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

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Date:	Sun, 27 Apr 2014 18:29:44 +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 18:16, Jiri Olsa <jolsa@...hat.com> wrote:
> 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

Well, it might work on your system but it won't work on mine. See this
bug, why: https://sourceware.org/bugzilla/show_bug.cgi?id=12492

> [...]
>>
>> > 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

Of course, it could be disabled, i.e. I could allow perf to get an
executable stack. Though, I don't like my stacks to be executable ;)

Thanks,
Mathias

>
> jirka
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