linux-kernel - Re: [PATCH 7/7] x86: Tell about irq stack coverage

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Message-ID: <CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com>
Date:	Wed, 25 Sep 2013 18:26:47 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@....ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	James Hogan <james.hogan@...tec.com>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Helge Deller <deller@....de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 7/7] x86: Tell about irq stack coverage

On Wed, Sep 25, 2013 at 5:40 PM, Joe Perches <joe@...ches.com> wrote:
>
> Huh?  That matches all the ARCH_HAS_<foo> patterns.

Right. And they are all crap. lib/string.c is a prime example of
something that should never have happened.

The ARCH_HAS_xyz pattern is totally retarded. It's wrong.

For big conceptual features, we should use Kconfig symbols.

And for smaller things - like lib/string.c - where we have
compatibility fallback functions but want architectures able to
override them with optimized ones one function at a time, we should
either use weak functions (appropriate for some cases), or the symbol
that protects them should the the SAME SYMBOL WE USE. Rather than some
made-up crap-for-brains new ARCH_HAS_xyz symbol. That way it shows up
in greps, and that way we don't have any question about what random
symbol pattern we use that particular day.

So for *bad* use, see lib/string.c, and the ARCH_AS_xyz horror.

For *good* use, see lib/div64.c or lib/find_next_bit.c.

Notice how div64.c doesn't make up new ARCH_HAS_random_crap names? And
no, you don't have to define those things as macros, you can define
them as functions (inline or not), and then just do

    #define find_next_zero_bit find_next_zero_bit

to tell the rest of the world "Look, I have this defined".

The whole "make up a totally unrelated second name for it" means that
we have things like __HAVE_ARCH_STRLEN but also things like
ARCH_HAS_PREFETCHW. Ugh.

                       Linus
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