On Feb 13, 2013, at 16:47, Alexey Belkevich wrote:
>> Hello, can someone please explain the reason (and how to cope with) that
>> ff_log2_tab is defined multiple times with #include "libavutil/log2_tab.c"
>> in the ffmpeg v1.1 libraries like libavcodec 54.91.102 and companions ??
You have identified the reason; ff_log2_tab is defined in libavutil/log2_tab.c,
which is included in files of the same name from libavcodec, libavformat and
libswresample. This may not be a problem when using dynamic libraries, but with
static libraries it can become one if the linker is forced to link in those
different log2_tab.o modules. And this will be the case even if the dependency
is "intra-library" (i.e., a module from lavc accessing ff_log2_tab and another
module from lavf also accessing ff_log2_tab).
Do you by any chance use this array in your own code? Do you confirm that you
do not get the error when linking ffmpeg in the same build environment? Either
way, add a line V=1 to the ffmpeg toplevel Makefile so you get to follow the
full build process, with the detailed invocations. It could be that you'll find
that the option to suppress or ignore duplicate symbols is specified at the
relevant linking stages.
Anyway, it seems like a workaround shouldn't be too hard. Is there any reason
to have ff_log2_tab be exported by 4 libraries, if at all (and if so, is there
a reason not to have an inter-library dependency on libavutil)? If not, a macro
could be defined in lib{avcodec,avformat,swresample}/*config.h to do a bit of
C++-style name mangling on ff_log2_tab, such that each library includes it from
the same single source but using a slightly different name. Or simpler, since
the number of files using the variable isn't large (and the table itself isn't
either), just declare it static in a header file and include that in each file
that accesses the variable.
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