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

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Date:	Sun, 27 Apr 2014 18:07:30 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Jiri Olsa <jolsa@...hat.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 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.

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

> 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
problem in the first place.


Thanks,
Mathias

>
> thanks,
> jirka
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