[Bug c++/51813] New: -fvisibility=hidden causes std::codecvt members to be undefined

[Bug c++/51813] New: -fvisibility=hidden causes std::codecvt members to be undefined

[sefi@s-e-f-i.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

             Bug #: 51813
           Summary: -fvisibility=hidden causes std::codecvt members to be
                    undefined
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sefi@s-e-f-i.de


The following program causes undefined symbols when -fvisibility=hidden is
used:

#include <locale>

int main()
{
        std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>
>(std::locale());
}

g++-4.7 -fvisibility=hidden test.cpp

/tmp/cclBRkzy.o: In function `main':
test.cpp:(.text+0x1d): undefined reference to `std::codecvt<wchar_t, char,
__mbstate_t> const& std::use_facet<std::codecvt<wchar_t, char, __mbstate_t>
>(std::locale const&)'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.7.0-alpha20120107/../../../../x86_64-pc-linux-gnu/bin/ld:
a.out: hidden symbol
`_ZSt9use_facetISt7codecvtIwc11__mbstate_tEERKT_RKSt6locale' isn't defined
/usr/lib/gcc/x86_64-pc-linux-gnu/4.7.0-alpha20120107/../../../../x86_64-pc-linux-gnu/bin/ld:
final link failed: Bad value
collect2: error: ld returned 1 exit status

It works with gcc-4.6.2.
use_facet is only an example. I had other functions like do_length, the
destructor, etc. reported as undefined as well.

[Bug c++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-01-13
                 CC|                            |jason at gcc dot gnu.org
            Summary|-fvisibility=hidden causes  |[4.7 Regression]
                   |std::codecvt members to be  |-fvisibility=hidden causes
                   |undefined                   |std::codecvt members to be
                   |                            |undefined
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-01-13 11:53:58 UTC ---
Jason, this happens only in mainline and I'm trying to figure if it may have to
do with our recent changes in the visibility area (like PR35688).

We have a problem with, for example, the std::use_facet specializations which
we declare extern template (in bits/codecvt.h):

  extern template
    const codecvt<wchar_t, char, mbstate_t>&
    use_facet<codecvt<wchar_t, char, mbstate_t> >(const locale&);

note that the latter happens in the namespace std as decorated visibility
default.

The library normally exports the required use_facet symbol from the .so but for
some reason, see Description, the linker doesn't find it.

Apparently the problem has more generally to do with extern template things.
Any idea what may be going wrong? Is there something the library should do
here?

[Bug c++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 15:57:35 UTC ---
The difference is that now for the same input, GCC marks the undefined
use_facet symbol as hidden, while 4.6 doesn't.  I'll take a look.

[Bug libstdc++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
          Component|c++                         |libstdc++

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 16:19:11 UTC ---
I see the problem: mbstate_t is hidden, so codecvt is hidden, so use_facet is
hidden.  This is indeed revealed by the fix for PR 35688.

What do we want to do about C library visibility?

[Bug libstdc++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-01-13 16:24:07 UTC ---
Eh, thanks for the analysis. Is there some sort of conservative option here? I
don't think we want to take risks at this stage only for the sake of hiding a
few more symbols ws 4.6. Could we somehow convince the compiler that mbstate_t
is not hidden?

[Bug libstdc++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-13 16:43:12 UTC ---
(In reply to comment #3)
> What do we want to do about C library visibility?

We can't redeclare all the types with default visibility, because we don't know
if e.g. mbstate_t is just a typedef.

This appears to fix it, but would it need to be done for any explicit
instantation relying on non-builtin types defined outside libstdc++?

  extern template
    __attribute__((visibility("default")))
    const codecvt<wchar_t, char, mbstate_t>&
    use_facet<codecvt<wchar_t, char, mbstate_t> >(const locale&);

[Bug libstdc++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-01-13 16:46:56 UTC ---
Thanks for your help Jon. Note the issue isn't just about std::use_facet, is
about std::codecvt too, any type we instantiate with mbstate_t.

[Bug libstdc++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 16:52:41 UTC ---
The right answer would seem to be wrapping includes of C headers in #pragma GCC
visibility push/pop, like many of the libsupc++ headers do.  But I'm not sure
why the compiler wants to emit a .hidden directive for this symbol but not
other hidden externs; I'll look into that.

[Bug c++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
          Component|libstdc++                   |c++
   Target Milestone|---                         |4.7.0

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 17:01:06 UTC ---
Mine.

[Bug c++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 17:51:04 UTC ---
Author: jason
Date: Fri Jan 13 17:50:58 2012
New Revision: 183156

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=183156
Log:
    PR c++/51813
    * decl2.c (constrain_visibility): Clear DECL_VISIBILITY_SPECIFIED
    when reducing the visibility.

Added:
    trunk/gcc/testsuite/g++.dg/ext/visibility/template9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl2.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/51813] [4.7 Regression] -fvisibility=hidden causes std::codecvt members to be undefined

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51813

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 17:52:47 UTC ---
Fixed.  I think the change to C header visibility would still be a good idea,
though.