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[Frama-c-discuss] Checking for side-effects

  • Subject: [Frama-c-discuss] Checking for side-effects
  • From: dganesan at fc-md.umd.edu (Dharmalingam Ganesan)
  • Date: Thu, 6 Feb 2014 14:47:39 -0500
Hi,

Is there a way to specific "negative" behaviours, for example, no variable should be updated except the given variable.

For example, for this little code, WP can able to prove all behaviours. That's great. But, I do not want any change in the state of the system except the "global" value. In this code, the dummy variable's state can also change, which is an undesirable side-effect (let's assume). 

For large and complex code, it appears specifying what is not allowed would also help to make sure implementation = specification.

I looked into -deps option to Frama-c, it appears to list the dependencies for each variable, which is helpful, but it does not quite check for undesired state changes. 

Any comments?
Dharma


int global = 0;
int dummy = 0;

/*@
    requires global == dummy;

    behavior GLOBAL_BELOW_5:
      assumes global < 5;
      ensures global == \old(global) + 1;
   
    behavior GLOBAL_ABOVE_5:
      assumes global > 5;
      ensures global == \old(global) - 1;

    behavior GLOBAL_EQUAL_5:
      assumes global == 5;
      assigns \nothing;
 
    complete behaviors;
    disjoint behaviors;
*/
void update()
{
   if(global < 5) {
       global++;
       dummy++;
   }

   if(global > 5) {
       global--;
       dummy--;
   }
}