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/*
* @test
* @bug 7004029 8131915
* @summary Ensure Scope impl can cope with hash collisions
* @library /tools/javac/lib
* @modules jdk.compiler/com.sun.tools.javac.api
* jdk.compiler/com.sun.tools.javac.code:+open
* jdk.compiler/com.sun.tools.javac.file
* jdk.compiler/com.sun.tools.javac.tree
* jdk.compiler/com.sun.tools.javac.util
* @build DPrinter HashCollisionTest
* @run main HashCollisionTest
*/
import java.lang.reflect.*;
import java.io.*;
import java.util.function.BiConsumer;
import com.sun.source.util.Trees;
import com.sun.tools.javac.api.JavacTrees;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Scope.*;
import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.file.JavacFileManager;
import com.sun.tools.javac.tree.JCTree.JCImport;
import com.sun.tools.javac.tree.TreeMaker;
import static com.sun.tools.javac.code.Kinds.Kind.*;
public class HashCollisionTest {
public static void main(String... args) throws Exception {
new HashCollisionTest().run();
}
void run() throws Exception {
// set up basic environment for test
Context context = new Context();
JavacFileManager.preRegister(context); // required by ClassReader which is required by Symtab
make = TreeMaker.instance(context);
names = Names.instance(context); // Name.Table impls tied to an instance of Names
symtab = Symtab.instance(context);
trees = JavacTrees.instance(context);
types = Types.instance(context);
// determine hashMask for an empty scope
Scope emptyScope = WriteableScope.create(symtab.unnamedModule.unnamedPackage); // any owner will do
Field field = emptyScope.getClass().getDeclaredField("hashMask");
field.setAccessible(true);
scopeHashMask = field.getInt(emptyScope);
log("scopeHashMask: " + scopeHashMask);
// 1. determine the Name.hashCode of "Entry", and therefore the index of
// Entry in an empty scope. i.e. name.hashCode() & Scope.hashMask
Name entry = names.fromString("Entry");
// 2. create names of the form *$Entry until we find a name with a
// hashcode which yields the same index as Entry in an empty scope.
// Since Name.hashCode is a function of position (and not content) it
// should work to create successively longer names until one with the
// desired characteristics is found.
Name outerName;
Name innerName;
StringBuilder sb = new StringBuilder("C");
int i = 0;
do {
sb.append(Integer.toString(i % 10));
innerName = names.fromString(sb + "$Entry");
} while (!clash(entry, innerName) && (++i) < MAX_TRIES);
if (clash(entry, innerName)) {
log("Detected expected hash collision for " + entry + " and " + innerName
+ " after " + i + " tries");
} else {
throw new Exception("No potential collision found after " + i + " tries");
}
outerName = names.fromString(sb.toString());
/*
* Now we can set up the scenario.
*/
// 3. Create a nested class named Entry
ClassSymbol cc = createClass(names.fromString("C"), symtab.unnamedModule.unnamedPackage);
ClassSymbol ce = createClass(entry, cc);
// 4. Create a package containing a nested class using the name from 2
PackageSymbol p = new PackageSymbol(names.fromString("p"), symtab.rootPackage);
p.members_field = WriteableScope.create(p);
ClassSymbol inner = createClass(innerName, p);
// we'll need this later when we "rename" cn
ClassSymbol outer = createClass(outerName, p);
// 5. Create a star-import scope
log ("createStarImportScope");
PackageSymbol pkg = new PackageSymbol(names.fromString("pkg"), symtab.rootPackage);
StarImportScope starImportScope = new StarImportScope(pkg);
dump("initial", starImportScope);
// 6. Insert the contents of the package from 4.
Scope fromScope = p.members();
ImportFilter typeFilter = new ImportFilter() {
@Override
public boolean accepts(Scope origin, Symbol sym) {
return sym.kind == TYP;
}
};
BiConsumer<JCImport, CompletionFailure> noCompletionFailure =
(imp, cf) -> { throw new IllegalStateException(); };
starImportScope.importAll(types, fromScope, typeFilter, make.Import(null, false), noCompletionFailure);
dump("imported p", starImportScope);
// 7. Insert the class from 3.
starImportScope.importAll(types, cc.members_field, typeFilter, make.Import(null, false), noCompletionFailure);
dump("imported ce", starImportScope);
/*
* Set the trap.
*/
// 8. Rename the nested class to Entry. so that there is a bogus entry in the star-import scope
p.members_field.remove(inner);
inner.name = entry;
inner.owner = outer;
outer.members_field.enter(inner);
// 9. Lookup Entry
Symbol found = starImportScope.findFirst(entry);
if (found != ce)
throw new Exception("correct symbol not found: " + entry + "; found=" + found);
dump("final", starImportScope);
}
/*
* Check for a (probable) hash collision in an empty scope.
*/
boolean clash(Name n1, Name n2) {
log(n1 + " hc:" + n1.hashCode() + " v:" + (n1.hashCode() & scopeHashMask) + ", " +
n2 + " hc:" + n2.hashCode() + " v:" + (n2.hashCode() & scopeHashMask));
return (n1.hashCode() & scopeHashMask) == (n2.hashCode() & scopeHashMask);
}
/**
* Create a class symbol, init the members scope, and add it to owner's scope.
*/
ClassSymbol createClass(Name name, Symbol owner) {
ClassSymbol sym = new ClassSymbol(0, name, owner);
sym.members_field = WriteableScope.create(sym);
if (owner != symtab.unnamedModule.unnamedPackage)
owner.members().enter(sym);
return sym;
}
/**
* Dump the contents of a scope to System.err.
*/
void dump(String label, Scope s) throws Exception {
PrintWriter pw = new PrintWriter(System.err);
new DPrinter(pw, trees).printScope(label, s);
pw.flush();
}
Object readField(Object scope, String fieldName) throws Exception {
Field field = scope.getClass().getDeclaredField(fieldName);
field.setAccessible(true);
return field.get(scope);
}
/**
* Write a message to stderr.
*/
void log(String msg) {
System.err.println(msg);
}
int MAX_TRIES = 100; // max tries to find a hash clash before giving up.
int scopeHashMask;
TreeMaker make;
Names names;
Symtab symtab;
Trees trees;
Types types;
}