1. 25 Nov, 2012 1 commit
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  3. 18 Nov, 2012 3 commits
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  17. 20 Oct, 2012 1 commit
  18. 19 Oct, 2012 2 commits
  19. 18 Oct, 2012 2 commits
    • Martin Storsjö's avatar
      Add support for building shared libraries with MSVC · d66c52c2
      Martin Storsjö authored
      This requires the makedef perl script by Derek, from the
      c89-to-c99 repo. That scripts produces a .def file, listing
      the symbols to be exported, based on the gcc version scripts
      and the built object files.
      To properly load non-function symbols from DLL files, the
      data symbol declarations need to have the attribute
      __declspec(dllimport) when building the calling code. (On mingw,
      the linker can fix this up automatically, which is why it has not
      been an issue so far. If this attribute is omitted, linking
      actually succeeds, but reads from the table will not produce the
      desired results at runtime.)
      MSVC seems to manage to link DLLs (and run properly) even if
      this attribute is present while building the library itself
      (which normally isn't recommended) - other object files in the
      same library manage to link to the symbol (with a small warning
      at link time, like "warning LNK4049: locally defined symbol
      _avpriv_mpa_bitrate_tab imported" - it doesn't seem to be possible
      to squelch this warning), and the definition of the tables
      themselves produce a warning that can be squelched ("warning C4273:
      'avpriv_mpa_bitrate_tab' : inconsistent dll linkage, see previous
      definition of 'avpriv_mpa_bitrate_tab').
      In this setup, mingw isn't able to link object files that refer to
      data symbols with __declspec(dllimport) without those symbols
      actually being linked via a DLL (linking avcodec.dll ends up with
      errors like "undefined reference to `__imp__avpriv_mpa_freq_tab'").
      The dllimport declspec isn't needed at all in mingw, so we simply
      choose not to declare it for other compilers than MSVC that requires
      it. (If ICL support later requires it, the condition can be extended
      later to include both of them.)
      This also implies that code that is built to link to a certain
      library as a DLL can't link to the same library as a static library.
      Therefore, we only allow building either static or shared but not
      both at the same time. (That is, static libraries as such can be,
      and actually are, built - this is used for linking the test tools to
      internal symbols in the libraries - but e.g. libavformat built to
      link to libavcodec as a DLL cannot link statically to libavcodec.)
      Also, linking to DLLs is slightly different from linking to shared
      libraries on other platforms. DLLs use a thing called import
      libraries, which is basically a stub library allowing the linker
      to know which symbols exist in the DLL and what name the DLL will
      have at runtime.
      In mingw/gcc, the import library is usually named libfoo.dll.a,
      which goes next to a static library named libfoo.a. This allows
      gcc to pick the dynamic one, if available, from the normal -lfoo
      switches, just as it does for libfoo.a vs libfoo.so on Unix. On
      MSVC however, you need to literally specify the name of the import
      library instead of the static library.
      Signed-off-by: 's avatarMartin Storsjö <martin@martin.st>
    • Martin Storsjö's avatar
      configure: Split out msvc as a separate target OS · 53e8cd68
      Martin Storsjö authored
      The name mingw32 as target OS is both misleading, and very little
      of the target OS specific settings actually match.
      Since the target OS default is set based on uname, the default
      (which on MSYS is set to mingw) is overridden by --toolchain=msvc.
      Signed-off-by: 's avatarMartin Storsjö <martin@martin.st>
  20. 17 Oct, 2012 3 commits
  21. 16 Oct, 2012 1 commit