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

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Message-ID: <20140427103915.GC1111@krava.brq.redhat.com>
Date:	Sun, 27 Apr 2014 12:39:15 +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 12:03:50PM +0200, Mathias Krause wrote:

SNIP

> >> 1.7.10.4
> >>
> >
> > hum, how about fixing this once and for all.. ;-)
> > please check attached patch, thanks
> 
> Yeah, I thought about this option too but declined it for two reasons:
> 1/ The kernel sources should provide good quality examples, even for
> usage outside of the kernel. Imagine somebody taking the memcpy
> implementation for his own project but not copying the LDFLAGS. That
> would make his code have an executable stack while with the .GNU-stack
> marker in the assembler file it won't.

that 'somebody' should check/know better ;-) but ok, fair enough

> 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?

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..

or insert test case for perf's executable stack to 'perf test'

thanks,
jirka
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