1 /*
2 * Copyright (c) 2008, 2013, 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package sun.invoke.util;
27
28 import java.lang.invoke.MethodType;
29 import sun.invoke.empty.Empty;
30
31 /**
32 * This class centralizes information about the JVM verifier
33 * and its requirements about type correctness.
34 * @author jrose
35 */
36 public class VerifyType {
37
38 private VerifyType() { } // cannot instantiate
39
40 /**
41 * True if a value can be stacked as the source type and unstacked as the
42 * destination type, without violating the JVM's type consistency.
43 * <p>
44 * If both types are references, we apply the verifier's subclass check
45 * (or subtyping, if keepInterfaces).
46 * If the src type is a type guaranteed to be null (Void) it can be converted
47 * to any other reference type.
48 * <p>
49 * If both types are primitives, we apply the verifier's primitive conversions.
50 * These do not include Java conversions such as long to double, since those
51 * require computation and (in general) stack depth changes.
52 * But very simple 32-bit viewing changes, such as byte to int,
53 * are null conversions, because they do not require any computation.
54 * These conversions are from any type to a wider type up to 32 bits,
55 * as long as the conversion is not signed to unsigned (byte to char).
56 * <p>
57 * The primitive type 'void' does not interconvert with any other type,
58 * even though it is legal to drop any type from the stack and "return void".
59 * The stack effects, though are difference between void and any other type,
60 * so it is safer to report a non-trivial conversion.
61 *
62 * @param src the type of a stacked value
63 * @param dst the type by which we'd like to treat it
64 * @param keepInterfaces if false, we treat any interface as if it were Object
65 * @return whether the retyping can be done without motion or reformatting
66 */
67 public static boolean isNullConversion(Class<?> src, Class<?> dst, boolean keepInterfaces) {
68 if (src == dst) return true;
69 // Verifier allows any interface to be treated as Object:
70 if (!keepInterfaces) {
71 if (dst.isInterface()) dst = Object.class;
72 if (src.isInterface()) src = Object.class;
73 if (src == dst) return true; // check again
74 }
75 if (isNullType(src)) return !dst.isPrimitive();
76 if (!src.isPrimitive()) return dst.isAssignableFrom(src);
77 if (!dst.isPrimitive()) return false;
78 // Verifier allows an int to carry byte, short, char, or even boolean:
79 Wrapper sw = Wrapper.forPrimitiveType(src);
80 if (dst == int.class) return sw.isSubwordOrInt();
81 Wrapper dw = Wrapper.forPrimitiveType(dst);
82 if (!sw.isSubwordOrInt()) return false;
83 if (!dw.isSubwordOrInt()) return false;
84 if (!dw.isSigned() && sw.isSigned()) return false;
85 return dw.bitWidth() > sw.bitWidth();
86 }
87
88 /**
89 * Specialization of isNullConversion to reference types.
90 * @param src the type of a stacked value
91 * @param dst the reference type by which we'd like to treat it
92 * @return whether the retyping can be done without a cast
93 */
94 public static boolean isNullReferenceConversion(Class<?> src, Class<?> dst) {
95 assert(!dst.isPrimitive());
96 if (dst.isInterface()) return true; // verifier allows this
97 if (isNullType(src)) return true;
98 return dst.isAssignableFrom(src);
99 }
100
101 /**
102 * Is the given type java.lang.Null or an equivalent null-only type?
103 */
104 public static boolean isNullType(Class<?> type) {
105 // Any reference statically typed as Void is guaranteed to be null.
106 // Therefore, it can be safely treated as a value of any
107 // other type that admits null, i.e., a reference type.
108 if (type == Void.class) return true;
109 // Locally known null-only class:
110 if (type == Empty.class) return true;
111 return false;
112 }
113
114 /**
115 * True if a method handle can receive a call under a slightly different
116 * method type, without moving or reformatting any stack elements.
117 *
118 * @param call the type of call being made
119 * @param recv the type of the method handle receiving the call
120 * @return whether the retyping can be done without motion or reformatting
121 */
122 public static boolean isNullConversion(MethodType call, MethodType recv, boolean keepInterfaces) {
123 if (call == recv) return true;
124 int len = call.parameterCount();
125 if (len != recv.parameterCount()) return false;
126 for (int i = 0; i < len; i++)
127 if (!isNullConversion(call.parameterType(i), recv.parameterType(i), keepInterfaces))
128 return false;
129 return isNullConversion(recv.returnType(), call.returnType(), keepInterfaces);
130 }
131
132 /**
133 * Determine if the JVM verifier allows a value of type call to be
134 * passed to a formal parameter (or return variable) of type recv.
135 * Returns 1 if the verifier allows the types to match without conversion.
136 * Returns -1 if the types can be made to match by a JVM-supported adapter.
137 * Cases supported are:
138 * <ul><li>checkcast
139 * </li><li>conversion between any two integral types (but not floats)
140 * </li><li>unboxing from a wrapper to its corresponding primitive type
141 * </li><li>conversion in either direction between float and double
142 * </li></ul>
143 * (Autoboxing is not supported here; it must be done via Java code.)
144 * Returns 0 otherwise.
145 */
146 public static int canPassUnchecked(Class<?> src, Class<?> dst) {
147 if (src == dst)
148 return 1;
149
150 if (dst.isPrimitive()) {
151 if (dst == void.class)
152 // Return anything to a caller expecting void.
153 // This is a property of the implementation, which links
154 // return values via a register rather than via a stack push.
155 // This makes it possible to ignore cleanly.
156 return 1;
157 if (src == void.class)
158 return 0; // void-to-something?
159 if (!src.isPrimitive())
160 // Cannot pass a reference to any primitive type (exc. void).
161 return 0;
162 Wrapper sw = Wrapper.forPrimitiveType(src);
163 Wrapper dw = Wrapper.forPrimitiveType(dst);
164 if (sw.isSubwordOrInt() && dw.isSubwordOrInt()) {
165 if (sw.bitWidth() >= dw.bitWidth())
166 return -1; // truncation may be required
167 if (!dw.isSigned() && sw.isSigned())
168 return -1; // sign elimination may be required
169 return 1;
170 }
171 if (src == float.class || dst == float.class) {
172 if (src == double.class || dst == double.class)
173 return -1; // floating conversion may be required
174 else
175 return 0; // other primitive conversions NYI
176 } else {
177 // all fixed-point conversions are supported
178 return 0;
179 }
180 } else if (src.isPrimitive()) {
181 // Cannot pass a primitive to any reference type.
182 // (Maybe allow null.class?)
183 return 0;
184 }
185
186 // Handle reference types in the rest of the block:
187
188 // The verifier treats interfaces exactly like Object.
189 if (isNullReferenceConversion(src, dst))
190 // pass any reference to object or an arb. interface
191 return 1;
192 // else it's a definite "maybe" (cast is required)
193 return -1;
194 }
195
196 public static boolean isSpreadArgType(Class<?> spreadArg) {
197 return spreadArg.isArray();
198 }
199 public static Class<?> spreadArgElementType(Class<?> spreadArg, int i) {
200 return spreadArg.getComponentType();
201 }
202 }