[BUG] LNK4217 and LNK4286 warnings when linking //:benchmark_main

[junyer]

…
INFO: From Linking regexp_benchmark.exe:
   Creating library bazel-out\x64_windows-dbg\bin\regexp_benchmark.lib and object bazel-out\x64_windows-dbg\bin\regexp_benchmark.exp
LINK : warning LNK4217: symbol '?RegisterBenchmarkInternal@internal@benchmark@@YAPEAVBenchmark@12@PEAV312@@Z (class benchmark::internal::Benchmark * __cdecl benchmark::internal::RegisterBenchmarkInternal(class benchmark::internal::Benchmark *))' defined in 'benchmark.lib(benchmark_register.obj)' is imported by 'regexp_benchmark.obj' in function '"void __cdecl re2::`dynamic initializer for 'benchmark_uniq_100_benchmark_''(void)" (??__Ebenchmark_uniq_100_benchmark_@re2@@YAXXZ)'
LINK : warning LNK4217: symbol '?InitializeStreams@internal@benchmark@@YAHXZ (int __cdecl benchmark::internal::InitializeStreams(void))' defined in 'benchmark.lib(benchmark.obj)' is imported by 'regexp_benchmark.obj' in function '"void __cdecl benchmark::internal::`dynamic initializer for 'stream_init_anchor''(void)" (??__Estream_init_anchor@internal@benchmark@@YAXXZ)'
LINK : warning LNK4286: symbol '?InitializeStreams@internal@benchmark@@YAHXZ (int __cdecl benchmark::internal::InitializeStreams(void))' defined in 'benchmark.lib(benchmark.obj)' is imported by 'benchmark_main.lib(benchmark_main.obj)'
…

(The full logs are here.)

[junyer]

Both warnings are essentially saying that __declspec(dllimport) is bogus in that linking context, which makes sense to me because the DLL wasn't involved. Does //:benchmark_main need local_defines = ["BENCHMARK_STATIC_DEFINE"] as well?

[junyer]

Oh, and I just noticed this too:

…
INFO: From Compiling src/benchmark_main.cc:
external/com_github_google_benchmark/src/benchmark_main.cc(18): warning C4273: 'main': inconsistent dll linkage
external/com_github_google_benchmark/src/benchmark_main.cc(17): note: see previous definition of 'main'
…

What's up with that? O_o

[sergiud]

I don't know what local_defines does, but when building and consuming a static library version of benchmark, BENCHMARK_EXPORT should never expand to __declspec(dllimport|dllexport) while BENCHMARK_STATIC_DEFINE should be set both when building and consuming benchmark.

To summarize, the following rules apply:

• Static library:
  • BENCHMARK_STATIC_DEFINE set the during the library build and propagated to dependencies
  • BENCHMARK_EXPORT is empty
  • (benchmark_EXPORTS not relevant)
• Shared library:
  • benchmark_EXPORTS set only during the build but not propagated to dependencies
  • BENCHMARK_EXPORT expands to __declspec(dllexport) during the build and __declspec(dllimport) when propagated to dependencies

There might be an inconsistency in the way Bazel propagates defines.

[junyer]

Do we need Bazel to create the dynamic library? I'm asking because I'm not aware of any way to make Bazel follow such rules, but we can easily stop Bazel from ever creating the dynamic library by setting linkstatic = True on the cc_library target. (The documentation for linkstatic describes this behaviour towards the end.)

[sergiud]

This is the easy way out. Alternatively, one could build two library variants separately.

[junyer]

@dominichamon, do you know whether anyone or anything expects Bazel to create the dynamic library? My experience has been entirely with dynamic libraries (e.g. Python extensions) that are opened at runtime (e.g. by Python), not linked by Bazel during dependent build actions. Unless the Bazel build needs to support a use case such as packaging, erring on the side of simplicity seems preferable for now.

[dmah42]

when building benchmark_main, i think either a dynamic or static library would be appropriate. i don't think there's much of an expectation either way more broadly.

[junyer]

Posted #1373 for review. :)

[junyer]

After following up with #1374, I reran the CI job for RE2 and it's now showing zero warnings related to the benchmark library across Linux, macOS and Windows. Thanks!