format PE GUI
entry start

include 'win32a.inc'

section '.text' code readable executable

  start:
    ; get handle to calling process
    push    0
    call    [GetModuleHandleA]

    ; make page writeable
    push    esp     ; old protect
    push    4       ; option PAGE_READWRITE
    push    1       ; size
    push    eax     ; address of starting page
    mov edi, eax    ; save handle in edi
    call    [VirtualProtect]

    ; erase header
    xor ecx, ecx
    mov ch, 0x10    ; set counter to 0x1000
    xor eax, eax    ; fill with 0 bytes
    rep stosb       ; will erase 0x1000 bytes
                    ; starting at edi = handle
    ; show our message
    push    0           ; type MB_OK
    push    _caption    ; dialog title
    push    _message    ; message
    push    0           ; no owner window
    call    [MessageBoxA]

    push    0           ; success
    call    [ExitProcess]

section '.data' data readable writeable

  _caption db 'Win32 assembly program',0
  _message db 'Header is erased, now try dumping',0

section '.idata' import data readable writeable

  library kernel,'KERNEL32.DLL',\
      user,'USER32.DLL'

  import kernel,\
     GetModuleHandleA, 'GetModuleHandleA',\
     ExitProcess,'ExitProcess',\
     VirtualProtect,'VirtualProtect'

  import user,\
     MessageBoxA, 'MessageBoxA'

section '.reloc' fixups data readable discardable