LinuxMusicians

Posted: **Sat Jul 30, 2022 10:33 am**

Currently I'm stuck with MinGW and DLL exports...

We have file1.cpp:

extern "C"
{
    __declspec(dllexport)
    int f() { return 1; }

    __declspec(dllexport)
    int g() { return 2; }

    int k() { return 3; }
}

And file2.cpp:

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extern "C"
{
    __declspec(dllexport)
    int l() { return 1; }

    __declspec(dllexport)
    int m() { return 2; }

    int n() { return 3; }
}

We compile them as:

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g++ -o file1.o -c file1.cpp -fPIC
g++ -o file2.o -c file2.cpp -fPIC

Consider the following linking example:

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g++ -o test1.dll file1.o file2.o -shared -fPIC
dumpbin /exports test1.dll

It works as expected, only __declspec(dllexport) symbols are exported:

But merging files into larger object file does not work:

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ld -r -o file3.o file1.o file2.o
g++ -o test2.dll file3.o -shared -fPIC
dumpbin /exports test2.dll

It gives all possible symbols exported in the DLL:

MinGW 8.1.0, tested different builds with the same result.
Any ideas how to make it work properly without using the DEF file?

Posted: **Sat Jul 30, 2022 6:27 pm**

Posted: **Sun Jul 31, 2022 10:20 am**

Finally, found the solution.
The problem was that original *.o files contain the additional .drectve section that holds export directives for the linker.
After processing these files with ld, we become new *.o file with omitted .drectve section.
So, the solution to get the expected result, is to force the ld to keep the .drectve section in the output object file.
Sadly, but there is no special option for ld.
But we can generate the default script for the [/b] ld where we observe the following:

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  /DISCARD/ :
  {
    *(.drectve)
    *(.debug$S)
    *(.debug$T)
    *(.debug$F)
  }

That means, that the .drectve section will be discarded in the output file.
So we need to patch this script:

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  .drectve  :
  {
    *(.drectve)
  }
  /DISCARD/ :
  {
    *(.debug$S)
    *(.debug$T)
    *(.debug$F)
  }

And pass this script as the -T option.
After that, all works fine.

LinuxMusicians

Stuck with DLL export

Stuck with DLL export

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