These changes come from @chadaustin in this commit: https://github.com/imvu/emscripten/commit/0b590e6d62970e9ed67ebf4d00d4ca30e9ef8d0c I checked that these changes are not present in libcxxabi trunk. Reverting this commit locally doesn't cause any warnings or build errors though.

I think Chad's fix is correct. %ld specifier is for 'long int', and the type that is passed is a size_t. On some platforms, long int can be 32-bit, whereas size_t can be 64-bit. The fix uses %lu for 'unsigned long' and makes the parameter match. Chad or @waywardmonkeys , do you know if this has already been reported to libcxxabi?