linux-kernel - Re: [PATCH 02/16] perf: Add ability to attach registers dump to sample

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Message-ID: <1337853048.9783.92.camel@laptop>
Date:	Thu, 24 May 2012 11:50:48 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	acme@...hat.com, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	eranian@...gle.com, gorcunov@...nvz.org, tzanussi@...il.com,
	mhiramat@...hat.com, robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org
Subject: Re: [PATCH 02/16] perf: Add ability to attach registers dump to
 sample

On Wed, 2012-05-23 at 21:32 +0200, Jiri Olsa wrote:
>  /*
> + * Values for sample_regs when PERF_SAMPLE_REGS is set.
> + * Defines register set to be attached to the sample.
> + */
> +enum perf_sample_regs {
> +       PERF_SAMPLE_REGS_USER   = 1U << 0, /* user registers */
> +       PERF_SAMPLE_REGS_MAX    = 1U << 1, /* non-ABI */
> +};



> +       __u64   sample_regs; /* enum perf_sample_regs */
> +
> +       /*
> +        * Arch specific mask for PERF_SAMPLE_REGS_USER setup.
> +        * Defines set of user regs to dump on samples.
> +        * See asm/perf_regs.h for details.
> +        */
> +       __u64   sample_regs_user; 

This all just smells.. :/

So you're wasting 64 bits to specify PERF_SAMPLE_REGS_USER while also
implying we'll need another u64 for every other value of
perf_sample_regs?

What are we doing here and why?

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