linux-kernel - Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:

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Date:	Thu, 31 Oct 2013 14:23:26 +0100
From:	Mark Wielaard <mjw@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Pekka Enberg <penberg@....fi>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Pekka Enberg <penberg@...nel.org>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	hegdevasant@...ux.vnet.ibm.com, Ingo Molnar <mingo@...hat.com>,
	anton@...hat.com, systemtap@...rceware.org,
	Namhyung Kim <namhyung@...nel.org>,
	aravinda@...ux.vnet.ibm.com, dsahern@...il.com,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:

On Thu, 2013-10-31 at 11:57 +0100, Ingo Molnar wrote:
> * Mark Wielaard <mjw@...hat.com> wrote:
> > On Wed, 2013-10-30 at 13:51 +0200, Pekka Enberg wrote:
> > > On 10/30/13 12:05 PM, Masami Hiramatsu wrote:
> > > > To find all system libraries, we can use ldconfig.
> > > >
> > > > $ ldconfig --print-cache
> > > >
> > > > shows what dynamic libraries will be loaded. On my own laptop (running
> > > > ubuntu13.04) shows ~1000 libs.
> > > 
> > > Good point. That definitely narrows down the scanned set.
> > 
> > It is fast. But that would miss the various libjvm.so variants for 
> > example. Or other programs, like libreoffice, which have SDT 
> > probes in their internal shared libraries that aren't in the 
> > default ldconfig paths.
> 
> I suppose those Java libraries ought to show up in 
> /etc/prelink.cache though, right?

Good point. Yes, all executables and libraries I was missing in ldconfig
--print-cache do show up with prelink -p.

Except libjvm.so itself... Apparently prelink is convinced that really
is never used. hmmm. Apparently all wrapper "java" executables only
dlopen it, so it is never directly linked, and prelink doesn't cache it.

But except for that special case, prelink -p is a good substitute.

Cheers,

Mark

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