isr1E:
	push byte 0
	push byte 1Eh
	jmp fault1
isr1F:
	push byte 0
	push byte 1Fh
	jmp fault1

; isr20 through isr2F are hardware interrupts. The 8259 programmable
; interrupt controller (PIC) chips must be reprogrammed to make these work.
isr20:
	push byte 0
	push byte 20h
	jmp fault1		; IRQ 0/timer interrupt
isr21:
	push byte 0
	push byte 21h
	jmp fault1		; IRQ 1/keyboard interrupt
isr22:
	push byte 0
	push byte 22h
	jmp fault1
isr23:
	push byte 0
	push byte 23h
	jmp fault1
isr24:
	push byte 0
	push byte 24h
	jmp fault1
isr25:
	push byte 0
	push byte 25h
	jmp fault1
isr26:
	push byte 0
	push byte 26h
	jmp fault1		; IRQ 6/floppy interrupt
isr27:
	push byte 0
	push byte 27h
	jmp fault1
isr28:
	push byte 0
	push byte 28h
	jmp fault1		; IRQ 8/real-time clock interrupt
isr29:
	push byte 0
	push byte 29h
	jmp fault1
isr2A:
	push byte 0
	push byte 2Ah
	jmp fault1
isr2B:
	push byte 0
	push byte 2Bh
	jmp fault1
isr2C:
	push byte 0
	push byte 2Ch
	jmp fault1
isr2D:
	push byte 0
	push byte 2Dh
	jmp fault1		; IRQ 13/math coprocessor interrupt
isr2E:
	push byte 0
	push byte 2Eh
	jmp fault1		; IRQ 14/primary ATA ("IDE") drive interrupt
isr2F:
	push byte 0
	push byte 2Fh
	jmp fault1		; IRQ 15/secondary ATA drive interrupt

; syscall software interrupt
isr30:
	push byte 0
	push byte 30h
	jmp fault1

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[SECTION .data]

; 32 ring 0 interrupt gates
idt:
	times 48	dw 0, SYS_CODE_SEL, 8E00h, 0

; one ring 3 interrupt gate for syscalls (INT 30h)
	dw 0			; offset 15:0
	dw SYS_CODE_SEL		; selector
	db 0			; (always 0 for interrupt gates)
	db 0EEh			; present,ring 3,'386 interrupt gate
	dw 0			; offset 31:16

idt_end:

idt_ptr:
	dw idt_end - idt - 1	; IDT limit
	dd idt			; linear adr of IDT (set above)

; we don't use the TSS for task-switching, but we still need it to store
; the kernel (ring 0) stack pointer while user (ring 3) code is running
; (also need it for the I/O permission bitmap)
tss:
	dw 0, 0			; back link
tss_esp0:
	dd 0			; ESP0
	dw SYS_DATA_SEL, 0	; SS0, reserved

	dd 0			; ESP1
	dw 0, 0			; SS1, reserved

	dd 0			; ESP2
	dw 0, 0			; SS2, reserved

	dd 0			; CR3
	dd 0, 0			; EIP, EFLAGS
	dd 0, 0, 0, 0		; EAX, ECX, EDX, EBX
	dd 0, 0, 0, 0		; ESP, EBP, ESI, EDI
	dw 0, 0			; ES, reserved
	dw 0, 0			; CS, reserved
	dw 0, 0			; SS, reserved
	dw 0, 0			; DS, reserved
	dw 0, 0			; FS, reserved
	dw 0, 0			; GS, reserved
	dw 0, 0			; LDT, reserved
	dw 0, 103		; debug, IO permission bitmap base

; null descriptor. gdt_ptr could be put here to save a few
; bytes, but that can be confusing.
gdt:
	dw 0			; limit 15:0
	dw 0			; base 15:0
	db 0			; base 23:16
	db 0			; type
	db 0			; limit 19:16, flags
	db 0			; base 31:24

; descriptor for task-state segment (TSS)
TSS_SEL		equ	$-gdt
gdt1:
	dw 103
	dw 0
	db 0
	db 89h			; ring 0 available 32-bit TSS
	db 0
	db 0

; ring 0 kernel code segment descriptor. Segmentation is deprecated
; by setting the segment limits to 4Gig - 1 and the segment bases to 0.
SYS_CODE_SEL	equ	$-gdt
gdt2:
	dw 0FFFFh
	dw 0
	db 0
	db 9Ah			; present,ring 0,code,non-conforming,readable
	db 0CFh
	db 0

; ring 0 kernel data segment descriptor
SYS_DATA_SEL	equ	$-gdt
gdt3:
	dw 0FFFFh
	dw 0
	db 0
	db 92h			; present,ring 0,data,expand-up,writable
	db 0CFh
	db 0

; ring 3 user code segment descriptor
USER_CODE_SEL	equ	($-gdt) | 3
	dw 0FFFFh
	dw 0
	db 0
	db 0FAh			; present,ring 3,code,non-conforming,readable
	db 0CFh
	db 0

; ring 3 user data segment descriptor
USER_DATA_SEL	equ	($-gdt) | 3
	dw 0FFFFh
	dw 0
	db 0
	db 0F2h			; present,ring 3,data,expand-up,writable
	db 0CFh
	db 0

; linear data segment descriptor
LINEAR_DATA_SEL	equ	$-gdt
	dw 0FFFFh
	dw 0
	db 0
	db 92h			; present,ring 0,data,expand-up,writable
	db 0CFh
	db 0

; linear code segment descriptor
LINEAR_CODE_SEL	equ	$-gdt
	dw 0FFFFh
	dw 0
	db 0
	db 9Ah			; present,ring 0,code,non-conforming,readable
	db 0CFh
	db 0
gdt_end:

gdt_ptr:
	dw gdt_end - gdt - 1	; GDT limit
	dd gdt			; linear adr of GDT (set above)

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[SECTION .bss]

; /------- START OF 4K BOOT DATA
EXPORT _conv_mem_size		; conventional memory size (bytes)
	resd 1

EXPORT _ext_mem_size		; extended memory size (bytes)
	resd 1

EXPORT _init_ramdisk_adr	; where the initial RAM disk is loaded
	resd 1

EXPORT _init_ramdisk_size	; size of initial RAM disk
	resd 1

				; kernel command line
	times (1024 - 4) resd 1	; padding to 4K
; \------- END OF 4K BOOT DATA

; task #0 page directory and tables
;
; *** WARNING ***: page tables must be aligned to page (4K) boundaries:
; 1. make sure the linker script aligns the BSS to a page boundary
; 2. make sure the bootloader loads the kernel to a page boundary
; 3. make sure that anything placed before the page tables in the BSS
;    (i.e. the boot data) is a multiple of 4K in size.

kernel_page_dir:
	times 1024 resd 1	; kernel page dir
kernel_page_table:
	times 1024 resd 1	; page table for mapping kernel memory
ram_page_table:
	times 1024 resd 1	; page table for identity-mapping <=4 meg RAM

; task #0 kernel stack
	resd 1024
stack:

EXPORT _kvirt_to_phys
	resd 1