From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM
Date: Tue, 3 Jan 2012 14:45:38 +0000 [thread overview]
Message-ID: <20120103144538.GU2914@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <CAOesGMgXRev24e0bmGD71J04=Aon7bs0YeK7mwX8Na12uR_b6A@mail.gmail.com>
On Sun, Jan 01, 2012 at 11:01:27PM -0800, Olof Johansson wrote:
> On Sun, Jan 1, 2012 at 6:44 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> > Commit 87e040b6456fd3416a1f6831c1eedaef5c0a94ff ("ARM: 7017/1: Use
> > generic BUG() handler") makes BUG() use BUILD_BUG_ON(). ?However,
> > BUILD_BUG_ON() is not defined in <linux/bug.h> but in <linux/kernel.h>.
> >
> > arch/include/asm/bug.h does not include <linux/kernel.h> and *cannot* do
> > so because the latter already includes <asm/bug.h>.
>
> Sure it can, but it's not ideal. Since the BUILD_BUG_ON is only used
> in bug.h in a #define, it will be resolved below the includes of
> either so there should be no ordering issue between the two.
I disagree - we should not be creating circular dependencies. This
creates a mess, and uncertain results. For instance, if we include
linux/bug.h or asm/bug.h before linux/kernel.h has been included,
then we end up with linux/kernel.h being parsed without a definition
for BUG_ON().
However, if linux/kernel.h is included first, we start parsing that,
include asm/bug.h, asm/bug.h then includes linux/kernel.h which produces
an empty file, and then we continue parsing asm/bug.h _without_
BUILD_BUG_ON() defined.
So, adding linux/kernel.h does _not_ solve the problem. It solves the
problem for _some_ cases only.
> > Maybe BUILD_BUG_ON() should be moved out to a header of its own, or else
> > this particular use should be moved to some other file. ?This needs to
> > be fixed somehow, as it obviously leads to build failures, e.g.:
> >
> > https://buildd.debian.org/status/fetch.php?pkg=linux-2.6&arch=armel&ver=3.2~rc7-1~experimental.1&stamp=1325142904
>
> Or perhaps moving BUILD_BUG_ON to include/linux/bug.h?
and change linux/kernel.h to include linux/bug.h rather than asm/bug.h.
> The quickest fix for now might be to take out the BUILD_BUG_ON(),
> especially so close to 3.2-final.
I think just remove the BUILD_BUG_ON. Other architectures have done
without it, so I see no reason we can't do as well.
next prev parent reply other threads:[~2012-01-03 14:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-02 2:44 Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM Ben Hutchings
2012-01-02 7:01 ` Olof Johansson
2012-01-02 18:54 ` Simon Glass
2012-01-03 14:45 ` Russell King - ARM Linux [this message]
2012-01-03 18:33 ` Simon Glass
2012-01-05 3:43 ` Paul Gortmaker
2012-01-06 4:12 ` Simon Glass
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