Messages in this thread | | | Date | Tue, 3 Jan 2012 14:45:38 +0000 | From | Russell King - ARM Linux <> | Subject | Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM |
| |
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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |