Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754572Ab0GIWCz (ORCPT ); Fri, 9 Jul 2010 18:02:55 -0400 Received: from pfepa.post.tele.dk ([195.41.46.235]:34491 "EHLO pfepa.post.tele.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752802Ab0GIWCy (ORCPT ); Fri, 9 Jul 2010 18:02:54 -0400 Date: Sat, 10 Jul 2010 00:02:52 +0200 From: Sam Ravnborg To: Steven Rostedt Cc: LKML , Ingo Molnar , Frederic Weisbecker , Linus Torvalds , Andrew Morton , Zeev Tarantov , "Rafael J. Wysocki" , Maciej@antispam.struernethosting.dk Subject: Re: [PATCH][GIT PULL][for 2.6.35] tracing: Add alignment to syscall metadata declarations Message-ID: <20100709220252.GA14080@merkur.ravnborg.org> References: <1278705402.1537.157.camel@gandalf.stny.rr.com> <20100709203301.GA13839@merkur.ravnborg.org> <1278708374.1537.161.camel@gandalf.stny.rr.com> <20100709205319.GA13941@merkur.ravnborg.org> <1278709550.1537.164.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1278709550.1537.164.camel@gandalf.stny.rr.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1603 Lines: 39 On Fri, Jul 09, 2010 at 05:05:50PM -0400, Steven Rostedt wrote: > On Fri, 2010-07-09 at 22:53 +0200, Sam Ravnborg wrote: > > > But in this case we have no control of the value of "." (current address) > > when we have processed (_ftrace_events) so it may even be at a 2 byte boundary. > > The linker will add padding as needed to satisfy the alignmnet of > > __syscalls_metadata - but that padding will be inbetween "." and the first > > member in __syscalls_metadata. > > Fine, but this is a separate issue. I doubt the "ALIGN(8);" would have > helped us anyway. Remember what the issue we had: > > ffffffff8173c438 <__start_syscalls_metadata>: > ... > > ffffffff8173c440 <__syscall_meta__mmap>: > > > __start_syscalls_metadata was already aligned to 8, but for some strange > reason, gcc decided to align the first member to 16. I found some more info in following bug: https://bugzillafiles.novell.org/attachment.cgi?id=344563 Jeff Mahoney says: GCC 4.5 introduced behavior that forces the alignment of structures to use the largest possible value. The default value is 32 bytes, so if some structures are defined with a 4-byte alignment and others aren't declared with an alignment constraint at all - it will align at 32-bytes. So according to this we can rely on 32 byte alignment and this is trivial to add in vmlinux.lds.h. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/