chord: a program analysis platform for java

Chord: A Program Analysis Platform for Java

CS 6340

What is Chord?

• Static and dynamic program analysis framework for Java

• Started in 2006 as static Checker of races and deadlocks

• Publicly available under New BSD License

• Key goals:– versatile: applies to various analyses, domains,

platforms– extensible: users can build own analyses atop given

ones– productive: facilitates rapid prototyping of analyses– robust: deterministic, handles partial programs, etc.

Key Features of Chord

• Many standard static and dynamic analyses

• Writing/solving analyses using Datalog/BDDs

• Analyses as “building blocks”

• Context-sensitive static analysis framework

• Dynamic analysis framework

Outline of Lecture

• Getting Started with Chord

• Program Representation

• Analysis Using Datalog/BDDs

• Chaining Analyses Together

• Context-Sensitive Analysis

Downloading Chord

• Stable Binary Release– http://jchord.googlecode.com/files/chord-bin-2.0.tar.gz

• Stable Source Release1. http://jchord.googlecode.com/files/chord-src-2.0.tar.gz

(mandatory)– Chord’s source code + JARs of libraries used by Chord

2. http://jchord.googlecode.com/files/chord-libsrc-2.0.tar.gz (optional)– (adapted) Java source code of libraries used by Chord

• Latest Development Snapshotsvn checkout http://jchord.googlecode.com/svn/trunk/ chord

Or checkout only relevant directories under trunk/:– main/ (released as 1 above) – libsrc/ (released as 2 above)– test/ (Chord’s regression test suite)– … (many more)

Compiling Chord

• Requirements:– JVM for Java 5 or higher– Apache Ant– C++ compiler

(not needed by default)

• Optional: edit chord.properties– to enable C BuDDy library:

set chord.use.buddy=true

– to enable C++ JVMTI agent:set chord.use.jvmti=true

• Run in main directory:

ant compile

main/

build.xml

chord.properties

agent/

bdd/

doc/

examples/

lib/

src/

web/

chord.jar

libbuddy.so | buddy.dll | libbuddy.dylib

libchord_instr_agent.so

Running Chord

• Requirements: JVM for Java 5 or higher• no other dependencies (e.g., Eclipse)

• Run either command in any directory:• ant –f <...>/build.xml [–Dkeyi=vali]* run

• requires Apache Ant• not available in Binary Release

• java –cp <…>/chord.jar [–Dkeyi=vali]* chord.project.Boot

where <…> denotes path of Chord’s main/ directory

–Dkeyi=vali sets value of system property keyi to vali

Chord Properties

• All inputs to Chord are specified via System Properties• conventionally named chord.* (e.g.,

chord.work.dir)

• Three choices with decreasing precedence:1. On command line via –Dkey=val format

• use to specify properties specific to the current Chord run

2. Via user-specified file denoted by chord.props.file• use to specify properties specific to program being

analyzed(e.g. its main class, classpath, etc.)

• default value = "[chord.work.dir]/chord.properties"

3. Via pre-defined file main/chord.properties• use to specify properties that must hold in every Chord

run(e.g., maximum memory to be used by JVM)

Architecture of Chord

Classic or Modern Runtime

bytecodetranslator

(joeq)

bytecodeinstrumentor(javassist)

saxon XSLT

bddbddb

BuDDy

Java2HTML

staticanalysis

Dataloganalysis

dynamicanalysis

programbytecode

domain D1

relation R12

relationR1

domain D2

relationR2

analysis result

in XML

analysis result

in HTML

programsource

programquadcode

relation R12

analysis

programinputs

domain D1

analysisdomain D2

analysis

example program analysis

Java

pro

gra

m

user demands this to run

starts, blocks on R2, D2

starts, runs to finish

starts, runs to finish

starts, blocks on D1, D2, R1, R12

starts, blocks on D1

resumes,runs to finish

resumes, runs to finish

starts, blocks on D1



Setting Up a Java Program for Analysis

Command to run in Chord’s main directory:

ant –Dchord.work.dir=<…>/example run

example/ src/ foo/ Main.java ... classes/ foo/ Main.class ... lib/ src/ taz/ ... jar/ taz.jar

chord.properties

chord_output/

bddbddb/

chord.main.class=foo.Mainchord.class.path=classes:lib/jar/taz.jarchord.src.path=src:lib/srcchord.run.ids=0,1chord.args.0="-thread 1 -n 10" chord.args.1="-thread 2 -n 50"

Outline of Lecture






Java Program Representations

Java source code.java

Java bytecode.class

javac

DisassembledJava bytecode

javap

Example: Java Source Code

1: package test;2:3: public class HelloWorld {4: public static void main(String[] args) {5: System.out.print("Hello World!");6: }7: }

File test/HelloWorld.java:

Pretty-Printing Java Bytecode

public class test.HelloWorld extends java.lang.Object

Constant pool: const #1 = Method #6.#20; // java/lang/Object."<init>":()V ...public static void main(java.lang.String[]);Code: Stack=2, Locals=1, Args_size=1 0: getstatic #2; // Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; // String Hello World! 5: invokevirtual #4; // Method java/io/PrintStream.println:... 8: return

javap –private –verbose –classpath <CLASS_PATH>

[–bootclasspath <BOOT_CLASS_PATH>] <CLASS_NAME>

SourceFile: "HelloWorld.java"

LineNumberTable: line 5: 0 line 6: 8LocalVariableTable: Start Length Slot Name Signature 0 9 0 args [Ljava/lang/String;

Run "javac –g" on .java files to keep debuginfo (lines, vars, source) in .class files



QuadcodeJava bytecode

.class

javac

Joeq


javap

Pretty-Printing Quadcode

Class: test.HelloWorldMethod: main:([Ljava/lang/String;)[email protected] 0#1 5#3 5#2 8#4Control flow graph:BB0 (ENTRY) (in: <none>, out: BB2)BB2 (in: BB0 (ENTRY), out: BB1 (EXIT))1: GETSTATIC_A T1, .out3: MOVE_A T2, AConst: "Hello World!" 2: INVOKEVIRTUAL_V println:(Ljava/lang/String;)[email protected], (T1,T2)4: RETURN_VBB1 (EXIT) (in: BB2, out: <none>)Exception handlers: []Register factory: Registers: 3

ant –Dchord.work.dir=<WORK_DIR> –Dchord.out.file=<OUTPUT_FILE>

–Dchord.print.classes=<CLASS_NAMES> –Dchord.verbose=0 run

Alternative options: –Dchord.print.methods=<METHOD_SIGNS> –Dchord.print.all.classes=true

Replace any `$` by `#` toprevent shell interpretation

Type Hierarchy

jq_Type

jq_Primitive jq_Reference

jq_Class jq_Array

(all defined in package joeq.Class)

chord.program.Program API

• static Program g()• fully-qualified name of the class, e.g., "java.lang.String[]"

• IndexSet<jq_Type> getTypes()• all types in classes that may be loaded

• IndexSet<jq_Reference> getClasses()• all classes that may be loaded

• IndexSet<jq_Method> getMethods()• all methods that may be called

joeq.Class.jq_Class API

• String getName()• fully-qualified name of the class, e.g., "java.lang.String[]"

• jq_InstanceField[] getDeclaredInstanceFields()• all instance fields declared in the class

• jq_StaticField[] getDeclaredStaticFields()• all static fields declared in the class

• jq_InstanceMethod[] getDeclaredInstanceMethods()• all instance methods declared in the class

• jq_StaticMethod[] getDeclaredStaticMethods()• all static methods declared in the class

joeq.Class.jq_Method API

• String getName().toString()• name of the method

• String getDesc().toString()• descriptor of the method, e.g., "(Ljava/lang/String;)V"

• jq_Class getDeclaringClass()• declaring class of the method

• ControlFlowGraph getCFG()• control-flow graph of the method

• Quad getQuad(int bci)• first quad at the given bytecode offset (null if missing)

• int getLineNumber(int bci)• line number of the given bytecode offset (-1 if

missing)

• String toString()• ID of the method in format mName:mDesc@cName

Control Flow Graphs (CFGs)

• Each CFG contains:• a set of registers (register factory) • a directed graph whose nodes are basic blocks

and edges denote control flow

• Register Factory:• one register per argument (local variables)

• named R0, R1, …, Rn

• one register per temporary (stack variables)• named Tn+1, Tn+2, …, Tm

• Basic Block (BB):• sequence of primitive statements (quads)• unique entry BB: no quads and no incoming

edges• unique exit BB: no quads and no outgoing edges

joeq.Compiler.Quad.ControlFlowGraph API

• RegisterFactory getRegisterFactory()• set of all local variables

• EntryOrExitBasicBlock entry()• unique entry basic block

• EntryOrExitBasicBlock exit()• unique exit basic block

• List<BasicBlock> reversePostOrder ()• List of all basic blocks in reverse post-order

• jq_Method getMethod()• containing method of the CFG

joeq.Compiler.Quad.BasicBlock API

• int size()• number of quads in the basic block

• Quad getQuad(int index)• quad at the given 0-based index

• List<BasicBlock> getPredecessors()• list of immediate predecessor basic blocks

• List<BasicBlock> getSuccessors()• list of immediately successor basic blocks

• jq_Method getMethod()• containing method of the basic block

Quad Instructions

• Each quad contains an operator and upto 4 operands

• Example: getfield l = b.f:

Operand lo = Getfield.getDest(q);Operand bo = Getfield.getBase(q);if (lo instanceof RegisterOperand && bo instanceof RegisterOperand) { Register l = ((RegisterOperand) lo).getRegister(); Register b = ((RegisterOperand) bo).getRegister(); jq_Field f = Getfield.getField(q).getField(); ...}

Kinds of Quads

joeq.Compiler.Quad.Operator

Move Getstatic Branch Invoke Phi Putstatic IntIfCmp

InvokeVirtual Unary Getfield Goto

InvokeStatic Binary Putfield Jsr

InvokeInterface New ALoad Ret NewArray AStore LookupSwitch MultiNewArray Checkcast TableSwitch Alength Instanceof Monitor Return

joeq.Compiler.Quad.Quad API

• Operator getOperator()• kind of the quad

• int getBCI()• bytecode offset of the quad in its containing method

• String toByteLocStr()• unique identifier of the quad in format offset!

mName:mDesc@cName

• String toJavaLocStr()• location of the quad in format fileName:lineNum in Java

source code

• String toLocStr()• location of the quad in both Java bytecode and source code

• String toVerboseStr()• verbose description of the quad (its location plus contents)

• BasicBlock getBasicBlock()• containing basic block of the quad

Traversing Quadcode

import chord.program.Program;import joeq.Class.jq_Method;import joeq.Compiler.Quad.*;

QuadVisitor qv = new QuadVisitor.EmptyVisitor() { public void visitNew(Quad q) { ... } public void visitPhi(Quad q) { ... } ...};

Program program = Program.g();for (jq_Method m : program.getMethods()) { if (!m.isAbstract()) { ControlFlowGraph cfg = m.getCFG(); for (BasicBlock bb : cfg.reversePostOrder()) for (Quad q : bb.getQuads()) q.accept(qv); }}




.class

HTMLizedJava source code

.html

j2h

Java2HTML

javac

Joeq


javap

HTMLizing Java Source Code

• Programmatically:

import chord.program.Program;

Program program = Program.g();program.HTMLizeJavaSrcFiles();

• From command line:

1. Use j2h:

ant –Djava.dir=<JAVA_DIR> –Dhtml.dir=<HTML_DIR> j2h_xref

2. Use Java2HTML:

ant –Djava.dir=<JAVA_DIR> –Dhtml.dir=<HTML_DIR> j2h_fast



Jasmin code.j


.class

HTMLizedJava source code

.html

j2h

Java2HTML

javac

Joeq

Chord


javap Jasmin

Analysis Scope Construction

• Determines which parts of the program to analyze

• Computed in either of these cases:• chord.build.scope=true

• chord.program.Program.g() is called

• Algorithm specified by chord.scope.kind=[rta|cha|dynamic]• Rapid Type Analysis (RTA)

• Class Hierarchy Analysis (CHA)

• Dynamic Analysis

• All three algorithms require specifying:• chord.main.class=<MAIN CLASS>

• chord.class.path=<CLASSPATH>

Analysis Scope Representation

• Reachable Methods• stored in file specified by chord.methods.file

(default = "[chord.out.dir]/methods.txt")

• Resolved Reflection• stored in file specified by chord.reflect.file

(default = "[chord.out.dir]/reflect.txt")

# resolvedClsForNameSites ...

# resolvedObjNewInstSites ...

# resolvedConNewInstSites ...

# resolvedAryNewInstSites ...

mname:mdesc@cname...

Class Class.forName(String)

Object Class.newInstance()

Object Constructor.newInstance(Object[])

Object Array.newInstance(Class, int)

bci!mname:mdesc@cname->cname1,cname2,...,cnameN

Rapid Type Analysis (RTA)

• Preferred (and default) scope construction algorithm

• Allows specifying reflection resolution via chord.reflect.kind=[none|static|dynamic]

• Preferred way to resolve reflection is ‘dynamic’ and requires specifying how to run program:• chord.run.args=id1,…,idN

• chord.args.id1=<ARGS1>, …, chord.args.idN=<ARGSN>

Dynamic Analysis Based Scope Construction

• Runs program and observes which classes are loaded

• Requires JVMTI (set chord.use.jvmti=true in file main/chord.properties)

• Requires specifying how to run program:• chord.run.args=id1,…,idN

• chord.args.id1=<ARGS1>, …, chord.args.idN=<ARGSN>

• All methods of each loaded class are deemed reachable

• Currently no support for reflection resolution

Additional Analysis Scope Features

• Scope Reuse• Enables using scope constructed by a previous run of

Chord

• Constructs scope from files specified by chord.methods.fileand chord.reflect.file

• Specified via chord.reuse.scope=true

• Scope Exclusion• Enables excluding certain classes from scope

• Treats all methods in such classes as no-ops

• Specified via three properties:

1. chord.std.scope.exclude (default = "")

2. chord.ext.scope.exclude (default = "")

3. chord.scope.exclude (default = "[chord.std.scope.exclude],[chord.ext.scope.exclude]")

Native Method Stubs

• Specified in file main/src/chord/program/stubs/stubs.txtin format:

mname:mdesc@cname stub_cname

where stub_cname denotes a class implementing:

public interface joeq.Compiler.Quad.ICFGBuilder { public ControlFlowGraph run(jq_Method m);}

• Example:start:()[email protected] chord.program.stubs.ThreadStartCFGBuilder

Example Native Method Stub

public ControlFlowGraph run(jq_Method m) { jq_Class c = m.getDeclaringClass(); jq_Method n = c.getDeclaredInstanceMethod( new jq_NameAndDesc("run", "()V")); RegisterFactory f = new RegisterFactory(0, 1); Register r = f.getOrCreateLocal(0, c); ControlFlowGraph cfg = new ControlFlowGraph(m, 1, 0, f); Quad q1 = Invoke.create(0, m, Invoke.INVOKEVIRTUAL_V.INSTANCE, null, new MethodOperand(n), 1); Invoke.setParam(q1, 0, new RegisterOperand(r, c)); Quad q2 = Return.create(1, m, RETURN_V.INSTANCE); BasicBlock bb = cfg.createBasicBlock(1, 1, 2, null); bb.appendQuad(q1); bb.appendQuad(q2); BasicBlock eb = cfg.entry(), xb = cfg.exit(); eb.addSuccessor(bb); bb.addPredecessor(eb); bb.addSuccessor(xb); xb.addPredecessor(bb); return cfg;}

void start() { this.run(); return; }

Outline of Lecture






Program Domain

• Building block for analyses based on Datalog/BDDs

• Represents an indexed set of values of a fixed kind• typically artifacts from program being analyzed

(e.g., set of all methods in the program)

• Assigns unique 0-based index to each value• everything in Datalog/BDDs must be numbered• indices given in order in which values are added• order affects efficiency of running analysis on large

sets• initial indices (0, 1, ...) typically given to frequently-

usedvalues (e.g., the main method)

• O(1) access to value given index, and vice versa

Example Predefined Program Domains

Name Description Defining Class

T types chord.analyses.type.DomT

M methods chord.analyses.method.DomM

F fields chord.analyses.field.DomF

V variables of ref type chord.analyses.var.DomV

P quads (program points)

chord.analyses.point.DomP

H object allocation quads

chord.analyses.alloc.DomH

I method call quads chord.analyses.invk.DomI

E heap-accessing quads chord.analyses.heapacc.DomE

A abstract threads chord.analyses.alias.DomA

C abstract method contexts

chord.analyses.alias.DomC

O abstract objects chord.analyses.alias.DomO

Writing a Program Domain Analysis

Domain M: all methods in the program– main method has index 0

– java.lang.Thread.start() method has index 1

package chord.analyses.method;

@Chord(name = "M")public class DomM extends ProgramDom<jq_Method> { @Override public void fill() { Program program = Program.g(); add(program.getMainMethod()); jq_Method start = program.getThreadStartMethod(); if (start != null) add(start); for (jq_Method m : program.getMethods()) add(m); }}

Running a Program Domain Analysis

ant –Dchord.work.dir=<…> –Dchord.run.analyses=M run



Running a Program Domain Analysis

main:([Ljava/lang/String;)V@Bldgstart:()[email protected]<init>:()V@Bldg…

M <N> M.map

<N>chord_output/

bddbddb/

M.map

M.dom



chord.project.analyses.ProgramDom<T> API

• void setName(String name)• set name of domain

• boolean add(T val)• add value to domain if not present; return true if added

• int getOrAdd(T val)• add value to domain if not present; return its index in either

case• void save()

• save domain to disk (.dom and .map files)• String toUniqueString(T val)

• unique string representation of value• int size()

• number of values in domain• T get(int index)

• value having the given index; IndexOutofBoundsEx if not found

• int indexOf(T val)• index of given value; -1 if not found

Note: values once added

cannot be removed!

Program Relation

• Building block for analyses based on Datalog/BDDs

• Represents a set of tuples over one or more fixed program domains

• Represented symbolically as a BDD• enables storing and manipulating large relations

efficiently

• Provides various relational operations• projection, selection, join, etc.

• BDD size and efficiency of operations depends heavily on encoding of relation content as opposed to size• ordering of values within program domains• relative ordering between program domains

Writing a Program Relation Analysis

Relation MI: tuples (m, i) such that method m contains call i

package chord.analyses.invk;

@Chord(name = "MI", sign = "M0,I0:M0_I0")public class RelMI extends ProgramRel { @Override public void fill() { DomI domI = (DomI) doms[1]; for (Quad q : domI) { jq_Method m = q.getMethod(); add(m, q); } }}

• M0_I0: Domain order• Only dictates

performance• Can also be I0_M0 or

I0xM0

• Easy to change over time

• M0,I0: Domain names• Order mnemonically

(hard to change over time)

• Suffix 0, 1, etc. distinguishes repeating domains

Writing a Program Relation Analysis

package chord.analyses.var;

@Chord(name = "VT", sign = "V0,T0:T0_V0")public class RelVT extends ProgramRel { @Override public void fill() { for (each RegisterOperand o of each quad) { Register v = o.getRegister(); jq_Type t = o.getType(); add(v, t); } }}

Relation VT: tuples (v, t) such that local variable v has type t

Running a Program Relation Analysis

ant –Dchord.work.dir=<…> –Dchord.run.analyses=VT run





Running a Program Relation Analysis

chord_output/

bddbddb/

V.dom, T.dom, V.map, T.map

VT.bdd

# V0:2 T0:2# 1 2# 3 46 42 1 4 37 4 0 16 3 7 15 3 0 74 2 5 03 2 6 52 1 3 4

Program Relation as Binary Function

Variable v0 has types t1, t2, t3

Variable v1 has type t3

Variable v2 has type t3

Relation VT = {

(0, 1), (0, 2), (0, 3),

(1, 3),

(2, 3)

}

V T

b1 b2 b3 b4 f

0 0 0 0 00 0 0 1 10 0 1 0 10 0 1 1 10 1 0 0 00 1 0 1 00 1 1 0 00 1 1 1 11 0 0 0 01 0 0 1 01 0 1 0 01 0 1 1 11 1 0 0 01 1 0 1 01 1 1 0 01 1 1 1 0

BDD: Binary Decision Diagrams (Bryant 1986)

b2

b4

b3 b3

b4 b4 b4

0 0 0 1 0 0 0 0

b2

b4

b3 b3

b4 b4 b4

0 1 1 1 0 0 0 1

b1 0 edge

1 edge

Graphical Encoding of a Binary Function

BDD: Collapsing Redundant Nodes

b2

b4

b3 b3

b4 b4 b4

0 0 0 1 0 0 0 0

b2

b4

b3 b3

b4 b4 b4

0 1 1 1 0 0 0 1

b1 0 edge

1 edge


b2

b4

b3 b3

b4 b4 b4

b2

b4

b3 b3

b4 b4 b4

0

b1

1

0 edge

1 edge


b2

b4

b3 b3

b2

b3 b3

b4 b4

0

b1

1

0 edge

1 edge


b2

b4

b3 b3

b2

b3

b4 b4

0

b1

1

0 edge

1 edge

BDD: Eliminating Unnecessary Nodes

b2

b4

b3 b3

b2

b3

b4 b4

0

b1

1

0 edge

1 edge

BDD: Eliminating Unnecessary Nodes

0 edge

1 edge

b2

b3

b2

b3

b4

0

b1

1

BDD Representation on Disk

b2

b3

b2

b3

b4

0

b1

1

2

3 4

6

5

7

chord_output/

bddbddb/


VT.bdd

# V0:2 T0:2# b1 b2# b3 b46 4b2 b1 b4 b37 b4 0 16 b3 7 15 b3 0 74 b2 5 03 b2 6 52 b1 3 4

BDDvariabl

eorder

# BDDvariable

s

# internalnodes

One entry per internal node of form:

<nodeId, varId, loNodeId, hiNodeId>

BDD Variable Order is Important

b1

b3

b4

0 1

b2

b1b2 + b3b4

b1 < b2 < b3 < b4 b1 < b3 < b2 < b4

b1

b3

b4

0 1

b2

b3

b2

chord.project.analyses.ProgramRel<T> API

• void setName(String name)• set name of relation

• void setSign(RelSign sign)• set signature (domain names and order) of relation

• void setDoms(Dom[] doms)• set domains of relation

• void zero() or one()• initialize contents of relation to zero (no tuples) or one (all

tuples)

• void add(T1 e1, …, TN eN)• add tuple (e1, …, eN) to relation

• void remove(T1 e1, …, TN eN)• remove tuple (e1, …, eN) from relation

• void save()• save contents of relation to disk

chord.project.analyses.ProgramRel<T> API

• void load()• load contents of relation from disk

• Iterable<T1,…,TN> getAryNValTuples()• iterate over all tuples in the relation

• int size()• number of tuples in the relation

• boolean contains(T1 e1, …, TN eN)• does relation contain tuple (e1, …, eN)?

• RelView getView()• obtain a copy of the relation upon which to do projection,

selection, etc. without affecting original relation

• void close()• free memory used to hold relation

Example: Pointer Analysis

class List { Obj[] elems; List() { Obj[] a = new Obj[…]; this.elems = a; }}

class Bldg { List events, floors; static void main(String[] a) { Bldg b = new Bldg(); } Bldg() { List el = new List(); this.events = el; List fl = new List(); this.floors = fl; for (int i = 0; i < K; i++) Event e = new Event(); el.elems[i] = e; for (int i = 0; i < M; i++) Floor f = new Floor(); fl.elems[i] = f; }}

0

List

Bldg

Event

List

events floors

Obj[]

elems

Obj[]

elems

Floor

0

Floor

1

Event

1

b

el fl

fe e f

a a

disjoint-reach(el, fl)?

Example: Call Graph (Base Case)

Code deemed reachable so far …

class List { Obj[] elems; List() { Obj[] a = new Obj[…]; this.elems = a; }}

for (int i = 0; i < K; i++)

for (int i = 0; i < M; i++)

class Bldg { List events, floors; static void main(String[] a) { Bldg b = new Bldg(); } Bldg() { List el = new List(); this.events = el; List fl = new List(); this.floors = fl; Event e = new Event(); el.elems[*] = e; Floor f = new Floor(); fl.elems[*] = f; }}

reachableM(0).

Example: Heap Abstraction

class List { Obj[] elems; List() { Obj[] a = new6 Obj[…]; this.elems = a; }}

for (int i = 0; i < K; i++)

for (int i = 0; i < M; i++)

class Bldg { List events, floors; static void main(String[] a) { Bldg b = new1 Bldg(); } Bldg() { List el = new2 List(); this.events = el; List fl = new3 List(); this.floors = fl; Event e = new4 Event(); el.elems[*] = e; Floor f = new5 Floor(); fl.elems[*] = f; }}

v = newh …

Rule for Object Allocation Sites

• Before:

• After:

v newh’

……

v

newh

newh’

……

VH(v, h) :- reachableM(m), MobjValAsgnInst(m, v, h).

v1 = v2

Rule for Copy Assignments

• Before:

• After:

v1 newh’

……

v1

newh

newh’

……

VH(v1, h) :- reachableM(m), MobjVarAsgnInst(m, v1, v2), VH(v2, h).

v2 newh

……

v2 newh

……

b.f = v

b

Rule for Heap Writes

• Before:

• After:

newh1

……

v newh2

……

v newh2

……

newh3newh1

……

newh1

f

newh2

newh3

……

……b newh1

…… f

f

f is instance field or [*] (array element)

HFH(h1, f, h2) :- reachableM(m), MputInstFldInst(m, b, f, v), VH(b, h1), VH(v, h2).

v = b.f

v

Rule for Heap Reads

newh

v

newh2

newh

……

……

……

b newh1

……

b newh1

……

newh2newh1

……

f

newh2newh1

……

f

f is instance field or [*] (array element)

• Before:

• After:

VH(v, h2) :- reachableM(m), MgetInstFldInst(m, v, b, f), VH(b, h1), HFH(h1, f, h2).

• Before:

• After:

Tn.bar() Tm.foo()

v.foo()

Rule for Dynamically Dispatching Calls

v newh

……

v newh…

…

T

T

i

i

Tn.bar() { …; ; …; }

CHA(T, foo) =

Tm.foo() { … }

Tm.foo() { … }

IM(i, m) :- reachableM(n), MI(n, i), virtIM(i, m’), IinvkArg0(i, v), VH(v, h), HT(h, t), CHA(t, m’, m).reachableM(m) :- IM(_, m).

#name=cipa-0cfa-dlog

.include "V.dom"

.include "T.dom"

...

.bddvarorder M0xI0_F0_V0xV1_T0_H0xH1

VT(v:V0, T0) inputreachableM(m:M0)FH(f:F0, h:H0) outputVH(v:V0, h:H0) outputHFH(h1:H0, f:F0, h2:H1) outputIM(i:I0, m:M0) output...

reachableM(m) :- IM(_, m)....

Writing a Datalog Analysis

analysis constraints(Horn clauses) solved via BDD

operations

input, intermediate, outputprogram relations

represented as BDDs

BDD variable order

program domains

Running a Datalog Analysis

chord_output/

bddbddb/


VT.bdd

reachableM.bdd

FH.bdd

VH.bdd

HFH.bdd

IM.bdd

#name=cipa-0cfa-dlog

.include "V.dom"

.include "T.dom"

...

.bddvarorder M0xI0_F0_V0xV1_T0_H0xH1

VT(v:V0, T0) inputreachableM(m:M0)FH(f:F0, h:H0) outputVH(v:V0, h:H0) outputHFH(h1:H0, f:F0, h2:H1) outputIM(i:I0, m:M0) output...

reachableM(m) :- IM(_, m)....

ant –Dchord.work.dir=<…> –Dchord.run.analyses=cipa-0cfa-dlog run

Example

b

new1 Bldg

el

new2 List

fl

new3 List

e

new5 Floor

new6 Obj[]

f

new4 Event

events floors

elems

[*][*]

12,3

a

for (int i = 0; i < K; i++)

for (int i = 0; i < M; i++)



elems

Printing Program Relations (Command Line)

Relation rVV:el!<init>:()V@Bldg, fl!<init>:()V@Bldg...

ant –Dwork.dir=<…>/chord_output/bddbddb –Ddlog.file=a.dlog solve

.include "V.dom"

.include "H.dom"

.include "F.dom"

.bddvarorder ...

VH(v:V0, h:H0) inputHFH(h1:H0, f:F0, h2:H1) inputrVH(v:V0, h:H0)rVV(v1:V0, v2:V1) printtuples

rVH(v, h) :- VH(v, h).rVH(v, h) :- rVH(v, h’), HFH(h’, _, h).rVV(v1, v2) :- v1<v2, rVH(v1, h), rVH(v2, h).


File a.dlog:b

new1 Bldg

el

new2 List

fl

new3 List

e

new5 Floor

new6 Obj[]

f

new4 Event

events floors

elems

[*][*] a

elems

Querying Program Relations (Command Line)

ant –Dwork.dir=<…>/chord_output/bddbddb –Ddlog.file=q.dlog debug

b!main:(…)@Bldg...

null1!main:(…)@Bldg2!<init>:()V@Bldg3!<init>:()V@Bldg...

.include "V.dom"

.include "H.dom"

.include "F.dom"

.bddvarorder ...

VH(v:V0, h:H0) inputHFH(h1:H0, f:F0, h2:H1) input

File H.map:

File V.map:

prompt> VH(0,h)?1!main:(…)@Bldg

prompt> HFH(1,_,h)?2!<init>:()V@Bldg3!<init>:()V@Bldg

File q.dlog:

b

new1 Bldg

el

new2 List

fl

new3 List

e

new5 Floor

new6 Obj[]

f

new4 Event

events floors

elems

[*][*] a

elems

Pros and Cons of Datalog/BDDs

1. Good for rapidly crafting initial versions of analysis with focus on false positive/negative rate instead of scalability

2. Good for analyses …1. whose constraint solving strategy is not obvious (e.g. best

known alternative is chaotic iteration)

2. on data with lots of redundancy and too large to compute/store/read using Java if represented explicitly (e.g. cloning-based analyses)

3. involving few simple rules (e.g. transitive closure)

3. Bad for analyses …1. with more complicated formulations (e.g. summary-based

analyses)

2. over domains not known exactly in advance (i.e. on-the-fly analyses)

3. involving many interdependent rules (e.g. points-to analyses)

4. Unintuitive effects of BDDs on performance (e.g. k-CFA: small non-uniform k across sites worse than large uniform k)

Outline of Lecture






Writing an Analysis in Chord

• Declaratively in Datalog or imperatively in Java

• Datalog analysis is any file that:• has extension .dlog or .datalog

• occurs in path specified by property chord.dlog.analysis.path

• Java analysis is any class that:• is annotated with @Chord

• occurs in path specified by property chord.java.analysis.path

• Create subclass of chord.project.analyses.JavaAnalysis:

• Compile above class to a location in path specified by any of:

@Chord(name = "my-java", consumes = { "C1", ..., "Cm" }, produces = { "P1", ..., "Pn" }, namesOfTypes = { “T1", ..., “Tk" }, types = { T1.class, ..., Tk.class }, namesOfSigns = { "S1", ..., "Sr" }, signs = { "...", ..., "..." })public class MyAnalysis extends JavaAnalysis { @Override public void run() { ... }}

Writing a Java Analysis

Property name Default value

chord.std.java.analysis.path

"chord.jar"

chord.ext.java.analysis.path

""

chord.java.analysis.path concat. of above two property values

mandatoryfield

target typesnot

inferableotherwiserelation signsnot

inferableotherwise

Chord Project

• Global entity for organizing all analyses and their inputs and outputs (collectively called analysis results)

• Computed if chord.project.Project.g() is called

• Consists of set of each of:• analyses called tasks

• analysis results called targets

• data/control dependencies between tasks and targets

• Either of two kinds chosen by chord.classic=[true|false]:• chord.project.ClassicProject (this tutorial)

• only data dependencies, can only run tasks sequentially

• chord.project.ModernProject (ongoing)• data and control dependencies, can run tasks in

parallel

Computing a Chord Project

• Compute all tasks:• Each file with extension .dlog/.datalog in

chord.dlog.analysis.path

• Each class having annotation @Chord in chord.java.analysis.path

• Compute all targets:• Each target consumed or produced by some task

• Compute dependency graph:• Nodes are all tasks and targets

• Edge from target C to task T if T consumes C

• Edge from task T to target P if T produces P

• Perform consistency checks• Error if target has no type or has multiple types, error if

relation has no sign, warn if target produced by multiple tasks, etc.

Example: Chord Project

T1 T2 T3

T4

R1 R2

R3 R4

{} T1 { R1 }

{} T2 { R1 }

{ R4} T3 { R2 }

{ R1, R2 } T4 { R3, R4 }

Each task has form { C1, …, Cm } T { P1, …, Pn } where:

– T is name of task

– C1, …, Cm are names of targets consumed by the task

– P1, …, Pn are names of targets produced by the task

Running a Java Analysis

ant –Dchord.work.dir=<…> –Dchord.run.analyses=my-java run

@Chord(name = "my-java", consumes = { "C1", ..., "Cm" }, produces = { "P1", ..., "Pn" })public class MyAnalysis extends JavaAnalysis { @Override public void run() { ... }}

• If done bit of this analysis is 1: do nothing

• Else do the following in order:• For each of C1, …, Cm whose done bit is 0:

• Recursively run unique analysis producing it

• Report runtime error if none or multiple such analyses exist

• Execute run() method of this analysis

• Set done bits of this analysis and P1, …, Pn to 1

Running a Java Analysis

T1 T2 T3

T4

R1 R2

R3 R4

{} T1 { R1 }

{} T2 { R1 }

{ R4} T3 { R2 }

{ R1, R2 } T4 { R3, R4 }

ant –Dchord.work.dir=<…> –Dchord.run.analyses=T1,T4 run

Predefined Analysis Templates

JavaAnalysis

ProgramDom

ProgramRel

DlogAnalysis

RHSAnalysis

ForwardRHSAnalysis

BackwardRHSAnalysis

BasicDynamicAnalysis DynamicAnalysis

Organized in a hierarchy in package chord.project.analyses:

chord.project.ClassicProject API

• ITask getTask(String name)• representation of named task

• Object getTrgt(String name)• representation of named target

• ITask runTask(String name)• run named task (and any needed tasks prior to it)

• boolean is[Task|Trgt]Done(String name)• is named task/target already executed/computed?

• void set[Task|Trgt]Done(String name)• set ‘done’ bit of named task/target to 1

• void reset[Task|Trgt]Done(String name)• Set ‘done’ bit of named task/target to 0

Example Java Analysis

package chord.analyses.alias;

@Chord(name = "cicg-java", consumes = { "IM" })public class CICGAnalysis extends JavaAnalysis { private ProgramRel cg; @Override public void run() { cg = (ProgramRel) ClassicProject.g().getTrgt("IM"); } public Set<jq_Method> getCallees(Quad q) { if (!cg.isOpen()) cg.load(); RelView view = cg.getView(); view.selectAndDelete(0, q); Iterable<jq_Method> res = view.getAry1ValTuples(); Set<jq_Method> callees = new HashSet<jq_Method>(); for (jq_Method m : res) callees.add(m); view.free(); return callees; } public void free() { if (cg.isOpen()) cg.close(); }}

Example Java Analysis

@Chord(name = "my-java")public class MyAnalysis extends JavaAnalysis { @Override public void run() { ClassicProject p = ClassicProject.g(); CICGAnalysis a = (CICGAnalysis) p.getTask("cicg-java"); p.runTask(a); for (Quad q : ...) { Set<jq_Method> tgts = a.getCallees(q); ... } a.free(); }}

Specialized Java Analyses

• ProgramDom:• Consumes targets specified in @Chord annotation• Produces only a single target (the defined program

domain itself)• run() method computes and saves domain to disk

• ProgramRel:• Consumes targets specified in @Chord annotation, plus

target of each of its program domains• Produces only a single target (the defined program

relation itself)• run() method computes and saves relation to disk

• DlogAnalysis:• Consumes only its declared domains and declared input

relations• Produces only its declared output relations• run() method runs bddbddb

Analyses as Building Blocks

1. Modularity• each analysis is written independently

2. Flexibility• analyses can interact in powerful ways with other

analyses (by user-specified data/control dependencies)

3. Efficiency• analyses executed in demand-driven fashion• results computed by each analysis automatically

cached for reuse by other analyses without re-computation

• independent analyses automatically executed in parallel

4. Reliability• result is independent of order in which analyses are

run

Outline of Lecture






Context-Sensitive Analysis

• Respects inter-procedural control-flow to varying degrees

• Broadly two kinds:• Bottom-Up: analyze method without any knowledge of

its callers

• Top-Down: analyze method only in called contexts

• Two kinds of top-down approaches:• Cloning-based (k-limited)

• Summary-based

• Fully context-sensitive approaches:• Bottom-up

• Top-down summary-based

Context-Sensitive Analysis in Chord

• Top-down: both cloning-based and summary-based

• Cloning-based analysis• k-CFA, k-object-sensitivity, hybrid

• Summary-based analysis• Tabulation algorithm from Reps, Horwitz, Sagiv (POPL’95)

Example: Context-Insensitive Analysis

1

2, 3

for (int i = 0; i < K; i++)

for (int i = 0; i < M; i++)

disjoint-reach(el, fl)?class Bldg { List events, floors; static void main(String[] a) { Bldg b = new1 Bldg(); } Bldg() { List el = new2 List(); this.events = el; List fl = new3 List(); this.floors = fl; Event e = new4 Event(); el.elems[*] = e; Floor f = new5 Floor(); fl.elems[*] = f; }}


b

new1 Bldg

el

new2 List

fl

new3 List

e

new5 Floor

new6 Obj[]

f

new4 Event

events floors

elems

[*][*] a

elems

Example: Cloning-Based Analysis

1

2

for (int i = 0; i < K; i++)

for (int i = 0; i < M; i++)

3

2 3


List() { Obj[] a = new6 Obj[…]; this.elems = a; }



b

new1 Bldg

el

new2 List

fl

new3 List

e

new5 Floor

new6 Obj[]

f

new4 Event

events floors

elems

[*][*] a

elems

Example: Cloning with Object Sensitivity

1

2

for (int i = 0; i < K; i++)

for (int i = 0; i < M; i++)

3

b

new1 Bldg

el

new2 List

fl

new3 List

e

new5 Floor

new6 Obj[]

f

new4 Event

events floors

elems elems

[*][*]a


new6 Obj[]

a

2 3

2 3


List() { Obj[] a = new6 Obj[…]; this.elems = a; }


Running Cloning-based Analyses in Chord

• chord.ctxt.kind=[ci|cs|co]• kind of context sensitivity for each method and its locals

• chord.inst.ctxt.kind=[ci|cs|co]• kind of context sensitivity for each instance method and

its locals

• chord.stat.ctxt.kind=[ci|cs|co]• kind of context sensitivity for each static method and its

locals

• chord.kobj.k=[1|2|…]• k value to use for each object allocation site

• chord.kcfa.k=[1|2|…]• k value to use for each method call site

ant –Dchord.work.dir=<…> –Dchord.run.analyses=<ONE OF ABOVE> run

cspa_0cfa.dlog, cspa_kcfa.dlog, cspa_kobj.dlog, cspa_hybrid.dlog

Output of Pointer/Call-Graph Analyses in Chord

cspa_0cfa.dlog, cspa_kcfa.dlog, cspa_kobj.dlog, cspa_hybrid.dlog

• rootCM• (c,m): m is entry method in ctxt c

• CICM• (c1,i,c2,m): call site i in ctxt c1 may call

method m in ctxt c2

• CVC• (c,v,o): local v may point to object o in

ctxt c of its declaring method

• FC• (f,o): static field f may point to object o

• CFC• (o1,f,o2): instance field f of object o1 may point to

object o2

cipa_0cfa.dlog

• rootM

• IM

• VH

• FH

• HFH

Cloning-Based vs. Summary-Based Analysis

• Cloning-based Analysis:• Flow-insensitive

• Notion of method contexts is somewhat arbitrary

• Summary-based Analysis:• Flow-sensitive

• Notion of method contexts is defined by the user

Related Open-Source Projects

• JikesRVM: Java Research Virtual Machine

• Soot + Paddle: Static analysis and transformation framework for Java bytecode

• IBM WALA: Static analysis framework for Java bytecode and related languages

Further Information

• Chord homepage:

http://jchord.googlecode.com/

• Chord user guide:

http://chord.stanford.edu/user_guide/

• Chord questions:

[email protected]

chord: a program analysis platform for java

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