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[Octoploid <1488254@xxxxxxxxxxxxxxxxxx>]

(In reply to comment #25)
> Following up on the Linaro Toolchain list[1], I found out a few facts:
> 
> 1. This feature was implemented in GCC and libstdc++ in 2012, after
> discussions on the cauldron with distro representatives.

No. It was implemented in April this year, shortly before the gcc-5 release.
I've pointed out compatibility issue immediately:
https://gcc.gnu.org/ml/gcc-patches/2015-04/msg00153.html

> 2. The feature is poorly documented, and may have changed behaviour until
> recently. I have no evidence of changes, is anyone does, please update.

The were no behavioral changes at all after that patch went in.
 
> 3. The problem only started because distros have chosen GCC 5 as their
> default compilers for the current releases, which defaults to C++11.

No gcc-5 doesn't default to C++11 and the issue here has nothing to do with 
C++98 vs. C++11.

Please try to get the facts strait, before posting long misleading
replies.

-- 
You received this bug notification because you are a member of Desktop
Packages, which is subscribed to llvm-toolchain-3.6 in Ubuntu.
https://bugs.launchpad.net/bugs/1488254

Title:
  clang++ no longer ABI-compatible with g++

Status in LLVM:
  Confirmed
Status in llvm-toolchain-3.6 package in Ubuntu:
  Confirmed

Bug description:
  $ cat foo.cc
  #include <string>
  std::string hello = "Hello, world!\n";
  $ cat bar.cc
  #include <string>
  #include <iostream>
  extern std::string hello;
  int main() {
      std::cout << hello;
      return 0;
  }
  $ g++ -c foo.cc && g++ foo.o bar.cc && ./a.out
  Hello, world!
  $ clang++ -c foo.cc && clang++ foo.o bar.cc && ./a.out
  Hello, world!
  $ g++ -c foo.cc && clang++ foo.o bar.cc && ./a.out
  /tmp/bar-34fb23.o: In function `main':
  bar.cc:(.text+0x14): undefined reference to `hello'
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  $ clang++ -c foo.cc && g++ foo.o bar.cc && ./a.out
  /tmp/ccqU38Mh.o: In function `main':
  bar.cc:(.text+0x5): undefined reference to `hello[abi:cxx11]'
  collect2: error: ld returned 1 exit status

  In practice, this means that many programs using C++ libraries other
  than libstdc++ fail to compile with clang++. For example, mosh fails
  with undefined references to
  google::protobuf::internal::empty_string_,
  google::protobuf::MessageLite::InitializationErrorString() const, and
  google::protobuf::MessageLite::SerializeAsString() const.

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