a more advanced technique

**Yarin** · 07-29-2008

Okay, this may sound like a more advanced technique (if it isn't, then I guess I'm really still a newbie.

). But I'm trying to copy a function from one program to another, not an address or anything, the whole function, assembly and all.

I am getting the function's base address with &MyFunction, but does this really work?
I tried to get the size by subtracting that from the address of a variable I placed directly after it, but I quickly realized that doesn't work. When I place another right before the function I see that the functions and variables aren't even stored in the same location in memory.

So... How do I get the starting point in memory of the function? And how do I get the function size?

**robwhit** · 07-29-2008

implementation-specific.

**Yarin** · 07-29-2008

I want to execute a function in one program in another, after the original function's program has ended.

**robwhit** · 07-29-2008

Oh. Well just use a lib then and system or something.

**medievalelks** · 07-29-2008

Originally Posted by Yarin

I want to execute a function in one program in another, after the original function's program has ended.

Export that function to a library, either static or dynamic, and have both programs link with it.

**Yarin** · 07-29-2008

No, the whole idea of this, is that once the function is done executing, there are no traces left that it ever existed.

**Yarin** · 07-29-2008

I'm using VirtualAllocEx and WriteProcessMemory, and using CreateRemoteThread to execute the new function I've copied over.
But when I do that, the computer instantly crashes. I'm guessing this is because the data that I copied over is not the right size or isn't the function at all. How do I accomplish this?

**robwhit** · 07-29-2008

What is the purpose of doing this?

**Yarin** · 07-29-2008

Self delete without possible restoration of the deleting agent(s).

**King Mir** · 07-29-2008

Originally Posted by Yarin

No, the whole idea of this, is that once the function is done executing, there are no traces left that it ever existed.

Doesn't that make it trivially impossible, since to execute the same function there must necessarily be a trace left to execute?

**Yarin** · 07-29-2008

Yes and no... Look, I have an idea on how to cover my footstep covering footsteps; to the point that it becomes innoteworthy dirt.

The thing is, I need to know how to do this.

**robwhit** · 07-29-2008

Seems like it would be a problem better suited for assembly language.

Why do you want to do this? It sounds like a virus or a misguided attempt at an uninstall program.

**eXeCuTeR** · 07-29-2008

If you just wanna export functions from other files, just create a DLL and include it in your code with LoadLibrary.
Then, get the function's address by using GetProcAddress.
Something like this..
dll.dll:

Code:

__cdecl(dllexport) void func()
{
 cout << "Hello world!";
}

includedll.cpp:

Code:

typedef void (*myFunc)();
myFunc func;
HANDLE dll = LoadLibrary("dll.dll");
func = (myFunc)GetProcAddress((HMODULE)dll, "func");
func();
FreeLibrary((HMODULE)dll);

**matsp** · 07-30-2008

As to why your "copy the function and execute" wont work, I suspect the problem is that the code isn't completely free of relocations (references to absolute memory locations, for example variables, constant data, vtables for C++ objects or jump tables for switch statements). You could check this by looking at the code in the executable file itself, and compare that with the code in memory - if it has changed, then you have relocations.

You may also find that if your application itself doesn't load a DLL that is needed by the code you are calling, you may have a relocation in the code referencing the DLL, and it will most likely point to invalid memory, which would lead to a crash.

--
Mats

**medievalelks** · 07-30-2008

Originally Posted by Yarin

Yes and no... Look, I have an idea on how to cover my footstep covering footsteps; to the point that it becomes innoteworthy dirt.

The thing is, I need to know how to do this.

OK, I'm curious too. What are you trying to do?

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