Re: [BLACKBOX] Secure Software - Dependable Software

From: Campbell, Robert (SELEX GALILEO, UK) <robert.d.campbell{([at]})nowhere.xy>
Date: Thu, 24 Sep 2009 09:43:28 +0100

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>> On Tue, 22 Sep 2009, Chris Burrows wrote:
>>
>> David Jackson of MIT has written an interesting article
>> titled "A Direct
>> Path to Dependable Software". In part he says ...

>> You can download the complete article from:

>> http://sdg.csail.mit.edu/pubs/2008/cacm-08.pdf


An interesting article ...

Some years ago I wrote a fairly extensive piece of code to solve a
difficult
mathematical problem in CP / BlackBox. Some time later a colleague (who
uses C# / .NET)
had the same problem, and so wanted access to my solution. I compiled
the code into a .NET
dll using the Gardens Point CP compiler, he linked it into his C#, and
all seemed well - a
success!.

A year or so later some inaccuracies were noticed, then the CP module
began to 'hang' in
infinite loops. This was a big problem, caused a lot of anguish, and
gave CP a bad name locally.

Ultimately we traced the immediate cause to the assumption made in the
CP code that the floating
point unit was working in 64 or 80 bits accuracy. In fact the C#
application had grown a 3D graphics
capability that used DirectX, which set the floating point unit to 32
bit accuracy, and left it there.

Result - a non-(*dependable*) programme.


Do we just accept this? - or should there be a solution? Maybe the CP
(*language*) needs a command
to set the floating point control register explicitly, and we should
call this in our source code
before each and every floating point operation?

I would prefer a more elegant and efficient solution.


Maybe some (*mistake*) was made in the way the C# application was coded
(I honestly don't
know whose 'fault', if indeed it was a fault, this problem was). But
that fact that such a
fault can occur without obvious prompting seems to me to be a
dependability issue very similar
to a memory leak or an out-of-bounds array access; things that a
dependable language would
simply eliminate.


Regards

Robert
SELEX Sensors and Airborne Systems Limited
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 3EL
A company registered in England & Wales. Company no. 02426132
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Received on Thu Sep 24 2009 - 10:43:28 UTC