Date: Sat, 27 Apr 2013 19:34:24 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Jacob Shin <jacob.shin@amd.com>
Cc: Ingo Molnar <mingo@redhat.com>, Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        x86@kernel.org, Stephane Eranian <eranian@google.com>,
        Jiri Olsa <jolsa@redhat.com>, linux-kernel@vger.kernel.org,
        Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH 2/3] perf tools: allow user to specify hardware
	breakpoint bp_len
Message-ID: <20130427173424.GA32506@redhat.com>
References: <1367002666-6910-1-git-send-email-jacob.shin@amd.com> <1367002666-6910-3-git-send-email-jacob.shin@amd.com> <20130427165856.GA30282@redhat.com>
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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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