Build error: read-only reference ‘value’ used as ‘asm’ output

[eyalroz]

Describe your environment

• SLES 15 SP 1
• g++ 7.4.1
• Kernel 4.12.14-195-default
• googletest-1.14.0 manually downloaded built and installed under /opt/gtest
• Google benchmark 1.8.3 manually downloaded built and installed under /opt/benchmark
• CMake 3.27.1 manually downloaded and installed under
• main branch, commit 0803e6a .

Steps to reproduce

• Used CMake to configure
• Used CMake to build

What is the expected behavior?

Build should have concluded successfully

What is the actual behavior?

During build, got the error:

In file included from /path/to/src/opentelemetry-cpp/sdk/test/trace/sampler_benchmark.cc:17:0:
/opt/benchmark/include/benchmark/benchmark.h: In instantiation of ‘typename std::enable_if<((! std::is_trivially_copyable<_Tp>::value) || (sizeof (Tp) > sizeof (Tp*)))>::type benchmark::DoNotOptimize(Tp&&) [with Tp = opentelemetry::v1::sdk::trace::ParentBasedSampler; typename std::enable_if<((! std::is_trivially_copyable<_Tp>::value) || (sizeof (Tp) > sizeof (Tp*)))>::type = void]’:
/path/to/src/opentelemetry-cpp/sdk/test/trace/sampler_benchmark.cc:49:85:   required from here
/opt/benchmark/include/benchmark/benchmark.h:540:46: error: read-only reference ‘value’ used as ‘asm’ output
   asm volatile("" : "+m"(value) : : "memory");
                                              ^
/opt/benchmark/include/benchmark/benchmark.h: In instantiation of ‘typename std::enable_if<((! std::is_trivially_copyable<_Tp>::value) || (sizeof (Tp) > sizeof (Tp*)))>::type benchmark::DoNotOptimize(Tp&&) [with Tp = opentelemetry::v1::sdk::trace::TraceIdRatioBasedSampler; typename std::enable_if<((! std::is_trivially_copyable<_Tp>::value) || (sizeof (Tp) > sizeof (Tp*)))>::type = void]’:
/path/to/src/opentelemetry-cpp/sdk/test/trace/sampler_benchmark.cc:58:60:   required from here
/opt/benchmark/include/benchmark/benchmark.h:540:46: error: read-only reference ‘value’ used as ‘asm’ output

Additional context

N/A

[marcalff]

Related:

• DoNotOptimize on values with const members google/benchmark#764

[eyalroz]

@marcalff : So, is this also a simple matter of calling the right overload? Or perhaps const-casting? Anyway, I would gladly try to build from a bugfix branch.

[marcalff]

First, please clarify which version of opentelemetry-cpp is used.

Regarding the error seen, the content of /opt/benchmark/include/benchmark/benchmark.h:540 is

https://github.com/google/benchmark/blob/main/include/benchmark/benchmark.h#L535-L541

template <class Tp>
inline BENCHMARK_ALWAYS_INLINE
    typename std::enable_if<!std::is_trivially_copyable<Tp>::value ||
                            (sizeof(Tp) > sizeof(Tp*))>::type
    DoNotOptimize(Tp&& value) {
  asm volatile("" : "+m"(value) : : "memory");
}

This sounds like a bug in google benchmark itself: if the std::enable_if condition is satisfied, then the method implemented inline should compile, and it does not.

Now, this header files has a few ifdef, in particular with BENCHMARK_HAS_CXX11 and friends.

Please clarify, and double check, which c++ options are used for this build (C++11/C++14/C++17/etc).

[psmoot]

I encountered this issue too.

I'm using OpenSUSE Leap 15.4 with gcc 7.5.0. I cloned the opentelemtry-cli repo at commit 0eaa794.

I tried this twice, once setting -DCMAKE_CXX_STANDARD=17 and once -DCMAKE_CXX_STANDARD=14. I had the same issue without setting the C++ standard at all. I'd let you know the versions of gtest and benchmark but TBH, I don't know how to figure those out.

[eyalroz]

@marcalff : Ah, yes, sorry. I followed the INSTALL.md instructions and used the main branch. See edit of initial comment.

[marcalff]

After investigations, it turns out that:

• building with both benchmark 1.8.2 and benchmark 1.8.3 fails.
• building with both opentelemetry-cpp 1.11.0 and main (0eaa794) fails

It seems this bug has been present for a long time, this is not a recent regression (opentelemetry-cpp changes to abandon C++11, or recent changes in benchmark).

Failed to build with:

• g++-12 (SUSE Linux) 12.3.0 (verified)
• g++-7 (SUSE Linux) 7.5.0 (verified)
• g++ 7.4.1 (reported)

[marcalff]

Filed upstream as:

• [BUG] DoNotOptimize build break with GCC google/benchmark#1675

as this looks like a problem in the benchmark header files with the work around implemented for GCC.

[psmoot]

@marcalff : Can you suggest a workaround while an actual fix is in progress?

For my purposes, I could skip benchmarking entirely. I just need it to work, working fast can be deferred.

I'm also quite rusty with CMake so short, simple instructions would be greatly appreciated.

[marcalff]

@psmoot

An obvious work around is to skip benchmarks entirely, which requires no code change:

cmake -DWITH_BENCHMARK=OFF

[eyalroz]

@marcalff : Thanks for that. Just remember that what's obvious for project developers is not always obvious to users, so it's a good thing to point this kind of stuff out when bugs are filed.