LZ4 test functions exposed, causing linker errors

[sybrenstuvel]

Description of Issue

Blender cannot link against USD library version 21.02, because the latter exports the names LZ4_compress_forceExtDict and LZ4_decompress_safe_forceExtDict.

This issue was likely introduced in commit df48692. As you can see in the commit message of 4da033b, the LZ4 symbols are supposed to be encapsulated in a C++ namespace. However, since df48692 these two symbols are marked as export "C" and thus collide with other libraries.

Steps to Reproduce

1. Build USD as static library
2. Run nm -C libusd_m.a | grep LZ4
3. See that LZ4_compress_forceExtDict and LZ4_decompress_safe_forceExtDict are listed.

System Information (OS, Hardware)

Kubuntu Linux 20.04 and CentOS 7

Package Versions

USD 21.02

Build Flags

We build with these extra flags, to ensure that USD uses the correct precompiled libraries used to build Blender:

  -DBoost_COMPILER:STRING=${BOOST_COMPILER_STRING}
  -DBoost_USE_MULTITHREADED=ON
  -DBoost_USE_STATIC_LIBS=ON
  -DBoost_USE_STATIC_RUNTIME=OFF
  -DBOOST_ROOT=${LIBDIR}/boost
  -DBoost_NO_SYSTEM_PATHS=ON
  -DBoost_NO_BOOST_CMAKE=ON
  -DTBB_INCLUDE_DIRS=${LIBDIR}/tbb/include
  -DTBB_LIBRARIES=${LIBDIR}/tbb/lib/${LIBPREFIX}${TBB_LIBRARY}${LIBEXT}
  -DTbb_TBB_LIBRARY=${LIBDIR}/tbb/lib/${LIBPREFIX}${TBB_LIBRARY}${LIBEXT}
  # USD wants the tbb debug lib set even when you are doing a release build
  # Otherwise it will error out during the cmake configure phase.
  -DTBB_LIBRARIES_DEBUG=${LIBDIR}/tbb/lib/${LIBPREFIX}${TBB_LIBRARY}${LIBEXT}

  # This is a preventative measure that avoids possible conflicts when add-ons
  # try to load another USD library into the same process space.
  -DPXR_SET_INTERNAL_NAMESPACE=usdBlender

  -DPXR_ENABLE_PYTHON_SUPPORT=OFF
  -DPXR_BUILD_IMAGING=OFF
  -DPXR_BUILD_TESTS=OFF
  -DBUILD_SHARED_LIBS=OFF
  -DPYTHON_EXECUTABLE=${PYTHON_BINARY}
  -DPXR_BUILD_MONOLITHIC=ON
  -DPXR_BUILD_USD_TOOLS=OFF

  -DCMAKE_DEBUG_POSTFIX=_d
  # USD is hellbound on making a shared lib, unless you point this variable to a valid cmake file
  # doesn't have to make sense, but as long as it points somewhere valid it will skip the shared lib.
  -DPXR_MONOLITHIC_IMPORT=${BUILD_DIR}/usd/src/external_usd/cmake/defaults/Version.cmake

[jilliene]

Filed as internal issue #USD-6563

[gitamohr]

Oof. Sorry for the trouble here. I'll get it fixed up.