From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-389265-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 24570 invoked by alias); 18 Apr 2012 17:04:43 -0000
Received: (qmail 24557 invoked by uid 22791); 18 Apr 2012 17:04:40 -0000
X-SWARE-Spam-Status: No, hits=-4.3 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00,KHOP_THREADED
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 18 Apr 2012 17:03:53 +0000
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/33925] gcc -Waddress lost some useful warnings
Date: Wed, 18 Apr 2012 17:04:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-33925-4-y2meTUq7sX@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-33925-4@http.gcc.gnu.org/bugzilla/>
References: <bug-33925-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2012-04/txt/msg01547.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33925

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-04-18 17:01:23 UTC ---
(In reply to comment #3)
> First, I think the C++ standard forbids a function from having a null 
> address:

But GCC extensions allow it, see the weakref attribute:

http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#index-g_t_0040code_007bweakref_007d-attribute-2648

That's used (among other places) by GCC's pthreads abstraction layer to declare
a weak alias to pthread_create, which has a null address unless libpthread is
linked to.  Testing whether the address is null (i.. whether the application
was linked to libpthread) is used for important optimisations.