derdrodt / crowbar-tool

Symbolic execution engine for ABS

Crowbar

Crowbar is a symbolic execution engine for ABS, based on BPL. Crowbar aims to provide a possibility to prototype novel deductive verification techniques for functional correctness of Active Objects. Contrary to KeY, which it aims to complement for ABS, and full interactive provers, Crowbar does not include a reasoning system. Instead, symbolic execution generates a set of first-order formulas that are passed to a backend solver in the SMT-LIB format (Test are checking with Z3 and CVC4).

Crowbar is at a very early development stage.

Example

Clone the code, generate an executable jar with ./gradlew shadowJar, save the following ABS code and call java -jar ./build/libs/crowbar-0.1-all.jar --class="Test.C" <file>

module Test;

data Spec = ObjInv(Bool)        //Object Invariants
          | Ensures(Bool)       //Pre-conditions of method and classes
          | Requires(Bool)      //Post-conditions
          | WhileInv(Bool);     //Loop invariants

[Spec : Requires(n > 0)]
[Spec : Ensures(result > 0)]
def Int fac(Int n) = if(n == 1) then 1 else n*fac(n-1);

interface I{
    [Spec : Ensures(result >= 0)]
    Int m(Int v);
}

[Spec : Requires(this.init > 0)]
[Spec : ObjInv(this.f > 0 && this.init > 0)]
class C(Int init) implements I {
    Int f = init;

    Int m(Int v){
        Int w = v;
        if(w > 0)  this.f = fac(w);
        else       this.f = fac(-w+init);
        return v*w;
    }
}

{
    I i = new C(10);
    i!m(fac(5));
}

Misc.

• Method preconditions are split into parameter preconditions in the interface and heap preconditions in the class.

  If you call a method asynchronously on this and you want to use parameter preconditions, it must be exposed. The heap precondition propagation is not implemented, you have to ensure that yourself.

  Right now, the restrictions on pre- and postconditions in general are not checked

• Please make sure that some SMT solver is installed and callable via command line. The tests use the z3 and cvc commands.

• Crowbar does not yet support any SPL option.

• Name clashes with internal expressions are not checked yet