1 /*
2 * Copyright (c) 2022, 2023, 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 java.lang.foreign;
27
28 import jdk.internal.access.JavaLangAccess;
29 import jdk.internal.access.SharedSecrets;
30 import jdk.internal.foreign.MemorySessionImpl;
31 import jdk.internal.foreign.Utils;
32 import jdk.internal.javac.PreviewFeature;
33 import jdk.internal.loader.BuiltinClassLoader;
34 import jdk.internal.loader.NativeLibrary;
35 import jdk.internal.loader.RawNativeLibraries;
36 import jdk.internal.reflect.CallerSensitive;
37 import jdk.internal.reflect.Reflection;
38
39 import java.lang.invoke.MethodHandles;
40 import java.nio.file.Path;
41 import java.util.Objects;
42 import java.util.Optional;
43 import java.util.function.BiFunction;
44
45 /**
46 * A <em>symbol lookup</em> retrieves the address of a symbol in one or more libraries.
47 * A symbol is a named entity, such as a function or a global variable.
48 * <p>
49 * A symbol lookup is created with respect to a particular library (or libraries). Subsequently, the {@link SymbolLookup#find(String)}
50 * method takes the name of a symbol and returns the address of the symbol in that library.
51 * <p>
52 * The address of a symbol is modelled as a zero-length {@linkplain MemorySegment memory segment}. The segment can be used in different ways:
53 * <ul>
54 * <li>It can be passed to a {@link Linker} to create a downcall method handle, which can then be used to call the foreign function at the segment's address.</li>
55 * <li>It can be passed to an existing {@linkplain Linker#downcallHandle(FunctionDescriptor, Linker.Option...) downcall method handle}, as an argument to the underlying foreign function.</li>
56 * <li>It can be {@linkplain MemorySegment#set(AddressLayout, long, MemorySegment) stored} inside another memory segment.</li>
57 * <li>It can be used to access the region of memory backing a global variable (this requires
58 * {@linkplain MemorySegment#reinterpret(long) resizing} the segment first).</li>
59 * </ul>
60 *
61 * <h2 id="obtaining">Obtaining a symbol lookup</h2>
62 *
63 * The factory methods {@link #libraryLookup(String, Arena)} and {@link #libraryLookup(Path, Arena)}
64 * create a symbol lookup for a library known to the operating system. The library is specified by either its name or a path.
65 * The library is loaded if not already loaded. The symbol lookup, which is known as a <em>library lookup</em>, and its
66 * lifetime is controlled by an {@linkplain Arena arena}. For instance, if the provided arena is a
67 * confined arena, the library associated with the symbol lookup is unloaded when the confined arena
68 * is {@linkplain Arena#close() closed}:
69 *
70 * {@snippet lang = java:
71 * try (Arena arena = Arena.ofConfined()) {
72 * SymbolLookup libGL = SymbolLookup.libraryLookup("libGL.so", arena); // libGL.so loaded here
73 * MemorySegment glGetString = libGL.find("glGetString").orElseThrow();
74 * ...
75 * } // libGL.so unloaded here
76 *}
77 * <p>
78 * If a library was previously loaded through JNI, i.e., by {@link System#load(String)}
79 * or {@link System#loadLibrary(String)}, then the library was also associated with a particular class loader. The factory
80 * method {@link #loaderLookup()} creates a symbol lookup for all the libraries associated with the caller's class loader:
81 *
82 * {@snippet lang=java :
83 * System.loadLibrary("GL"); // libGL.so loaded here
84 * ...
85 * SymbolLookup libGL = SymbolLookup.loaderLookup();
86 * MemorySegment glGetString = libGL.find("glGetString").orElseThrow();
87 * }
88 *
89 * This symbol lookup, which is known as a <em>loader lookup</em>, is dynamic with respect to the libraries associated
90 * with the class loader. If other libraries are subsequently loaded through JNI and associated with the class loader,
91 * then the loader lookup will expose their symbols automatically.
92 * <p>
93 * Note that a loader lookup only exposes symbols in libraries that were previously loaded through JNI, i.e.,
94 * by {@link System#load(String)} or {@link System#loadLibrary(String)}. A loader lookup does not expose symbols in libraries
95 * that were loaded in the course of creating a library lookup:
96 *
97 * {@snippet lang = java:
98 * libraryLookup("libGL.so", arena).find("glGetString").isPresent(); // true
99 * loaderLookup().find("glGetString").isPresent(); // false
100 *}
101 *
102 * Note also that a library lookup for library {@code L} exposes symbols in {@code L} even if {@code L} was previously loaded
103 * through JNI (the association with a class loader is immaterial to the library lookup):
104 *
105 * {@snippet lang = java:
106 * System.loadLibrary("GL"); // libGL.so loaded here
107 * libraryLookup("libGL.so", arena).find("glGetString").isPresent(); // true
108 *}
109 *
110 * <p>
111 * Finally, each {@link Linker} provides a symbol lookup for libraries that are commonly used on the OS and processor
112 * combination supported by that {@link Linker}. This symbol lookup, which is known as a <em>default lookup</em>,
113 * helps clients to quickly find addresses of well-known symbols. For example, a {@link Linker} for Linux/x64 might choose to
114 * expose symbols in {@code libc} through the default lookup:
115 *
116 * {@snippet lang = java:
117 * Linker nativeLinker = Linker.nativeLinker();
118 * SymbolLookup stdlib = nativeLinker.defaultLookup();
119 * MemorySegment malloc = stdlib.find("malloc").orElseThrow();
120 *}
121 *
122 * @since 19
123 */
124 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
125 @FunctionalInterface
126 public interface SymbolLookup {
127
128 /**
129 * Returns the address of the symbol with the given name.
130 * @param name the symbol name.
131 * @return a zero-length memory segment whose address indicates the address of the symbol, if found.
132 */
133 Optional<MemorySegment> find(String name);
134
135 /**
136 * {@return a composed symbol lookup that returns result of finding the symbol with this lookup if found,
137 * otherwise returns the result of finding the symbol with the other lookup}
138 *
139 * @apiNote This method could be used to chain multiple symbol lookups together, e.g. so that symbols could
140 * be retrieved, in order, from multiple libraries:
141 * {@snippet lang = java:
142 * var lookup = SymbolLookup.libraryLookup("foo", arena)
143 * .or(SymbolLookup.libraryLookup("bar", arena))
144 * .or(SymbolLookup.loaderLookup());
145 *}
146 * The above code creates a symbol lookup that first searches for symbols in the "foo" library. If no symbol is found
147 * in "foo" then "bar" is searched. Finally, if a symbol is not found in neither "foo" nor "bar", the {@linkplain
148 * SymbolLookup#loaderLookup() loader lookup} is used.
149 *
150 * @param other the symbol lookup that should be used to look for symbols not found in this lookup.
151 */
152 default SymbolLookup or(SymbolLookup other) {
153 Objects.requireNonNull(other);
154 return name -> find(name).or(() -> other.find(name));
155 }
156
157 /**
158 * Returns a symbol lookup for symbols in the libraries associated with the caller's class loader.
159 * <p>
160 * A library is associated with a class loader {@code CL} when the library is loaded via an invocation of
161 * {@link System#load(String)} or {@link System#loadLibrary(String)} from code in a class defined by {@code CL}.
162 * If that code makes further invocations of {@link System#load(String)} or {@link System#loadLibrary(String)},
163 * then more libraries are loaded and associated with {@code CL}. The symbol lookup returned by this method is always
164 * current: it reflects all the libraries associated with the relevant class loader, even if they were loaded after
165 * this method returned.
166 * <p>
167 * Libraries associated with a class loader are unloaded when the class loader becomes
168 * <a href="../../../java/lang/ref/package.html#reachability">unreachable</a>. The symbol lookup
169 * returned by this method is associated with a fresh {@linkplain MemorySegment.Scope scope} which keeps the caller's
170 * class loader reachable. Therefore, libraries associated with the caller's class loader are kept loaded
171 * (and their symbols available) as long as a loader lookup for that class loader, or any of the segments
172 * obtained by it, is reachable.
173 * <p>
174 * In cases where this method is called from a context where there is no caller frame on the stack
175 * (e.g. when called directly from a JNI attached thread), the caller's class loader defaults to the
176 * {@linkplain ClassLoader#getSystemClassLoader system class loader}.
177 *
178 * @return a symbol lookup for symbols in the libraries associated with the caller's class loader.
179 * @see System#load(String)
180 * @see System#loadLibrary(String)
181 */
182 @CallerSensitive
183 static SymbolLookup loaderLookup() {
184 Class<?> caller = Reflection.getCallerClass();
185 // If there's no caller class, fallback to system loader
186 ClassLoader loader = caller != null ?
187 caller.getClassLoader() :
188 ClassLoader.getSystemClassLoader();
189 Arena loaderArena;// builtin loaders never go away
190 if ((loader == null || loader instanceof BuiltinClassLoader)) {
191 loaderArena = Arena.global();
192 } else {
193 MemorySessionImpl session = MemorySessionImpl.heapSession(loader);
194 loaderArena = session.asArena();
195 }
196 return name -> {
197 Objects.requireNonNull(name);
198 if (Utils.containsNullChars(name)) return Optional.empty();
199 JavaLangAccess javaLangAccess = SharedSecrets.getJavaLangAccess();
200 // note: ClassLoader::findNative supports a null loader
201 long addr = javaLangAccess.findNative(loader, name);
202 return addr == 0L ?
203 Optional.empty() :
204 Optional.of(MemorySegment.ofAddress(addr)
205 .reinterpret(loaderArena, null));
206 };
207 }
208
209 /**
210 * Loads a library with the given name (if not already loaded) and creates a symbol lookup for symbols in that library.
211 * The lifetime of the returned library lookup is controlled by the provided arena.
212 * For instance, if the provided arena is a confined arena, the library
213 * associated with the returned lookup will be unloaded when the provided confined arena is
214 * {@linkplain Arena#close() closed}.
215 * <p>
216 * This method is <a href="package-summary.html#restricted"><em>restricted</em></a>.
217 * Restricted methods are unsafe, and, if used incorrectly, their use might crash
218 * the JVM or, worse, silently result in memory corruption. Thus, clients should refrain from depending on
219 * restricted methods, and use safe and supported functionalities, where possible.
220 *
221 * @implNote The process of resolving a library name is OS-specific. For instance, in a POSIX-compliant OS,
222 * the library name is resolved according to the specification of the {@code dlopen} function for that OS.
223 * In Windows, the library name is resolved according to the specification of the {@code LoadLibrary} function.
224 *
225 * @param name the name of the library in which symbols should be looked up.
226 * @param arena the arena associated with symbols obtained from the returned lookup.
227 * @return a new symbol lookup suitable to find symbols in a library with the given name.
228 * @throws IllegalStateException if {@code arena.scope().isAlive() == false}
229 * @throws WrongThreadException if {@code arena} is a confined arena, and this method is called from a
230 * thread {@code T}, other than the arena's owner thread.
231 * @throws IllegalArgumentException if {@code name} does not identify a valid library.
232 * @throws IllegalCallerException If the caller is in a module that does not have native access enabled.
233 */
234 @CallerSensitive
235 static SymbolLookup libraryLookup(String name, Arena arena) {
236 Reflection.ensureNativeAccess(Reflection.getCallerClass(), SymbolLookup.class, "libraryLookup");
237 if (Utils.containsNullChars(name)) {
238 throw new IllegalArgumentException("Cannot open library: " + name);
239 }
240 return libraryLookup(name, RawNativeLibraries::load, arena);
241 }
242
243 /**
244 * Loads a library from the given path (if not already loaded) and creates a symbol lookup for symbols
245 * in that library. The lifetime of the returned library lookup is controlled by the provided arena.
246 * For instance, if the provided arena is a confined arena, the library
247 * associated with the returned lookup will be unloaded when the provided confined arena is
248 * {@linkplain Arena#close() closed}.
249 * <p>
250 * This method is <a href="package-summary.html#restricted"><em>restricted</em></a>.
251 * Restricted methods are unsafe, and, if used incorrectly, their use might crash
252 * the JVM or, worse, silently result in memory corruption. Thus, clients should refrain from depending on
253 * restricted methods, and use safe and supported functionalities, where possible.
254 *
255 * @implNote On Linux, the functionalities provided by this factory method and the returned symbol lookup are
256 * implemented using the {@code dlopen}, {@code dlsym} and {@code dlclose} functions.
257 * @param path the path of the library in which symbols should be looked up.
258 * @param arena the arena associated with symbols obtained from the returned lookup.
259 * @return a new symbol lookup suitable to find symbols in a library with the given path.
260 * @throws IllegalStateException if {@code arena.scope().isAlive() == false}
261 * @throws WrongThreadException if {@code arena} is a confined arena, and this method is called from a
262 * thread {@code T}, other than the arena's owner thread.
263 * @throws IllegalArgumentException if {@code path} does not point to a valid library.
264 * @throws IllegalCallerException If the caller is in a module that does not have native access enabled.
265 */
266 @CallerSensitive
267 static SymbolLookup libraryLookup(Path path, Arena arena) {
268 Reflection.ensureNativeAccess(Reflection.getCallerClass(), SymbolLookup.class, "libraryLookup");
269 return libraryLookup(path, RawNativeLibraries::load, arena);
270 }
271
272 private static <Z> SymbolLookup libraryLookup(Z libDesc, BiFunction<RawNativeLibraries, Z, NativeLibrary> loadLibraryFunc, Arena libArena) {
273 Objects.requireNonNull(libDesc);
274 Objects.requireNonNull(libArena);
275 // attempt to load native library from path or name
276 RawNativeLibraries nativeLibraries = RawNativeLibraries.newInstance(MethodHandles.lookup());
277 NativeLibrary library = loadLibraryFunc.apply(nativeLibraries, libDesc);
278 if (library == null) {
279 throw new IllegalArgumentException("Cannot open library: " + libDesc);
280 }
281 // register hook to unload library when 'libScope' becomes not alive
282 MemorySessionImpl.toMemorySession(libArena).addOrCleanupIfFail(new MemorySessionImpl.ResourceList.ResourceCleanup() {
283 @Override
284 public void cleanup() {
285 nativeLibraries.unload(library);
286 }
287 });
288 return name -> {
289 Objects.requireNonNull(name);
290 if (Utils.containsNullChars(name)) return Optional.empty();
291 long addr = library.find(name);
292 return addr == 0L ?
293 Optional.empty() :
294 Optional.of(MemorySegment.ofAddress(addr)
295 .reinterpret(libArena, null));
296 };
297 }
298 }