linux-kernel - Re: [PATCH] perf x86: Fix perf to use non-executable stack, again

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Message-ID: <20140427161632.GA27784@krava.brq.redhat.com>
Date:	Sun, 27 Apr 2014 18:16:32 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Mathias Krause <minipli@...glemail.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf x86: Fix perf to use non-executable stack, again

On Sun, Apr 27, 2014 at 06:07:30PM +0200, Mathias Krause wrote:
> On 27 April 2014 12:39, Jiri Olsa <jolsa@...hat.com> wrote:
> > On Sun, Apr 27, 2014 at 12:03:50PM +0200, Mathias Krause wrote:
> > [...]
> >> 2/ What if somebody tries to add/link code to perf that makes use of
> >> nested functions? That'll make perf fail as the trampoline code
> >> generated by gcc won't be executable due to the enforced
> >> non-executable stack by -Wl,-z,noexecstack.
> >
> > I guess in that case he would change the Makefile as well?
> 
> Not necessarily. What if a later version of a library already used by
> perf needs an executable stack because it now makes use of nested
> functions? Unlikely, though in that case no change to perf would be
> made, but perf would then require an executable stack, too.

I tried you can run binary with noexecstack having dynamic
library dependency wit execstack

> 
> Anyway, as Ingo votes for the global linker option as well, I'll send
> a v2 of the patch containing your suggested linker flag.

cool

> 
> > anyway I have no objection for leaving that code in assembly
> > objects, but I suggest we use the global option as well to
> > prevent any future surprise..
> 
> Okay.
> 
> > or insert test case for perf's executable stack to 'perf test'
> 
> That won't work for systems preventing processes getting an executable
> stack in the first place. That was the reason I stumbled about the

could be disabled on such systems

jirka
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