Home | History | Annotate | Download | only in form 
      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      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.android.dexgen.dex.code.form;
     18 
     19 import com.android.dexgen.dex.code.CstInsn;
     20 import com.android.dexgen.dex.code.DalvInsn;
     21 import com.android.dexgen.dex.code.InsnFormat;
     22 import com.android.dexgen.rop.code.RegisterSpec;
     23 import com.android.dexgen.rop.code.RegisterSpecList;
     24 import com.android.dexgen.rop.cst.Constant;
     25 import com.android.dexgen.rop.cst.CstMethodRef;
     26 import com.android.dexgen.rop.cst.CstType;
     27 import com.android.dexgen.rop.type.Type;
     28 import com.android.dexgen.util.AnnotatedOutput;
     29 
     30 /**
     31  * Instruction format {@code 45cc}. See the instruction format spec
     32  * for details.
     33  */
     34 public final class Form45cc extends InsnFormat {
     35     /** {@code non-null;} unique instance of this class */
     36     public static final InsnFormat THE_ONE = new Form45cc();
     37 
     38     /** Maximal number of operands */
     39     private static final int MAX_NUM_OPS = 5;
     40 
     41     /**
     42      * Constructs an instance. This class is not publicly
     43      * instantiable. Use {@link #THE_ONE}.
     44      */
     45     private Form45cc() {
     46         // This space intentionally left blank.
     47     }
     48 
     49     /** {@inheritDoc} */
     50     @Override
     51     public String insnArgString(DalvInsn insn) {
     52         RegisterSpecList regs = explicitize(insn.getRegisters());
     53         return regListString(regs) + ", " + cstString(insn);
     54     }
     55 
     56     /** {@inheritDoc} */
     57     @Override
     58     public String insnCommentString(DalvInsn insn, boolean noteIndices) {
     59         if (noteIndices) {
     60             return cstComment(insn);
     61         } else {
     62             return "";
     63         }
     64     }
     65 
     66     /** {@inheritDoc} */
     67     @Override
     68     public int codeSize() {
     69         return 4;
     70     }
     71 
     72     /** {@inheritDoc} */
     73     @Override
     74     public boolean isCompatible(DalvInsn insn) {
     75         if (!(insn instanceof CstInsn)) {
     76             return false;
     77         }
     78 
     79         CstInsn ci = (CstInsn) insn;
     80         int cpi = ci.getIndex();
     81 
     82         if (! unsignedFitsInShort(cpi)) {
     83             return false;
     84         }
     85 
     86         Constant cst = ci.getConstant();
     87         if (!((cst instanceof CstMethodRef) ||
     88               (cst instanceof CstType))) {
     89             return false;
     90         }
     91 
     92         RegisterSpecList regs = ci.getRegisters();
     93         return (wordCount(regs) >= 0);
     94     }
     95 
     96     /** {@inheritDoc} */
     97     @Override
     98     public InsnFormat nextUp() {
     99         return Form4rcc.THE_ONE;
    100     }
    101 
    102     /** {@inheritDoc} */
    103     @Override
    104     public void writeTo(AnnotatedOutput out, DalvInsn insn) {
    105         int cpi = ((CstInsn) insn).getIndex();
    106         RegisterSpecList regs = explicitize(insn.getRegisters());
    107         int sz = regs.size();
    108         int r0 = (sz > 0) ? regs.get(0).getReg() : 0;
    109         int r1 = (sz > 1) ? regs.get(1).getReg() : 0;
    110         int r2 = (sz > 2) ? regs.get(2).getReg() : 0;
    111         int r3 = (sz > 3) ? regs.get(3).getReg() : 0;
    112         int r4 = (sz > 4) ? regs.get(4).getReg() : 0;
    113 
    114         write(out,
    115               opcodeUnit(insn,
    116                          makeByte(r4, sz)), // encode the fifth operand here
    117               (short) cpi,
    118               codeUnit(r0, r1, r2, r3));
    119     }
    120 
    121     /**
    122      * Gets the number of words required for the given register list, where
    123      * category-2 values count as two words. Return {@code -1} if the
    124      * list requires more than five words or contains registers that need
    125      * more than a nibble to identify them.
    126      *
    127      * @param regs {@code non-null;} the register list in question
    128      * @return {@code >= -1;} the number of words required, or {@code -1}
    129      * if the list couldn't possibly fit in this format
    130      */
    131     private static int wordCount(RegisterSpecList regs) {
    132         int sz = regs.size();
    133 
    134         if (sz > MAX_NUM_OPS) {
    135             // It can't possibly fit.
    136             return -1;
    137         }
    138 
    139         int result = 0;
    140 
    141         for (int i = 0; i < sz; i++) {
    142             RegisterSpec one = regs.get(i);
    143             result += one.getCategory();
    144             /*
    145              * The check below adds (category - 1) to the register, to
    146              * account for the fact that the second half of a
    147              * category-2 register has to be represented explicitly in
    148              * the result.
    149              */
    150             if (!unsignedFitsInNibble(one.getReg() + one.getCategory() - 1)) {
    151                 return -1;
    152             }
    153         }
    154 
    155         return (result <= MAX_NUM_OPS) ? result : -1;
    156     }
    157 
    158     /**
    159      * Returns a register list which is equivalent to the given one,
    160      * except that it splits category-2 registers into two explicit
    161      * entries. This returns the original list if no modification is
    162      * required
    163      *
    164      * @param orig {@code non-null;} the original list
    165      * @return {@code non-null;} the list with the described transformation
    166      */
    167     private static RegisterSpecList explicitize(RegisterSpecList orig) {
    168         int wordCount = wordCount(orig);
    169         int sz = orig.size();
    170 
    171         if (wordCount == sz) {
    172             return orig;
    173         }
    174 
    175         RegisterSpecList result = new RegisterSpecList(wordCount);
    176         int wordAt = 0;
    177 
    178         for (int i = 0; i < sz; i++) {
    179             RegisterSpec one = orig.get(i);
    180             result.set(wordAt, one);
    181             if (one.getCategory() == 2) {
    182                 result.set(wordAt + 1,
    183                            RegisterSpec.make(one.getReg() + 1, Type.VOID));
    184                 wordAt += 2;
    185             } else {
    186                 wordAt++;
    187             }
    188         }
    189 
    190         result.setImmutable();
    191         return result;
    192     }
    193 }
    194