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/*
* Copyright (C) 2024 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package transformer;
import annotations.ConstantMethodHandle;
import annotations.ConstantMethodType;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Handle;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
/**
* Class for transforming invoke static bytecodes into constant method handle loads and constant
* method type loads.
*
* <p>When a parameterless private static method returning a MethodHandle is defined and annotated
* with {@code ConstantMethodHandle}, this transformer will replace static invocations of the method
* with a load constant bytecode with a method handle in the constant pool.
*
* <p>Suppose a method is annotated as: <code>
* @ConstantMethodHandle(
* kind = ConstantMethodHandle.STATIC_GET,
* owner = "java/lang/Math",
* fieldOrMethodName = "E",
* descriptor = "D"
* )
* private static MethodHandle getMathE() {
* unreachable();
* return null;
* }
* </code> Then invocations of {@code getMathE} will be replaced by a load from the constant pool
* with the constant method handle described in the {@code ConstantMethodHandle} annotation.
*
* <p>Similarly, a parameterless private static method returning a {@code MethodType} and annotated
* with {@code ConstantMethodType}, will have invocations replaced by a load constant bytecode with
* a method type in the constant pool.
*/
class ConstantTransformer {
static class ConstantBuilder extends ClassVisitor {
private final Map<String, ConstantMethodHandle> constantMethodHandles;
private final Map<String, ConstantMethodType> constantMethodTypes;
ConstantBuilder(
int api,
ClassVisitor cv,
Map<String, ConstantMethodHandle> constantMethodHandles,
Map<String, ConstantMethodType> constantMethodTypes) {
super(api, cv);
this.constantMethodHandles = constantMethodHandles;
this.constantMethodTypes = constantMethodTypes;
}
@Override
public MethodVisitor visitMethod(
int access, String name, String desc, String signature, String[] exceptions) {
MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);
return new MethodVisitor(this.api, mv) {
@Override
public void visitMethodInsn(
int opcode, String owner, String name, String desc, boolean itf) {
if (opcode == org.objectweb.asm.Opcodes.INVOKESTATIC) {
ConstantMethodHandle constantMethodHandle = constantMethodHandles.get(name);
if (constantMethodHandle != null) {
insertConstantMethodHandle(constantMethodHandle);
return;
}
ConstantMethodType constantMethodType = constantMethodTypes.get(name);
if (constantMethodType != null) {
insertConstantMethodType(constantMethodType);
return;
}
}
mv.visitMethodInsn(opcode, owner, name, desc, itf);
}
private Type buildMethodType(Class<?> returnType, Class<?>[] parameterTypes) {
Type rType = Type.getType(returnType);
Type[] pTypes = new Type[parameterTypes.length];
for (int i = 0; i < pTypes.length; ++i) {
pTypes[i] = Type.getType(parameterTypes[i]);
}
return Type.getMethodType(rType, pTypes);
}
private int getHandleTag(int kind) {
switch (kind) {
case ConstantMethodHandle.STATIC_PUT:
return Opcodes.H_PUTSTATIC;
case ConstantMethodHandle.STATIC_GET:
return Opcodes.H_GETSTATIC;
case ConstantMethodHandle.INSTANCE_PUT:
return Opcodes.H_PUTFIELD;
case ConstantMethodHandle.INSTANCE_GET:
return Opcodes.H_GETFIELD;
case ConstantMethodHandle.INVOKE_STATIC:
return Opcodes.H_INVOKESTATIC;
case ConstantMethodHandle.INVOKE_VIRTUAL:
return Opcodes.H_INVOKEVIRTUAL;
case ConstantMethodHandle.INVOKE_SPECIAL:
return Opcodes.H_INVOKESPECIAL;
case ConstantMethodHandle.NEW_INVOKE_SPECIAL:
return Opcodes.H_NEWINVOKESPECIAL;
case ConstantMethodHandle.INVOKE_INTERFACE:
return Opcodes.H_INVOKEINTERFACE;
}
throw new Error("Unhandled kind " + kind);
}
private void insertConstantMethodHandle(ConstantMethodHandle constantMethodHandle) {
Handle handle =
new Handle(
getHandleTag(constantMethodHandle.kind()),
constantMethodHandle.owner(),
constantMethodHandle.fieldOrMethodName(),
constantMethodHandle.descriptor(),
constantMethodHandle.ownerIsInterface());
mv.visitLdcInsn(handle);
}
private void insertConstantMethodType(ConstantMethodType constantMethodType) {
Type methodType =
buildMethodType(
constantMethodType.returnType(),
constantMethodType.parameterTypes());
mv.visitLdcInsn(methodType);
}
};
}
}
private static void throwAnnotationError(
Method method, Class<?> annotationClass, String reason) {
StringBuilder sb = new StringBuilder();
sb.append("Error in annotation ")
.append(annotationClass)
.append(" on method ")
.append(method)
.append(": ")
.append(reason);
throw new Error(sb.toString());
}
private static void checkMethodToBeReplaced(
Method method, Class<?> annotationClass, Class<?> returnType) {
final int PRIVATE_STATIC = Modifier.STATIC | Modifier.PRIVATE;
if ((method.getModifiers() & PRIVATE_STATIC) != PRIVATE_STATIC) {
throwAnnotationError(method, annotationClass, " method is not private and static");
}
if (method.getTypeParameters().length != 0) {
throwAnnotationError(method, annotationClass, " method expects parameters");
}
if (!method.getReturnType().equals(returnType)) {
throwAnnotationError(method, annotationClass, " wrong return type");
}
}
private static void transform(Path inputClassPath, Path outputClassPath) throws Throwable {
Path classLoadPath = inputClassPath.toAbsolutePath().getParent();
URLClassLoader classLoader =
new URLClassLoader(new URL[] {classLoadPath.toUri().toURL()},
ClassLoader.getSystemClassLoader());
String inputClassName = inputClassPath.getFileName().toString().replace(".class", "");
Class<?> inputClass = classLoader.loadClass(inputClassName);
final Map<String, ConstantMethodHandle> constantMethodHandles = new HashMap<>();
final Map<String, ConstantMethodType> constantMethodTypes = new HashMap<>();
for (Method m : inputClass.getDeclaredMethods()) {
ConstantMethodHandle constantMethodHandle = m.getAnnotation(ConstantMethodHandle.class);
if (constantMethodHandle != null) {
checkMethodToBeReplaced(m, ConstantMethodHandle.class, MethodHandle.class);
constantMethodHandles.put(m.getName(), constantMethodHandle);
continue;
}
ConstantMethodType constantMethodType = m.getAnnotation(ConstantMethodType.class);
if (constantMethodType != null) {
checkMethodToBeReplaced(m, ConstantMethodType.class, MethodType.class);
constantMethodTypes.put(m.getName(), constantMethodType);
continue;
}
}
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
try (InputStream is = Files.newInputStream(inputClassPath)) {
ClassReader cr = new ClassReader(is);
ConstantBuilder cb =
new ConstantBuilder(
Opcodes.ASM7, cw, constantMethodHandles, constantMethodTypes);
cr.accept(cb, 0);
}
try (OutputStream os = Files.newOutputStream(outputClassPath)) {
os.write(cw.toByteArray());
}
}
public static void main(String[] args) throws Throwable {
transform(Paths.get(args[0]), Paths.get(args[1]));
}
}
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