Messages in this thread | | | Date | Tue, 3 Jan 2012 10:33:40 -0800 | Subject | Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM | From | Simon Glass <> |
| |
Hi Russell,
On Tue, Jan 3, 2012 at 6:45 AM, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > 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.
OK I will send a patch to do this, it is safest. Any interest in (for a later release) putting a check in the C file as I suggested?
Regards, Simon -- 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/
| |