; tiny.asm

BITS 32

;
; MZ header
;
; The only two fields that matter are e_magic and e_lfanew

mzhdr:
    dw "MZ"       ; e_magic
    dw 0          ; e_cblp UNUSED

;
; PE signature
;

pesig:
    dd "PE"       ; e_cp, e_crlc UNUSED       ; PE signature

;
; PE header
;

pehdr:
    dw 0x014C     ; e_cparhdr UNUSED          ; Machine (Intel 386)
    dw 1          ; e_minalloc UNUSED         ; NumberOfSections

;   dd 0xC3582A6A ; e_maxalloc, e_ss UNUSED   ; TimeDateStamp UNUSED

; Entry point

start:
    push byte 42
    pop eax
    ret

    dd 0          ; e_sp, e_csum UNUSED       ; PointerToSymbolTable UNUSED
    dd 0          ; e_ip, e_cs UNUSED         ; NumberOfSymbols UNUSED
    dw sections-opthdr ; e_lsarlc UNUSED      ; SizeOfOptionalHeader
    dw 0x103      ; e_ovno UNUSED             ; Characteristics

;
; PE optional header
;
; The debug directory size at offset 0x94 from here must be 0

filealign equ 4
sectalign equ 4   ; must be 4 because of e_lfanew

%define round(n, r) (((n+(r-1))/r)*r)

opthdr:
    dw 0x10B      ; e_res UNUSED              ; Magic (PE32)
    db 8                                      ; MajorLinkerVersion UNUSED
    db 0                                      ; MinorLinkerVersion UNUSED

;
; PE code section
;

sections:
    dd round(codesize, filealign)             ; SizeOfCode UNUSED                  ; Name UNUSED
    dd 0          ; e_oemid, e_oeminfo UNUSED ; SizeOfInitializedData UNUSED
    dd codesize   ; e_res2 UNUSED             ; SizeOfUninitializedData UNUSED     ; VirtualSize
    dd start                                  ; AddressOfEntryPoint                ; VirtualAddress
    dd codesize                               ; BaseOfCode UNUSED                  ; SizeOfRawData
    dd start                                  ; BaseOfData UNUSED                  ; PointerToRawData
    dd 0x400000                               ; ImageBase                          ; PointerToRelocations UNUSED
    dd sectalign  ; e_lfanew                  ; SectionAlignment                   ; PointerToLinenumbers UNUSED
    dd filealign                              ; FileAlignment                      ; NumberOfRelocations, NumberOfLinenumbers UNUSED
    dw 4                                      ; MajorOperatingSystemVersion UNUSED ; Characteristics UNUSED
    dw 0                                      ; MinorOperatingSystemVersion UNUSED
    dw 0                                      ; MajorImageVersion UNUSED
    dw 0                                      ; MinorImageVersion UNUSED
    dw 4                                      ; MajorSubsystemVersion
    dw 0                                      ; MinorSubsystemVersion UNUSED
    dd 0                                      ; Win32VersionValue UNUSED
    dd round(hdrsize, sectalign)+round(codesize,sectalign) ; SizeOfImage
    dd round(hdrsize, filealign)              ; SizeOfHeaders
    dd 0                                      ; CheckSum UNUSED
    dw 2                                      ; Subsystem (Win32 GUI)
    dw 0                                      ; DllCharacteristics UNUSED
    dd 0                                      ; SizeOfStackReserve
    dd 0                                      ; SizeOfStackCommit
    dd 0                                      ; SizeOfHeapReserve
    dd 0                                      ; SizeOfHeapCommit
    dd 0                                      ; LoaderFlags UNUSED
    dd 2                                      ; NumberOfRvaAndSizes

;
; Data directories
;
; The debug directory size at offset 0x34 from here must be 0

    dd 0                                      ; Export Table UNUSED
    dd 0
    dd idata                                  ; Import Table
    dd idatasize

hdrsize equ $ - $$

; Import table (array of IMAGE_IMPORT_DESCRIPTOR structures)

idata:
    dd ilt                                    ; OriginalFirstThunk UNUSED
    dd 0                                      ; TimeDateStamp UNUSED
    dd 0                                      ; ForwarderChain UNUSED
    dd kernel32                               ; Name
    dd iat                                    ; FirstThunk

    ; empty IMAGE_IMPORT_DESCRIPTOR structure

    dd 0                                      ; OriginalFirstThunk UNUSED
    dd 0                                      ; TimeDateStamp UNUSED
    dd 0                                      ; ForwarderChain UNUSED
    dd 0                                      ; Name UNUSED
    dd 0                                      ; FirstThunk

idatasize equ $ - idata

; Import address table (array of IMAGE_THUNK_DATA structures)

iat:
    dd 0x80000001                             ; Import function 1 by ordinal
    dd 0

; Import lookup table (array of IMAGE_THUNK_DATA structures)

ilt:
    dd 0x80000001                             ; Import function 1 by ordinal
    dd 0

kernel32:
    db "KERNEL32.dll", 0

codesize equ $ - start

filesize equ $ - $$