linux-kernel - Re: [PATCH 10/11] perf tools: Add probing for udev86 library

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Message-ID: <20160330144219.GC9083@tassilo.jf.intel.com>
Date:	Wed, 30 Mar 2016 07:42:19 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 10/11] perf tools: Add probing for udev86 library

On Wed, Mar 30, 2016 at 12:43:27PM +0200, Ingo Molnar wrote:
> 
> * Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> 
> > From: Andi Kleen <ak@...ux.intel.com>
> > 
> > Add autoprobing for the udev86 disassembler library.
> 
> So the typo in the title is confusing, what is 'udev86'?

Agreed, it's confusing. It was meant to be udis86.

http://udis86.sourceforge.net

The next patch that uses it had the URL too, but that didn't make it
when this patch was split off.

> 
> Also, this library does not seem to be available on stock Ubuntu. We should not be 
> adding library dependencies that cannot be resolved on major distros:
> 
>  ...                     get_cpuid: [ on  ]
>  ...                           bpf: [ on  ]
>  ...                        udis86: [ OFF ]

It's a chicken'n'egg problem. Likely when perf needs it they will add it soon.
For now it's fairly easy to install manually.

Using a real disassembler in perf has a lot of advantages over objdump. It allows
full instruction traces with PT, which is useful for debugging. It also
allows hot path analysis of branch mispredictions and automatic micro benchmarks
using LBRs (implemented inn https://lkml.org/lkml/2016/3/28/331). Possibly
more in the future.

-Andi