Created attachment 9162 [details]
libstdc++.log for AIX, demonstrating issue

This is a regression in that you no longer can use the debug mode with -fno-weak.

AIX 5.2 does support weak, so I believe that there is something wrong with the
analysis.

Actually if you look into the email which David sent, you would see:
# 0 "<built-in>"
#define __GXX_WEAK__

Which means there is weak support.

Humm, I wonder whether the problem isn't *really* trivial :)
In include/bits/c++config we have:

#ifdef _GLIBCXX_DEBUG
# if __GXX_WEAK__
#  define _GLIBCXX_STD __gnu_norm
#  define _GLIBCXX_EXTERN_TEMPLATE 0
...
...
# else
#  warning debug mode disabled due to lack of weak symbol support
# endif

Should be, instead, 'ifdef __GXX_WEAK__' ?!?

Or, wrt Andrew's comment, AIX should really have, consistently with the docs:
#define __GXX_WEAK__ 1

??

I do not understand the comment about GCC for AIX setting GXX_WEAK consistently.
    The value is set by GCC itself, not overridden by AIX.

GXX_WEAK is defined by c-cppbuiltin.c:

      if (flag_weak && SUPPORTS_ONE_ONLY) 
        cpp_define (pfile, "__GXX_WEAK__=1");
      else
        cpp_define (pfile, "__GXX_WEAK__=0");

and depends on SUPPORTS_ONE_ONLY, not just weak support.  I will test if setting
MAKE_DECL_ONE_ONLY works on AIX.

A clarification about __GXX_WEAK__: Andrew reports that, on AIX we have:
#define __GXX_WEAK__
If that is really the case (I cannot check, sorry), then the library is not
checking correctly the macro, because uses:
# if __GXX_WEAK__
which should be changed to:
# ifdef __GXX_WEAK__
Alternately, on AIX we should have:
#define __GXX_WEAK__ 1

I'm saying everywhere "on AIX" because for sure many other "weak" targets
are ok as they are. 

Agreed?

I tried overriding libstdc++'s definition of __GXX_WEAK__ and GCC's definition
of ONE_ONLY.  Both caused additional C++ testsuite failures.  AIX does support
weak, but not exactly the way that G++ is expecting.

A real good question is why does debug mode need link once at all?

It was discovered that to use string, you have to do all this magic with the
debug mode that involves not using extern template and a bunch of the other
linkage optimizations. There were some PRs about this.

That's why systems without weak will no longer support the debug mode. That's
not going to change.

However, fixing this so that debug mode is not tested (marked unsupported)
instead of failing seems reasonable.

Working on a patch...

Subject: Bug 22205

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	bkoz@gcc.gnu.org	2005-09-15 18:58:04

Modified files:
	libstdc++-v3   : ChangeLog 
	libstdc++-v3/include/bits: c++config 
	libstdc++-v3/testsuite/21_strings/basic_string/element_access/char: 
	                                                                    21674.cc 
	libstdc++-v3/testsuite/21_strings/basic_string/element_access/wchar_t: 
	                                                                       21674.cc 
	libstdc++-v3/testsuite/lib: dg-options.exp libstdc++.exp 

Log message:
	2005-09-15  Benjamin Kosnik  <bkoz@redhat.com>
	
	PR libstdc++/21674
	PR libstdc++/22205
	PR libstdc++/22222
	* include/bits/c++config: Set _GLIBCXX_STD regardless of __GXX_WEAK__.
	Add in check for __NO_INLINE__ for warning.
	* testsuite/lib/dg-options.exp (dg-require-debug-mode): New.
	* testsuite/lib/libstdc++.exp (check_v3_target_debug_mode): New.
	* testsuite/21_strings/basic_string/element_access/char/21674.cc:
	Use it.
	* testsuite/21_strings/basic_string/element_access/wchar_t/21674.cc:
	Use it.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libstdc++-v3/ChangeLog.diff?cvsroot=gcc&r1=1.3107&r2=1.3108
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libstdc++-v3/include/bits/c++config.diff?cvsroot=gcc&r1=1.1408&r2=1.1409
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libstdc++-v3/testsuite/21_strings/basic_string/element_access/char/21674.cc.diff?cvsroot=gcc&r1=1.1&r2=1.2
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libstdc++-v3/testsuite/21_strings/basic_string/element_access/wchar_t/21674.cc.diff?cvsroot=gcc&r1=1.1&r2=1.2
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libstdc++-v3/testsuite/lib/dg-options.exp.diff?cvsroot=gcc&r1=1.5&r2=1.6
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libstdc++-v3/testsuite/lib/libstdc++.exp.diff?cvsroot=gcc&r1=1.48&r2=1.49

Fixed.