[req] rva enabled in ms coff

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kempis

Joined: 12 Jun 2008
Posts: 49

kempis 13 Oct 2008, 15:08

Hello...
First, i'm sorry for my English

code:

Code:

format MS COFF
section ".idata$4"
__imp__MessageBoxA@16 dd rva MessageBoxA%text-2

section ".idata$7"
MessageBoxA%text db "MessageBoxA",0

extrn __dll__user32
public __imp__MessageBoxA@16

I tried to make an import archive, but fasm disable rva expressions in ms coff format.
req: I suggest that fasm can enable rva expressions in ms coff format

13 Oct 2008, 15:08

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 13 Oct 2008, 15:27

I think that COFF format cannot support RVA because the linker won't know how to update the offset when it is linked?

13 Oct 2008, 15:27

kempis

Joined: 12 Jun 2008
Posts: 49

kempis 13 Oct 2008, 17:06

RVA = VA - base address
because base address is known, rva must be known when linked
(just like plt/rva in elf format)[/code]

13 Oct 2008, 17:06

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 13 Oct 2008, 17:23

But how do you tell the linker that?

13 Oct 2008, 17:23

kempis

Joined: 12 Jun 2008
Posts: 49

kempis 13 Oct 2008, 17:31

I have ever read the PE and MS COFF format documentation. And there is something that tell the linker. I think it's the type of address.

13 Oct 2008, 17:31

kempis

Joined: 12 Jun 2008
Posts: 49

kempis 13 Oct 2008, 17:52

this is in pe/coff documentation

Quote:

IMAGE_REL_I386_ABSOLUTE 0x0000 This relocation is ignored.
IMAGE_REL_I386_DIR16 0x0001 Not supported.
IMAGE_REL_I386_REL16 0x0002 Not supported.
IMAGE_REL_I386_DIR32 0x0006 The target’s 32-bit virtual address.
IMAGE_REL_I386_DIR32NB 0x0007 The target’s 32-bit relative virtual address.
IMAGE_REL_I386_SEG12 0x0009 Not supported.
IMAGE_REL_I386_SECTION 0x000A The 16-bit-section index of the section containing the
target. This is used to support debugging information.
IMAGE_REL_I386_SECREL 0x000B The 32-bit offset of the target from the beginning of its
section. This is used to support debugging information
as well as static thread local storage.
IMAGE_REL_I386_REL32 0x0014 The 32-bit relative displacement to the target. This
supports the x86 relative branch and call instructions.

13 Oct 2008, 17:52

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 05 Nov 2008, 09:03

kempis,

I think it's about IMAGE_REL_I386_DIR32NB not supported by fasm COFF formatter, thus rva operator is allowed only in PE and ELF formats.

Nevertheless, you have sources…

05 Nov 2008, 09:03

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 06 Nov 2008, 11:01

Yeah, sorry, that was just my laziness - I never though someone would need to use RVA operator in COFF object. Wink

06 Nov 2008, 11:01

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 06 Nov 2008, 17:29

Tomasz Grysztar,

Don't be sorry: we must be thankful that you release your sources, not only binaries. So if somebody need some feature, he/she is free to modify the sources to achieve that goal. There ain't such a thing as a free lunch. Wink

06 Nov 2008, 17:29

kempis

Joined: 12 Jun 2008
Posts: 49

kempis 12 Nov 2008, 13:50

Thank's for all. Razz

OK, it's difficult for me but I will try to modify the source.

12 Nov 2008, 13:50

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 12 Nov 2008, 22:48

no need to modify, it will come soon.

12 Nov 2008, 22:48

kempis

Joined: 12 Jun 2008
Posts: 49

kempis 15 Nov 2008, 03:29

OK thank's very much.

BTW, I've modified it...

EXPRESSI.INC

Code:

      calculate_rva:
   cmp     word [edi+8],0
      jne     invalid_expression
  cmp     [output_format],5
   je      calculate_gotoff
    cmp     [output_format],3
   ;jne     invalid_expression
 ;modified
   jne     calculate_coff_rva
  ;/modified
  test    [format_flags],8
    jnz     pe64_rva
    mov     al,2
        bt      [resolver_flags],0
  jc      rva_type_ok
 xor     al,al
      rva_type_ok:
     cmp     byte [edi+12],al
    je      rva_ok
      cmp     [error_line],0
      jne     rva_ok
      mov     eax,[current_line]
  mov     [error_line],eax
    mov     [error],invalid_use_of_symbol
      rva_ok:
  mov     byte [edi+12],0
     mov     eax,[code_start]
    mov     eax,[eax+34h]
       cdq
 sub     [edi],eax
   sbb     [edi+4],edx
 add     edi,14h
     jmp     calculation_loop
      ;modified
      calculate_coff_rva:
        mov     dl,9
        cmp     byte[edi+12],2
      jne     incorrect_change_of_value_type
      jmp     change_value_type
      ;/modified

another code in EXPRESSI.INC

Code:

get_address_value:
      mov     [address_size],0
    mov     [value_size],8
      calculate_address:
      cmp     byte [esi],'.'
    je      invalid_address
     call    calculate_expression
        mov     eax,[edi+16]
        mov     [address_symbol],eax
        mov     al,[edi+12]
 mov     [value_type],al
     cmp     al,6
        je      plt_address
 ;modified
   cmp     al,9
        je      plt_address
 ;/modified
  cmp     al,5
        je      gotoff_address
      ja      invalid_use_of_symbol

FORMATS.INC

Code:

mark_coff_relocation:
    cmp     [value_type],3
      je      coff_relocation_relative
    ;modified
   cmp     [value_type],9
      je      coff_relocation_rva
 ;/modified
  push    ebx eax
     test    [format_flags],8
    jnz     coff_64bit_relocation
       mov     al,6
        jmp     coff_relocation
     ;modified
      coff_relocation_rva:
 push    ebx eax
     mov     al,7
        jmp     coff_relocation
     ;/modified

But I still wait for new version... Very Happy

15 Nov 2008, 03:29

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