linux-kernel - Re: [PATCH 3/5] uml: Fix warning due to missing task

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Message-ID: <20100421060651.GB4467@cr0.nay.redhat.com>
Date:	Wed, 21 Apr 2010 14:06:51 +0800
From:	Amerigo Wang <xiyou.wangcong@...il.com>
To:	Jan Kiszka <jan.kiszka@....de>
Cc:	Jeff Dike <jdike@...toit.com>,
	Amerigo Wang <xiyou.wangcong@...il.com>, trivial@...nel.org,
	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH 3/5] uml: Fix warning due to missing task_struct
 declaration

On Tue, Apr 20, 2010 at 07:09:15PM +0200, Jan Kiszka wrote:
>Jeff Dike wrote:
>> On Tue, Apr 20, 2010 at 06:09:49PM +0800, Amerigo Wang wrote:
>>> On Mon, Apr 19, 2010 at 11:53:06PM +0200, Jan Kiszka wrote:
>>>> We can't pull in linux/sched.h, so just declare the struct.
>>>>
>>> Did you meet any build error? If yes, please include it.
>> 
>> What does this patch fix, aside from being a bit cleaner?
>
>  CC      arch/um/sys-i386/elfcore.o
>In file included from /data/linux-2.6/include/linux/elf.h:8,
>                 from /data/linux-2.6/arch/um/sys-i386/elfcore.c:2:
>/data/linux-2.6/arch/um/sys-i386/asm/elf.h:78: warning: ‘struct task_struct’ declared inside parameter list
>/data/linux-2.6/arch/um/sys-i386/asm/elf.h:78: warning: its scope is only this definition or declaration, which is probably not what you want
>
>I guess not many people build against i386 hosts anymore, so this
>remained widely unnoticed.
>
>> 
>> If it built before, without having a task_struct declaration, I think
>> that means that the elf_core_copy_fpregs was never used.  The
>> task_struct * in the declaration would become a private task_struct,
>> known only to the declaration.  If the implementation or callers have
>> the regular task_struct, it will be a different one, and the
>> prototypes will conflict due to the different types of the first
>> parameter.
>
>This is just a forward declaration (that many arch elf header include),
>so no such problem exists.
>
>BTW, to answer the other question in this thread: We have a circular
>dependency that prevents including sched.h.
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is the right reason to do this. Ok then, thanks.

But it looks like x86_64 needs this too.


BTW, I don't think compile warning fixes are trivial enough to go
to trivial@...nel.org.
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