More weird behaviour on PowerPC.

[Joel Sherrill]

On 05/24/2010 03:00 PM, Nick Thomas wrote:
> Hi
>
> My colleague and I have spent the last couple of days upgrading our RTEMS OS
> from 4.7.1 to 4.7.3. At the same time we have added the -fno-strict-aliasing
> flag to the compiler.
>
> I don't this these modifications have helped in our stability issues,
> because I have just observed a weird thing with the new build :(
>
>    
I hate to ask the obvious, but have you blown a stack?  It would not
be for FILTER_Task but either the one created before or after it.
I don't remember which in 4.7.x.  I think it would be the one created
next after it but not 100% sure.
> It's just taken a 0x0700 (Program Exception). And looking at the call stack
> I see:
>
> (gdb) bt
> #0  0x00000014 in ?? ()
> #1  0x00000010 in ?? ()
> #2  0x00325148 in FILTER_Task_Entry ()
> #3  0x003197b8 in task_launch ()
>
>
> The last good address is 0x00325148. Which is indeed in FILTER_Task_Entry,
> the disassembly around 0x00325148 is:
>
> 0x0032513c<FILTER_Task_Entry+540>:	stw     r10,1864(r16)
> 0x00325140<FILTER_Task_Entry+544>:	sth     r0,4(r11)
> 0x00325144<FILTER_Task_Entry+548>:	bl      0x323964
> <FILTER_String_Length+60>
> 0x00325148<FILTER_Task_Entry+552>:	b       0x325024
> <FILTER_Task_Entry+260>
> 0x0032514c<FILTER_Task_Entry+556>:	lwz     r4,1912(r19)
> 0x00325150<FILTER_Task_Entry+560>:	li      r5,0
>
> So, at 0x00325148 is a simple branch instruction to an address earlier
> inside the same function. But, the call stack shows that it next went to
> 0x00000010 !!!!
>
> What on earth could make it do that?
>
> I don't know if this is useful, but here is the dump of the memory at those
> locations:
>
>    
>> md 0x0032513c 6
>>      
> 0032513c : 0x91500748  -1857026232 .P.H
> 00325140 : 0xb00b0004  -1341456380 ....
> 00325144 : 0x4bffe821   1275062305 K..!
> 00325148 : 0x4bfffedc   1275068124 K...
> 0032514c : 0x80930778  -2137847944 ...x
> 00325150 : 0x38a00000    950009856
>
> Regards
>
> Nick
>
>
> -----------------------------
> Nick Thomas
> Email: nick.thomas at pixsan.com
>
>
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>    


-- 
Joel Sherrill, Ph.D.             Director of Research&  Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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