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

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Message-ID: <CALCETrVQ2pX8dDrHgnymZjTe=dpGsoaNA=XGpAVV7J=ON+U7Ng@mail.gmail.com>
Date:	Wed, 10 Jun 2015 11:24:05 -0700
From:	Andy Lutomirski <luto@...capital.net>
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 ML <x86@...nel.org>,
	live-patching@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 00/10] x86/asm: Compile-time asm code validation

On Wed, Jun 10, 2015 at 5:06 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> The previous version of this patch set was named "Compile-time stack
> frame pointer validation".  I changed the subject from "frame pointer
> validation" to "asm code validation" because the focus of the patch set
> has changed to be less frame pointer-focused and more asm-focused.  I
> also renamed the tool to asmvalidate (it was previously called
> stackvalidate) and basically rewrote most of the code.
>

Slightly off-topic, but this reminds me: when writing inline asm that
needs to push to the stack (for whatever reason), it's incredibly
messy to get the annotations right -- they're different depending on
whether the previous frame base (is that what "CFA" is?) is currently
sp + constant, in which case we need an annotation adjusting the
constant or whether it's independent of sp (bp + constant), in which
case we shouldn't adjust the offset.  (If it's some other function of
sp, we're screwed.)

Regardless of whether these types of annotations end up being done by
hand or by script, should we consider asking the binutils people to
give us some nice .cfi_adjust_for_push and .cfi_adjust_for_pop or
similar directives?

See here for Jan Beulich's solution, which is incomprehensible to me:

http://thread.gmane.org/gmane.linux.kernel/1820765

--Andy
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