DllMain implementation

This is a discussion on DllMain implementation within the C++ Programming forums, part of the General Programming Boards category; Thanks Elysia, I do not know what do you mean "mess around with the linker". My question is why main.obj ...

  1. #16
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    Thanks Elysia,


    I do not know what do you mean "mess around with the linker". My question is why main.obj is not shown as input command line of linker?

    Quote Originally Posted by Elysia View Post
    Whatever does it matter? You're using Visual Studio so you shouldn't have to mess around with the linker.

    regards,
    George

  2. #17
    C++まいる!Cをこわせ! Elysia's Avatar
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    My point is, why do you need to know? Visual Studio automatically passes everything correct to the linker, so you don't have to worry about it.
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  3. #18
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    So, you are building an executable with a funciton called dllmain? I would still expect to see all object files being fed to the linker, but it may not be part of the command-line, as it may be part of an indirect input.

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  4. #19
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    Hi Elysia,


    The reason why I am doing this, is because all our previous discussion is just theory discussion -- i.e. linker will search obj files before searching lib files. So, I want to make my hands dirty to make some test to show obj files are input before lib or something.

    BTW: do you have any practice for us to illustrate (prove) your point -- linker will search obj files before searching lib files?

    Quote Originally Posted by Elysia View Post
    My point is, why do you need to know? Visual Studio automatically passes everything correct to the linker, so you don't have to worry about it.
    Hi Mats,


    "you are building an executable with a funciton called dllmain"

    No, I am building the dll itself. I think if you tried in your own environment, I think you will find similar issues -- no object files as input to linker.

    Quote Originally Posted by matsp View Post
    So, you are building an executable with a funciton called dllmain? I would still expect to see all object files being fed to the linker, but it may not be part of the command-line, as it may be part of an indirect input.

    --
    Mats

    regards,
    George

  5. #20
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    Code:
    /OUT:"D:\Visual Studio 2008\Projects\test_link1\Debug\test_link1.exe"
    Really?

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  6. #21
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    My mistake, Mats!


    Sorry, here is the correct information. You can see still no main.obj.

    /OUT:"D:\Visual Studio 2008\Projects\test_link1\Debug\test_dll_link1.dll" /NOLOGO /DLL /MANIFEST /MANIFESTFILE:"Debug\test_dll_link1.dll.intermediat e.manifest" /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /DEBUG /PDB:"d:\Visual Studio 2008\Projects\test_link1\Debug\test_dll_link1.pdb" /DYNAMICBASE /NXCOMPAT /MACHINE:X86 /ERRORREPORT:PROMPT kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib


    regards,
    George

  7. #22
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    The command line shown in the project properties is the result of your project settings. The actual input files are added when building.

    You need to look at the log of the build process to find the real linker command line.
    All the buzzt!
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  8. #23
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    Right, I haven't got Visual Studio at work, so I can't say where the main.obj would be, but are you saying that your text is not being output when the DLL is "started"?

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  9. #24
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    You are correct, CornedBee!


    Cool! Here is the build log and seems main.obj is appended as the end of linker input.

    So, coming back to my original question, why do you think user provided DllMain (in main.obj) will be selected to be linked other than using CRT default one -- because obj has higher priority than lib?

    --------------------
    Creating temporary file "d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\RSP0 0000168926972.rsp" with contents
    [
    /Od /D "_WINDLL" /D "_MBCS" /Gm /EHsc /RTC1 /MDd /Fo"Debug\\" /Fd"Debug\vc90.pdb" /W3 /c /ZI /TP ".\main.cpp"
    ]
    Creating command line "cl.exe @"d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\RSP0 0000168926972.rsp" /nologo /errorReportrompt"
    Creating temporary file "d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\RSP0 0000268926972.rsp" with contents
    [
    /OUT:"D:\Visual Studio 2008\Projects\test_link1\Debug\test_dll_link1.dll" /DLL /MANIFEST /MANIFESTFILE:"Debug\test_dll_link1.dll.intermediat e.manifest" /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /DEBUG /PDB:"D:\Visual Studio 2008\Projects\test_link1\Debug\test_dll_link1.pdb" /DYNAMICBASE /NXCOMPAT /MACHINE:X86 kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib

    ".\Debug\main.obj"
    ]
    Creating command line "link.exe @"d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\RSP0 0000268926972.rsp" /NOLOGO /ERRORREPORT:PROMPT"
    Creating temporary file "d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\RSP0 0000368926972.rsp" with contents
    [
    /outputresource:"..\Debug\test_dll_link1.dll;#2" /manifest

    ".\Debug\test_dll_link1.dll.intermediate.manif est"
    ]
    Creating command line "mt.exe @"d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\RSP0 0000368926972.rsp" /nologo"
    Creating temporary file "d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\BAT0 0000468926972.bat" with contents
    [
    @echo Manifest resource last updated at %TIME% on %DATE% > ".\Debug\mt.dep"
    ]
    Creating command line """d:\Visual Studio 2008\Projects\test_link1\test_dll_link1\Debug\BAT0 0000468926972.bat"""
    --------------------

    Quote Originally Posted by CornedBee View Post
    The command line shown in the project properties is the result of your project settings. The actual input files are added when building.

    You need to look at the log of the build process to find the real linker command line.

    Hi Mats,


    I have found in the build log, other than in the linker command line window, main.obj is added. And it is at the end of the command line. So the theory of sequence matters is not correct.

    So, what is your point? Function in obj always has higher priority than in lib?

    Quote Originally Posted by matsp View Post
    Right, I haven't got Visual Studio at work, so I can't say where the main.obj would be, but are you saying that your text is not being output when the DLL is "started"?

    --
    Mats

    regards,
    George

  10. #25
    Malum in se abachler's Avatar
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    Quote Originally Posted by George2 View Post
    Thanks Mats,


    abachler and Elysia, any comments to my below points?
    1. I do not think linker program writes special code for DllMain, and it should have a general rule to deal with how to use user defined one as higher priority if there is also a default one in lib;

    regards,
    George
    Code:
    #ifndef DllMain
     
    BOOL APIENTRY DllMain( HANDLE hModule, 
                           DWORD  ul_reason_for_call, 
                           LPVOID lpReserved
          )
    {
        switch (ul_reason_for_call)
     {
      case DLL_PROCESS_ATTACH:
                 break;
      case DLL_THREAD_ATTACH:
                break;
      case DLL_THREAD_DETACH:
                break;
      case DLL_PROCESS_DETACH:
                break;
        }
        return TRUE;
    }
     
    #endif
    or something similar. Im assuming though that rather than it being in some hidden headr file, that it actually just adds some generic code to the DLL. Now that I think about it Im almost positive it would have to be in the linker itself.
    Last edited by abachler; 02-13-2008 at 08:46 AM.
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  11. #26
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    I guess MS linker works a bit differently than the gnu ld then - because there the order is definitely important. But it makes some sense to perform lib resolution AFTER the object files "enforced", as you do want all object files always, whilst lib content is optional.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
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  12. #27
    Malum in se abachler's Avatar
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    hmm, Ive never tried overloading a function that was in a library Im linking to, perhaps that is how they do it?
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  13. #28
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    Quote Originally Posted by abachler View Post
    hmm, Ive never tried overloading a function that was in a library Im linking to, perhaps that is how they do it?
    I have created my own malloc, using this method, for example.

    --
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  14. #29
    Malum in se abachler's Avatar
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    Thats probably how its done then, some required lib for making a dll contains the generic DllMain, and the logic that subverts overloaded lib functions handles that one the same way. Oh now it almost makes me want to write my own compiler... almost.
    Until you can build a working general purpose reprogrammable computer out of basic components from radio shack, you are not fit to call yourself a programmer in my presence. This is cwhizard, signing off.

  15. #30
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    Why would the generic DllMain have to be in some library? The linker might just have it hardcoded. We don't know, because MS doesn't document this stuff. But it also shouldn't matter.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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