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

[Jonathan Wakely <jwakely@redhat.com>]

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.

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
>