Currently, ffms2 attempts to link against ffmpeg to determine whether the -Wl,-Bsymbolic flag is required:
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AC_DEFUN([TEST_FFMPEG], |
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[AC_LINK_IFELSE([AC_LANG_PROGRAM([[ |
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#include <libavformat/avformat.h> |
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#include <libswscale/swscale.h> |
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]],[[ |
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avformat_network_init(); |
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swscale_version(); |
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]])], [eval $1=yes], [eval $1=no]) |
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]) |
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AC_MSG_CHECKING([whether FFmpeg works]) |
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LIBS="$_LIBS $FFMPEG_LIBS" |
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TEST_FFMPEG([FFMPEG_WORKS]) |
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AC_MSG_RESULT([$FFMPEG_WORKS]) |
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if test "$FFMPEG_WORKS" = no; then |
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AC_MSG_FAILURE([cannot link with FFmpeg]) |
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fi |
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src_core_libffms2_la_LDFLAGS="" |
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AC_MSG_CHECKING([whether -Wl,-Bsymbolic is needed]) |
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if test "$enable_shared" = yes; then |
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_LDFLAGS="$LDFLAGS" |
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LDFLAGS="$LDFLAGS -shared $lt_prog_compiler_pic" |
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TEST_FFMPEG([no_bsymbolic]) |
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if test "$no_bsymbolic" = "no"; then |
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LDFLAGS="$LDFLAGS -Wl,-Bsymbolic" |
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TEST_FFMPEG([bsymbolic]) |
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if test "$bsymbolic" = "yes"; then |
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src_core_libffms2_la_LDFLAGS="$src_core_libffms2_la_LDFLAGS -Wl,-Bsymbolic" |
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else |
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AC_MSG_RESULT($bsymbolic) |
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AC_MSG_FAILURE([cannot build ffms2 as a shared library]) |
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fi |
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else |
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bsymbolic=no |
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fi |
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LDFLAGS="$_LDFLAGS" |
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src_core_libffms2_la_LDFLAGS="$src_core_libffms2_la_LDFLAGS -version-info $VERSION_INFO" |
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else |
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bsymbolic=no |
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fi |
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AC_SUBST([src_core_libffms2_la_LDFLAGS]) |
ffmpeg documentation explains when this flag is necessary: https://ffmpeg.org/platform.html#Advanced-linking-configuration
The problem is that ffmpeg may not be available at configure time. For example when the user is relying on a *-uninstalled.pc (ex: libswresample-uninstalled.pc) file. In this situation, the current test will fail, making it impossible to build ffms2.
