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EXELOADADDR 	equ 0x00100000
;; _IMAGE_DOS_HEADER.e_magic: Should be "MZ"
sigMZ			equ esi
;; _IMAGE_DOS_HEADER.e_lfanew: Offset into file where PE header is
PEheaderOffset	equ esi+60
;; _IMAGE_NT_HEADERS.Signature: Should be "PE\0\0"
sigPE			equ esi
;; _IMAGE_NT_HEADERS.FileHeader.NumberOfSections: Self explanatory
NumSections		equ esi+6
;; _IMAGE_NT_HEADERS.IMAGE_OPTIONAL_HEADERS.BaseOfCode: Where the code section should go
BaseOfCode		equ esi+52
;; _IMAGE_NT_HEADERS.IMAGE_OPTIONAL_HEADERS.AddressOfEntryPoint: Offset, relative to load address, of the entry point
EntryAddressOffset	equ esi+40
;; sizeof(_IMAGE_NT_HEADERS.IMAGE_OPTIONAL_HEADERS) + sizeof(_IMAGE_NT_HEADERS.FileHeader): to get to the section directory
SizeOfNT_HEADERS	equ 248

SectionSize		equ esi+8

SectionBase		equ esi+12

SectionFileOffset	equ esi+20

SizeOfSECTION_HEADER	equ 40

	;; Now, let's map in the PE file and run it!
	
	mov esi, EXELOADADDR
	mov eax, [sigMZ]
	;; Compare the first signature
	cmp ax, 0x5A4D
	jnz badPE
	;; If we got here, it's a 'valid' exe.
	;; Let's get the offset to the PE header:
	mov eax, [PEheaderOffset]
	
	add esi, eax
	mov eax, [sigPE]
	;; Now the second
	cmp eax, 0x00004550
	jnz badPE2
	
	;; let us assume (for now) that the PE is for the x86 platform,
	;;  and not, say, ARM or something...
	
	xor edx, edx
	mov dx, [NumSections]
	mov eax, [BaseOfCode]
	mov ebx, [EntryAddressOffset]
	
	;; Add the base of the code to the entry point offset
	;; to get the function pointer
	add ebx, eax
	;; ebx now equals loader's entry point, so let's save it
	push ebx
	
	;; skip the PE header, since we don't need the rest for this simple loader
	add esi, SizeOfNT_HEADERS

.loadloop:
	;; eax still contains BaseOfCode
	;; and dx still contains the number of sections

	;; Get the size of the section
	mov ecx, [SectionSize]
	;; Get the relative address of the section
	mov edi, [SectionBase]
	;; calculate the actual address of the section
	add edi, eax
	;; now get the file offset of the section
	mov ebx, [SectionFileOffset]
	;; and add the load address to get the memory location of the section
	add ebx, EXELOADADDR
	
	;; save where we are in the file
	push esi
	
	;; and copy the section data
	mov esi, ebx
	rep movsb
	
	;; restore our location...
	pop esi
	;; and skip to the next section
	add esi, SizeOfSECTION_HEADER
	
	;; That's one more section down
	dec edx
	;; Are we done yet?
	or edx, edx
	jnz .loadloop

	;; Yes we are! Let's get the entry function pointer and go there!
	pop ebx
	jmp ebx

badPE:
	call cls32
	mov esi, fbLoaderBad
	call putStr32
	cli
	hlt

badPE2:
	call cls32
	mov esi, fbLoaderBad2
	call putStr32
	cli
	hlt

fbLoaderBad:
	db "/BOOT/FBLOADER.EXE is not a valid executable file!",0

fbLoaderBad2:
	db "/BOOT/FBLOADER.EXE is not a Win32/Firebird executable file!",0