[Bug libstdc++/66902] New: _S_debug_messages is unneccessary public

[Bug libstdc++/66902] New: _S_debug_messages is unneccessary public

[persgray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

            Bug ID: 66902
           Summary: _S_debug_messages is unneccessary public
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: persgray at gmail dot com
  Target Milestone: ---

Created attachment 36000
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36000&action=edit
proposed patch

The _S_debug_messages array is defined in libstdc++-v3/src/c++11/debug.cc
without "static" modifier, therefore becoming exported one. But it isn't used
in GCC anywhere outside the debug.cc source module. I found no users installed
in my laptop running many KDE-, GTK- and console-based programs.

On the other side, size of _S_debug_messages differs in different versions of
libstdc++. This way, while libstdc++ 4.9 is ABI-compatible with libstdc++ 4.2,
this particular symbol causes warnings from ld.so (at least here on OpenBSD).
Yes, libstdc++ versions are "mixed": some software requires decent versions of
GCC and doesn't build on the base one (4.2.1); therefore, such software gets
built and linked with GCC 4.9 (as of now), and libstdc++ 4.9 is forced to be
searched for symbols before libstdc++ 4.2. This works in general, but there is
a nasty warning produced:

WARNING: symbol(_ZN11__gnu_debug17_S_debug_messagesE) size mismatch, relink
your program

This happens because _S_debug_messages contains different number of strings in
different libstdc++ versions.

Since there is no real reason to keep _S_debug_messages public, I propose
making it static. There is an interface for accessing this array:

  const _Error_formatter&
  _Error_formatter::_M_message(_Debug_msg_id __id) const
  { return this->_M_message(_S_debug_messages[__id]); }

So the lack of "static" keyword looks like a simple overlook problem.

The attached patch simply adds "static" keyword. I've been running with this
patch for many weeks without any problem on OpenBSD/amd64.

[Bug libstdc++/66902] _S_debug_messages is unneccessary public

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-07-17
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The symbol is not exported on targets using a linker script for symbol
versioning (GNU, Solaris, possibly Windows), so I see no reason we can't make
that true for all targets.

[Bug libstdc++/66902] _S_debug_messages is unneccessary public

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |6.0

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk.

[Bug libstdc++/66902] _S_debug_messages is unneccessary public

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Thu Sep  3 19:05:15 2015
New Revision: 227466

URL: https://gcc.gnu.org/viewcvs?rev=227466&root=gcc&view=rev
Log:
        PR libstdc++/66902
        * src/c++11/debug.cc (_S_debug_messages): Make array const.

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/src/c++11/debug.cc

[Bug libstdc++/66902] _S_debug_messages is unneccessary public

[persgray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

--- Comment #5 from Vadim Zhukov <persgray at gmail dot com> ---
(In reply to Jonathan Wakely from comment #4)
> Author: redi
> Date: Thu Sep  3 19:05:15 2015
> New Revision: 227466
> 
> URL: https://gcc.gnu.org/viewcvs?rev=227466&root=gcc&view=rev
> Log:
> 	PR libstdc++/66902
> 	* src/c++11/debug.cc (_S_debug_messages): Make array const.
> 
> Modified:
>     trunk/libstdc++-v3/ChangeLog
>     trunk/libstdc++-v3/src/c++11/debug.cc

I see that you removed "static" modifier in that commit, effectively making the
array in question exported again. Was it intended?
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg546

--- Comment #2 from Rainer Emrich <rainer@emrich-ebersheim.de> ---
(In reply to Kai Tietz from comment #1)
> I added to mingw-w64's libwinpthread a work-a-round for this sloopy code in
> libgomp.  Nevertheless issue should be fixed IMO in libgomp, too

Wrong PR, this belongs to PR67141.

[Bug libstdc++/66902] _S_debug_messages is unneccessary public

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
3.5 [basic.link]:

-3-  A name having namespace scope (3.3.6) has internal linkage if it is the
     name of
      — a variable, function or function template that is explicitly declared
        static; or,
      — a variable of non-volatile const-qualified type that is neither
        explicitly declared extern nor previously declared to have external
        linkage; or
      — a data member of an anonymous union.

The first bullet applied when it was explicitly declared static and the second
bullet applies now that it is a const-qualified type at namespace scope. In
both cases it has internal linkage, so you should not see a global symbol and
should not get the warning.
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Subject: [Bug rtl-optimization/58517] ifcvt (after combine) puts ccreg clobbering insn between ccset insn and ccreg use
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idX517

Oleg Endo <olegendo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kyrylo.tkachov at arm dot com

--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> ---
Kyrill, since you are currently working on ifcvt related things, could you
maybe have a look at this issue?  I haven't checked it in a while, so I don't
know if it's still a problem.

[Bug libstdc++/66902] _S_debug_messages is unneccessary public

[persgray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66902

--- Comment #7 from Vadim Zhukov <persgray at gmail dot com> ---
(In reply to Jonathan Wakely from comment #6)
> 3.5 [basic.link]:
> 
> -3-  A name having namespace scope (3.3.6) has internal linkage if it is the
>      name of
>       — a variable, function or function template that is explicitly declared
>         static; or,
>       — a variable of non-volatile const-qualified type that is neither
>         explicitly declared extern nor previously declared to have external
>         linkage; or
>       — a data member of an anonymous union.
> 
> The first bullet applied when it was explicitly declared static and the
> second bullet applies now that it is a const-qualified type at namespace
> scope. In both cases it has internal linkage, so you should not see a global
> symbol and should not get the warning.

Sorry, I've missed that. Thank you for clarification.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idX517

--- Comment #7 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to ktkachov from comment #6)
> Huh, I wasn't aware of this BZ.
> This looks eerily similar to what I think is the root cause of PR 67481,
> which I'm working on now.
>
> After I'm done with PR 67481 it would be interesting to have a look whether
> they are indeed the same issue

OK, thanks!