Implementing C structures in x86 assembly

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alkap

Joined: 18 Feb 2015
Posts: 44
Location: Dnipro, Ukraine

alkap 17 May 2015, 06:26

Is this how C structures are implemented in x86 Linux assembly?
I believe the Windows fasm distribution defines a 'struc' macros, while the Linux one does not. Correct me if I am wrong. Thanks.

Code:

; fasm struct_test.fasm struct_test

format ELF executable 3
entry start

segment readable executable

start:

        mov     eax, 4
        mov     ebx, 1
        mov     ecx, msg.str
        mov     edx, msg.len
        int     80h

        mov     eax,1
        xor     ebx,ebx
        int     80h

segment readable writeable

msg:                                                    ; struct msg?
        .str    db 'Hello world!',0xA
        .len = $-.str

17 May 2015, 06:26

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20454
Location: In your JS exploiting you and your system

revolution 17 May 2015, 07:25

You can also use the struct macros for linux code if you wish to. They are quite a nice convenience. On the other hand you could manually construct them using the struc macro. Or on the third hand you can do what you did above and have no structure at all but instead do all the computations independently.

17 May 2015, 07:25

alkap

Joined: 18 Feb 2015
Posts: 44
Location: Dnipro, Ukraine

alkap 17 May 2015, 07:54

Understood. Thanks.
I did look through the include files that come with the Linux distribution of fasm, but failed to find where the 'struct' macro is defined.
Do I have to include the Windows STRUCT.INC in my Linux source files to make use of the 'struct' macro?
Thanks.

17 May 2015, 07:54

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20454
Location: In your JS exploiting you and your system

revolution 17 May 2015, 09:58

alkap wrote:

I did look through the include files that come with the Linux distribution of fasm, but failed to find where the 'struct' macro is defined.
Do I have to include the Windows STRUCT.INC in my Linux source files to make use of the 'struct' macro?

Yes, you will need to include it in some way to make use of it. You could also copy the text and paste it into your main source if that makes more sense to you to avoid having includes.

17 May 2015, 09:58

alkap

Joined: 18 Feb 2015
Posts: 44
Location: Dnipro, Ukraine

alkap 17 May 2015, 14:04

Understood. I'll give that a try. Thanks.

17 May 2015, 14:04

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