1 /*
2 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24 /*
25 * @test
26 * @bug 7004029
27 * @summary Ensure Scope impl can cope with hash collisions
28 */
29
30 import java.lang.reflect.*;
31 import java.io.*;
32 import com.sun.tools.javac.util.*;
33 import com.sun.tools.javac.code.*;
34 import com.sun.tools.javac.code.Scope.*;
35 import com.sun.tools.javac.code.Symbol.*;
36 import com.sun.tools.javac.file.JavacFileManager;
37 import static com.sun.tools.javac.code.Kinds.*;
38
39 public class HashCollisionTest {
40 public static void main(String... args) throws Exception {
41 new HashCollisionTest().run();
42 }
43
44 void run() throws Exception {
45 // set up basic environment for test
46 Context context = new Context();
47 JavacFileManager.preRegister(context); // required by ClassReader which is required by Symtab
48 names = Names.instance(context); // Name.Table impls tied to an instance of Names
49 symtab = Symtab.instance(context);
50
51 // determine hashMask for an empty scope
52 Scope emptyScope = new Scope(symtab.unnamedPackage); // any owner will do
53 Field sHashMask = Scope.class.getDeclaredField("hashMask");
54 sHashMask.setAccessible(true);
55 scopeHashMask = sHashMask.getInt(emptyScope);
56 log("scopeHashMask: " + scopeHashMask);
57
58 // 1. determine the Name.hashCode of "Entry", and therefore the index of
59 // Entry in an empty scope. i.e. name.hashCode() & Scope.hashMask
60 Name entry = names.fromString("Entry");
61
62 // 2. create names of the form *$Entry until we find a name with a
63 // hashcode which yields the same index as Entry in an empty scope.
64 // Since Name.hashCode is a function of position (and not content) it
65 // should work to create successively longer names until one with the
66 // desired characteristics is found.
67 Name outerName;
68 Name innerName;
69 StringBuilder sb = new StringBuilder("C");
70 int i = 0;
71 do {
72 sb.append(Integer.toString(i % 10));
73 innerName = names.fromString(sb + "$Entry");
74 } while (!clash(entry, innerName) && (++i) < MAX_TRIES);
75
76 if (clash(entry, innerName)) {
77 log("Detected expected hash collision for " + entry + " and " + innerName
78 + " after " + i + " tries");
79 } else {
80 throw new Exception("No potential collision found after " + i + " tries");
81 }
82
83 outerName = names.fromString(sb.toString());
84
85 /*
86 * Now we can set up the scenario.
87 */
88
89 // 3. Create a nested class named Entry
90 ClassSymbol cc = createClass(names.fromString("C"), symtab.unnamedPackage);
91 ClassSymbol ce = createClass(entry, cc);
92
93 // 4. Create a package containing a nested class using the name from 2
94 PackageSymbol p = new PackageSymbol(names.fromString("p"), symtab.rootPackage);
95 p.members_field = new Scope(p);
96 ClassSymbol inner = createClass(innerName, p);
97 // we'll need this later when we "rename" cn
98 ClassSymbol outer = createClass(outerName, p);
99
100 // 5. Create a star-import scope
101 log ("createStarImportScope");
102
103 // if StarImportScope exists, use it, otherwise, for testing legacy code,
104 // fall back on ImportScope
105 Scope starImportScope;
106 Method importAll;
107 PackageSymbol pkg = new PackageSymbol(names.fromString("pkg"), symtab.rootPackage);
108 try {
109 Class<?> c = Class.forName("com.sun.tools.javac.code.Scope$StarImportScope");
110 Constructor ctor = c.getDeclaredConstructor(new Class[] { Symbol.class });
111 importAll = c.getDeclaredMethod("importAll", new Class[] { Scope.class });
112 starImportScope = (Scope) ctor.newInstance(new Object[] { pkg });
113 } catch (ClassNotFoundException e) {
114 starImportScope = new ImportScope(pkg);
115 importAll = null;
116 }
117
118 dump("initial", starImportScope);
119
120 // 6. Insert the contents of the package from 4.
121 Scope p_members = p.members();
122 if (importAll != null) {
123 importAll.invoke(starImportScope, p_members);
124 } else {
125 Scope fromScope = p_members;
126 Scope toScope = starImportScope;
127 // The following lines are taken from MemberEnter.importAll,
128 // before the use of StarImportScope.importAll.
129 for (Scope.Entry e = fromScope.elems; e != null; e = e.sibling) {
130 if (e.sym.kind == TYP && !toScope.includes(e.sym))
131 toScope.enter(e.sym, fromScope);
132 }
133 }
134
135 dump("imported p", starImportScope);
136
137 // 7. Insert the class from 3.
138 starImportScope.enter(ce, cc.members_field);
139 dump("imported ce", starImportScope);
140
141 /*
142 * Set the trap.
143 */
144
145 // 8. Rename the nested class to Entry. so that there is a bogus entry in the star-import scope
146 p.members_field.remove(inner);
147 inner.name = entry;
148 inner.owner = outer;
149 outer.members_field.enter(inner);
150
151 // 9. Lookup Entry
152 Scope.Entry e = starImportScope.lookup(entry);
153 dump("final", starImportScope);
154
155 if (e.sym == null)
156 throw new Exception("symbol not found: " + entry);
157 }
158
159 /*
160 * Check for a (probable) hash collision in an empty scope.
161 */
162 boolean clash(Name n1, Name n2) {
163 log(n1 + " hc:" + n1.hashCode() + " v:" + (n1.hashCode() & scopeHashMask) + ", " +
164 n2 + " hc:" + n2.hashCode() + " v:" + (n2.hashCode() & scopeHashMask));
165 return (n1.hashCode() & scopeHashMask) == (n2.hashCode() & scopeHashMask);
166 }
167
168 /**
169 * Create a class symbol, init the members scope, and add it to owner's scope.
170 */
171 ClassSymbol createClass(Name name, Symbol owner) {
172 ClassSymbol sym = new ClassSymbol(0, name, owner);
173 sym.members_field = new Scope(sym);
174 if (owner != symtab.unnamedPackage)
175 owner.members().enter(sym);
176 return sym;
177 }
178
179 /**
180 * Dump the contents of a scope to System.err.
181 */
182 void dump(String label, Scope s) throws Exception {
183 dump(label, s, System.err);
184 }
185
186 /**
187 * Dump the contents of a scope to a stream.
188 */
189 void dump(String label, Scope s, PrintStream out) throws Exception {
190 out.println(label);
191 Field sTable = Scope.class.getDeclaredField("table");
192 sTable.setAccessible(true);
193
194 out.println("owner:" + s.owner);
195 Scope.Entry[] table = (Scope.Entry[]) sTable.get(s);
196 for (int i = 0; i < table.length; i++) {
197 if (i > 0)
198 out.print(", ");
199 out.print(i + ":" + toString(table[i], table, false));
200 }
201 out.println();
202 }
203
204 /**
205 * Create a string showing the contents of an entry, using the table
206 * to help identify cross-references to other entries in the table.
207 * @param e the entry to be shown
208 * @param table the table containing the other entries
209 */
210 String toString(Scope.Entry e, Scope.Entry[] table, boolean ref) {
211 if (e == null)
212 return "null";
213 if (e.sym == null)
214 return "sent"; // sentinel
215 if (ref) {
216 int index = indexOf(table, e);
217 if (index != -1)
218 return String.valueOf(index);
219 }
220 return "(" + e.sym.name + ":" + e.sym
221 + ",shdw:" + toString(e.next(), table, true)
222 + ",sibl:" + toString(e.sibling, table, true)
223 + ((e.sym.owner != e.scope.owner)
224 ? (",BOGUS[" + e.sym.owner + "," + e.scope.owner + "]")
225 : "")
226 + ")";
227 }
228
229 <T> int indexOf(T[] array, T item) {
230 for (int i = 0; i < array.length; i++) {
231 if (array[i] == item)
232 return i;
233 }
234 return -1;
235 }
236
237 /**
238 * Write a message to stderr.
239 */
240 void log(String msg) {
241 System.err.println(msg);
242 }
243
244 int MAX_TRIES = 100; // max tries to find a hash clash before giving up.
245 int scopeHashMask;
246
247 Names names;
248 Symtab symtab;
249 }