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

[Jonathan Wakely <jwakely@redhat.com>]

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On Fri, 28 Apr 2023 at 08:34, Jakub Jelinek <jakub@redhat.com> wrote:

> Hi!
>
> 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!
>
> Bootstrapped/regtested on x86_64-linux, i686-linux and
> sparc-sun-solaris2.11
>
> On the last 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?
>
> Ok for trunk and after a while for GCC 13.2?
>

Yes, for both, thanks for the fix.

After it lands on the gcc-13 branch I'll also update the manual with:

--- a/libstdc++-v3/doc/xml/manual/abi.xml
+++ b/libstdc++-v3/doc/xml/manual/abi.xml
@@ -275,6 +275,7 @@ compatible.
    <listitem><para>GCC 11.1.0: libstdc++.so.6.0.29</para></listitem>
    <listitem><para>GCC 12.1.0: libstdc++.so.6.0.30</para></listitem>
    <listitem><para>GCC 13.1.0: libstdc++.so.6.0.31</para></listitem>
+    <listitem><para>GCC 13.2.0: libstdc++.so.6.0.32</para></listitem>
    </itemizedlist>
    <para>
      Note 1: Error should be libstdc++.so.3.0.3.




>
> 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.
>
> --- libstdc++-v3/config/abi/pre/gnu.ver.jj      2023-04-20
> 09:36:09.415371050 +0200
> +++ libstdc++-v3/config/abi/pre/gnu.ver 2023-04-27 17:58:44.599675359 +0200
> @@ -2514,6 +2514,10 @@ GLIBCXX_3.4.31 {
>
>  } GLIBCXX_3.4.30;
>
> +GLIBCXX_3.4.32 {
> +    _ZSt21ios_base_library_initv;
> +} GLIBCXX_3.4.31;
> +
>  # Symbols in the support library (libsupc++) have their own tag.
>  CXXABI_1.3 {
>
> --- libstdc++-v3/testsuite/util/testsuite_abi.cc.jj     2023-01-16
> 11:52:17.495713257 +0100
> +++ libstdc++-v3/testsuite/util/testsuite_abi.cc        2023-04-27
> 17:30:39.651173917 +0200
> @@ -213,6 +213,7 @@ check_version(symbol& test, bool added)
>        known_versions.push_back("GLIBCXX_LDBL_3.4.29");
>        known_versions.push_back("GLIBCXX_3.4.30");
>        known_versions.push_back("GLIBCXX_3.4.31");
> +      known_versions.push_back("GLIBCXX_3.4.32");
>        known_versions.push_back("GLIBCXX_LDBL_3.4.31");
>        known_versions.push_back("GLIBCXX_IEEE128_3.4.29");
>        known_versions.push_back("GLIBCXX_IEEE128_3.4.30");
> @@ -251,7 +252,7 @@ check_version(symbol& test, bool added)
>         test.version_status = symbol::incompatible;
>
>        // Check that added symbols are added in the latest pre-release
> version.
> -      bool latestp = (test.version_name == "GLIBCXX_3.4.31"
> +      bool latestp = (test.version_name == "GLIBCXX_3.4.32"
>           // XXX remove next 2 lines when baselines have been regenerated.
>                      || test.version_name == "GLIBCXX_IEEE128_3.4.31"
>                      || test.version_name == "GLIBCXX_LDBL_3.4.31"
> --- libstdc++-v3/src/c++98/ios_init.cc.jj       2023-01-16
> 11:52:16.995720625 +0100
> +++ libstdc++-v3/src/c++98/ios_init.cc  2023-04-27 18:34:46.121276617 +0200
> @@ -199,5 +199,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      return __ret;
>    }
>
> +#ifdef _GLIBCXX_SYMVER_GNU
> +  void ios_base_library_init (void)
> +  __attribute__((alias ("_ZNSt8ios_base4InitC1Ev")));
> +#endif
> +
>  _GLIBCXX_END_NAMESPACE_VERSION
>  } // namespace
> --- libstdc++-v3/acinclude.m4.jj        2023-02-02 09:53:31.745525704 +0100
> +++ libstdc++-v3/acinclude.m4   2023-04-27 17:27:51.071626279 +0200
> @@ -3841,7 +3841,7 @@ changequote([,])dnl
>  fi
>
>  # For libtool versioning info, format is CURRENT:REVISION:AGE
> -libtool_VERSION=6:31:0
> +libtool_VERSION=6:32:0
>
>  # Everything parsed; figure out what files and settings to use.
>  case $enable_symvers in
> --- libstdc++-v3/include/std/iostream.jj        2023-01-16
> 11:52:16.968721023 +0100
> +++ libstdc++-v3/include/std/iostream   2023-04-27 18:34:07.479837226 +0200
> @@ -77,6 +77,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    // in the compiled library instead (src/c++98/globals_io.cc).
>  #if !__has_attribute(__init_priority__)
>    static ios_base::Init __ioinit;
> +#elif defined(_GLIBCXX_SYMVER_GNU)
> +  __extension__ __asm (".globl _ZSt21ios_base_library_initv");
>  #endif
>
>  _GLIBCXX_END_NAMESPACE_VERSION
> --- libstdc++-v3/configure.jj   2023-02-02 09:53:31.795524981 +0100
> +++ libstdc++-v3/configure      2023-04-27 17:29:13.263429963 +0200
> @@ -68652,7 +68652,7 @@ $as_echo "$as_me: WARNING: === Symbol ve
>  fi
>
>  # For libtool versioning info, format is CURRENT:REVISION:AGE
> -libtool_VERSION=6:31:0
> +libtool_VERSION=6:32:0
>
>  # Everything parsed; figure out what files and settings to use.
>  case $enable_symvers in
>
>         Jakub
>
>