1 /* 2 * Copyright 2016 Google Inc. All Rights Reserved. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.turbine.bytecode; 18 19 import com.google.common.io.ByteArrayDataInput; 20 import com.google.turbine.model.Const; 21 22 /** A JVMS 4.4 constant pool reader. */ 23 public class ConstantPoolReader { 24 25 // JVMS table 4.3 26 static final int CONSTANT_CLASS = 7; 27 static final int CONSTANT_FIELDREF = 9; 28 static final int CONSTANT_METHODREF = 10; 29 static final int CONSTANT_INTERFACE_METHODREF = 11; 30 static final int CONSTANT_STRING = 8; 31 static final int CONSTANT_INTEGER = 3; 32 static final int CONSTANT_FLOAT = 4; 33 static final int CONSTANT_LONG = 5; 34 static final int CONSTANT_DOUBLE = 6; 35 static final int CONSTANT_NAME_AND_TYPE = 12; 36 static final int CONSTANT_UTF8 = 1; 37 static final int CONSTANT_METHOD_HANDLE = 15; 38 static final int CONSTANT_METHOD_TYPE = 16; 39 static final int CONSTANT_INVOKE_DYNAMIC = 18; 40 41 /** A table that maps constant pool entries to byte offsets in {@link #byteReader}. */ 42 private final int[] constantPool; 43 44 /** The constant pool data. */ 45 private final ByteReader byteReader; 46 47 private ConstantPoolReader(int[] constantPool, ByteReader byteReader) { 48 this.constantPool = constantPool; 49 this.byteReader = byteReader; 50 } 51 52 /** 53 * Skips over all constant pool entries, saving the byte offset of each index so it can be read 54 * later if it's needed. 55 */ 56 public static ConstantPoolReader readConstantPool(ByteReader reader) { 57 int constantPoolCount = reader.u2(); 58 int[] constantPool = new int[constantPoolCount - 1]; 59 for (int i = 0; i < constantPoolCount - 1; ) { 60 constantPool[i] = reader.pos(); 61 i += skipConstantPool(reader); 62 } 63 return new ConstantPoolReader(constantPool, reader); 64 } 65 66 /** Skips over the data for a single constant pool entry and returns the size of the entry. */ 67 private static int skipConstantPool(ByteReader reader) { 68 int tag = reader.u1(); 69 switch (tag) { 70 case CONSTANT_CLASS: 71 case CONSTANT_METHOD_TYPE: 72 case CONSTANT_STRING: 73 reader.skip(2); 74 return 1; 75 case CONSTANT_DOUBLE: 76 case CONSTANT_LONG: 77 reader.skip(8); 78 // "In retrospect, making 8-byte constants take two constant pool entries 79 // was a poor choice." -- JVMS 4.4.5 80 return 2; 81 case CONSTANT_FIELDREF: 82 case CONSTANT_METHODREF: 83 case CONSTANT_INTERFACE_METHODREF: 84 case CONSTANT_INTEGER: 85 case CONSTANT_FLOAT: 86 case CONSTANT_NAME_AND_TYPE: 87 case CONSTANT_INVOKE_DYNAMIC: 88 reader.skip(4); 89 return 1; 90 case CONSTANT_UTF8: 91 reader.skip(reader.u2()); 92 return 1; 93 case CONSTANT_METHOD_HANDLE: 94 reader.skip(3); 95 return 1; 96 default: 97 throw new AssertionError(String.format("bad constant pool tag: 0x%x", tag)); 98 } 99 } 100 101 /** Reads the CONSTANT_Class_info at the given index. */ 102 public String classInfo(int index) { 103 ByteArrayDataInput reader = byteReader.seek(constantPool[index - 1]); 104 byte tag = reader.readByte(); 105 if (tag != CONSTANT_CLASS) { 106 throw new AssertionError(String.format("bad tag: %x", tag)); 107 } 108 int nameIndex = reader.readUnsignedShort(); 109 return utf8(nameIndex); 110 } 111 112 /** Reads the CONSTANT_Utf8_info at the given index. */ 113 public String utf8(int index) { 114 ByteArrayDataInput reader = byteReader.seek(constantPool[index - 1]); 115 byte tag = reader.readByte(); 116 if (tag != CONSTANT_UTF8) { 117 throw new AssertionError(String.format("bad tag: %x", tag)); 118 } 119 return reader.readUTF(); 120 } 121 122 /** 123 * Reads a constant value at the given index, which must be one of CONSTANT_String_info, 124 * CONSTANT_Integer_info, CONSTANT_Float_info, CONSTANT_Long_info, or CONSTANT_Double_info. 125 */ 126 Const.Value constant(int index) { 127 ByteArrayDataInput reader = byteReader.seek(constantPool[index - 1]); 128 byte tag = reader.readByte(); 129 switch (tag) { 130 case CONSTANT_LONG: 131 return new Const.LongValue(reader.readLong()); 132 case CONSTANT_FLOAT: 133 return new Const.FloatValue(reader.readFloat()); 134 case CONSTANT_DOUBLE: 135 return new Const.DoubleValue(reader.readDouble()); 136 case CONSTANT_INTEGER: 137 return new Const.IntValue(reader.readInt()); 138 case CONSTANT_STRING: 139 return new Const.StringValue(utf8(reader.readUnsignedShort())); 140 default: 141 throw new AssertionError(String.format("bad tag: %x", tag)); 142 } 143 } 144 } 145
