Public bug reported: On Linux, the distros often use libstdc++ rather than libc++ for Clang. Building libcxx is an art that I have never been able to untangle, and I think the maintainers have discovered the same.
Below, I'm catching a UB finding when using Clang and libstdc++. This one has been around for some time. I first encountered it on Apple platforms. I regularly encounter it on Debian and Ubuntu. The fix is fairly easy, and I usually just do it: a couple of casts among unsigned and the flags. Also see http://lists.llvm.org/pipermail /cfe-dev/2015-January/040753.html. ********** $ cat ub.cxx #include <iostream> int main(int argc, char* argv[]) { std::cout << std::hex << argc << std::endl; std::cout << std::dec << argc << std::endl; return 0; } $ clang++ -fsanitize=undefined ub.cxx -o ub.exe $ ./ub.exe /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/ios_base.h:96:24: runtime error: load of value 4294967221, which is not a valid value for type 'std::_Ios_Fmtflags' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/ios_base.h:76:67: runtime error: load of value 4294967221, which is not a valid value for type 'std::_Ios_Fmtflags' 1 1 ********** $ g++ --version g++ (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4 $ uname -a Linux ubuntu 3.13.0-66-generic #108-Ubuntu SMP Wed Oct 7 15:20:27 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux $ lsb_release No LSB modules are available. ********** $ apt-cache show g++ Package: g++ Priority: optional Section: devel Installed-Size: 34 Maintainer: Ubuntu Developers <ubuntu-devel-disc...@lists.ubuntu.com> Original-Maintainer: Debian GCC Maintainers <debian-...@lists.debian.org> Architecture: amd64 Source: gcc-defaults (1.124ubuntu6) Version: 4:4.8.2-1ubuntu6 Provides: c++-compiler Depends: cpp (>= 4:4.8.2-1ubuntu6), gcc (>= 4:4.8.2-1ubuntu6), g++-4.8 (>= 4.8.2-5~), gcc-4.8 (>= 4.8.2-5~) Suggests: g++-multilib Filename: pool/main/g/gcc-defaults/g++_4.8.2-1ubuntu6_amd64.deb Size: 1490 MD5sum: 7332a4e9116b821e167a3d0236ca413a SHA1: 2c7201808be1029d21b7691c5a855535a4fcbd51 SHA256: 02c3d204efe6c34bf3de655aaf6a9ce524511977aedf92d7bce7093d0581f977 Description-en: GNU C++ compiler This is the GNU C++ compiler, a fairly portable optimizing compiler for C++. . This is a dependency package providing the default GNU C++ compiler. Description-md5: 4d44b18774ae5123b7c3f70d940cf655 Bugs: https://bugs.launchpad.net/ubuntu/+filebug Build-Essential: yes Origin: Ubuntu Supported: 5y ** Affects: gcc-defaults (Ubuntu) Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1514309 Title: Undefined Behavior in GCC 4.8 ios_base.h To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gcc-defaults/+bug/1514309/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
