[Bug 1824721] Re: g++-8 in disco is broken with libstdc++6 from gcc9 and libstdc++fs

[Łukasz Zemczak]

Hello Roger, or anyone else affected,

Accepted gcc-8 into bionic-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/gcc-8/8.3.0-26ubuntu1~18.04 in a
few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-bionic to verification-done-bionic. If it does not
fix the bug for you, please add a comment stating that, and change the
tag to verification-failed-bionic. In either case, without details of
your testing we will not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: gcc-8 (Ubuntu Bionic)
       Status: New => Fix Committed

** Tags added: verification-needed verification-needed-bionic

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https://bugs.launchpad.net/bugs/1824721

Title:
  g++-8 in disco is broken with libstdc++6 from gcc9 and libstdc++fs

Status in gcc:
  Invalid
Status in gcc-8 package in Ubuntu:
  Fix Released
Status in gcc-8 source package in Bionic:
  Fix Committed

Bug description:
  There is a significant incompatibility here which leaves the default
  C++ compiler broken with C++17 std::filesystem usage.  Unfortunately,
  there isn't an obvious workaround since there's only one libstdc++6
  package, and it's using the non-default and unreleased GCC9 version of
  libstdc++, making it impossible to use the compatible GCC8 version of
  the library.

  % cat testpath.cpp
  #include <filesystem>

  int main()
  {
    std::filesystem::path p("test");
  }

  g++-9 -std=c++17 -lstdc++fs -g3 -o testpath testpath.cpp 
  % ./testpath

  % g++-8 -std=c++17 -lstdc++fs -g3 -o testpath testpath.cpp
  % ./testpath                                              
  zsh: segmentation fault (core dumped)  ./testpath

  % gdb testpath
  GNU gdb (Ubuntu 8.2.91.20190405-0ubuntu3) 8.2.91.20190405-git
  Copyright (C) 2019 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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  There is NO WARRANTY, to the extent permitted by law.
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  This GDB was configured as "x86_64-linux-gnu".
  Type "show configuration" for configuration details.
  For bug reporting instructions, please see:
  <http://www.gnu.org/software/gdb/bugs/>.
  Find the GDB manual and other documentation resources online at:
      <http://www.gnu.org/software/gdb/documentation/>.

  For help, type "help".
  Type "apropos word" to search for commands related to "word"...
  Reading symbols from testpath...
  (gdb) run
  Starting program: /tmp/testpath 

  Program received signal SIGSEGV, Segmentation fault.
  0x000055555555649b in std::vector<std::filesystem::__cxx11::path::_Cmpt, std::allocator<std::filesystem::__cxx11::path::_Cmpt> >::~vector (this=0x23, __in_chrg=<optimised out>) at /usr/include/c++/8/bits/stl_vector.h:567
  567             std::_Destroy(this->_M_impl._M_start, this->_M_impl._M_finish,
  (gdb) bt
  #0  0x000055555555649b in std::vector<std::filesystem::__cxx11::path::_Cmpt, std::allocator<std::filesystem::__cxx11::path::_Cmpt> >::~vector (this=0x23, __in_chrg=<optimised out>) at /usr/include/c++/8/bits/stl_vector.h:567
  #1  0x0000555555556314 in std::filesystem::__cxx11::path::~path (this=0x3, __in_chrg=<optimised out>)
      at /usr/include/c++/8/bits/fs_path.h:208
  #2  0x0000555555556f5c in std::filesystem::__cxx11::path::_Cmpt::~_Cmpt (this=0x3, __in_chrg=<optimised out>)
      at /usr/include/c++/8/bits/fs_path.h:643
  #3  0x0000555555556f77 in std::_Destroy<std::filesystem::__cxx11::path::_Cmpt> (__pointer=0x3)
      at /usr/include/c++/8/bits/stl_construct.h:98
  #4  0x0000555555556e27 in std::_Destroy_aux<false>::__destroy<std::filesystem::__cxx11::path::_Cmpt*> (
      __first=0x3, __last=0x0) at /usr/include/c++/8/bits/stl_construct.h:108
  #5  0x0000555555556a98 in std::_Destroy<std::filesystem::__cxx11::path::_Cmpt*> (__first=0x3, __last=0x0)
      at /usr/include/c++/8/bits/stl_construct.h:137
  #6  0x00005555555567a9 in std::_Destroy<std::filesystem::__cxx11::path::_Cmpt*, std::filesystem::__cxx11::path::_Cmpt> (__first=0x3, __last=0x0) at /usr/include/c++/8/bits/stl_construct.h:206
  #7  0x00005555555564b1 in std::vector<std::filesystem::__cxx11::path::_Cmpt, std::allocator<std::filesystem::__cxx11::path::_Cmpt> >::~vector (this=0x7fffffffe310, __in_chrg=<optimised out>)
      at /usr/include/c++/8/bits/stl_vector.h:567
  #8  0x0000555555556314 in std::filesystem::__cxx11::path::~path (this=0x7fffffffe2f0, __in_chrg=<optimised out>)
      at /usr/include/c++/8/bits/fs_path.h:208
  #9  0x0000555555556230 in main () at testpath.cpp:5
  (gdb) quit
  A debugging session is active.

          Inferior 1 [process 2414] will be killed.

  Quit anyway? (y or n) y

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