[ale] tech "magic"

[Geoffrey]

Michael H. Warfield wrote:
> On Wed, 2009-05-27 at 09:18 -0400, Geoffrey wrote:
>> Rev. Johnny Healey wrote:
>>> There's a great wikipedia article on unusual software bugs:
>>>
>>> http://en.wikipedia.org/wiki/Unusual_software_bug
>>>
>>> I actually ran into a schroedinbug in an apache config file today.
>> I actually identified a bug in an old c compiler on SVR3 years ago that 
>> would be defined as a heisenbug.  A piece of code was dropping core at a 
>> particular point.  I put in a printf and a comment above it, recompiled 
>> and it ran fine.  Remove the printf and comment, drops core.  We finally 
>> figured out that we could remove the printf and leave the comment in the 
>> code and the code would run.  Remove the comment and it would drop core. 
>>   We eventually simply placed a comment that said something like:
> 
>> /* don't remove this comment, the code will drop core with out it */
> 
> 	Sounds like an optimizer problem.  Use to run into those all quite
> often at high optimizer settings.  Sometimes entire loops would get
> optimized into non-existence and volatile variables were a laugh,
> especially in system/kernel code.  I forget what compiler it was but I
> remember reading the documentation and the optimizer when from 0 (no
> optimization) through several levels that included in-line optimization
> and unrolling loops and speed vs size.  The highest level of
> optimization was described in the documentation as "Dearly beloved we
> are gathered here...".

Seems to me, that you've jogged some cobwebs and I do believe that this 
was related to optimization.  It's been a while though, at least 15 
years ago, I think.


> 
> 	Mike
> 
>>> -Johnny
>>>
>>> On Tue, May 26, 2009 at 10:07 PM, Jim Kinney <jim.kinney at gmail.com> wrote:
>>>> Everyone here has had it happen. Something fails and you get called to
>>>> "take a look at it". You get there. take it and it isn't working. So
>>>> you methodically take it apart, inspecting everything alonmg the way
>>>> looking for failure points and find
>>>>
>>>>
>>>> nothing
>>>>
>>>>
>>>>
>>>> it all looks fine
>>>>
>>>>
>>>>
>>>> So you start testing a few thing as you put it back together.
>>>>
>>>>
>>>>
>>>> all the parts work correctly even though 20 minutes ago they were all
>>>> totally dead
>>>>
>>>>
>>>>
>>>> Finally you plug in the reassembled device and it comes up normally
>>>> and works perfectly.
>>>>
>>>>
>>>>
>>>> The 3Com switch I noted last Thursday that likely had a dead power
>>>> supply just ran me through that exact process. It works fine now.
>>>> Power supply puts out a rock solid 14V (no load) and 12.01V at 10A
>>>> load. All the fans work just fine.
>>>>
>>>> At least I don't have to explain "what I fixed" in an invoice...
>>>>
>>>> --
>>>> --
>>>> James P. Kinney III
>>>> Actively in pursuit of Life, Liberty and Happiness
>>>> _______________________________________________
>>>> Ale mailing list
>>>> Ale at ale.org
>>>> http://mail.ale.org/mailman/listinfo/ale
>>>>
>>> _______________________________________________
>>> Ale mailing list
>>> Ale at ale.org
>>> http://mail.ale.org/mailman/listinfo/ale
>>>
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale


-- 
Until later, Geoffrey

Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety.
  - Benjamin Franklin