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

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Date:	Sat, 20 Apr 2013 17:47:57 -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>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] perf: Add hardware breakpoint address mask

On Sat, Apr 20, 2013 at 06:53:34PM +0200, Oleg Nesterov wrote:
> On 04/09, Jacob Shin wrote:
> >
> > The following patchset adds address masks to existing perf hardware
> > breakpoint mechanism to allow trapping on an address range (currently
> > only single address) on supported architectures.
> >
> > perf uapi is updated, x86 AMD implementation (for AMD Family 16h and
> > beyond) is provided, and perf tool has been extended to do:
> >
> >   $ perf stat -e mem:0x1000:w:0xf a.out
> >                               ^^^
> >                               "don't care" bit mask
> >
> >   which will count writes to [0x1000 ~ 0x1010)
> 
> Please help me understand...
> 
> Assuming that cpu_has_bpext == T, suppose that
> 
> 	bp_addr		= 0x1001;
> 	bp_bp_addr_mask	= 0xf;
> 
> Is it the same as 0x1000/0xf above?
> 
> IOW, what exactly this mask means? I guess, mem:ADDR:w:MASK
> should trigger the trap if CPU writes to the addr and
> 
> 	(addr & ~MASK) == (ADDR & ~MASK)
> 
> correct?

Yes that is correct.

> 
> 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.

Thanks,

-Jacob

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