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glog, gflags, and C++ ABI

Publish date: Jun 12, 2020
Last updated: May 22, 2021

I recently got back to one of my previous project, which uses the two excellent Google-developed libraries: glog and gflags. My project used to work well, but since the time I’ve been away is long, and the system has been upgraded and modified by others somehow, it unfortunately cannot be successfully built, and the major problem lied in glog and gflags. The error message is as follows:

undefined reference to `google::base::CheckOpMessageBuilder::NewString[abi:cxx11]()'

Luckily, I have fixed this problem in the end and realized that the key problem was related to the C++ ABI, but the whole progress of locating and resolving the problem was exhaustive and tedious. Therefore, I would like to share my experience and thoughts on this problem, in case others suffer from the same trap.

Setup

The test code -

#include <glog/logging.h>

int main(int argc, char *argv[]) {
  google::InitGoogleLogging(argv[0]);

  CHECK_EQ(1, 2) << "1 doesn't equal to 2";

  return 0;
}

The compiler I use is GCC 7.3.0. cmake should be available as well.

To compile the previous code snippet, I’ve downloaded glog==0.4.0 and gflags==2.2.2, both from their corresponding GitHub repositories.

gflags/gflags

google/glog

Here are the commends that I used to compile these two libraries:

# compile gflags
wget https://github.com/gflags/gflags/archive/v2.2.2.tar.gz
tar xvf v2.2.0.tar.gz
cd gflags-2.2.2 && mkdir build && cd build 
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/.local -DBUILD_SHARED_LIBS=ON -DCMAKE_CXX_FLAGS="-std=c++11 -D_GLIBCXX_USE_CXX11_ABI=1"
make install
# compile glog
wget https://github.com/google/glog/archive/v0.4.0.tar.gz
tar xvf v0.4.0.tar.gz
cd glog-0.4.0 && mkdir build cd build
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/.local -DBUILD_SHARED_LIBS=ON -DCMAKE_CXX_FLAGS="-std=c++11 -D_GLIBCXX_USE_CXX11_ABI=1"
make install

The CMAKE_INSTALL_PREFIX can be anywhere you prefer. Please note that there is a -D_GLIBCXX_USE_CXX11_ABI=1 in -DCMAKE_CXX_FLAGS parameter of the cmake command. We will get back to this later.

Once you’ve successfully compiled them, you can create a file [main.cc](http://main.cc) that includes the test code above, and then compile it by

g++ main.cc -o main -I$HOME/.local/include -L$HOME/.local/lib -lglog -lgflags

And you will find the following error messages:

/tmp/ccoKxaIW.o: In function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >* google::MakeCheckOpString<int, int>(int const&, int const&, char const*)':
main.cc:(.text._ZN6google17MakeCheckOpStringIiiEEPNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_RKT0_PKc[_ZN6google17MakeCheckOpStringIiiEEPNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_RKT0_PKc]+0x6c): undefined reference to `google::base::CheckOpMessageBuilder::NewString[abi:cxx11]()'
$HOME/.local/lib/libglog.so: undefined reference to `google::FlagRegisterer::FlagRegisterer<std::string>(char const*, char const*, char const*, std::string*, std::string*)'
collect2: error: ld returned 1 exit status

Basically, you cannot find references to:

  1. google::base::CheckOpMessageBuilder::NewString[abi:cxx11]();

  2. google::FlagRegisterer::FlagRegisterer<std::string>(...);

Now it is our turn to find out what the actual problem is.

Two types of string

The error messages say we cannot find references to some symbols, but is this really the case? We can use nm to find it out.

nm $HOME/.local/lib/libgflags.so | grep FlagRegisterer | c++filt

This command looks up [libgflags.so](http://libgflags.so) and tries to find whether there exists FlagRegisterer. Its output is as follows:

0000000000026406 W google::FlagRegisterer::FlagRegisterer<bool>(char const*, char const*, char const*, bool*, bool*)
00000000000266e0 W google::FlagRegisterer::FlagRegisterer<double>(char const*, char const*, char const*, double*, double*)
0000000000026498 W google::FlagRegisterer::FlagRegisterer<int>(char const*, char const*, char const*, int*, int*)
000000000002652a W google::FlagRegisterer::FlagRegisterer<unsigned int>(char const*, char const*, char const*, unsigned int*, unsigned int*)
00000000000265bc W google::FlagRegisterer::FlagRegisterer<long>(char const*, char const*, char const*, long*, long*)
000000000002664e W google::FlagRegisterer::FlagRegisterer<unsigned long>(char const*, char const*, char const*, unsigned long*, unsigned long*)
0000000000026772 W google::FlagRegisterer::FlagRegisterer<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(char const*, char const*, char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*)
0000000000026406 W google::FlagRegisterer::FlagRegisterer<bool>(char const*, char const*, char const*, bool*, bool*)
00000000000266e0 W google::FlagRegisterer::FlagRegisterer<double>(char const*, char const*, char const*, double*, double*)
0000000000026498 W google::FlagRegisterer::FlagRegisterer<int>(char const*, char const*, char const*, int*, int*)
000000000002652a W google::FlagRegisterer::FlagRegisterer<unsigned int>(char const*, char const*, char const*, unsigned int*, unsigned int*)
00000000000265bc W google::FlagRegisterer::FlagRegisterer<long>(char const*, char const*, char const*, long*, long*)
000000000002664e W google::FlagRegisterer::FlagRegisterer<unsigned long>(char const*, char const*, char const*, unsigned long*, unsigned long*)
0000000000026772 W google::FlagRegisterer::FlagRegisterer<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(char const*, char const*, char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*)

So [libgflags.so](http://libgflags.so) has FlagRegisterer, while it is not specialized for type std::string. Such that we cannot find a reference to FlagRegisterer<std::string>.

There is a specialization quite close to our need:

0000000000026772 W google::FlagRegisterer::FlagRegisterer<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(char const*, char const*, char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*)

It is clear that this is a C++ ABI problem. libglog.so, which the reference problems originate from, wants a string type that is not C++11 ABI compatible. Since we compile gflags with -D_GLIBCXX_USE_CXX11_ABI=1, which is the default setting for GCC ≥ 5.1 (source), FlagRegisterer is only specialized for string under namespace std::__cxx11.

We can compile again the gflags library with -D_GLIBCXX_USE_CXX11_ABI=0. This time, we can get FlagRegisterer related symbols as follows:

0000000000022ac6 W google::FlagRegisterer::FlagRegisterer<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >(char const*, char const*, char const*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >*)

See? There is no std::__cxx11 in the template argument.

Mystery glog

You may come up with a question: since you’ve compiled both glog and gflags in with C++11 ABI, why the problem still exists? In another word, shouldn’t glog search for std::__cxx11::string instead?

I’m afraid I’ve got no answer for that. And I don’t think I can figure out an answer in short time. If anyone can show a hint I will be very happy 😃

Anyway, it seems that we should recompile both glog and gflags with -D_GLIBCXX_USE_CXX11_ABI=0.

Summary

The final solution to my problem is that, I should compile both glog an gflags without C++11 ABI, as well as the application that linked to them:

g++ main.cc -o main -I$HOME/.local/include -L$HOME/.local/lib -lglog -lgflags -D_GLIBCXX_USE_CXX11_ABI=0

The solution looks simple, but the path to find it was not that easy. The final takeaway might be, keep that C++ ABI problem in mind, and when you cannot correctly get a reference to some symbol, use nm to look into the library file.

Happy coding!

References

Converting std::__cxx11::string to std::string

Dual ABI

Cxx11AbiCompatibility - GCC Wiki

undefined reference to ‘FlagRegisterer::FlagRegisterer’ · Issue #203 · gflags/gflags