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[Frama-c-discuss] Assigns-clauses in preconditions and ghost variable assignment

  • Subject: [Frama-c-discuss] Assigns-clauses in preconditions and ghost variable assignment
  • From: rafael.bachmann.93 at (Rafael Bachmann)
  • Date: Mon, 26 Nov 2018 17:49:09 +0100

while verifying the following function, it occurred to me that WP considers
assignments to ghost variables to be regular assignments, i.e. a function
which only assigns ghost variables cannot fulfil the property "assigns

//@ ghost int interrupt_status = INTERRUPTS_ON;

/*@ ensures interrupt_status == INTERRUPTS_ON;
   assigns interrupt_status; */
void interrupts_on() {
   //@ ghost interrupt_status = INTERRUPTS_ON;

I would have assumed that assignment of a ghost variable does not have an
effect on the actual implementation of the function, and hence should not
count as assignment.

Is this behaviour intentional? If so, is there a workaround or a
recommended different strategy?

Thanks very much,

Rafael Bachmann
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