a more advanced technique

This is a discussion on a more advanced technique within the C++ Programming forums, part of the General Programming Boards category; Okay, this may sound like a more advanced technique (if it isn't, then I guess I'm really still a newbie. ...

  1. #1
    Unregistered User Yarin's Avatar
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    a more advanced technique

    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?
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

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    implementation-specific.

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    Unregistered User Yarin's Avatar
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    I want to execute a function in one program in another, after the original function's program has ended.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

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

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    Quote Originally Posted by Yarin View Post
    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.

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    Unregistered User Yarin's Avatar
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    No, the whole idea of this, is that once the function is done executing, there are no traces left that it ever existed.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

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    Unregistered User Yarin's Avatar
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    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?
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

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    What is the purpose of doing this?

  9. #9
    Unregistered User Yarin's Avatar
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    Self delete without possible restoration of the deleting agent(s).
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

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    Quote Originally Posted by Yarin View Post
    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?
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

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    Unregistered User Yarin's Avatar
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    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.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

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    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.

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    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);
    Last edited by eXeCuTeR; 07-29-2008 at 09:21 PM.

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    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
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Quote Originally Posted by Yarin View Post
    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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