linux-kernel - Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load

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Message-ID: <20140805210728.GH13858@redhat.com>
Date:	Tue, 5 Aug 2014 17:07:28 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Josh Boyer <jwboyer@...oraproject.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jakub Jelinek <jakub@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	Michel Dänzer <michel@...nzer.net>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Josh Stone <jistone@...hat.com>
Subject: Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

Hi -

> >>.  I don't disagree it should be
> >> disabled by default, but making it unconditional is going to force the
> >> distributions that care about perf, systemtap, and debuggers to
> >> manually revert this.
> >
> > Bah. I bet I use 'perf' more than most, and it doesn't care about
> > debug info. 

Actually, "perf probe" does (via HAVE_DWARF_SUPPORT), to place probes
and to extract variables at those probes, much as systemtap does.
Without var-tracking, probes placed at most interior points of
functions will make variables inaccessible.

Do you need a fully worked out example to see this?

- FChE
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