[Bug c++/17470] New: Visibility attribute ignored for explicit template instantiation

[Bug c++/17470] New: Visibility attribute ignored for explicit template instantiation

[austern at apple dot com]

[isolde:tmp]$ cat foo.cc
template <class T> T identity(T t) { return t; }
template int identity(int);
template  __attribute__((visibility("default"))) double identity(double);
[isolde:tmp]$ /work/root.u/bin/g++ -fvisibility=hidden -c foo.cc
[isolde:tmp]$ nm -m foo.o
00000024 (__TEXT,__text) private external __Z8identityIdET_S0_
00000000 (absolute) private external __Z8identityIdET_S0_.eh
00000000 (__TEXT,__text) private external __Z8identityIiET_S0_
00000000 (absolute) private external __Z8identityIiET_S0_.eh
[isolde:tmp]$

-- 
           Summary: Visibility attribute ignored for explicit template
                    instantiation
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: austern at apple dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc-apple-darwin7.5.0
  GCC host triplet: powerpc-apple-darwin7.5.0
GCC target triplet: powerpc-apple-darwin7.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-09-13 23:40 -------
May I remark that I would find it quite odd to have attributes 
for functions on a template _instantiations_? I would think that 
the attribute should be at either the declaration or the definition. 
I understand that this precludes giving different instantiations 
different visibility, but it would make the system somewhat less 
odd... 
 
W. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[austern at apple dot com]

------- Additional Comments From austern at apple dot com  2004-09-14 02:20 -------
Tastes differ, I suppose!  My own feeling is that it's unnatural, when declaring an unbounded set of 
functions, to have to say that either all of them or none of them get exported.  I find it more likely that 
a dynamic library author would decide that a selected few specializations are the library's interface.

However, I don't insist on that point.  What I do insist on: it's wrong for the compiler to silently ignore 
the visibility attribute on explicit instantiations.  Either it should be honored, or else it should be 
documented and diagnosed as an error.  Silently ignoring it is a nasty trap for users.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-09-14 03:48 -------
That latter point is most certainly uncontested! :-) 
W. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[efrias at syncad dot com]

------- Additional Comments From efrias at syncad dot com  2004-12-13 20:46 -------
I just ran into this quirk too.  It looks like you can work around by using
"#pragma GCC visibility push(default)" before the explicit instantiation and
then popping afterwards.  I'd greatly prefer the __attribute__ syntax because
that would permit me to use one macro for porting __declspec(dllexport)
constructs from windows code.  Even displaying a warning or error for the
ignored __attribute__ would've saved me some grief.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |efrias at syncad dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[nomis80 at nomis80 dot org]

------- Additional Comments From nomis80 at nomis80 dot org  2004-12-22 20:54 -------
I just got hit with that bug and spent too much time figuring out what was
wrong. Here's my code, just to show an example of real-life usage:

//////////////////////////////////////////////////////////////////////////
/**
 * Returns the unsigned version of \a number.
 */
template< class T >
T abs( T number )
{
    // This is the default implementation, using comparison to zero and unary
    // negation operator.
    if ( number < 0 ) {
        return -number;
    }
    return number;
}

// Here are some specific implementations.

template<> bool             WRAP_API abs( bool           number );
template<> char             WRAP_API abs( char           number );
template<> unsigned char    WRAP_API abs( unsigned char  number );
template<> short            WRAP_API abs( short          number );
template<> unsigned short   WRAP_API abs( unsigned short number );
template<> int              WRAP_API abs( int            number );
template<> unsigned int     WRAP_API abs( unsigned int   number );
template<> long             WRAP_API abs( long           number );
template<> unsigned long    WRAP_API abs( unsigned long  number );
template<> float            WRAP_API abs( float          number );
template<> double           WRAP_API abs( double         number );
//////////////////////////////////////////////////////////////////////////

Please fix this bug!

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |s_gccbugzilla at nedprod dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[nomis80 at nomis80 dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nomis80 at nomis80 dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-28 23:52 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-12-28 23:52:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470

[Bug c++/17470] Visibility attribute ignored for explicit template instantiation

[jmegq at radiance dot com]

------- Additional Comments From jmegq at radiance dot com  2005-09-02 00:16 -------
Regarding macros -- I just found out about the _Pragma directive from C99, so at
least you can do something like this (paraphrasing some ACE code):

#define EXPORT_SINGLETON_DECLARE (SINGLETON_TYPE, CLASS, LOCK) \
        _Pragma ("GCC visibility push(default)")               \
        template class SINGLETON_TYPE <CLASS, LOCK>;           \
        _Pragma ("GCC visibility pop")

#define IMPORT_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK) extern template
class SINGLETON_TYPE <CLASS, LOCK>;

Then define SINGLETON_DECLARE to depending on whether you're building the lib or
not.

A possible issue with this is that it must come before, say, a typedef of the
template type.  The example below works on VS but not g++ (not that VS matters,
but I'm using code that does this):

typedef Singleton_T<Foo, Mutex> FOO_SINGLETON;

SINGLETON_DECLARE(Singleton_T, Foo, Mutex)

Instead, the SINGLETON_DECLARE needs to come before the typedef or it will get
hidden visibility on g++.  I'm curious as to why the typedef causes the symbols
to get hidden visibility -- is that in spec, or is a bug?

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470