netdev - Re: [PATCH 00/33] Compile-time stack metadata validation

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Date:	Mon, 15 Feb 2016 21:02:01 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alok Kataria <akataria@...are.com>,
	Ingo Molnar <mingo@...hat.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	linux-watchdog@...r.kernel.org, Pedro Alves <palves@...hat.com>,
	Pavel Machek <pavel@....cz>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Michal Marek <mmarek@...e.cz>,
	Namhyung Kim <namhyung@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Waiman Long <Waiman.Long@....com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Jiri Slaby <jslaby@...e.cz>, kvm@...r.kernel.org,
	x86@...nel.org, Arnaldo Carvalho de Melo <acme@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Borislav Petkov <bp@...en8.de>,
	Chris Wright <chrisw@...s-sol.org>,
	Andy Lutomirski <luto@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Wim Van Sebroeck <wim@...ana.be>,
	David Vrabel <david.vrabel@...rix.com>,
	live-patching@...r.kernel.org, netdev@...r.kernel.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Gleb Natapov <gleb@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Chris J Arges <chris.j.arges@...onical.com>,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
	Andi Kleen <andi@...stfloor.org>,
	Len Brown <len.brown@...el.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 00/33] Compile-time stack metadata validation

> > There are two ways to fix the warnings:
> >
> > 1. get rid of the thunks and call the C functions directly; or
> 
> No. Not until gcc learns about per-function callibg conventions (so that it can
> be marked as not clobbering registers).

It does already for static functions in 5.x (with -fipa-ra).
And with LTO it can be used even somewhat globally.

Even older version supported it, for only for x86->SSE on 32bit, which
is useless for the kernel. But the new IPA-RA propagates which registers
are clobbered.

That said it will probably be a long time until we can drop support for
older compilers.  So for now the manual method is still needed.

-Andi