mingw -fvisibility=hidden does not seem to work

6
votes

I have a shared library which is supposed to export only one function which is marked with __attribute__ ((visibility ("default"))). It also links with another static library (fftw), and

#include<fftw3.h>

is preceded with:

#pragma GCC visibility push(hidden)

The linker command used:

g++.exe -fvisibility=hidden -shared -o mylib.dll -Wl,--out-implib,mylib.dll.a -Wl,--no-whole-archive libfftw3.a libfftw3_omp.a -lgomp

Now the resulting library is huge and if I check the exported functions it includes ALL fftw functions, and ALL function from my files. It looks like mingw ignores visibility options. I read that previously it gave warning about -fvisibility, but now it compiles with no warnings whatsoever.

Does mingw and gcc 4.6.1 support visibility flags? If yes, how do I get rid of all unnecessary stuff in my shared library?

2
shared-librariesmingwvisibility

2 Answers

4
votes

Mingw is a Windows port of GCC toolchain but Windows dll are not Linux so. Especially the link part is different. To specify the visibility with MingGW you have to go the Windows way and annotate your classes and functions with :

  • __declspec(dllexport) while compiling the library
  • __declspec(dllimport) while linking

If you want multiplatform support for the GCC toolchain you can add a header in your project doing that for you. For a step by step example and lots of details have a look at GCC's visibility guide.

2
votes

Windows PE object files do not have visibility attributes. The closest is dllexport/dllimport, but that's only for shared libraries (DLL's). So either you don't mark all FFTW functions with __declspec(dllexport), and hope linking the static library does The Right Thing (tm), or you take care not to link to FFTW if linking with your library.

It should warn about bad visibility attributes, perhaps you need to turn up the warning level -Wall -Wextra -pedantic).