linux-kernel - [Patch 1/4] Allow arch-specific cleanup before breakpoint unregistration

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Message-ID: <1274787559_8162@mail4.comsite.net>
Date:	Tue, 25 May 2010 06:39:19 -0500
From:	Millton Miller <miltonm@....com>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
Cc:	Michael Neuling <mikey@...ling.org>,
	Benjamin Herrenschmidt <benh@....ibm.com>,
	shaggy@...ux.vnet.ibm.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Gibson <dwg@....ibm.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>,
	"linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
	Paul Mackerras <paulus@...ba.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [Patch 1/4] Allow arch-specific cleanup before breakpoint
	unregistration

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 <prasad@...ux.vnet.ibm.com>
> ---
>  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.

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?

milton
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