Re: [Qemu-devel] Fiber switching and stack protection

[Bob Breuer]

On 4/13/2012 6:25 AM, Pavel Dovgaluk wrote:
>> -----Original Message-----
>> From: Paolo Bonzini [mailto:address@hidden
>> Sent: Thursday, April 12, 2012 8:57 PM
>> To: Stefan Weil
>> Cc: Kevin Wolf; 'qemu-devel'; Pavel Dovgaluk
>> Subject: Re: [Qemu-devel] Fiber switching and stack protection
>>
>> Il 12/04/2012 18:31, Stefan Weil ha scritto:
>>> Am 12.04.2012 12:18, schrieb Paolo Bonzini:
>>>> Il 12/04/2012 12:13, Kevin Wolf ha scritto:
>>>>> I guess it's this non-thread-local TLS once again, basically a
>>>>> compiler bug.
> 
>   You are right, this is a compiler bug with non-thread-local TLS.
> 
>>>>> Paolo, wasn't there a compiler option that works around the problem?
>>>>>
>>>> I asked to test it (-D_MT) but never got any answer.
>>>
>>> I'd be surprised if defining _MT helped against compiler bugs.
>>
>> Well, -mthreads fixed it, and it should be the same as -D_MT -lmingwthrd.  
>> But we shouldn't
>> need libmingwthrd, or do we?
> 
>   I've tried to add -mthreads to compiler options but nothing has changed, 
> qemu still fails.


This is likely a different bug than the original thread related bug.
I'm using the mingw gcc 4.6.2, and I see the same thing as shown here:
http://virtuallyfun.superglobalmegacorp.com/?p=1846

Something goes wrong during optimization with gcc 4.6.2, but it doesn't
appear to be TLS related.  Digging into it a bit,
qemu_coroutine_switch() seems to break if it gets inlined.  Can anyone
else confirm if this one-line patch works for them?

diff --git a/coroutine-win32.c b/coroutine-win32.c
index 4179609..504873b 100644
--- a/coroutine-win32.c
+++ b/coroutine-win32.c
@@ -36,6 +36,7 @@ typedef struct
 static __thread CoroutineWin32 leader;
 static __thread Coroutine *current;

+__attribute__ ((noinline))
 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
                                       CoroutineAction action)
 {


Bob