linux-kernel - Re: [PATCH v5 00/10] x86/asm: Compile-time asm code validation

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Message-ID: <20150610130814.GN19417@two.firstfloor.org>
Date:	Wed, 10 Jun 2015 15:08:14 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	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>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 00/10] x86/asm: Compile-time asm code validation


> 2. Each callable function must never leave its own bounds (i.e. with a
>    jump to outside the function) except when returning.

That prevents a lot of optimizations with out of line code.

In fact even gcc with the right options can generate code that violates
this. Standard Linux constructions, such as exception handling,
also violate this.

If your tool needs that your tool is broken.

BTW any other frame pointer requirement should be also optional,
as it slows down a number of CPUs, such as Atoms.

-Andi

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