linux-kernel - Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall

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Message-ID: <BANLkTi=-xJizWP5H9vNvaJhRN-Vm-ubraA@mail.gmail.com>
Date:	Tue, 14 Jun 2011 23:43:50 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Andrew Lutomirski <luto@....edu>
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall_64.c

On Tue, Jun 14, 2011 at 12:06 AM, Andrew Lutomirski <luto@....edu> wrote:
> On Mon, Jun 13, 2011 at 4:45 AM, Rakib Mullick <rakib.mullick@...il.com> wrote:
>> On Mon, Jun 13, 2011 at 10:54 AM, Rakib Mullick <rakib.mullick@...il.com> wrote:
>>> On Mon, Jun 13, 2011 at 8:52 AM, Andrew Lutomirski <luto@....edu> wrote:
>>>> On Sun, Jun 12, 2011 at 1:12 AM, Rakib Mullick <rakib.mullick@...il.com> wrote:
>>>>> On Sat, Jun 11, 2011 at 5:01 PM, Andrew Lutomirski <luto@....edu> wrote:
>>>>>> On Sat, Jun 11, 2011 at 3:31 AM, Rakib Mullick <rakib.mullick@...il.com> wrote:
>>>>
>>>> I think there are three separate issues here:
>>>>
>>>> 1. Can ret be used uninitialized?  I say no, even as seen by the
>>>> compiler.  If vsyscall_nr is 0, 1, or 2, then ret is initialized.  If
>>>> vsyscall_nr is 3, then the BUG gets hit.  BUG is defined as some
>>>> assembly magic followed by unreachable(), and the compiler is supposed
>>>> to know that code after unreachable() is qunreachable.  So how can ret
>>>> be used uninitialized?
>>>>
>>> I don't have much knowledge of advance assembly, so I really don't
>>> understand that part - how BUG handles this. If it really makes sure
>>> that, it will handle it properly then I think you can drop this patch.
>>>
>>>> What version of gcc do you have?  gcc (GCC) 4.6.0 20110530 (Red Hat
>>>> 4.6.0-9) does not produce this warning.
>>>>
>>> Currently, I'm replying from outside my home. I'll let you know when
>>> I'm back home.
>>>
>> Here is my GCC version - gcc version 4.5.1 20100924 (Red Hat 4.5.1-4)
>> (GCC). I'm using Fedora 14.
>
> I also have gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4) on another box,
> and I still can't reproduce this.
>
> Can you tell me which git revision you're building and send me your
> .config and the output of:
>
I'm using 3.0.0-rc2 (lastly I pulled tip tree 3 days ago). I've
attached the .config (config.log).

> $ touch arch/x86/kernel/vsyscall_64.o
> $ make V=1 arch/x86/kernel/vsyscall_64.o
>
Output of the above steps are attached (vsyscall_64.log). Hope that will help.

Thanks,
Rakib


> Thanks,
> Andy
>

Download attachment "config.log" of type "application/octet-stream" (54891 bytes)

Download attachment "vsyscall_64.log" of type "application/octet-stream" (11015 bytes)