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Hooking address (GCC)

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NoMercy
Master Cheater

Reputation: 1

Joined: 09 Feb 2009
Posts: 289

Posted: Tue Mar 22, 2011 12:21 pm Post subject: Hooking address (GCC)

Hello,

I'm trying to hook a function, I know the address, but the problem is I'm using GCC now, I used to be using VS and my method does not work anymore,

Code:

void Hooks::EnableHooks ()
{
*(char*)ulSend = 0xE9;
*(long*)ulSend + 1 = NewSendFun - ulSend - 5; // error line
}

/* New functions for hooked Functions */
void Hooks::NewSendFun()
{
__asm__ (
"mov [ppSendPacket],%esp\n\t"
"pusha\n\t"
"call SendPacketCallback\n\t"
"popa\n\t"
"jmp *%ulSendRet]\n\t"
);
}

The error line gives this error:
invalid use of member(did you forget the '&'?)

Hope someone can help me.

AhMunRa
Grandmaster Cheater Supreme

Reputation: 27

Joined: 06 Aug 2010
Posts: 1117

Posted: Tue Mar 22, 2011 12:39 pm Post subject:

Missed brackets should be NewSendFun() _________________ <Wiccaan> Bah that was supposed to say 'not saying its dead' lol. Fixing >.>

hcavolsdsadgadsg
I'm a spammer

Reputation: 26

Joined: 11 Jun 2007
Posts: 5801

Posted: Tue Mar 22, 2011 3:32 pm Post subject:

AhMunRa wrote:

Missed brackets

should be NewSendFun()

he wants the address of the function, not the return.

you need to be explicit when you want the address of a member function in C++. it's ok to assign a function pointer like that in C but in, with member function pointers (a difference!) in C++ you'd need: &class::mf

NoMercy
Master Cheater

Reputation: 1

Joined: 09 Feb 2009
Posts: 289

Posted: Wed Mar 23, 2011 1:53 am Post subject:

slovach wrote:

AhMunRa wrote:

Missed brackets

should be NewSendFun()

I made the function static in my class, at least I can compile now:)

so I've to change

&Hooks::NewFunction

Jani
Grandmaster Cheater

Reputation: 2

Joined: 29 Dec 2006
Posts: 804

Posted: Wed Mar 23, 2011 4:15 am Post subject:

NoMercy wrote:

I made the function static in my class, at least I can compile now:)

You don't have to make the whole class static. Only the member receiving the callback. This is because the compiler can't just run a method of a class, which doesn't have an instance. The other way would be to tell the compiler which instance of the object to use and then call the member: ((class).*(member))(args). But seeing the case, using a static member is much more easier.

Deltron Z
Expert Cheater

Reputation: 1

Joined: 14 Jun 2009
Posts: 164

Posted: Wed Mar 23, 2011 12:23 pm Post subject:

Jani wrote:

I'm not sure what you mean by "((class).*(member))(args)", because dot is used with class instance - objects, not class, you should've used :: instead. and by member I assumed you meant the function, and then I don't understand what's the dereference operator for... get the function's... value? and the call it with the arguments?
I think you meant:
((return_type (call_convention*)(void*))class::member)(&object)
for example:
((int (__cdecl*)(void*, other_params))class::member)(&object, other_param)
because "this" pointer is passed as a paramater.

Unfortunatly, the compiler didn't like me converting a class method to a pointer (int*, char*, void*, nothing...) even though it worked perfectly fine with functions that didn't belong to a class, so I had to write a warper, nothing too complicated, just a few lines of inline assembly.
Here's an example:

Code:

#include <stdio.h>

class Class
{
public:
void* __stdcall GetThisPointer() { return (void*)this; }
};

//This is how the compiler implements the function
//"this" pointer is passed as a paramater
void* GetThisPointer_Implementation(Class* object)
{
return (void*)object;
}

//Proof of Concept
int __declspec(naked) GetThisPointer_PoC(Class* object)
{
__asm
{
   PUSH EBP //since we specified __declspec(naked)
   MOV EBP, ESP //fix stack
   //if GetThisPointer was __cdecl (by default) then
   //you should've used "MOV ECX, object" instead of "PUSH object"
   PUSH object //Pass "this" pointer as a parameter
   LEA EAX, [Class::GetThisPointer]
   CALL EAX
   POP EBP
   RETN 4
}
}

int main()
{
Class Object;

printf("Object (%p) = this (%p)\n", &Object, Object.GetThisPointer());
printf("Implementation: %p\n", GetThisPointer_Implementation(&Object));
printf("Proof of Concept: %p\n", GetThisPointer_PoC(&Object));

return 0;
}

_________________

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"When I find my code in tons of trouble,
Friends and colleagues come to me...
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Write in C."

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