linux-kernel - Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

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Message-ID: <87lhgb0wi3.fsf@tassilo.jf.intel.com>
Date:	Tue, 26 May 2015 16:06:28 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
	live-patching@...r.kernel.org,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

Ingo Molnar <mingo@...nel.org> writes:
>
> Especially on modern x86 CPUs with stack engines (latest Intel and AMD 
> CPUs) that keeps ESP updates out of the later stages of execution 
> pipelines, going from RBP framepointers to direct ESP use is 
> beneficial to performance and compresses I$ footprint as well:

Note that Atom doesn't have this stack engine, so you'll likely
see even more difference there.

> So the performance advantages of not doing framepointers is not 
> something we can ignore IMHO:

Agreed.

> but obviously performance isn't 
> everything - so if stack unwinding is unrobust, then we need and
> want frame pointers.

It wasn't that bad in the old days with the approx stack traces.  In
fact I bet it would be possible to write an automated tool that weeds
out many (most?) false positives automatically with a static
compile-time callgraph.

It would be good to at least make it easier building without them
again. Currently it's very difficult because a lot of subsystems force
select frame pointers.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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