linux-kernel - Re: [PATCH RESEND] bug: When !CONFIG_BUG, simplify WARN_ON

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Message-ID: <10646.1393243751@warthog.procyon.org.uk>
Date:	Mon, 24 Feb 2014 12:09:11 +0000
From:	David Howells <dhowells@...hat.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	dhowells@...hat.com, Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] bug: When !CONFIG_BUG, simplify WARN_ON_ONCE and family

Josh Triplett <josh@...htriplett.org> wrote:

> > This means we actually want BUG() to end with __builtin_unreachable()
> > as in the CONFIG_BUG=y case, and also ensure it actually is
> > unreachable. As I have shown in [1], the there is a small overhead
> > of doing this in terms of code size.
> 
> I agree that allowing BUG() to become a no-op seems suboptimal, if only
> because of the resulting warnings and mis-optimizations.  However, I
> think the overhead could be cut down massively, such that BUG() just
> compiles down to a one-byte undefined instruction.  (__builtin_trap()
> might do the right thing here; worth checking.)

Is it possible to use an inline function with an empty body in this?  Let the
compiler prune away all the arguments?

David
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