linux-kernel - Re: [PATCH 2/3] perf tools: allow user to specify hardware breakpoint bp

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Message-ID: <20130427173424.GA32506@redhat.com>
Date:	Sat, 27 Apr 2013 19:34:24 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jacob Shin <jacob.shin@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.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,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 2/3] perf tools: allow user to specify hardware
	breakpoint bp_len

On 04/27, Oleg Nesterov wrote:
>
> On 04/26, Jacob Shin wrote:
> >
> > @@ -518,12 +518,10 @@ int parse_events_add_breakpoint(struct list_head **list, int *idx,
> >  	if (parse_breakpoint_type(type, &attr))
> >  		return -EINVAL;
> >
> > -	/*
> > -	 * We should find a nice way to override the access length
> > -	 * Provide some defaults for now
> > -	 */
> >  	if (attr.bp_type == HW_BREAKPOINT_X)
> >  		attr.bp_len = sizeof(long);
> > +	else if (len)
> > +		attr.bp_len = len;
> >  	else
> >  		attr.bp_len = HW_BREAKPOINT_LEN_4;
>
> Stupid question... So X86_FEATURE_BPEXT only works for r/w? I mean, it
> doesn't allow to specify the mask for an execute breakpoint?
>
> Otherwise the code above should be probably updated, say,
>
> 	if (!len) {
> 		len = attr.bp_type == HW_BREAKPOINT_X ?
> 			sizeof(long) : HW_BREAKPOINT_LEN_4;
> 	}
> 	attr.bp_len = len;

OK, we can't do this until we change arch_build_bp_info() which
insists on sizeof(long) and sets X86_BREAKPOINT_LEN_X == 1.

Please ignore...

Oleg.

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