linux-kernel - Re: better patch for linux/bitops.h

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Date:	Thu, 5 May 2016 17:34:50 -0400
From:	Sandy Harris <sandyinchina@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>,
	Jeffrey Walton <noloader@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, John Denker <jsd@...n.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephan Mueller <smueller@...onox.de>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Andi Kleen <andi@...stfloor.org>,
	Sandy Harris <sandyinchina@...il.com>,
	Jason Cooper <cryptography@...edaemon.net>,
	linux-crypto@...r.kernel.org
Subject: Re: better patch for linux/bitops.h

On Wed, May 4, 2016 at 11:50 PM, Theodore Ts'o <tytso@....edu> wrote:

> Instead of arguing over who's "sane" or "insane", can we come up with
> a agreed upon set of tests, and a set of compiler and compiler
> versions ...

I completely fail to see why tests or compiler versions should be
part of the discussion. The C standard says the behaviour in
certain cases is undefined, so a standard-compliant compiler
can generate more-or-less any code there.

As long as any of portability, reliability or security are among our
goals, any code that can give undefined behaviour should be
considered problematic.

> But instead of arguing over what works and doesn't, let's just create
> the the test set and just try it on a wide range of compilers and
> architectures, hmmm?

No. Let's just fix the code so that undefined behaviour cannot occur.

Creating test cases for a fix and trying them on a range of systems
would be useful, perhaps essential, work. Doing tests without a fix
would be a complete waste of time.