lea eax,[esi-buffer]

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comrade

Joined: 16 Jun 2003
Posts: 1140
Location: Russian Federation

comrade

Code:

lea eax,[esi-buffer]

Cannot compile that line... MASM can.

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24 Jun 2003, 02:58

BiDark

Joined: 22 Jun 2003
Posts: 109
Location: .th

BiDark

I guess relocation cause Rolling Eyes

(It's not absolute value, buffer address can be change everytime you load?)

Just a guess Rolling Eyes

24 Jun 2003, 06:47

roticv

Joined: 19 Jun 2003
Posts: 374
Location: Singapore

roticv

Code:

lea eax,[esi-buffer]

Weird, what are you doing actaully?

24 Jun 2003, 07:43

BiDark

Joined: 22 Jun 2003
Posts: 109
Location: .th

BiDark

Try my quick fix,

Code:


  imagebase = 400000h
  lea  eax,[esi-rva buffer or imagebase]

Will be its absolute value.

24 Jun 2003, 08:05

scientica
Retired moderator

Joined: 16 Jun 2003
Posts: 689
Location: Linköping, Sweden

scientica

comrade wrote:

Code:

lea eax,[esi-buffer]

What is buffer? Is it a local, a global variable?

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24 Jun 2003, 11:56

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8017
Location: Kraków, Poland

Tomasz Grysztar

It will work for you in binary mode, but not in PE/COFF/ELF output modes, because addresses there are relocatable.

24 Jun 2003, 13:15

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound

Hi, Privalov.

Is it imposible to make lea instruction with relocateable operand, like:

jmp buffer

or

mov eax, buffer

Actually loader simply adds some constants to some memory locations. Hm, or my question is stupid? Very Happy

24 Jun 2003, 14:34

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8017
Location: Kraków, Poland

Tomasz Grysztar

Yes, you can use lea instruction with such operand, but the problem was with substracting relocatable constant to some absolute value instead of adding it, and such type of fixups is not available in PE/COFF formats.

02 Jul 2003, 12:04

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8017
Location: Kraków, Poland

Tomasz Grysztar

If you are sure you won't need relocation info for your program, you can override this problem this way:

Code:

BASE_ADDRESS = 400000h

format PE at BASE_ADDRESS
entry start

section '.bss' readable writeable

  buffer = BASE_ADDRESS + RVA $
  rb 100h

section '.code' code readable executable

start:
        lea     eax,[esi-buffer]
        ret

02 Jul 2003, 12:12

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8017
Location: Kraków, Poland

Tomasz Grysztar

I've just realized it can be done much better, only few definitions at the beginning of source and then everything in normal way (assuming you won't include the relocation info):

Code:

BASE_ADDRESS = 400000h

format PE at BASE_ADDRESS
entry start-BASE_ADDRESS+$-RVA $

macro section params
 { section params
   org BASE_ADDRESS + RVA $ }


section '.bss' readable writeable

  buffer rb 100h

section '.code' code readable executable

start:
        lea     eax,[esi-buffer]
        ret

10 Jul 2003, 08:57

comrade

Joined: 16 Jun 2003
Posts: 1140
Location: Russian Federation

comrade

Cool, thanks!

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10 Jul 2003, 12:27

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