Re: [PATCH] libstdc++: Fix stream initialization with static library [PR107701]

[Jonathan Wakely <jwakely@redhat.com>]

On Wed, 16 Nov 2022 at 10:55, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> On Wed, 16 Nov 2022 at 02:46, Patrick Palka via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > When linking with a static library, the linker seems to exclude a
> > constituent .o object (including its global initializers) if nothing
> > from it is referenced by the program (unless e.g. --whole-archive is
> > used).  This behavior breaks iostream when linking with static libstdc++.a
> > (on systems that support init priorities) because we're defining the
> > global initializer for the standard stream objects in a separate TU
> > (ios_init.cc) from the stream objects definitions (globals_io.cc).
> >
> > Thus in order to ensure that the global initializer for the standard
> > stream objects doesn't get wrongly dropped when statically linking,
> > we need to perform the initialization from the same TU that actually
> > defines the stream objects.
> >
> > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>
> OK, thanks.

Oops, I missed the v2. That's definitely better with the improve comments.

OK for v2.


>
> I'm a little nervous that future improvements to --gc-sections or LTO
> could cause the same problem, but I think we're OK for now.
>
>
> >
> >         PR libstdc++/107701
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * src/c++98/globals_io.cc: Include "io_base_init.h" here
> >         instead of ...
> >         * src/c++98/ios_init.cc: ... here.
> >         * testsuite/17_intro/static.cc: Run the test as well.
> > ---
> >  libstdc++-v3/src/c++98/globals_io.cc      | 2 ++
> >  libstdc++-v3/src/c++98/ios_init.cc        | 2 --
> >  libstdc++-v3/testsuite/17_intro/static.cc | 2 +-
> >  3 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/libstdc++-v3/src/c++98/globals_io.cc b/libstdc++-v3/src/c++98/globals_io.cc
> > index 04fecb22aeb..bfd808b5bbd 100644
> > --- a/libstdc++-v3/src/c++98/globals_io.cc
> > +++ b/libstdc++-v3/src/c++98/globals_io.cc
> > @@ -69,6 +69,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >    fake_wostream wclog;
> >  #endif
> >
> > +#include "ios_base_init.h"
> > +
> >  _GLIBCXX_END_NAMESPACE_VERSION
> >  } // namespace
> >
> > diff --git a/libstdc++-v3/src/c++98/ios_init.cc b/libstdc++-v3/src/c++98/ios_init.cc
> > index 4016fcab785..1b5132f1c2d 100644
> > --- a/libstdc++-v3/src/c++98/ios_init.cc
> > +++ b/libstdc++-v3/src/c++98/ios_init.cc
> > @@ -75,8 +75,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >    extern wostream wclog;
> >  #endif
> >
> > -#include "ios_base_init.h"
> > -
> >    ios_base::Init::Init()
> >    {
> >      if (__gnu_cxx::__exchange_and_add_dispatch(&_S_refcount, 1) == 0)
> > diff --git a/libstdc++-v3/testsuite/17_intro/static.cc b/libstdc++-v3/testsuite/17_intro/static.cc
> > index ffa7ecb7077..a0d6ed081f8 100644
> > --- a/libstdc++-v3/testsuite/17_intro/static.cc
> > +++ b/libstdc++-v3/testsuite/17_intro/static.cc
> > @@ -1,4 +1,4 @@
> > -// { dg-do link { target c++11 } }
> > +// { dg-do run { target c++11 } }
> >  // { dg-require-static-libstdcxx }
> >  // { dg-options "-static-libstdc++" }
> >
> > --
> > 2.38.1.436.geea7033409
> >