linux-kernel - Re: Does perf support different length of user-space hw

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Message-ID: <20140513120046.GB1138@krava.brq.redhat.com>
Date:	Tue, 13 May 2014 14:00:46 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	xiakaixu <xiakaixu@...wei.com>
Cc:	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	paulus@...ba.org, Ingo Molnar <mingo@...nel.org>,
	a.p.zijlstra@...llo.nl, Arnaldo Carvalho de Melo <acme@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Huxinwei <huxinwei@...wei.com>, peifeiyue@...wei.com,
	fweisbec@...il.com
Subject: Re: Does perf support different length of user-space hw_breakpoint?

On Mon, May 12, 2014 at 03:52:54PM +0800, xiakaixu wrote:
> Hi guys,
> 
> Does perf support different length of user-space hw_breakpoint,
> such as  HW_BREAKPOINT_LEN_1/HW_BREAKPOINT_LEN_2/HW_BREAKPOINT_LEN_4/
> HW_BREAKPOINT_LEN_8?
> 
> Seems perf only support HW_BREAKPOINT_LEN_4/sizeof(long)
> by default from the source code and simple test.

right..

        /*
         * 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
                attr.bp_len = HW_BREAKPOINT_LEN_4;

> 
> May I have your opinions if I want to trace different bytes of
> hw_breakpoint addr?

I guess that depends on what you want to do ;-)

jirka
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