Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[Ben Hutchings]

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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>.

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

Ben.

-- 
Ben Hutchings
All the simple programs have been written, and all the good names taken.

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Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[Olof Johansson]

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 coincidentally posted a patch earlier to do just that, I didn't see
your email until later.

> 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?

The quickest fix for now might be to take out the BUILD_BUG_ON(),
especially so close to 3.2-final.


-Olof

Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[Simon Glass]

Hi Ben, Olof,

On Sun, Jan 1, 2012 at 11:01 PM, Olof Johansson <olof@lixom.net> 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 coincidentally posted a patch earlier to do just that, I didn't see
> your email until later.
>
>> 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?
>
> The quickest fix for now might be to take out the BUILD_BUG_ON(),
> especially so close to 3.2-final.

Yes I like that idea as the check isn't funtional. Perhaps ultimately
the BUILD_BUG_ON check for sizeof(struct bug_entry) should really go
in lib/bug.c. Something like, in the header:

#define GENERIC_BUG_ENTRY_SIZE 12

and then in lib/bug.c:

#ifdef GENERIC_BUG_ENTRY_SIZE
BUILD_BUG_ON(GENERIC_BUG_ENTRY_SIZE != sizeof(struct bug_entry))
#endif

The other more fragile option might be to make sure all files include
<linux/kernel.h>?

Regards,
Simon

>
>
> -Olof

Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[Russell King - ARM Linux]

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.

Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[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

Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[Paul Gortmaker]

On Tue, Jan 3, 2012 at 9:45 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.

Actually, kernel.h doesn't need to include any variant of bug.h at all.

I started on cleaning this up a few weeks back, but didn't have the time
to get it ready for 3.3 -- so my intent is to do so for linux-next that will
be the 3.4 release.  The Work In Progress can be seen here:

http://git.kernel.org/?p=linux/kernel/git/paulg/linux.git;a=shortlog;h=refs/heads/bug.h-cleanup-WIP

I only mention it here since I'd hate to see anyone waste time on
duplicating work that is already done.

Thanks,
Paul.

---

>
>> 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
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> Please read the FAQ at  http://www.tux.org/lkml/

Re: Circular dependency between <linux/kernel.h> and <asm/bug.h> on ARM

[Simon Glass]

On Wed, Jan 4, 2012 at 7:43 PM, Paul Gortmaker
<paul.gortmaker@windriver.com> wrote:
> On Tue, Jan 3, 2012 at 9:45 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.
>
> Actually, kernel.h doesn't need to include any variant of bug.h at all.
>
> I started on cleaning this up a few weeks back, but didn't have the time
> to get it ready for 3.3 -- so my intent is to do so for linux-next that will
> be the 3.4 release.  The Work In Progress can be seen here:
>
> http://git.kernel.org/?p=linux/kernel/git/paulg/linux.git;a=shortlog;h=refs/heads/bug.h-cleanup-WIP
>
> I only mention it here since I'd hate to see anyone waste time on
> duplicating work that is already done.

Thanks Paul, I hope it goes well.

Regards,
Simon

>
> Thanks,
> Paul.
>
> ---
>
>>
>>> 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/