Hi, is it possible somehow to get size or end address of a procedure, preferably without modifying procedure itself?

 

e.g:

 

Procedure Asem;

begin

asm

 mov eax, 5;

 add eax,8

 shl eax,1

end;

end;

I want from my application determine size(number of  bytes) of its own procedure, let's say, when I press a button. It's quite easy by using pointers to get start address of first line mov eax, 5, but how to get address of the last line(eventually RET)? For the sake of simplicity let's say the procedure is pretty simple with only one exit point and no external jumps outside of itself.

 

 

 

For sake of simplicity, use address of first byte of the next procedure.

{$APPTYPE CONSOLE}

uses Windows, Classes, Sysutils;

 

Procedure Asem;

begin

asm

 mov eax, 5;

 add eax,8

 shl eax,1

end;

end;

 

Procedure Bla;

begin

   Writeln('whatever');

end;

 

begin

   Writeln(Format('start of Asem: 0x%x', [dword(@Asem)]));

   Writeln(Format('start of next proc: 0x%x', [dword(@Bla)]));

   Writeln(Format('approximate size of Asem: 0x%x', [dword(@Bla)-dword(@Asem)]));

end.

Edited July 4, 201510 yr by kao

it really gives only approximate size 

Well, unless you want to use some disassembly engine (BeaEngine/Capstone/etc.) that's the best I can think of.

Borland's inline assembler is too limited to do anything better.

Would it help if the procedure was pure delphi/pascal instead of assembler?

Only solution I came up with is to compile some markers in $I directive, but that's not a very clever solution........ scanning a file

Edited July 4, 201510 yr by JustAGuy

Let's look at it from the another perspective - why do you need it? An why is approximate size not good enough for you?

so why don't you keep reading byte from memory until ret instruction(it is better to use TitanEngine...etc)

program Project2;
{$APPTYPE CONSOLE}
uses

  SysUtils,Windows;

function GetSize(Address:Pointer):Cardinal;

var

  C3:Byte;

  tempaddress:Cardinal;

  i:integer;

begin

  i:=0;

  tempaddress:=Cardinal(Address);

  while(not(C3 = $C3)) do

  begin

    i:=i+1;

    CopyMemory(@C3,ptr(tempaddress+i),1);

  end;

  result:=i+1;

end;
Procedure Asem;

begin

asm

 mov eax, 5;

 add eax,8

 shl eax,1

end;

end;
begin

      Writeln(Format('%p',[@Asem]));

      Writeln(Format('%d',[GetSize(@Asem)]));

      Readln;

end.

Edited July 4, 201510 yr by n0th!ng

because ret instruction isnt always 0xc3.. and what if you have mov eax, 0c3c3c3c3h ?

kao;  to get binary part of code I write without  tedious manual extraction

 

n0th!ng: thank you, but I did want to do it with search I was hoping to find some neat solution , but there probably is not any

because ret instruction isnt always 0xc3.. and what if you have mov eax, 0c3c3c3c3h ?

 

also it would cause trouble if there were more than one 0xc3

Hi,

 

so if I do understand you correctly then you want to find out any entire routine size lenght of your own coded source right?If you don't wanna find out each size lenght of all commands etc and you only wanna have routine entry / end then just log them both in your own table somewhere.

01020000  00401035 Routine Start

01020004  00401400 Routine End
00401035   PUSH EBP

......................

00401400   MOV EAX,0x1

00401405   LEAVE

00401406   RETN 0x10

On the other hand if your routine used more end outputs (more than only one) then you need to log them too.Or you do write some static code into each routine like this...

00401000 >    E8 00000000         CALL 00401005

00401005      5F                  POP EDI

00401006      83EF 05             SUB EDI,0x5 ; top in edi

00401009      90                  NOP

0040100A      90                  NOP

0040100B      90                  NOP

0040100C      90                  NOP

0040100D      90                  NOP

0040100E      90                  NOP

0040100F      90                  NOP

00401010      E8 00000000         CALL 00401015

00401015      5E                  POP ESI

00401016      2BF7                SUB ESI,EDI ; = lenght

00401018      83C6 07             ADD ESI,0x7 ; + add till ret

0040101B      C3                  RETN

= 1C lenght.Maybe you do something like this.All in all I think its not so easy to get the entire routine lenght without to check all possibly dynamic commands + to follow them to find all ends & real end of routine if its using a real end.Some don't use returns so this can also be dynamic (just a example if you also wanna check unknown codes).If you only wanna check this with your own codes then use only one routine output and log them all and sub the top from the end = size of routine.No idea what you do plan to do later with that infos or for what it should be important etc.

 

greetz

If you want to get the size after the procedure gets executed, you can use EIP to save the address at the very end of it (so u can easily calculate the size).

begin

asm

 mov eax, 5;

 add eax,8

 shl eax,1

 mov dword ptr [var], eip

end;

end;

Otherwise, u've gotta search for RET(C3).

I think using nested routines and labels can solve your issue.

procedure TForm1.Button2Click(Sender: TObject);

label _end;

var

  pStart : Pointer;

  pEnd : Pointer;

  procedure myproc;

  begin

    asm //Dummy code:

      pushad

      mov eax, 5

      add eax, 6

      shl eax, 1

      mov eax, ebx

      pop dword ptr ss:[esp]

      sub esp, 4

      popad

    _end:

    end;

  end;

begin

  pStart := @myproc;

  lstLog.AddItem('Start = 0x' + IntToHex(DWORD(pStart), 8), Sender);

  asm

    push eax

    lea eax, _end //label points to 1 byte further than real end point.

    mov pEnd, eax

    pop eax

  end;

  lstLog.AddItem('End = 0x' + IntToHex(DWORD(pEnd), 8), Sender);
  lstLog.AddItem('myproc size = 0x' + IntToHex(DWORD(pEnd) - DWORD(pStart) - 1, 8), Sender);

end;

 

GetProcSize.rar

@Alzri2

mov r/m, eip

or

mov eip, r/m

is not possible.

 

From Intel® 64 and IA-32 Architectures Software Developer’s Manual (2015) :

 

The processor fetches instructions from the code segment, using a logical address that consists of the segment selector in the CS register and the contents of the EIP register. The EIP register contains the offset within the code segment of the next instruction to be executed. The CS register cannot be loaded explicitly by an application program. Instead, it is loaded implicitly by instructions or internal processor operations that change program control (such as, procedure calls, interrupt handling, or task switching).

 

The EIP register cannot be accessed directly by software; it is controlled implicitly by control-transfer instructions (such as JMP, Jcc, CALL, and RET), interrupts, and exceptions. The only way to read the EIP  register is to execute a CALL instruction and then read the value of the return instruction pointer from the procedure stack. The EIP register can be loaded indirectly by modifying the value of a return instruction pointer on the procedure stack and executing a return instruction (RET or IRET).

 

@Gyrus:

You're right, I forgot about the limitations of accessing EIP reg

As an alternative, I tried this (don't have delphi to make an example):

.data

vEIP dd ?
.code

start:

	call GetEIP
	invoke ExitProcess, 0
GetEIP proc

	push [esp]

	pop [vEIP]

	ret

GetEIP endp
end start

and now its not threadsafe too...

Why not ?

I think the stack is dealt with safely in this one.

.data

vEIP dd ?

last time i checked, that isnt stack

for those of you interested I solved EIP problem this way 

 @a1:

    lea eax,[@a1]   

    mov _end, eax