Re: gdb "hangs" on delay loop

Charles Manning wrote:
> On Saturday 02 May 2009 07:03:10 Gene Smith wrote:
>> With -O0 opt level, gdb refuses to step (S) over a delay loop like this:
>>
>> code1; //<-- steps over this OK
>> for(c=0; c<10000; c++);   //<--- hangs here
>> code2;
>>
>> If I control-c and examine c it seems to be increasing slowly.
>>
>> When I change the code structure like this:
>>
>> code1;
>> for(c=0; c<10000; )
>> 	c++;
>> code2;
>>
>> then I can step.
>>
>> This is with embedded arm. See the same thing with arm-insight and
>> arm-gdb. Haven't tried this with native.
>>
>> Is this to be expected?
> 
> The stepping in ARM, and perhaps other CPUs, is prone to getting stuck like 
> this.
> 
> To get out of this either:
> * restructure code
> * set break at the next line and continue.
> * -if you're brave - try improve gdb :-).
> 

It seems to be "stepping" 10000 times in the background to get over this 
instruction so it will take a while. I think I verified this by setting 
c to 9995 and it took just a short time to step to the next source line. 
  I think another "improvement" would be to eliminate erratic stepping 
when optimization is applied (if that is possible).