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[Bero-b <1488254@xxxxxxxxxxxxxxxxxx>]

OpenMandriva has successfully changed the compiler to clang (3.7.1 for
now, will update to 3.8 as it is released), but decided to stick with
libstdc++ to preserve binary compatibility with other Linux
distributions -- users want to run non-open source stuff like steam, and
that stuff doesn't get built for OSes that don't have a giant user base.

OpenMandriva could switch system libraries etc. to libc++, but even then
problems would likely arise (e.g. binary-only application links to Qt
and expects Qt to be linked to libstdc++ -- the only "fix" would be
providing 2 different versions of all C++ libraries and even then things
would likely break, with e.g. libstdc++-Qt not being able to load style
plugins built for libc++-Qt and vice versa, so custom installed widget
themes wouldn't work for binary-only applications).

So yes, there indeed is a use case for building the entire OS with clang
but not libc++ until we get to a point where relevant closed source
stuff switches to libc++ (or better yet, gets open sourced so people can
link it to any STL they like).

-- 
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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