Static Analysis of Object References in RMI-based Java Software

1. Static Analysis of Object References in RMI-based Java Software Mariana Sharp Atanas (Nasko) Rountev Ohio State University

2. Reference Analysis for Java x o1 f y o2 • Which objects may variable x refer to? • Builds a points-to graph x = new A(); y = new B(); x.f = y; Nasko Rountev - ICSM'05

3. Uses of Reference Information • Clients: SE tools and compilers • Object read-write information • Side-effect analysis, dependence analysis • Call graph construction • For interprocedural static analyses • De-virtualization and inlining • Escape analysis • Object lifetime for dependence analysis; synchronization removal; stack allocation Nasko Rountev - ICSM'05

4. RMI-Based Distributed Java Applications • Java Remote Method Invocation (RMI) • Object references that cross JVM boundaries • Invocations of remote methods • Parameter passing for entire object graphs • Open questions • Correct semantic definition of reference analysis for RMI-based Java applications • Practical analysis algorithms Nasko Rountev - ICSM'05

5. Contributions • Theoretical definition of reference analysis for distributed RMI-based Java applications • Foundation for many other analyses • Analysis algorithm • Generalizes an algorithm for non-distributed Java programs • Static analyses for program understanding • Inter-component dependencies • Reducing the cost of serialization at RMI calls • Analysis implementation and evaluation Nasko Rountev - ICSM'05

6. RMI Basics • Code for a set of components C1, C2, …, Cn • Each Ci executes on a different JVM • Remote class: implements java.rmi.Remote • Remote object: instance of a remote class • Remote reference: pointer to a remote object • Remote call: x.m( ), x is a remote reference interface Listener extends java.rmi.Remote { void update(Event b); } class MyListener implements Listener extends … { void update(Event b) { … } } Nasko Rountev - ICSM'05

7. Component “Channel” interface Channel extends java.rmi.Remote { void add(Listener c); void notify(Event d); } class MyChannel implements Channel extends … { private Listener[ ] LST = new Listener[100]; void add(Listener c) { LST[n++] = c; } void notify(Event d) { … } static void main() { Channel e = new MyChannel(); Naming.bind(“foo”,e); } … } Nasko Rountev - ICSM'05

8. Adding a Listener Component C1 RMI Registry Component C2 “foo” f MyChannel LST g array MyListener c Channel f = (Channel) Naming.lookup(“foo”); Listener g = new MyListener(); f.add(g); LST[n++] = c; Nasko Rountev - ICSM'05

9. Component “Channel” class Event implements Serializable { … private Date dt = new Date(); } interface Listener extends java.rmi.Remote { void update(Event b); } class MyChannel implements Channel extends … { void notify(Event d) { for (…) LST[i].update(d); } … } Nasko Rountev - ICSM'05

10. Announcing an Event b d dt Eventcopy Datecopy dt Event Date Component C1 Component C2 MyChannel MyListener LST array notify(new Event()); LST[i].update(d); Nasko Rountev - ICSM'05

11. Theoretical Model • Names for locals and formals: v 1, v 2, v 3, … • Label with the component id • Names for site s “new X()” – s 1, s 2, s 3, … • Names for de-serialized objects: s k,i • Exists in the JVM of Ci, but the original object was created inside the JVM of Ck • Local points-to edges in component Ci • ( v i , s x)L or ( s1 y , fld, s2 x )L • x = i or x = k,i ; y = i or y = k,i Nasko Rountev - ICSM'05

12. Theoretical Model (cont) • Remote points-to edges in component Ci • ( v i , s x )R or ( s1 y , fld, s2 x )R • the target object is a remote object • Effects of v1 = v2 in Ci • For ( v2 i , s y)L/R create ( v1 i , s y)L/R • Effects of v1 = v2.fld in Ci • For ( v2 i , s2 y)L and ( s2 y , fld, s1 x)L/R create ( v1 i , s1 x)L/R Nasko Rountev - ICSM'05

13. Theoretical Model (cont) • Effects of v.m(w) in Ci for ( v i , s x)R • Remote call to method m in Cx • Create ( m.this x , s x)L • For ( w i , s2 y)L/R if s2 yis a remote object • Create ( p x , s2 y)R for formal p • For ( w i , s2 y)L if s2 yis a non-remote serializable object • Take the graph of serializable objects starting at s2 y and create a copy of the graph in Cx • Create ( p x , s2 z)L for formal p Nasko Rountev - ICSM'05

14. Analysis Algorithm • Pointer Assignment Graph [LhotakHendrenCC03] • Nodes are variables and object fields • Edges represent the flow of values • Each node has a local points-to set PtL and a remote points-to set PtR • v1 = v2 in Ci : edge node(v2 i )node(v1 i ) • Represents the subset relationships PtL(v2 i )  PtL(v1 i ) and PtR(v2 i )  PtR(v1 i ) Nasko Rountev - ICSM'05

15. Analyses for Program Understanding • Inter-component dependencies between • a remote call from Ci to Ck • some statement in Ck • due to a memory location in Ck • Inter-component dependencies between • a remote call from Ci to Ck • a remote call from Cj to Ck • due to a memory location in Ck • Specialized serialization at remote calls • Acyclic object graph; unique types Nasko Rountev - ICSM'05

16. Experimental Study • 11 RMI applications • Between 12 and 125 methods • Analysis includes ~7000 library methods • Implementation: Soot 2.1 (McGill U.) • Generalized the points-to analysis in Soot • Analysis running time • 2.8 GHz PC with 1 GB memory • Time: ~ 5-6 minutes per application • Special handling of libraries – no replication • Open issue: pre-computed summary info Nasko Rountev - ICSM'05

17. Remote Call Sites • Passing of remote references and serialization are common • High precision of the call graph at remote calls • All remote call sites with serialization: used acyclic and uniquely-typed object graphs Nasko Rountev - ICSM'05

18. Conclusions and Future Work • Theoretical foundations for reference analysis • Practical algorithm • Needs more work on handling of the libraries • Initial precision results are promising • Open questions • Theoretical definitions of other analyses for RMI software (e.g., for slicing) • More experimental results • Additional RMI applications • Precision for other analyses (e.g., analysis of inter-component dependencies) Nasko Rountev - ICSM'05

19. Questions? Nasko Rountev - ICSM'05