linux-kernel - Re: [PATCH] kobject: Suppress compiler warning with gcc 3.x

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Message-ID: <20100603085248.GC5580@cr0.nay.redhat.com>
Date:	Thu, 3 Jun 2010 16:52:48 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	ebiederm@...stanetworks.com, randy.dunlap@...cle.com,
	gregkh@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kobject: Suppress compiler warning with gcc 3.x

On Thu, Jun 03, 2010 at 08:46:27AM +0200, Eric Dumazet wrote:
>Le jeudi 03 juin 2010 à 14:23 +0800, Américo Wang a écrit :
>> On Wed, Jun 02, 2010 at 11:02:28PM -0700, Eric W. Biederman wrote:
>> >Américo Wang <xiyou.wangcong@...il.com> writes:
>> >
>> >> On Thu, Jun 03, 2010 at 07:31:41AM +0200, Eric Dumazet wrote:
>> >>>Le jeudi 03 juin 2010 à 14:23 +0900, Tetsuo Handa a écrit :
>> >>>> Gcc 3.x generates a warning
>> >>>> 
>> >>>>   include/linux/sysfs.h:183: warning: parameter has incomplete type
>> >>>> 
>> >>>> on each file.
>> >>>> Suppress the warning by moving the definition of "enum kobj_ns_type"
>> >>>> to before "#include <linux/sysfs.h>".
>> >>>> 
>> >>>> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>> >>>
>> >>>
>> >>>I was about to submit same patch, but I was also reverting 27eabc7cb4b3
>> >>>(sysfs: Don't use enums in inline function declaration.)
>> >>>
>> >>>So that sysfs_exit_ns() prototype is consistent regardless of
>> >>>CONFIG_SYSFS
>> >>>
>> >>>What do you think ?
>> >>>
>> >>
>> >> This looks odd, in sysfs.h we do have a forward declaration of
>> >> enum kobj_ns_type... I am wondering why gcc 3.x doesn't recognize it.
>> >
>> >Because the replacement is an inline, and we are passing the enum by value
>> >gcc wants to see the full definition, at the point where the inline function
>> >is declared.
>> >
>> 
>> But sysfs_exit_ns() is not inlined if CONFIG_SYSFS here.
>> 
>
> 
># gcc -v
>Reading specs from /usr/lib/gcc/i386-redhat-linux/3.4.6/specs
>Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
>--infodir=/usr/share/info --enable-shared --enable-threads=posix
>--disable-checking --with-system-zlib --enable-__cxa_atexit
>--disable-libunwind-exceptions --enable-java-awt=gtk
>--host=i386-redhat-linux
>Thread model: posix
>gcc version 3.4.6 20060404 (Red Hat 3.4.6-10)
>
>
># cat try.c
>enum kobj_ns_type;
>void sysfs_exit_ns(enum kobj_ns_type type, const void *tag);
>int main(int argc, char *argv[])
>{
>	return 0;
>}
># gcc -O2 -Wall -o try try.c
>try.c:2: warning: parameter has incomplete type

This sounds like a bug of gcc 3.x, gcc 4.x would complain about it.

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