From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753287Ab0EZGvn (ORCPT ); Wed, 26 May 2010 02:51:43 -0400 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:48099 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752766Ab0EZGvm (ORCPT ); Wed, 26 May 2010 02:51:42 -0400 Date: Wed, 26 May 2010 12:21:29 +0530 From: "K.Prasad" To: Millton Miller Cc: Michael Neuling , Benjamin Herrenschmidt , shaggy@linux.vnet.ibm.com, Frederic Weisbecker , Linux Kernel Mailing List , David Gibson , "linuxppc-dev@ozlabs.org" , Alan Stern , Paul Mackerras , Andrew Morton , Roland McGrath Subject: Re: [Patch 1/4] Allow arch-specific cleanup before breakpoint unregistration Message-ID: <20100526065129.GA3746@in.ibm.com> Reply-To: prasad@linux.vnet.ibm.com References: <20100525083055.342788418@linux.vnet.ibm.com> <20100525091356.GB29003@in.ibm.com> <1274787559_8162@mail4.comsite.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1274787559_8162@mail4.comsite.net> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 25, 2010 at 06:39:19AM -0500, Millton Miller wrote: > On Tue, 25 May 2010 at 14:43:56 +0530, K.Prasad wrote: > > Certain architectures (such as PowerPC Book III S) have a need to cleanup > > data-structures before the breakpoint is unregistered. This patch introduces > > an arch-specific hook in release_bp_slot() along with a weak definition in > > the form of a stub funciton. > > > > Signed-off-by: K.Prasad > > --- > > kernel/hw_breakpoint.c | 12 ++++++++++++ > > 1 file changed, 12 insertions(+) > > > My understanding is weak function definitions must appear in a different C > file than their call sites to work on some toolchains. > Atleast, there are quite a few precedents inside the Linux kernel for __weak functions being invoked from the file in which they are defined (arch_hwblk_init, arch_enable_nonboot_cpus_begin and hw_perf_disable to name a few). Moreover the online GCC docs haven't any such constraints mentioned. > Andrew, can you confirm the above statement? > > > Index: linux-2.6.ppc64_test/kernel/hw_breakpoint.c > > =================================================================== > > --- linux-2.6.ppc64_test.orig/kernel/hw_breakpoint.c > > +++ linux-2.6.ppc64_test/kernel/hw_breakpoint.c > > @@ -242,6 +242,17 @@ toggle_bp_slot(struct perf_event *bp, bo > > } > > > > /* > > + * Function to perform processor-specific cleanup during unregistration > > + */ > > +__weak void arch_unregister_hw_breakpoint(struct perf_event *bp) > > +{ > > + /* > > + * A weak stub function here for those archs that don't define > > + * it inside arch/.../kernel/hw_breakpoint.c > > + */ > > +} > > + > > +/* > > * Contraints to check before allowing this new breakpoint counter: > > * > > * == Non-pinned counter == (Considered as pinned for now) > > @@ -339,6 +350,7 @@ void release_bp_slot(struct perf_event * > > { > > mutex_lock(&nr_bp_mutex); > > > > + arch_unregister_hw_breakpoint(bp); > > __release_bp_slot(bp); > > > > mutex_unlock(&nr_bp_mutex); > > > > > Since the weak version is empty, should it just be delcared (in > a header, put the comment there) and not defined? > The initial thinking behind defining it in the .c file was, for one, the function need not be moved (from .h to .c) when other architectures have a need to populate them. Secondly, given that powerpc (which has a 'strong' definition for arch_unregister_hw_breakpoint()) includes the header file (in which this can be moved to) I wasn't sure about possible conflicts. > milton > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev Thanks, K.Prasad