desktop-packages team mailing list archive

[Renato Golin <1488254@xxxxxxxxxxxxxxxxxx>]

(In reply to comment #42)
> 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.

If you ship GCC at all, and if that happens to be 5.x, and you happen to
choose to enable the CXX11 ABI by default, you'll run into the exact
same problem. Doesn't matter who's on top.


> 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).

That, in addition to multilib/multiarch will be a major pain for all
distros. This really isn't a solution.


> 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).

Even if the day Clang and libc++ become the top dog on most Linux
distributions ever comes, we'll still have to cope with legacy GCC and
libstdc++ for a good number of decades from then on.

Coexisting is the only solution for this century.

-- 
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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