linux-kernel - Re: [PATCH 1/5] perf: Add hardware breakpoint address mask

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Date:	Mon, 22 Apr 2013 16:57:44 -0500
From:	Jacob Shin <jacob.shin@....com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] perf: Add hardware breakpoint address mask

On Mon, Apr 22, 2013 at 04:37:15PM -0500, Jacob Shin wrote:
> On Sun, Apr 21, 2013 at 07:02:02PM +0200, Oleg Nesterov wrote:
> > On 04/20, Jacob Shin wrote:
> > >
> > > On Sat, Apr 20, 2013 at 06:53:34PM +0200, Oleg Nesterov wrote:
> > > >
> > > > And does attr.bp_len "contribute" to the mask?
> > > >
> > > > I mean, if bp_len == X86_BREAKPOINT_LEN_8, does this mean that
> > > > bp_bp_addr_mask and (bp_bp_addr_mask | 7) have the same effect?
> > >
> > > Yes it has the same effect.
> > 
> > OK, thanks...
> > 
> > So this is the "natural" extension. Given that currently bp_addr
> > should be aligned, bp_len could be already bp_mask but I guess it
> > is too late to change this, so we need another field.
> > 
> > Hmm. Perhaps arch_has_hw_breakpoint_addr_mask(void) should be turned
> > into arch_validate_hw_breakpoint_addr_mask(bp) which should also
> > check that (bp_addr & bp_addr_mask) == 0. But I won't insist.
> 
> Yes I can do that .. in that case should the Kconfig
> CONFIG_HAVE_HW_BREAKPOINT_ADDR_MASK go away, and in every non-x86
> hw_breakpoint.c do:
> 
> bool arch_validate_hw_breakpoint_addr_mask(struct perf_event *bp)
> {
> 	return false;

Sorry, of course what I meant was,

       return bp->attr.bp_addr_mask == 0;
> }
> 
> ?
> 
> Or keep CONFIG_HAVE_HW_BREAKPOINT_ADDR_MASK and in
> include/linux/hw_breakpoint.h do:
> 
> #ifndef CONFIG_HAVE_HW_BREAKPOINT_ADDR_MASK
> static inline bool arch_validate_hw_breakpoint_addr_mask(struct perf_event *bp)
> {
> 	return falase;

here too.

> }
> #endif
> 
> ?
> 
> Thanks,

Just reading your other email, you said a __weak function would suffice.
So I'll do that .. sorry for answering my own question.

I'll send out a revised patchset sometime later tonight ..

Thanks again!

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