Undefinded Symbol "mov [f.cb],sizeof.STARTUPINFO"

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Havok

Joined: 29 Oct 2011
Posts: 7

Havok

Hello all,

Sorry for another noob question,but this is starting to drive me nutty. I took revolution's advice and declared all the structures but ran into a problem with FASM telling me "mov [f.cb],sizeof.STARTUPINFO" is undefined.

Code:

format pe gui

struc sockaddr_in
{
.sin_family dw ?
.sin_port   dw ?
.sin_addr   dd ?
.sin_zero   db 8 dup (?)
}
struc STARTUPINFO
{
.cb              dd ?
.lpReserved     dd ?
.lpDesktop      dd ?
.lpTitle        dd ?
.dwX            dd ?
.dwY            dd ?
.dwXSize        dd ?
.dwYSize        dd ?
.dwXCountChars  dd ?
.dwYCountChars  dd ?
.dwFillAttribute dd ?
.dwFlags       dd ?
.wShowWindow    dw ?
.cbReserved2    dw ?
.lpReserved2    dd ?
.hStdInput      dd ?
.hStdOutput     dd ?
.hStdError      dd ?
.size      = $-.cb
}

push a 
push 0202h
call [WSAStartup]
push 0
push 0
push 0
push 6
push 1
push 2
call [WSASocket]
mov [b],eax
mov [c.sin_family],2
push d
call [htons]
mov [c.sin_port],ax
push 0
call [htonl]
mov [c.sin_addr],eax
push e
push c
call [accept]
mov [f.cb],sizeof.STARTUPINFO

a db WSADATA
b dd 0
c sockaddr_in
d db '80',0
e db sizeof.sockaddr_in
f STARTUPINFO

Thanks for any help you can provide.

05 Nov 2011, 22:28

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17930
Location: In your JS exploiting you and your system

revolution

Use STARTUPINFO.size

You never defined sizeof.STARTUPINFO anywhere.

Same with sizeof.sockaddr_in. It will be undefined also.

05 Nov 2011, 22:42

Havok

Joined: 29 Oct 2011
Posts: 7

Havok

It says I haven't defined "STARTUPINFO.size" either when I use it. I obviously have to learn how to define these things correctly.

05 Nov 2011, 22:49

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 7861
Location: Kraków, Poland

Tomasz Grysztar

You should have used it this way:

Code:

mov [f.cb],f.size

STRUC directive is just a kind of macro, that's why it doesn't define any constants by itself, only when you actually use it. Note that sometimes the structure may not have fixed size and then you'd have "f.size" be different from "g.size" even when "f" and "g" were defined using the same "struc" macro.

05 Nov 2011, 22:55

Havok

Joined: 29 Oct 2011
Posts: 7

Havok

Ah now i'm starting to understand it. Thanks to the both of you. Tomasz you've made a wonderful assembler, thank you. Taking a bit to get used to, but I can't wait to get more involved in it.

05 Nov 2011, 23:07

AsmGuru62

Joined: 28 Jan 2004
Posts: 1423
Location: Toronto, Canada

AsmGuru62

You get sizeof 'thingy' when using struct/ends macros, like MASM declares it.

05 Nov 2011, 23:13

Havok

Joined: 29 Oct 2011
Posts: 7

Havok

thanks for that AsmGuru62. I haven't look at any MASM examples. I need to do more homework it seems Smile

05 Nov 2011, 23:30

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