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295 lines
16 KiB
Java
295 lines
16 KiB
Java
/*
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* Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.lang.foreign;
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import jdk.internal.access.JavaLangAccess;
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import jdk.internal.access.SharedSecrets;
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import jdk.internal.foreign.MemorySessionImpl;
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import jdk.internal.foreign.Utils;
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import jdk.internal.javac.PreviewFeature;
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import jdk.internal.loader.BuiltinClassLoader;
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import jdk.internal.loader.NativeLibrary;
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import jdk.internal.loader.RawNativeLibraries;
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import jdk.internal.reflect.CallerSensitive;
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import jdk.internal.reflect.Reflection;
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import java.lang.invoke.MethodHandles;
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import java.nio.file.Path;
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import java.util.Objects;
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import java.util.Optional;
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import java.util.function.BiFunction;
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/**
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* A <em>symbol lookup</em> retrieves the address of a symbol in one or more libraries.
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* A symbol is a named entity, such as a function or a global variable.
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* <p>
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* A symbol lookup is created with respect to a particular library (or libraries). Subsequently, the {@link SymbolLookup#find(String)}
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* method takes the name of a symbol and returns the address of the symbol in that library.
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* <p>
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* The address of a symbol is modelled as a zero-length {@linkplain MemorySegment memory segment}. The segment can be used in different ways:
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* <ul>
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* <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>
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* <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>
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* <li>It can be {@linkplain MemorySegment#set(AddressLayout, long, MemorySegment) stored} inside another memory segment.</li>
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* <li>It can be used to access the region of memory backing a global variable (this requires
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* {@link MemorySegment#reinterpret(long)} () resizing} the segment first).</li>
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* </ul>
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*
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* <h2 id="obtaining">Obtaining a symbol lookup</h2>
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*
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* The factory methods {@link #libraryLookup(String, Arena)} and {@link #libraryLookup(Path, Arena)}
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* create a symbol lookup for a library known to the operating system. The library is specified by either its name or a path.
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* The library is loaded if not already loaded. The symbol lookup, which is known as a <em>library lookup</em>, and its
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* lifetime is controlled by an {@linkplain Arena arena}. For instance, if the provided arena is a
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* confined arena, the library associated with the symbol lookup is unloaded when the confined arena
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* is {@linkplain Arena#close()}:
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*
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* {@snippet lang = java:
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* try (Arena arena = Arena.ofConfined()) {
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* SymbolLookup libGL = SymbolLookup.libraryLookup("libGL.so", arena); // libGL.so loaded here
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* MemorySegment glGetString = libGL.find("glGetString").orElseThrow();
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* ...
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* } // libGL.so unloaded here
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*}
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* <p>
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* If a library was previously loaded through JNI, i.e., by {@link System#load(String)}
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* or {@link System#loadLibrary(String)}, then the library was also associated with a particular class loader. The factory
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* method {@link #loaderLookup()} creates a symbol lookup for all the libraries associated with the caller's class loader:
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*
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* {@snippet lang=java :
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* System.loadLibrary("GL"); // libGL.so loaded here
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* ...
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* SymbolLookup libGL = SymbolLookup.loaderLookup();
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* MemorySegment glGetString = libGL.find("glGetString").orElseThrow();
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* }
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*
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* This symbol lookup, which is known as a <em>loader lookup</em>, is dynamic with respect to the libraries associated
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* with the class loader. If other libraries are subsequently loaded through JNI and associated with the class loader,
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* then the loader lookup will expose their symbols automatically.
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* <p>
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* Note that a loader lookup only exposes symbols in libraries that were previously loaded through JNI, i.e.,
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* by {@link System#load(String)} or {@link System#loadLibrary(String)}. A loader lookup does not expose symbols in libraries
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* that were loaded in the course of creating a library lookup:
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*
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* {@snippet lang = java:
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* libraryLookup("libGL.so", arena).find("glGetString").isPresent(); // true
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* loaderLookup().find("glGetString").isPresent(); // false
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*}
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*
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* Note also that a library lookup for library {@code L} exposes symbols in {@code L} even if {@code L} was previously loaded
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* through JNI (the association with a class loader is immaterial to the library lookup):
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*
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* {@snippet lang = java:
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* System.loadLibrary("GL"); // libGL.so loaded here
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* libraryLookup("libGL.so", arena).find("glGetString").isPresent(); // true
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*}
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*
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* <p>
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* Finally, each {@link Linker} provides a symbol lookup for libraries that are commonly used on the OS and processor
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* combination supported by that {@link Linker}. This symbol lookup, which is known as a <em>default lookup</em>,
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* helps clients to quickly find addresses of well-known symbols. For example, a {@link Linker} for Linux/x64 might choose to
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* expose symbols in {@code libc} through the default lookup:
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*
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* {@snippet lang = java:
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* Linker nativeLinker = Linker.nativeLinker();
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* SymbolLookup stdlib = nativeLinker.defaultLookup();
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* MemorySegment malloc = stdlib.find("malloc").orElseThrow();
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*}
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*/
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@PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
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@FunctionalInterface
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public interface SymbolLookup {
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/**
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* Returns the address of the symbol with the given name.
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* @param name the symbol name.
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* @return a zero-length memory segment whose address indicates the address of the symbol, if found.
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*/
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Optional<MemorySegment> find(String name);
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/**
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* {@return a composed symbol lookup that returns result of finding the symbol with this lookup if found,
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* otherwise returns the result of finding the symbol with the other lookup}
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*
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* @apiNote This method could be used to chain multiple symbol lookups together, e.g. so that symbols could
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* be retrieved, in order, from multiple libraries:
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* {@snippet lang = java:
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* var lookup = SymbolLookup.libraryLookup("foo", arena)
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* .or(SymbolLookup.libraryLookup("bar", arena))
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* .or(SymbolLookup.loaderLookup());
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*}
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* The above code creates a symbol lookup that first searches for symbols in the "foo" library. If no symbol is found
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* in "foo" then "bar" is searched. Finally, if a symbol is not found in neither "foo" nor "bar", the {@linkplain
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* SymbolLookup#loaderLookup() loader lookup} is used.
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*
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* @param other the symbol lookup that should be used to look for symbols not found in this lookup.
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*/
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default SymbolLookup or(SymbolLookup other) {
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Objects.requireNonNull(other);
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return name -> find(name).or(() -> other.find(name));
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}
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/**
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* Returns a symbol lookup for symbols in the libraries associated with the caller's class loader.
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* <p>
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* A library is associated with a class loader {@code CL} when the library is loaded via an invocation of
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* {@link System#load(String)} or {@link System#loadLibrary(String)} from code in a class defined by {@code CL}.
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* If that code makes further invocations of {@link System#load(String)} or {@link System#loadLibrary(String)},
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* then more libraries are loaded and associated with {@code CL}. The symbol lookup returned by this method is always
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* current: it reflects all the libraries associated with the relevant class loader, even if they were loaded after
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* this method returned.
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* <p>
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* Libraries associated with a class loader are unloaded when the class loader becomes
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* <a href="../../../java/lang/ref/package.html#reachability">unreachable</a>. The symbol lookup
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* returned by this method is associated with a fresh {@linkplain MemorySegment.Scope scope} which keeps the caller's
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* class loader reachable. Therefore, libraries associated with the caller's class loader are kept loaded
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* (and their symbols available) as long as a loader lookup for that class loader, or any of the segments
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* obtained by it, is reachable.
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* <p>
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* In cases where this method is called from a context where there is no caller frame on the stack
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* (e.g. when called directly from a JNI attached thread), the caller's class loader defaults to the
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* {@linkplain ClassLoader#getSystemClassLoader system class loader}.
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*
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* @return a symbol lookup for symbols in the libraries associated with the caller's class loader.
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* @see System#load(String)
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* @see System#loadLibrary(String)
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*/
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@CallerSensitive
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static SymbolLookup loaderLookup() {
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Class<?> caller = Reflection.getCallerClass();
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// If there's no caller class, fallback to system loader
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ClassLoader loader = caller != null ?
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caller.getClassLoader() :
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ClassLoader.getSystemClassLoader();
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Arena loaderArena;// builtin loaders never go away
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if ((loader == null || loader instanceof BuiltinClassLoader)) {
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loaderArena = Arena.global();
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} else {
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MemorySessionImpl session = MemorySessionImpl.heapSession(loader);
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loaderArena = session.asArena();
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}
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return name -> {
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Objects.requireNonNull(name);
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if (Utils.containsNullChars(name)) return Optional.empty();
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JavaLangAccess javaLangAccess = SharedSecrets.getJavaLangAccess();
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// note: ClassLoader::findNative supports a null loader
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long addr = javaLangAccess.findNative(loader, name);
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return addr == 0L ?
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Optional.empty() :
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Optional.of(MemorySegment.ofAddress(addr)
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.reinterpret(loaderArena, null));
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};
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}
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/**
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* Loads a library with the given name (if not already loaded) and creates a symbol lookup for symbols in that library.
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* The lifetime of the returned library lookup is controlled by the provided arena.
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* For instance, if the provided arena is a confined arena, the library
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* associated with the returned lookup will be unloaded when the provided confined arena is
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* {@linkplain Arena#close() closed}.
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* @implNote The process of resolving a library name is OS-specific. For instance, in a POSIX-compliant OS,
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* the library name is resolved according to the specification of the {@code dlopen} function for that OS.
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* In Windows, the library name is resolved according to the specification of the {@code LoadLibrary} function.
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* <p>
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* This method is <a href="package-summary.html#restricted"><em>restricted</em></a>.
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* Restricted methods are unsafe, and, if used incorrectly, their use might crash
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* the JVM or, worse, silently result in memory corruption. Thus, clients should refrain from depending on
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* restricted methods, and use safe and supported functionalities, where possible.
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*
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* @param name the name of the library in which symbols should be looked up.
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* @param arena the arena associated with symbols obtained from the returned lookup.
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* @return a new symbol lookup suitable to find symbols in a library with the given name.
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* @throws IllegalStateException if {@code arena.scope().isAlive() == false}
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* @throws WrongThreadException if {@code arena} is a confined arena, and this method is called from a
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* thread {@code T}, other than the arena's owner thread.
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* @throws IllegalArgumentException if {@code name} does not identify a valid library.
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* @throws IllegalCallerException If the caller is in a module that does not have native access enabled.
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*/
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@CallerSensitive
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static SymbolLookup libraryLookup(String name, Arena arena) {
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Reflection.ensureNativeAccess(Reflection.getCallerClass(), SymbolLookup.class, "libraryLookup");
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if (Utils.containsNullChars(name)) {
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throw new IllegalArgumentException("Cannot open library: " + name);
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}
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return libraryLookup(name, RawNativeLibraries::load, arena);
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}
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/**
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* Loads a library from the given path (if not already loaded) and creates a symbol lookup for symbols
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* in that library. The lifetime of the returned library lookup is controlled by the provided arena.
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* For instance, if the provided arena is a confined arena, the library
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* associated with the returned lookup will be unloaded when the provided confined arena is
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* {@linkplain Arena#close() closed}.
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* <p>
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* This method is <a href="package-summary.html#restricted"><em>restricted</em></a>.
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* Restricted methods are unsafe, and, if used incorrectly, their use might crash
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* the JVM or, worse, silently result in memory corruption. Thus, clients should refrain from depending on
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* restricted methods, and use safe and supported functionalities, where possible.
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*
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* @implNote On Linux, the functionalities provided by this factory method and the returned symbol lookup are
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* implemented using the {@code dlopen}, {@code dlsym} and {@code dlclose} functions.
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* @param path the path of the library in which symbols should be looked up.
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* @param arena the arena associated with symbols obtained from the returned lookup.
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* @return a new symbol lookup suitable to find symbols in a library with the given path.
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* @throws IllegalStateException if {@code arena.scope().isAlive() == false}
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* @throws WrongThreadException if {@code arena} is a confined arena, and this method is called from a
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* thread {@code T}, other than the arena's owner thread.
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* @throws IllegalArgumentException if {@code path} does not point to a valid library.
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* @throws IllegalCallerException If the caller is in a module that does not have native access enabled.
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*/
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@CallerSensitive
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static SymbolLookup libraryLookup(Path path, Arena arena) {
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Reflection.ensureNativeAccess(Reflection.getCallerClass(), SymbolLookup.class, "libraryLookup");
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return libraryLookup(path, RawNativeLibraries::load, arena);
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}
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private static <Z> SymbolLookup libraryLookup(Z libDesc, BiFunction<RawNativeLibraries, Z, NativeLibrary> loadLibraryFunc, Arena libArena) {
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Objects.requireNonNull(libDesc);
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Objects.requireNonNull(libArena);
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// attempt to load native library from path or name
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RawNativeLibraries nativeLibraries = RawNativeLibraries.newInstance(MethodHandles.lookup());
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NativeLibrary library = loadLibraryFunc.apply(nativeLibraries, libDesc);
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if (library == null) {
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throw new IllegalArgumentException("Cannot open library: " + libDesc);
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}
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// register hook to unload library when 'libScope' becomes not alive
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MemorySessionImpl.toMemorySession(libArena).addOrCleanupIfFail(new MemorySessionImpl.ResourceList.ResourceCleanup() {
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@Override
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public void cleanup() {
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nativeLibraries.unload(library);
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}
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});
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return name -> {
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Objects.requireNonNull(name);
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if (Utils.containsNullChars(name)) return Optional.empty();
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long addr = library.find(name);
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return addr == 0L ?
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Optional.empty() :
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Optional.of(MemorySegment.ofAddress(addr)
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.reinterpret(libArena, null));
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};
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}
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}
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