[Mingw-notify] [ mingw-Bugs-1205393 ] type attributes are honored only at type definition

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Bugs item #1205393, was opened at 2005-05-20 13:51
Message generated for change (Comment added) made by dannysmith
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Category: gcc
Group: Known bugs
>Status: Closed
>Resolution: Later
Priority: 5
Submitted By: ofv (ofv)
Assigned to: Danny Smith (dannysmith)
Summary: type attributes are honored only at type definition

Initial Comment:
This is a look-ahead bug report, just in case you are not 
aware of the issue.

With a gcc 4.0 binary downloaded from

http://www.thisiscool.com/gcc_mingw.htm

(I was unable to build it from sources)

t:/tkidb # g++ -v
Using built-in specs.
Target: i686-pc-mingw32
Configured with: /datal/gcc/gcc/configure 
--prefix=/datal/gcc/build/wingcc --build=i686-pc-linux-gnu 
--host=i686-pc-mingw32 --target=i686-pc-mingw32 
--enable-languages=c,c++,java --with-gcc --with-gnu-as 
--with-gnu-ld --enable-threads=win32 --disable-nls 
--disable-win32-registry --disable-shared --disable-debug 
--without-newlib --enable-libgcj --disable-java-awt 
--without-x --enable-java-gc=boehm --disable-libgcj-debug 
--enable-interpreter --enable-hash-synchronization 
--enable-sjlj-exceptions --enable-libgcj-multifile 
--enable-libgcj-mingw-osapi=ansi
Thread model: win32
gcc version 4.0.0 20050324 (prerelease)

t:/tkidb # g++ -c f.cpp
f.cpp:1: warning: type attributes are honored only at type 
definition

f.cpp: 

class __declspec(dllexport) Foo;

class Foo {
  Foo();
};

As the warning hints, __declspec(dllexport) is ignored 
and no symbol is exported. This differs from previous gcc 
versions and all other Windows compilers.


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>Comment By: Danny Smith (dannysmith)
Date: 2006-07-25 14:03

Message:
Logged In: YES 
user_id=11494

This is fixed on gcc trunk (4.2).



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Comment By: Danny Smith (dannysmith)
Date: 2005-05-20 20:24

Message:
Logged In: YES 
user_id=11494

Sorry, I referred to wrong patch.  This is the one that caused 
the change.

2004-01-14  Danny Smith  
<dannysmith@users,sourceforge.net>

	PR c++/9021
	PR c++/11005
	* parser.c (cp_parser_elaborated_type_specifier): 
Warn about
	attributes and discard.
	* decl.c (xref_tag): Don't overwite existing 
attributes with
	NULL_TREE.

This message talks about what you want:

http://gcc.gnu.org/ml/gcc-patches/2003-12/msg01004.html

The thread was broken over Christmas, but sometime in that 
period Gabriel dos Reis suggested that attributes should 
apply to classes at definition time only. That suggestion 
made everything else a lot simpler to maintain -- dllimport of 
classes is a recurring source of new bug reports.  

Any way, IIRC, one of the patches that I submitted actually 
did preserve compatibility with MS compiler -- attributes on 
forward decls being propagated to definition, but I can't find it 
now. It just checked that no new attributes were added 
__after__ class definition, ie:"If !COMPLETE_TYPE_P, merge 
attributes, else ignore the new attributes"

Danny


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Comment By: ofv (ofv)
Date: 2005-05-20 15:26

Message:
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user_id=1281994

Hi Danny.

I'm confused. The gcc-patches thread you mention seems to 
indicate that your patch was accepted without further 
discussion:

Your report plus patch:

http://gcc.gnu.org/ml/gcc-bugs/2003-12/msg00556.html

Mark Mitchell's fix notice:

http://gcc.gnu.org/ml/gcc-bugs/2003-12/msg00739.html


Then, the docs about the new visibility feature for 4.0 explicitly 
mentions putting __attribute__ on the declaration:

http://gcc.gnu.org/wiki/Visibility

http://gcc.gnu.org/onlinedocs/gcc-4.0.
0/gcc/Code-Gen-Options.html#Code-Gen-Options

http://www.nedprod.com/programs/gccvisibility.html

which seems to contradict the gcc documentation you quoted, 
but I confirmed that gcc 4.0 emits the same warning on Linux 
when using ((visibility("default")) on declarations. I'll file a bug 
report on this.

Now, the question: is there any real (read technical) reason for 
gcc doing this and breaking lots of Windows libraries?

Regards,
Oscar


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Comment By: Danny Smith (dannysmith)
Date: 2005-05-20 14:50

Message:
Logged In: YES 
user_id=11494

This is what gcc.info says (and has said for awhile):

5.32 Specifying Attributes of Types
===================================

The keyword `__attribute__' allows you to specify special 
attributes of
`struct' and `union' types when you define such types.


If you are asking that dllimport/dllexport be treated as an 
exception, please submit a patch (including a patch to the 
documentation) to gcc.  

You may be want to search for the discussion on gcc-ptches 
that led to this change. 
2003-12-05  Danny Smith <dan...@gc...>
	    Mark Mitchell  <ma...@co...>

	PR c++/13305
	* parser.c (cp_parser_elaborated_type_specifier): 
Accept
	attributes.


Danny

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