DEFAULT_HANDLER_SIZE:	equ 9			; size of exception/interrupt stub
SYS_CODE_SEL:		equ 0x20		; 32-bit code selector in GDT
PE_OFFSET_IN_MZ_STUB:	equ 0x3c		; place in MsDos stub for offset to PE Header
VGA_FB:			equ 0x000b8000		; VGA framebuffer for 80x25 mono mode
VGA_LINE:		equ 80 * 2		; # bytes in one line
BASE_ADDR_32:		equ 0x00021000
STACK_TOP:		equ 0x001ffff0
SIZE:			equ 0x1000

struc EFILDR_IMAGE
.CheckSum:	resd 1
.Offset:	resd 1
.Length:	resd 1
.FileName:	resb 52
endstruc

struc EFILDR_HEADER
.Signature:		resd 1
.HeaderCheckSum:	resd 1
.FileLength:		resd 1
.NumberOfImages:	resd 1
endstruc

struc PE_HEADER
			resb 6
.NumberOfSections:	resw 1
			resb 12
.SizeOfOptionalHeader:	resw 1
			resb 2
.Magic:			resb 16
.AddressOfEntryPoint:	resd 1
			resb 8
.ImageBase32:		resd 1
endstruc

struc PE_SECTION_HEADER
			resb 12
.VirtualAddress:	resd 1
.SizeOfRawData:		resd 1
.PointerToRawData:	resd 1
			resb 16
endstruc

%macro StubWithNoCode 1
	push	0	; push error code place holder on the stack
	push	%1
	jmp	strict dword commonIdtEntry
%endmacro

%macro StubWithACode 1
	times 2 nop
	push	%1
	jmp	strict dword commonIdtEntry
%endmacro

%macro PrintReg 2
	mov	esi, %1
	call	PrintString
	mov	eax, [ebp + %2]
	call	PrintDword
%endmacro

	bits 32
	org BASE_ADDR_32
global _start
_start:
	mov	ax, bx
	mov	ds, eax
	mov	es, eax
	mov	fs, eax
	mov	gs, eax
	mov	ss, eax
	mov	esp, STACK_TOP

;
; Populate IDT with meaningful offsets for exception handlers...
;
	sidt	[Idtr]

	mov	eax, StubTable
	mov	ebx, eax		; use bx to copy 15..0 to descriptors
	shr	eax, 16			; use ax to copy 31..16 to descriptors
	mov	ecx, 0x78		; 78h IDT entries to initialize with unique entry points
	mov	edi, [Idtr + 2]

.StubLoop:	; loop through all IDT entries exception handlers and initialize to default handler
	mov	[edi], bx			; write bits 15..0 of offset
	mov	word [edi + 2], SYS_CODE_SEL	; SYS_CODE_SEL from GDT
	mov	word [edi + 4], 0x8e00		; type = 386 interrupt gate, present
	mov	[edi + 6], ax			; write bits 31..16 of offset
	add	edi, 8				; move up to next descriptor
	add	ebx, DEFAULT_HANDLER_SIZE	; move to next entry point
	loop	.StubLoop			; loop back through again until all descriptors are initialized

;
; Load EFILDR
;
	mov	esi, BlockSignature + 2
	add	esi, [esi + EFILDR_HEADER_size + EFILDR_IMAGE.Offset]	; esi = Base of EFILDR.C
	mov	ebp, [esi + PE_OFFSET_IN_MZ_STUB]
	add	ebp, esi					; ebp = PE Image Header for EFILDR.C
	mov	edi, [ebp + PE_HEADER.ImageBase32]		; edi = ImageBase
	mov	eax, [ebp + PE_HEADER.AddressOfEntryPoint]	; eax = EntryPoint
	add	eax, edi					; eax = ImageBase + EntryPoint
	mov	[.EfiLdrOffset], eax				; Modify jump instruction for correct entry point

	movzx	ebx, word [ebp + PE_HEADER.NumberOfSections]	; bx = Number of sections
	movzx	eax, word [ebp + PE_HEADER.SizeOfOptionalHeader]; ax = Optional Header Size
	add	ebp, eax
	add	ebp, PE_HEADER.Magic				; ebp = Start of 1st Section

.SectionLoop:
	push	esi						; Save Base of EFILDR.C
	push	edi						; Save ImageBase
	add	esi, [ebp + PE_SECTION_HEADER.PointerToRawData]	; esi = Base of EFILDR.C + PointerToRawData
	add	edi, [ebp + PE_SECTION_HEADER.VirtualAddress]	; edi = ImageBase + VirtualAddress
	mov	ecx, [ebp + PE_SECTION_HEADER.SizeOfRawData]	; ecx = SizeOfRawData

	cld
	shr	ecx, 2
	rep movsd

	pop	edi				; Restore ImageBase
	pop	esi				; Restore Base of EFILDR.C

	add	ebp, PE_SECTION_HEADER_size	; ebp = Pointer to next section record
	dec	ebx
	jnz	.SectionLoop

	movzx	eax, word [Idtr]	; get size of IDT
	inc	eax
	add	eax, [Idtr + 2]		; add to base of IDT to get location of memory map...
	push	eax			; push memory map location on stack for call to EFILDR...

	push	eax			; push return address (useless, just for stack balance)

.EfiLdrOffset:	equ $ + 1
	mov	eax, 0x00401000
	jmp	eax			; jump to entry point

StubTable:
%assign i 0
%rep 8
	StubWithNoCode  i
%assign i i+1
%endrep
	StubWithACode   8	; Double Fault
	StubWithNoCode  9
	StubWithACode  10	; Invalid TSS
	StubWithACode  11	; Segment Not Present
	StubWithACode  12	; Stack Fault
	StubWithACode  13	; GP Fault
	StubWithACode  14	; Page Fault
	StubWithNoCode 15
	StubWithNoCode 16
	StubWithACode  17	; Alignment Check
%assign i 18
%rep 102
	StubWithNoCode i
%assign i i+1
%endrep

commonIdtEntry:
	pushad
	mov	ebp, esp
;
;   At this point the stack looks like this:
;
;       eflags
;       Calling CS
;       Calling EIP
;       Error code or 0
;       Int num or 0ffh for unknown int num
;       eax
;       ecx
;       edx
;       ebx
;       esp
;       ebp
;       esi
;       edi <------- ESP, EBP
;

;	call	ClearScreen
	mov	edi, VGA_FB
	mov	esi, String1
	call	PrintString
	mov	eax, [ebp + 8 * 4]		; move Int number into EAX
	cmp	eax, 19
	ja	.PrintDefaultString
	mov	esi, [eax * 4 + StringTable]	; get offset from StringTable to actual string address
	jmp	.PrintTheString
.PrintDefaultString:
	mov	esi, IntUnknownString
; patch Int number
	mov	edx, eax
	call	A2C
	mov	[esi + 1], al
	mov	eax, edx
	shr	eax, 4
	call	A2C
	mov	[esi], al
.PrintTheString:
	call	PrintString
	PrintReg String2, 11 * 4	; CS
	mov	byte [edi], ':'
	add	edi, 2
	mov	eax, [ebp + 10 * 4]	; EIP
	call	PrintDword
	mov	esi, String3
	call	PrintString

	mov	edi, VGA_FB + 2 * VGA_LINE

	PrintReg StringEax, 7 * 4

	PrintReg StringEbx, 4 * 4

	PrintReg StringEcx, 6 * 4

	PrintReg StringEdx, 5 * 4

	PrintReg StringEcode, 9 * 4

	mov	edi, VGA_FB + 3 * VGA_LINE

	PrintReg StringEsp, 3 * 4

	PrintReg StringEbp, 2 * 4

	PrintReg StringEsi, 4

	PrintReg StringEdi, 0

	PrintReg StringEflags, 12 * 4

	mov	edi, VGA_FB + 5 * VGA_LINE

	mov	esi, ebp
	add	esi, 13 * 4	; stack beyond eflags
	mov	ecx, 8

.OuterLoop:
	push	ecx
	mov	ecx, 8
	mov	edx, edi

.InnerLoop:
	mov	eax, [esi]
	call	PrintDword
	add	esi, 4
	mov	byte [edi], ' '
	add	edi, 2
	loop	.InnerLoop

	pop	ecx
	add	edx, VGA_LINE
	mov	edi, edx
	loop	.OuterLoop

	mov	edi, VGA_FB + 15 * VGA_LINE

	mov	esi, [ebp + 10 * 4]	; EIP
	sub	esi, 32 * 4		; code preceding EIP

	mov	ecx, 8

.OuterLoop1:
	push	ecx
	mov	ecx, 8
	mov	edx, edi

.InnerLoop1:
	mov	eax, [esi]
	call	PrintDword
	add	esi, 4
	mov	byte [edi], ' '
	add	edi, 2
	loop	.InnerLoop1

	pop	ecx
	add	edx, VGA_LINE
	mov	edi, edx
	loop	.OuterLoop1

.Halt:
	hlt
	jmp	.Halt
;
; Return
;
	mov	esp, ebp
	popad
	add	esp, 8 ; error code and INT number
	iretd

PrintString:
	push	eax
.loop:
	mov	al, [esi]
	test	al, al
	jz	.done
	mov	[edi], al
	inc	esi
	add	edi, 2
	jmp	.loop
.done:
	pop	eax
	ret

; EAX contains dword to print
; EDI contains memory location (screen location) to print it to

PrintDword:
	push	ecx
	push	ebx
	push	eax
	mov	ecx, 8
.looptop:
	rol	eax, 4
	mov	bl, al
	and	bl, 15
	add	bl, '0'
	cmp	bl, '9'
	jbe	.is_digit
	add	bl, 7
.is_digit:
	mov	[edi], bl
	add	edi, 2
	loop	.looptop
	pop	eax
	pop	ebx
	pop	ecx
	ret

ClearScreen:
	push	eax
	push	ecx
	mov	ax,  0x0c20
	mov	edi, VGA_FB
	mov	ecx, 80 * 25
	rep stosw
	mov	edi, VGA_FB
	pop	ecx
	pop	eax
	ret

A2C:
	and	al, 15
	add	al, '0'
	cmp	al, '9'
	jbe	.is_digit
	add	al, 7
.is_digit:
	ret

String1:	db '*** INT ', 0

Int0String:	db '00h Divide by 0 -', 0
Int1String:	db '01h Debug exception -', 0
Int2String:	db '02h NMI -', 0
Int3String:	db '03h Breakpoint -', 0
Int4String:	db '04h Overflow -', 0
Int5String:	db '05h Bound -', 0
Int6String:	db '06h Invalid opcode -', 0
Int7String:	db '07h Device not available -', 0
Int8String:	db '08h Double fault -', 0
Int9String:	db '09h Coprocessor seg overrun (reserved) -', 0
Int10String:	db '0Ah Invalid TSS -', 0
Int11String:	db '0Bh Segment not present -', 0
Int12String:	db '0Ch Stack fault -', 0
Int13String:	db '0Dh General protection fault -', 0
Int14String:	db '0Eh Page fault -', 0
Int15String:	db '0Fh (Intel reserved) -', 0
Int16String:	db '10h Floating point error -', 0
Int17String:	db '11h Alignment check -', 0
Int18String:	db '12h Machine check -', 0
Int19String:	db '13h SIMD Floating-Point Exception -', 0
IntUnknownString:	db '??h Unknown interrupt -', 0

	align 4, db 0

StringTable:
%assign i 0
%rep 20
	dd Int%[i]String
%assign i i+1
%endrep

String2:	db ' HALT!! *** (', 0
String3:	db ')', 0
StringEax:	db 'EAX=', 0
StringEbx:	db ' EBX=', 0
StringEcx:	db ' ECX=', 0
StringEdx:	db ' EDX=', 0
StringEcode:	db ' ECODE=', 0
StringEsp:	db 'ESP=', 0
StringEbp:	db ' EBP=', 0
StringEsi:	db ' ESI=', 0
StringEdi:	db ' EDI=', 0
StringEflags:	db ' EFLAGS=', 0

	align 2, db 0
Idtr:
	times SIZE - 2 - $ + $$ db 0
BlockSignature:
	dw 0xaa55