linux-kernel - Re: [PATCH 1/2] liblockdep: Fix compile errors

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Message-ID: <20160614102557.GA14577@c50.bag.software>
Date:	Tue, 14 Jun 2016 12:26:00 +0200
From:	Vishal Thanki <vishalthanki@...il.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] liblockdep: Fix compile errors

On Mon, Jun 13, 2016 at 04:38:01PM -0400, Sasha Levin wrote:
> On 06/11/2016 04:36 AM, Vishal Thanki wrote:
> > On Sat, Jun 11, 2016 at 5:53 AM, Sasha Levin <sasha.levin@...cle.com> wrote:
> >> On 06/09/2016 09:34 AM, Vishal Thanki wrote:
> >>> dfaaf3fa0: (Use __jhash_mix() for iterate_chain_key())
> >>> Fixed by adding jhash.h with minimal stuff required
> >>
> >> Can we, instead of copying it over, include jhash.h directly
> >> (just like we do for hash.h)?
> >>
> >>
> > That was the first thing I tried, but then it caused more compilation
> > errors due to nested header dependencies and I ended up taking the
> > only required stuff. Better ideas are welcome.
> 
> I just gave it a quick go and didn't see anything beyond needing to take
> in linux/unaligned/packed_struct.h as well. What sort of errors did you
> hit?
> 

Yes, you are right about just adding the linux/unaligned/packed_struct.h should
work. However I hit the following errors when I did that:


CC       lockdep.o
In file included from ./uinclude/linux/jhash.h:27:0,
                 from ../../../kernel/locking/lockdep.c:49,
                 from lockdep.c:8:
./uinclude/linux/unaligned/packed_struct.h:7:29: error: conflicting types for
‘__packed’
 struct __una_u32 { u32 x; } __packed;
                             ^
./uinclude/linux/unaligned/packed_struct.h:6:29: note: previous declaration of
‘__packed’ was here
 struct __una_u16 { u16 x; } __packed;
                             ^
./uinclude/linux/unaligned/packed_struct.h:8:29: error: conflicting types for
‘__packed’
 struct __una_u64 { u64 x; } __packed;
                             ^
./uinclude/linux/unaligned/packed_struct.h:6:29: note: previous declaration of
‘__packed’ was here
 struct __una_u16 { u16 x; } __packed;
                             ^
which I overlooked and had nothing to do with header dependencies, pardon my
ignorance.

I think gcc on my machine (version 5.3.1 on Fedora 22) throws the above error
which I think can be fixed by adding a define in uinclude/linux/compile.h like
following:

#define __packed       __attribute__((__packed__))

After fixing, I hit following warning:

In file included from ../../../kernel/locking/lockdep.c:49:0,
                 from lockdep.c:8:
./uinclude/linux/jhash.h: In function ‘jhash’:
./uinclude/linux/jhash.h:37:16: warning: implicit declaration of function
‘rol32’ [-Wimplicit-function-declaration]
  a -= c;  a ^= rol32(c, 4);  c += b; \

which can be fixed by adding the inline definition of rol32 from kernel's
biopts.h file to uinclude/linux/bitops.h file (which is empty as of now).

I will rework the patch with the fixes and send again.

Thanks,
Vishal