Archive

Archive for the ‘Formal verification of C programs’ Category

Verifying a binary search, part 2

May 6, 2010 2 comments

In my last entry I showed how to use a correct-by-construction approach to develop a binary search function. We got as far as specifying the function and the loop, but we left the loop body undefined. The function declaration looked like this: Read more…

Verifying a binary search

May 5, 2010 Comments off

In the last post, I covered some different levels of formal verification that you may be interested in, and showed how to add minimum annotation to the linearization example to allow ArC to prove predictable execution. The example provided a prototype for the binary search function it called, to which we added a minimal postcondition, so that it looked like this:

size_t bSearch(const LinEntry* array table, size_t nElems, uint16_t key)
 post(result <= nElems);

Read more…

What are you trying to prove?

April 27, 2010 9 comments

If you’re thinking of using formal verification to increase the quality and reliability of your software, one of the first decisions you need to make is what you want to prove. Roughly speaking, you have three levels to choose from: Read more…

Verifying loops: proving termination

March 31, 2010 6 comments

If you’ve stuck with me so far in this mini-series on verifying loops, give yourself a pat on the back  before reading further. When it comes to formal verification of single-threaded software, loops are the most challenging constructs to verify. Read more…

Verifying loops – part 2

March 29, 2010 2 comments

Last time I showed how it was possible to analyse a loop-free and recursion-free program or function to determine its semantics (i.e. its weakest precondition and its postcondition), but that this didn’t work when we have loops. To make it possible to analyze loops thoroughly, Read more…

Verifying loops in C and C++ (intro)

March 22, 2010 1 comment

When it comes to formal verification of single-threaded programs, one of the hardest constructs to verify is the humble loop. If a function contains no loops and no function calls, then a static analyser can trace through the function, looking for constructs (such as indexing an array, or dividing one number by another) that have an implied precondition Read more…

Using and Abusing Unions

March 12, 2010 4 comments

The C union type is one of those features that is generally frowned on by those who set programming standards for critical systems, yet is quite often used. MISRA C 2004 rule 18.4 bans them (“unions shall not be used”) on the grounds that there is a risk that the data may be misinterpreted. However, it goes on to say that deviations are acceptable for packing and unpacking of data, and for implementing variant records provided that the variants are differentiated by a common field. Read more…