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*
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
/*
* @test
* @bug 7004029
* @summary Ensure Scope impl can cope with hash collisions
*/
import java.lang.reflect.*;
import java.io.*;
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 static com.sun.tools.javac.code.Kinds.*;
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
names = Names.instance(context); // Name.Table impls tied to an instance of Names
symtab = Symtab.instance(context);
// determine hashMask for an empty scope
Scope emptyScope = new Scope(symtab.unnamedPackage); // any owner will do
Field sHashMask = Scope.class.getDeclaredField("hashMask");
sHashMask.setAccessible(true);
scopeHashMask = sHashMask.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.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 = new Scope(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");
// if StarImportScope exists, use it, otherwise, for testing legacy code,
// fall back on ImportScope
Scope starImportScope;
Method importAll;
PackageSymbol pkg = new PackageSymbol(names.fromString("pkg"), symtab.rootPackage);
try {
Class<?> c = Class.forName("com.sun.tools.javac.code.Scope$StarImportScope");
Constructor ctor = c.getDeclaredConstructor(new Class[] { Symbol.class });
importAll = c.getDeclaredMethod("importAll", new Class[] { Scope.class });
starImportScope = (Scope) ctor.newInstance(new Object[] { pkg });
} catch (ClassNotFoundException e) {
starImportScope = new ImportScope(pkg);
importAll = null;
}
dump("initial", starImportScope);
// 6. Insert the contents of the package from 4.
Scope p_members = p.members();
if (importAll != null) {
importAll.invoke(starImportScope, p_members);
} else {
Scope fromScope = p_members;
Scope toScope = starImportScope;
// The following lines are taken from MemberEnter.importAll,
// before the use of StarImportScope.importAll.
for (Scope.Entry e = fromScope.elems; e != null; e = e.sibling) {
if (e.sym.kind == TYP && !toScope.includes(e.sym))
toScope.enter(e.sym, fromScope);
}
}
dump("imported p", starImportScope);
// 7. Insert the class from 3.
starImportScope.enter(ce, cc.members_field);
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
Scope.Entry e = starImportScope.lookup(entry);
dump("final", starImportScope);
if (e.sym == null)
throw new Exception("symbol not found: " + entry);
}
/*
* 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 = new Scope(sym);
if (owner != symtab.unnamedPackage)
owner.members().enter(sym);
return sym;
}
/**
* Dump the contents of a scope to System.err.
*/
void dump(String label, Scope s) throws Exception {
dump(label, s, System.err);
}
/**
* Dump the contents of a scope to a stream.
*/
void dump(String label, Scope s, PrintStream out) throws Exception {
out.println(label);
Field sTable = Scope.class.getDeclaredField("table");
sTable.setAccessible(true);
out.println("owner:" + s.owner);
Scope.Entry[] table = (Scope.Entry[]) sTable.get(s);
for (int i = 0; i < table.length; i++) {
if (i > 0)
out.print(", ");
out.print(i + ":" + toString(table[i], table, false));
}
out.println();
}
/**
* Create a string showing the contents of an entry, using the table
* to help identify cross-references to other entries in the table.
* @param e the entry to be shown
* @param table the table containing the other entries
*/
String toString(Scope.Entry e, Scope.Entry[] table, boolean ref) {
if (e == null)
return "null";
if (e.sym == null)
return "sent"; // sentinel
if (ref) {
int index = indexOf(table, e);
if (index != -1)
return String.valueOf(index);
}
return "(" + e.sym.name + ":" + e.sym
+ ",shdw:" + toString(e.next(), table, true)
+ ",sibl:" + toString(e.sibling, table, true)
+ ((e.sym.owner != e.scope.owner)
? (",BOGUS[" + e.sym.owner + "," + e.scope.owner + "]")
: "")
+ ")";
}
<T> int indexOf(T[] array, T item) {
for (int i = 0; i < array.length; i++) {
if (array[i] == item)
return i;
}
return -1;
}
/**
* 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;
Names names;
Symtab symtab;
}