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Re: [Qemu-devel] [Bug 902148] Re: qemu-img V1.0 hangs on creating Image


From: Zhi Yong Wu
Subject: Re: [Qemu-devel] [Bug 902148] Re: qemu-img V1.0 hangs on creating Image (0.15.1 runs)
Date: Mon, 16 Jan 2012 10:44:07 +0800

On Sun, Jan 15, 2012 at 7:14 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Sat, Jan 14, 2012 at 3:40 PM, Zhi Yong Wu <address@hidden> wrote:
>> On Mon, Jan 9, 2012 at 9:00 PM, Stefan Hajnoczi <address@hidden> wrote:
>>> On Mon, Jan 9, 2012 at 11:25 AM, Kevin Wolf <address@hidden> wrote:
>>>> Am 20.12.2011 17:49, schrieb Stefan Hajnoczi:
>>>>> On Tue, Dec 20, 2011 at 3:25 PM, Michael Niehren
>>>>> <address@hidden> wrote:
>>>>>> here we are. Attached the tgz. I am using no spezial distribution, it's 
>>>>>> a self compiled LFS with
>>>>>> gcc V4.5.1
>>>>>>
>>>>>> Is there a different compiler-call if i use --enable-debug, which then
>>>>>> works ?
>>>>>
>>>>> Richard Sandiford looked at your gcc -fdump-tree-all-details output
>>>>> and suggests that this bug has been fixed in gcc 4.5.3:
>>>>>
>>>>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45967
>>>>>
>>>>> Using the most recent gcc should fix the issue you are seeing.
>>>>
>>>> Can we add some workaround? Not sure what will work, maybe a simple
>>>> compiler barrier?
>>>
>>> Sure though it seems like a very rare case - OP was running Linux From
>>> Scratch and hence got the broken gcc.  But if someone does a small
>>> workaround and tests it then that would be nice.
>> How to do this workaround in qemu since it is one gcc bug?
>
> The problem is that that compiler keeps values in registers across a
> point where C semantics require that they be reloaded.
>
> There are several ways to force a compiler to reload values including
> a barrier (which Kevin suggested) or the volatile keyword.  One of
> these techniques can probably be used as a workaround, but it would be
> necessary to check gcc 4.5.1 output to make sure it's effective.
thanks
>
> I think it's not worth doing unless we think more users will be
> affected.  Unless a distro ships the broken compiler version or it's
> the latest gcc release that people would build from source, I bet the
> number of users is very small.
>
> Stefan



-- 
Regards,

Zhi Yong Wu



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