Mislinking when using bazel with clang and libc++

[Thomas Köppe]

I am trying to use the clang C++ compiler with Bazel, as well as the libc++ standard library implementation. To this end I set my system up as follows:

• Install clang, libc++-dev, libc++abi-dev
• Symlink /usr/lib/llvm-11/include/c++/v1 to /usr/include/c++/v1
• Cet the environment CC=clang-11

At this point, note that regular building works as expected and uses clang, but still with libstdc++.

Now I switch to libc++ by using the following build flags:

• --copt=-stdlib=libc++ --linkopt=-lc++abi --linkopt=-lc++
  

What I now see is that the resulting binary is linked _both_ against libc++ and libstdc++. I made a tiny toy cc_library :foo, and here are the relevant entries in bazel-bin/foo-2.params:

-o

bazel-out/k8-opt/bin/foo

-fuse-ld=/usr/bin/ld.gold

-Wl,-no-as-needed

-Wl,-z,relro,-z,now

-B/usr/bin

-lstdc++

-lm

-Wl,--gc-sections

bazel-out/k8-opt/bin/_objs/foo/foo.o

-lc++abi

-lc++

Is there anything I'm doing wrong, and how should I go about using libc++?

Thank you!

Thomas

[re:fi.64]

Check out Envoy's libc++ config, important parts start here: https://github.com/envoyproxy/envoy/blob/master/.bazelrc#L113

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[tko...@google.com]

Thank you very much, that works like a charm!

For the record, the solution is to use the following flags instead:

--action_env=CXXFLAGS=-stdlib=libc++ --action_env=LDFLAGS=-stdlib=libc++ --action_env=BAZEL_CXXOPTS=-stdlib=libc++ --action_env=BAZEL_LINKOPTS=-lc++:-lm