Properly handle static interface methods as entrypoints

[hjjandy]

When a static Interface method is selected as an Entrypoint, WALA creates an invokeinterface instead of an invokestatic instruction in FakeRootMethod. This will lead to an out-of-array read when resolving the receiver for an interface invocation.

A test can be simply an Android app generated by Android Studio for a Basic Activity demo (either Java or Kotlin). In my case, the problem occurs for handling:

40149 = invokeinterface < Application, Landroidx/window/layout/WindowMetricsCalculator, getOrCreate()Landroidx/window/layout/WindowMetricsCalculator; > @32353 exception:40150

And the exception is as follows:

java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.lambda$getTargetsForCall$0(SSAPropagationCallGraphBuilder.java:2072)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder$CrossProductRec.rec(SSAPropagationCallGraphBuilder.java:542)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.iterateCrossProduct(SSAPropagationCallGraphBuilder.java:2055)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.getTargetsForCall(SSAPropagationCallGraphBuilder.java:2079)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder$ConstraintVisitor.visitInvokeInternal(SSAPropagationCallGraphBuilder.java:1159)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder$ConstraintVisitor.visitInvoke(SSAPropagationCallGraphBuilder.java:1115)
at com.ibm.wala.ssa.SSAInvokeInstruction.visit(SSAInvokeInstruction.java:94)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.addBlockInstructionConstraints(SSAPropagationCallGraphBuilder.java:273)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.addNodeInstructionConstraints(SSAPropagationCallGraphBuilder.java:250)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.unconditionallyAddConstraintsFromNode(SSAPropagationCallGraphBuilder.java:226)
at com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder.addConstraintsFromNode(SSAPropagationCallGraphBuilder.java:191)
at com.ibm.wala.ipa.callgraph.propagation.PropagationCallGraphBuilder.addConstraintsFromNewNodes(PropagationCallGraphBuilder.java:308)
at com.ibm.wala.ipa.callgraph.propagation.StandardSolver.solve(StandardSolver.java:53)
at com.ibm.wala.ipa.callgraph.propagation.PropagationCallGraphBuilder.makeCallGraph(PropagationCallGraphBuilder.java:248)

This commit prioritizes a static method over an interface method and addresses the above problem.

[msridhar]

The changes look good to me! And thanks for the contribution! But can we add a test case for this? I think it shouldn't be too hard, but if you need help let me know

[hjjandy]

I have included a test, with the Android app, the test code and the needed JAR files. The WALA jars are compiled from an earlier snapshot that has the mentioned issue.
Test.zip

[msridhar]

@hjjandy I meant that we should add a unit test. My feeling is this issue should occur with any static interface Entrypoint method; I don't think it has anything to do with Android. Our test inputs are here:

https://github.com/wala/WALA/tree/master/core/src/testSubjects/java

You could add another small Java source file, and then create a JUnit test like this one:

https://github.com/wala/WALA/blob/master/core/src/test/java/com/ibm/wala/core/tests/callGraph/DefaultMethodsTest.java

Your test would create the appropriate Entrypoint and ensure the exception does not occur. Does that make sense?

[msridhar]

@hjjandy I went ahead and added a unit test so we can merge. Please see the code in case you'd like to contribute and add tests in the future.