[Bug libstdc++/108969] [13/14 Regression] Initializing iostreams in the library needs a GLIBCXX_3.4.31 versioned symbol

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108969

--- Comment #27 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:9a41d2cdbcd2af77a3a91a840a3a13f0eb39971b

commit r14-321-g9a41d2cdbcd2af77a3a91a840a3a13f0eb39971b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Apr 28 10:49:40 2023 +0200

    libstdc++: Another attempt to ensure g++ 13+ compiled programs enforce gcc
13.2+ libstdc++.so.6 [PR108969]

    GCC used to emit an instance of an empty ios_base::Init class in
    every TU which included <iostream> to ensure it is std::cout etc.
    is initialized, but thanks to Patrick work on some targets (which have
    init_priority attribute support) it is now initialized only inside of
    libstdc++.so.6/libstdc++.a.

    This causes a problem if people do something that has never been supported,
    try to run GCC 13 compiled C++ code against GCC 12 or earlier
    libstdc++.so.6 - std::cout etc. are then never initialized because code
    including <iostream> expects the library to initialize it and the library
    expects code including <iostream> to do that.

    The following patch is second attempt to make this work cheaply as the
    earlier attempt of aliasing the std::cout etc. symbols with another symbol
    version didn't work out due to copy relocation breaking the aliases appart.

    The patch forces just a _ZSt21ios_base_library_initv undefined symbol
    into all *.o files which include <iostream> and while there is no runtime
    relocation against that, it seems to enforce the right version of
    libstdc++.so.6.  /home/jakub/src/gcc/obj08i/usr/local/ is the install
    directory of trunk patched with this patch, /home/jakub/src/gcc/obj06/
    is builddir of trunk without this patch, system g++ is GCC 12.1.1.
    $ cat /tmp/hw.C
     #include <iostream>

    int
    main ()
    {
      std::cout << "Hello, world!" << std::endl;
    }
    $ cd /home/jakub/src/gcc/obj08i/usr/local/bin
    $ ./g++ -o /tmp/hw /tmp/hw.C
    $ readelf -Wa /tmp/hw 2>/dev/null | grep initv
         4: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
_ZSt21ios_base_library_initv@GLIBCXX_3.4.32 (4)
        71: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
_ZSt21ios_base_library_initv@GLIBCXX_3.4.32
    $ /tmp/hw
    /tmp/hw: /lib64/libstdc++.so.6: version `GLIBCXX_3.4.32' not found
(required by /tmp/hw)
    $ LD_LIBRARY_PATH=/home/jakub/src/gcc/obj08i/usr/local/lib64/ /tmp/hw
    Hello, world!
    $
LD_LIBRARY_PATH=/home/jakub/src/gcc/obj06/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/
/tmp/hw
    /tmp/hw:
/home/jakub/src/gcc/obj06/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6:
version `GLIBCXX_3.4.32' not found (required by /tmp/hw)
    $ g++ -o /tmp/hw /tmp/hw.C
    $ /tmp/hw
    Hello, world!
    $
LD_LIBRARY_PATH=/home/jakub/src/gcc/obj06/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/
/tmp/hw
    Hello, world!
    $ LD_LIBRARY_PATH=/home/jakub/src/gcc/obj08i/usr/local/lib64/ /tmp/hw
    Hello, world!

    On sparc-sun-solaris2.11 one I've actually checked a version which had
    defined(_GLIBCXX_SYMVER_SUN) next to defined(_GLIBCXX_SYMVER_GNU), but
    init_priority attribute doesn't seem to be supported there and so I
couldn't
    actually test how this works there.  Using gas and Sun ld, Rainer, does one
    need to use gas + gld for init_priority or something else?

    2023-04-28  Jakub Jelinek  <jakub@redhat.com>

            PR libstdc++/108969
            * config/abi/pre/gnu.ver (GLIBCXX_3.4.32): Export
            _ZSt21ios_base_library_initv.
            * testsuite/util/testsuite_abi.cc (check_version): Add
GLIBCXX_3.4.32
            symver and make it the latestp.
            * src/c++98/ios_init.cc (ios_base_library_init): New alias.
            * acinclude.m4 (libtool_VERSION): Change to 6:32:0.
            * include/std/iostream: If init_priority attribute is supported
            and _GLIBCXX_SYMVER_GNU, force undefined
_ZSt21ios_base_library_initv
            symbol into the object.
            * configure: Regenerated.