;INFO: Debugger standardne nespracovava obsluhy vynimiek (pokial to nema nastavene)
;      Tento Anti-Debug tento fakt vyuziva a spolieha sa na to, ze SEH_handler (catch sekvencia) sa nemusi vykonat vzdy automaticky
;      Aplikacia spustena bez debuggera vykona SEH_HANDLER automaticky
;Nastavenie:
;      Zapnut: "Options->Options | Exceptions | Integer division by 0"	- pripadne aj dalsie druhy vynimiek (ak je chyba sposobena cez inu vynimku)
;
;
;Pre lepsie pochopenie obdobny kod v C++:
;  dbg_found = 1;
;  try {
;    int i = 5 / 0; //sposobenie chyby.
;  } catch (..){
;    dbg_found = 0;
;  }
;  if (dbg_found==1) {
;    ShowMessage("FOUND..",..)
;  } else {
;    ShowMessage("OK..",..)
;  }


format PE GUI 4.0 at 0x400000

include 'win32a.inc'

section '.text' code readable executable
		; We clear our information about breakpoint
		mov dword [DBG_FOUND], 1
		
		; SEH Handler "installation"
		push SEH_HANDLER
		push dword [fs:0]
		mov [fs:0], ESP
		
		; chyba c.1: - na tejto chybe debugger zastane a nedovoli ju prejst
		xor eax, eax
		idiv eax  ;this cause exception (0 div 0 = error :-) , handler "SEH_HANDLER" is executed!)
		; chyba c.2: - zebugger zastane, ale po stlaceni F8 touto debugger "prelezie"
		;int 02dh ; Tato chyba vyzaduje zaskrtnut aj  "INT 3 breaks" druh chyby
		
		;tieto tri nopy by sa nemali nikdy vykonat. pri chybe c.2 a pri postupnom krokovani sa vsak vykonaju
		nop
		nop
		nop
		
	SEH_UNWIND:
		pop dword [fs:0]
		add esp, 4
		
	CONTINUE_H:
		cmp [DBG_FOUND], 1
		je MSG_FOUND
	MSG_OK:
		invoke MessageBoxA, 0, message_ok	,message_caption, MB_OK+MB_ICONINFORMATION
		jmp EXIT
	MSG_FOUND:
		invoke MessageBoxA, 0, message_found,message_caption, MB_OK+MB_ICONINFORMATION
	EXIT:
		ret
	;------------------------------------------------
	SEH_HANDLER:
		mov dword [DBG_FOUND],0
		mov edx, [esp+0Ch]		      ; CONTEXT
		mov dword [edx+0B8h], SEH_UNWIND  ; CONTEXT.EIP
		mov eax,0 ; OK
		ret
	;------------------------------------------------

section '.bss' readable writeable
	DBG_FOUND	dd ?

section '.data' readable
	message_caption db 'MSG',0
	message_ok	    db 'OK',0
	message_found   db 'Debugger found!',0
section '.idata' import data readable writeable
	library \
		kernel32,'KERNEL32.DLL',\
		user32	,'USER32.DLL'
	import kernel32,\
		VirtualProtect	   ,'VirtualProtect'
	import user32,\
		MessageBoxA	   ,'MessageBoxA'

;section '.reloc' fixups data readable discardable