(In reply to comment #32) > (In reply to comment #31) > > (In reply to comment #28) > > > The incompatibility was introduced by gcc's "automatic tagging of > > > functions > > > and variables with tagged types where the tags are not already reflected > > > in > > > the mangled name". > > > > > > Now every library function with e.g a std::string return type causes > > > linker > > > errors. > > > > > > To solve this issue, Clang only would have to implement the return type > > > ABI > > > tagging. All other ABI tags are irrelevant AFAIK. > > > > The change was necessary to support dual-abi in one binary; you need to > > be able to distinguish different ABIs in the return type. > > No, the "automatic tagging of function return types" was unnecessary. The new > ABI was working perfectly fine with both compilers before that change.
As long as you keep the ABIs completely separated it works, yes. To get basic dual ABI support you could require manual tagging of all functions which need tags (like, say, `std::string std::to_string(int)`) - but such procedure would be way too much work and error prone. Especially if you have third party libraries providing such functions (like boost), which certainly would not start manual tagging, the linker could let you use functions you really must not use. I really see no option in this; if the return type is tagged, the tag must be present in the signature somehow, or you can never mix different ABIs in the same binary. (I would have preferred to simply make tagged return (and variable!) types part of the name, which would have been straightforward compared to the mess GCC implemented: if the tag is already present in certain places, it is not added, depending on the context it might not be added at all, ...) -- 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. To manage notifications about this bug go to: https://bugs.launchpad.net/llvm/+bug/1488254/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp