Re: [committed] libstdc++: Fix symbol versioning for Solaris 11.3 [PR103407]

[Jonathan Wakely <jwakely@redhat.com>]

On Fri, 18 Mar 2022 at 12:47, Rainer Orth wrote:
>
> Hi Jonathan,
>
> > I did some very brief testing and it seemed like a program linked to
> > the Solaris 11.3 libstdc++.so.6.0.30 (with from_chars@GLIBCXX_3.4.30)
> > can still run against libstdc++.so.6.0.30 with
> > from_chars@GLIBCXX_3.4.29 (which should match what you get on Solaris
> > 11.4 if I correctly fiddled with the versioning). So I don't
>
> indeed.  You can observe the symbols provided and consumed by shared
> objects and executables with pvs.
>
> E.g. on 11.4:
>
> $ pvs -dsvo libstdc++.so|grep _ZSt10from_charsPKcS0_R
> libstdc++.so -  GLIBCXX_3.4.29: _ZSt10from_charsPKcS0_RfSt12chars_format;
> libstdc++.so -  GLIBCXX_3.4.29: _ZSt10from_charsPKcS0_ReSt12chars_format;
> libstdc++.so -  GLIBCXX_3.4.29: _ZSt10from_charsPKcS0_RdSt12chars_format;
>
> for the provider side vs. 11.3:
>
> $ pvs -dsvo libstdc++.so|grep _ZSt10from_charsPKcS0_R
> libstdc++.so -  GLIBCXX_3.4.30: _ZSt10from_charsPKcS0_ReSt12chars_format;
> libstdc++.so -  GLIBCXX_3.4.30: _ZSt10from_charsPKcS0_RdSt12chars_format;
> libstdc++.so -  GLIBCXX_3.4.30: _ZSt10from_charsPKcS0_RfSt12chars_format;
>
> pvs -r shows symbols and versions required by an executable.
>
> > understand how the Solaris runtime linker handles symbol versions, but
> > it seems like there's no backwards compatibility problem for the
> > Solaris 11.4 build of libstdc++.so.6.0.30.
>
> You can observe this at runtime with LD_DEBUG=versions or
> versions,detail.  LD_DEBUG=help <some command> gives the full info.
>
> IIRC Solaris ld.so.1 just checks if the versions required by an
> executable are provided by a shared object, but doesn't look into
> individual symbols in advance.  It may well be that some checks have
> been relaxed in the 11.4 timeframe, though.

Ah that would explain it. The libstdc++.so built on Solaris 11.4 has
the std::from_chars symbols and it has version GLIBCXX_3.4.30, so that
satisfies the requirements for a program linked against the
libstdc++.so on Solaris 11.3.