linux-kernel - Re: [PATCH v5 02/10] x86: Compile-time asm code validation

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Message-ID: <20150611141000.GC11517@treble.redhat.com>
Date:	Thu, 11 Jun 2015 09:10:00 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	live-patching@...r.kernel.org, X86 ML <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 02/10] x86: Compile-time asm code validation

On Thu, Jun 11, 2015 at 08:10:50AM +0200, Ingo Molnar wrote:
> * Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > > I imagine that an automatic CFI annotation adder would walk through functions 
> > > one instruction at a time and keep track of the frame state. If so, then it 
> > > could verify that common jump targets had identical state and continue walking 
> > > through them and annotating.  I think this would get this case right, and it 
> > > might be necessary anyway to handle jumps within functions.
> > 
> > This would definitely add complexity to both asmvalidate and the CFI generator.  
> > In fact it sounds like it would push the CFI generator out of its current awk 
> > script territory and more into complex C code territory.
> 
> I'd count that as a plus: awk isn't a common skillset while C is, and properly 
> written it doesn't have to be _that_ complex.

The thing is, C is quite painful for text processing.  And I think we'd
have to do the analysis at the source text level in order to generate
the .cfi_* instructions to pass to the gnu assembler.

C would definitely make more sense when analyzing object code.  In fact,
asmvalidate is written in C.  But then I guess we'd have to re-implement
the .cfi stuff and populate the DWARF sections manually instead of
letting the assembler do it.

-- 
Josh
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