linux-kernel - Re: [next:akpm 129/309] net/core/sock.c:274:36: error: initializer element is not constant

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Message-ID: <BLU0-SMTP2254F8872DDE5FA6035CDE97DD0@phx.gbl>
Date:	Mon, 23 Jul 2012 11:13:23 -0400
From:	John David Anglin <dave.anglin@...l.net>
To:	Fengguang Wu <fengguang.wu@...el.com>
CC:	Mel Gorman <mgorman@...e.de>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	kernel-janitors@...r.kernel.org,
	Kyle McMartin <kyle@...isc-linux.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Parisc List <linux-parisc@...r.kernel.org>
Subject: Re: [next:akpm 129/309] net/core/sock.c:274:36: error: initializer element is not constant

On 23-Jul-12, at 8:29 AM, Fengguang Wu wrote:

> On Mon, Jul 23, 2012 at 12:42:58PM +0100, Mel Gorman wrote:
>> On Mon, Jul 23, 2012 at 12:20:20PM +0100, James Bottomley wrote:
>>> [Parisc list cc added]
>>> On Mon, 2012-07-23 at 12:16 +0100, Mel Gorman wrote:
>>>> On Mon, Jul 23, 2012 at 12:30:58AM +0800, Fengguang Wu wrote:
>>>>> Hi Mel,
>>>>>
>>>>> To be frank, I don't quite understand this build failure..
>>>>>
>>>>> tree:   next/akpm akpm
>>>>> head:   37e2ad4953983527f7bdb6831bf478eedcc84082
>>>>> commit: 799dc3a908b1df8b766c35aefc24c1b5356aa051 [129/309]  
>>>>> netvm: allow skb allocation to use PFMEMALLOC reserves
>>>>> config: parisc-defconfig (attached as .config)
>>>>>
>>>>> All related error/warning messages:
>>>>>
>>>>> net/core/sock.c:274:36: error: initializer element is not constant
>>>>> net/core/sock.c:274:36: error: (near initialization for  
>>>>> 'memalloc_socks')
>>>>> net/core/sock.c:274:36: error: initializer element is not constant
>>>>>
>>>>
>>>> It looks parisc specific so am adding some parisc because this  
>>>> builds but
>>>> I am less sure if it is actually correct. If it's correct, it  
>>>> should be
>>>> appear before the swap-over-nfs patches to avoid bisection  
>>>> problems.
>>>> I've added some parisc folk for review.
>>>>
>>>> ---8<---
>>>> parisc: Redefine ATOMIC_INIT and ATOMIC64_INIT like other  
>>>> architectures
>>>>
>>>> The following build error occured during a parisc build with
>>>> swap-over-NFS patches applied.
>>>>
>>>> net/core/sock.c:274:36: error: initializer element is not constant
>>>> net/core/sock.c:274:36: error: (near initialization for  
>>>> 'memalloc_socks')
>>>> net/core/sock.c:274:36: error: initializer element is not constant
>>>>
>>>> It's not obvious but this is due to how ATOMIC_INIT is defined on
>>>> parisc. It should affect any user of STATIC_KEY_INIT_FALSE on that
>>>> platform.
>>>>
>>>> This patch makes the definition of ATOMIC_INIT on parisc to look  
>>>> like
>>>> other arches definition.
>>>>
>>>> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
>>>> Signed-off-by: Mel Gorman <mgorman@...e.de>
>>>> ---
>>>> arch/parisc/include/asm/atomic.h |    4 ++--
>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/parisc/include/asm/atomic.h b/arch/parisc/ 
>>>> include/asm/atomic.h
>>>> index 6c6defc..af9cf30 100644
>>>> --- a/arch/parisc/include/asm/atomic.h
>>>> +++ b/arch/parisc/include/asm/atomic.h
>>>> @@ -141,7 +141,7 @@ static __inline__ int  
>>>> __atomic_add_unless(atomic_t *v, int a, int u)
>>>>
>>>> #define atomic_sub_and_test(i,v)	(atomic_sub_return((i),(v)) == 0)
>>>>
>>>> -#define ATOMIC_INIT(i)	((atomic_t) { (i) })
>>>> +#define ATOMIC_INIT(i)	{ (i) }
>>>>
>>>> #define smp_mb__before_atomic_dec()	smp_mb()
>>>> #define smp_mb__after_atomic_dec()	smp_mb()
>>>> @@ -150,7 +150,7 @@ static __inline__ int  
>>>> __atomic_add_unless(atomic_t *v, int a, int u)
>>>>
>>>> #ifdef CONFIG_64BIT
>>>>
>>>> -#define ATOMIC64_INIT(i) ((atomic64_t) { (i) })
>>>> +#define ATOMIC64_INIT(i) { (i) }
>>>>
>>>> static __inline__ s64
>>>> __atomic64_add_return(s64 i, atomic64_t *v)
>>>
>>> OK, I don't understand this either ... why would not casting to the
>>> appropriate type suddenly stop warning about the initialiser being  
>>> non
>>> constant.  It looks like some type of gcc bug to me.
>>

Possibly, the cast causes the const attribute to be dropped...

>> I agree. I could not see any functional difference as such either  
>> but also
>> could not figure out why gcc would get it right for some arches and  
>> not
>> for others.
>
> Will gcc create a temporary (and hence non constant) value for the
> conversion?

Parisc is a callee copies architecture.  Thus, a structure passed as an
argument may be copied to a temporary.  This has been a source of
numerous bugs as the majority of architectures do it the other way  
round.

It would be easier to see what's happening with preprocessed source.

>
>>> Our toolchain
>>> expert (Dave) hangs out on the parisc list ... he'll want to know  
>>> your
>>> gcc -v.
>>>
>>
>> I'm using the cross-compiler from
>> ftp://ftp.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.3/. I  
>> do
>> not know what compiler Fengguang Wu was using.
>
> Yeah that's handy binaries and I'm using them in the x86 compile
> servers. However this particular parisc-defconfig is compile tested in
> an ia64 machine which is built from debian's gcc-4.7 source:
>
> Using built-in specs.
> COLLECT_GCC=/opt/cross/bin/hppa-linux-gcc
> COLLECT_LTO_WRAPPER=/opt/cross/libexec/gcc/hppa-linux/4.7/lto-wrapper
> Target: hppa-linux
> Configured with: /home/wfg/buildall/gcc-4.7-4.7.1/src/configure -- 
> target=hppa-linux --enable-targets=all --prefix=/opt/cross --enable- 
> lang
> uages=c --without-headers --enable-sjlj-exceptions --with-system- 
> libunwind --disable-nls --disable-threads --disable-shared --disable- 
> libmudflap --disable-libssp --disable-libgomp --disable-decimal- 
> float --disable-libquadmath --enable- 
> checking=release                         Thread model: single
> gcc version 4.7.1 (GCC)
>
> Thanks,
> Fengguang
>
>> Using built-in specs.
>> COLLECT_GCC=/home/mel/git-public/cross-compilers/gcc-4.6.3-nolibc/ 
>> hppa-linux/bin/hppa-linux-gcc
>> COLLECT_LTO_WRAPPER=/home/mel/git-public/cross-compilers/gcc-4.6.3- 
>> nolibc/hppa-linux/bin/../libexec/gcc/hppa-linux/4.6.3/lto-wrapper
>> Target: hppa-linux
>> Configured with: /home/tony/buildall/src/gcc/configure
>> --target=hppa-linux --host=x86_64-linux-gnu --build=x86_64-linux-gnu
>> --enable-targets=all --prefix=/opt/cross/gcc-4.6.3-nolibc/hppa-linux/
>> --enable-languages=c --with-newlib --without-headers
>> --enable-sjlj-exceptions --with-system-libunwind --disable-nls
>> --disable-threads --disable-shared --disable-libmudflap --disable- 
>> libssp
>> --disable-libgomp --disable-decimal-float --enable-checking=release
>> --with-mpfr=/home/tony/buildall/src/sys-x86_64
>> --with-gmp=/home/tony/buildall/src/sys-x86_64 --disable-bootstrap
>> --disable-libquadmath
>> Thread model: single
>> gcc version 4.6.3 (GCC)
>>
>> -- 
>> Mel Gorman
>> SUSE Labs
> --
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--
John David Anglin	dave.anglin@...l.net



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