static_link_cpp_runtimes doesn't link the libstdc++ statically

[tomgr]

Description of the problem / feature request:

The static_link_cpp_runtimes feature doesn't link libstdc++ statically despite appearing to be intended to as per https://docs.bazel.build/versions/main/cc-toolchain-config-reference.html#well-known-features.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Create the following files:

BUILD:

cc_binary(
  name = "test",
  srcs = ["main.cc"],
  features = ["static_link_cpp_runtimes"],
)

main.cc:

#include <iostream>

int main(int argc, char** argv) { 
  std::cout << "Hello" << std::endl;
}

WORKSPACE:

Running bazel build //:test && ldd bazel-bin/test gives:

        linux-vdso.so.1 (0x00007fffccffa000)
        libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f3b2a2c9000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f3b2a1e5000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3b29fbd000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f3b2a4ea000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f3b29fa3000)

What operating system are you running Bazel on?

Ubuntu 22.04, but observed on several other Linuxes

What's the output of bazel info release?

release 6.0.0-pre.20211110.1. Using last_green with bazelisk also shows the same error (when I ran this last_green was cd4bc7c).

Have you found anything relevant by searching the web?

#8672 has a similar problem with fully_static_link, but this also statically links glibc, which we don't want. The solution there also depends on setting BAZEL_LINKLIBS but we'd like to be able to control which targets link libstdc++ statically individually. static_link_cpp_runtimes is also compiler-independent (if supported by the toolchain), unlike BAZEL_LINKLIBS.

[keith]

I just looked briefly but it looks to me like this just isn't supported in bazel, maybe it is in blaze

bazel/src/main/java/com/google/devtools/build/lib/rules/cpp/CcModule.java

Line 1225 in 3678d6a

/* supportsEmbeddedRuntimes= */ false,

[tomgr]

Thanks. I think it's only the auto-configuration that's not enabled as it seems you can define the static_link_cpp_runtimes feature yourself. If I copy the auto-generated local_config_cc and patch cc_toolchain_config.bzl to add:

    static_link_cpp_runtimes_feature = feature(
        name = "static_link_cpp_runtimes",
        enabled = False,
        flag_sets = [
            flag_set(
                actions = [
                    ACTION_NAMES.cpp_link_executable,
                    ACTION_NAMES.cpp_link_dynamic_library,
                    ACTION_NAMES.lto_index_for_executable,
                    ACTION_NAMES.lto_index_for_dynamic_library,
                ],
                flag_groups = [flag_group(flags = ["-static-libstdc++"])],
            ),
        ],
    )

(and also add this to the list of features that are exported), then I can get static linking to work by setting features = ["static_link_cpp_runtimes"]. To ensure that normal cc_binary targets remain dynamically linked I also had to modify the user_link_flags feature to add another flag set:

            flag_set(
                actions = all_link_actions + lto_index_actions,
                flag_groups = [flag_group(flags = ["-lstdc++"])],
                with_features = [
                    with_feature_set(
                        not_features = ["static_link_cpp_runtimes"],
                    ),
                ],
            ),

and then I modified the default value of BAZEL_LINKLIBS to remove "-lstdc++".

I wonder if it's worth patching bazel's unix_cc_configure.bzl to:

• Accept a user-definable list of flags that would be used to dynamically link the C++ runtime (maybe BAZEL_CXXSTDLIB_DYNAMIC). This would default to -lstdc++ and -lstdc++ would be removed from BAZEL_LINKLIBS.
• Accept a user-definable list of flags that would be used to statically link the C++ runtime (maybe BAZEL_CXXSTDLIB_STATIC). This would default to -static-libstdc++.

This would make it much easier to statically or dynamically link the c++ standard library than it is now, and would enable users to enable it either per binary, or globally. I'd be happy to work on a patch if this sounds like a useful direction.

[fmeum]

I would find this very useful. Making the auto-configured toolchains work well with all advertised Bazel features is also especially helpful for those new to Bazel.

[github-actions]

Thank you for contributing to the Bazel repository! This issue has been marked as stale since it has not had any activity in the last 1+ years. It will be closed in the next 14 days unless any other activity occurs or one of the following labels is added: "not stale", "awaiting-bazeler". Please reach out to the triage team (@bazelbuild/triage) if you think this issue is still relevant or you are interested in getting the issue resolved.

[fhanau]

This is an ongoing issue and should not be marked as stale.

The workaround of setting BAZEL_LINKLIBS works for me on Linux (e.g. BAZEL_LINKLIBS='-l%:libc++.a -lm -static-libgcc' when using libc++) and by using --action_env it can also be used through the command line or bazelrc. Still, it would be much nicer to have the feature flag supported so this can be set on the target level.

[Synss]

I've added the feature to unix_cc_toolchain_config.bzl based on @tomgr's comment. Maybe that's useful to others as well.

• add_static_link... is the patch documented by Tom.
• fork_cc_toolchain_config is a repository rule that makes unix_cc_toolchain_config available under a different name and adds the feature with the patch. Note that it has to be a repo rule as we're patching some basic Bazel functionality and no external dependency. When https://github.com/bazelbuild/rules_cc/blob/main/cc/private/toolchain/unix_cc_toolchain_config.bzl becomes public, then patching will be as simple as with any other 3rd party.

That's basically all there is to it.

Change is Checkmk/checkmk@3ee513a

[fmeum]

@Synss Would you be willing to send a PR to Bazel with this change? It looks good to me and I can also help find a reviewer.

[Synss]

Of course! I’ll be happy if the patch gets upstreamed and I don’t have to maintain it! 😉 I’ll look into sending a PR tomorrow.

[apivovarov]

Related Discussion:

How to build cpp executable with static libsdtc++.a? -lstdc++ is hardcoded in bazel!!!
#23324

Solution:

export BAZEL_LINKLIBS="-l%:libstdc++.a:-lm"

After that all executables generated by bazel build will have libstdc++ linked statically.