Size of DLL files

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Icefex

Joined: 11 Feb 2009
Posts: 17

Icefex 01 Jul 2009, 15:41

While coding a simple DLL i came across a bug/feature/annoyance. I first wrote the DLL in C, (simply as a helper for doing it in asm) compiled it and it had a size of 2kb. Then I translated it to asm and it was 3.5kb. Well, I never thought that a C compiler (tcc in my case) would produce a smaller file than hand written assembly...
I looked at the sections of the dlls and surprise, those from the assembly dll where smaller (ASM: 246bytes, C: 416bytes). So my question is why is the ASM dll larger?

Attached are the source files I used

Description:		Download
Filename:	dll_test.zip
Filesize:	2.85 KB
Downloaded:	256 Time(s)

01 Jul 2009, 15:41

arigity

Joined: 22 Dec 2008
Posts: 45

arigity 01 Jul 2009, 15:55

the C dll mashed imports exports and data into 1 section while the asm dll has separate sections for all 3.

01 Jul 2009, 15:55

asmcoder

Joined: 02 Jun 2008
Posts: 784

asmcoder 01 Jul 2009, 15:58

[content deleted]

Last edited by asmcoder on 14 Aug 2009, 14:49; edited 2 times in total

01 Jul 2009, 15:58

Icefex

Joined: 11 Feb 2009
Posts: 17

Icefex 01 Jul 2009, 15:59

Well, is then there a way to get the sections smaller? Because they are padded to 512bytes afaik.

01 Jul 2009, 15:59

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 01 Jul 2009, 16:02

Code:

; DLL creation example

format PE GUI 4.0 DLL
entry DllEntryPoint

include 'win32a.inc'

section '.text' code readable executable

proc DllEntryPoint hinstDLL,fdwReason,lpvReserved
        mov     eax,TRUE
        ret
endp

proc TestFunction
        invoke  MessageBox,0,_message,_caption,MB_OK
        ret
endp

section '.data' data readable writeable

  _caption db 'Win32 assembly',0
  _message db 'Some text no one cares about!',0

;section '.idata' import data readable writeable
data import
  library user,'USER32.DLL'

  import user,\
         MessageBox,'MessageBoxA'
end data

;section '.edata' export data readable
data export

  export 'TEST.DLL',\
         TestFunction,'TestFunction'

end data

section '.reloc' fixups data discardable
; data fixups ; using this instead of a separate section would shave 512 bytes
; end data

2 KB and replicates the sections of the C version.

01 Jul 2009, 16:02

arigity

Joined: 22 Dec 2008
Posts: 45

arigity 01 Jul 2009, 16:03

here, i modified your example to fit imports and exports and data in 1 section

Code:

; DLL creation example

format PE GUI 4.0 DLL
entry DllEntryPoint

include 'win32a.inc'

section '.text' code readable executable

proc DllEntryPoint hinstDLL,fdwReason,lpvReserved
        mov     eax,TRUE
        ret
endp

proc TestFunction
        invoke  MessageBox,0,_message,_caption,MB_OK
        ret
endp

section '.data' data readable writeable

  _caption db 'Win32 assembly',0
  _message db 'Some text no one cares about!',0

data import

  library user,'USER32.DLL'

  import user,\
         MessageBox,'MessageBoxA'

end data

data export
  export 'TEST.DLL',\
         TestFunction,'TestFunction'
end data

section '.reloc' fixups data discardable

edit >_> woops loco beat me :/

01 Jul 2009, 16:03

Icefex

Joined: 11 Feb 2009
Posts: 17

Icefex 01 Jul 2009, 16:12

w00t! Thank you guys!

01 Jul 2009, 16:12

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 01 Jul 2009, 16:21

BTW, actually to replicate the C version even further you should add "align 16" before "data import" and "data export".

01 Jul 2009, 16:21

Icefex

Joined: 11 Feb 2009
Posts: 17

Icefex 01 Jul 2009, 16:27

Actually my intention was not replicating the C version, but making it as small. But you guys helped my a lot with this.

01 Jul 2009, 16:27

asmcoder

Joined: 02 Jun 2008
Posts: 784

asmcoder 01 Jul 2009, 16:33

[content deleted]

Last edited by asmcoder on 14 Aug 2009, 14:49; edited 1 time in total

01 Jul 2009, 16:33

Icefex

Joined: 11 Feb 2009
Posts: 17

Icefex 01 Jul 2009, 16:53

I think there is no such import/export in coff, but functions can be declared as extern. And when a coff is linked the linker tries to resolve those. Also there are afaik no exports, because they would be kinda useless in a coff file...

P.S.: I give no guarantee for accuracy

01 Jul 2009, 16:53

asmcoder

Joined: 02 Jun 2008
Posts: 784

asmcoder 01 Jul 2009, 17:12

[content deleted]

Last edited by asmcoder on 14 Aug 2009, 14:49; edited 1 time in total

01 Jul 2009, 17:12

Icefex

Joined: 11 Feb 2009
Posts: 17

Icefex 01 Jul 2009, 17:16

No, not coff itself but the linker tries to resolve not known functions. Coff itself only contains code and data.

01 Jul 2009, 17:16

manfred

Joined: 28 Feb 2009
Posts: 43
Location: Racibórz, Poland

manfred 01 Jul 2009, 17:29

Read The Friendly PE Manual.
These informations is stored in (AFAIK) symbol table.

_________________
Sorry for my English...

01 Jul 2009, 17:29

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