assembler/AssemblerBufferWithConstantPool.h

   1 /*
   2  * Copyright (C) 2009 University of Szeged
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY UNIVERSITY OF SZEGED ``AS IS'' AND ANY
  15  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  17  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL UNIVERSITY OF SZEGED OR
  18  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  19  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  20  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  21  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  22  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  24  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #ifndef AssemblerBufferWithConstantPool_h
  28 #define AssemblerBufferWithConstantPool_h
  29
  30 #if ENABLE(ASSEMBLER)
  31
  32 #include "AssemblerBuffer.h"
  33 #include <wtf/SegmentedVector.h>
  34
  35 #define ASSEMBLER_HAS_CONSTANT_POOL 1
  36
  37 namespace JSC {
  38
  39 /*
  40     On a constant pool 4 or 8 bytes data can be stored. The values can be
  41     constants or addresses. The addresses should be 32 or 64 bits. The constants
  42     should be double-precisions float or integer numbers which are hard to be
  43     encoded as few machine instructions.
  44
  45     TODO: The pool is desinged to handle both 32 and 64 bits values, but
  46     currently only the 4 bytes constants are implemented and tested.
  47
  48     The AssemblerBuffer can contain multiple constant pools. Each pool is inserted
  49     into the instruction stream - protected by a jump instruction from the
  50     execution flow.
  51
  52     The flush mechanism is called when no space remain to insert the next instruction
  53     into the pool. Three values are used to determine when the constant pool itself
  54     have to be inserted into the instruction stream (Assembler Buffer):
  55
  56     - maxPoolSize: size of the constant pool in bytes, this value cannot be
  57         larger than the maximum offset of a PC relative memory load
  58
  59     - barrierSize: size of jump instruction in bytes which protects the
  60         constant pool from execution
  61
  62     - maxInstructionSize: maximum length of a machine instruction in bytes
  63
  64     There are some callbacks which solve the target architecture specific
  65     address handling:
  66
  67     - TYPE patchConstantPoolLoad(TYPE load, int value):
  68         patch the 'load' instruction with the index of the constant in the
  69         constant pool and return the patched instruction.
  70
  71     - void patchConstantPoolLoad(void* loadAddr, void* constPoolAddr):
  72         patch the a PC relative load instruction at 'loadAddr' address with the
  73         final relative offset. The offset can be computed with help of
  74         'constPoolAddr' (the address of the constant pool) and index of the
  75         constant (which is stored previously in the load instruction itself).
  76
  77     - TYPE placeConstantPoolBarrier(int size):
  78         return with a constant pool barrier instruction which jumps over the
  79         constant pool.
  80
  81     The 'put*WithConstant*' functions should be used to place a data into the
  82     constant pool.
  83 */
  84
  85 template <int maxPoolSize, int barrierSize, int maxInstructionSize, class AssemblerType>
  86 class AssemblerBufferWithConstantPool: public AssemblerBuffer {
  87     typedef SegmentedVector<uint32_t, 512> LoadOffsets;
  88 public:
  89     enum {
  90         UniqueConst,
  91         ReusableConst,
  92         UnusedEntry,
  93     };
  94
  95     AssemblerBufferWithConstantPool()
  96         : AssemblerBuffer()
  97         , m_numConsts(0)
  98         , m_maxDistance(maxPoolSize)
  99         , m_lastConstDelta(0)
 100     {
 101         m_pool = static_cast<uint32_t*>(fastMalloc(maxPoolSize));
 102         m_mask = static_cast<char*>(fastMalloc(maxPoolSize / sizeof(uint32_t)));
 103     }
 104
 105     ~AssemblerBufferWithConstantPool()
 106     {
 107         fastFree(m_mask);
 108         fastFree(m_pool);
 109     }
 110
 111     void ensureSpace(int space)
 112     {
 113         flushIfNoSpaceFor(space);
 114         AssemblerBuffer::ensureSpace(space);
 115     }
 116
 117     void ensureSpace(int insnSpace, int constSpace)
 118     {
 119         flushIfNoSpaceFor(insnSpace, constSpace);
 120         AssemblerBuffer::ensureSpace(insnSpace);
 121     }
 122
 123     bool isAligned(int alignment)
 124     {
 125         flushIfNoSpaceFor(alignment);
 126         return AssemblerBuffer::isAligned(alignment);
 127     }
 128
 129     void putByteUnchecked(int value)
 130     {
 131         AssemblerBuffer::putByteUnchecked(value);
 132         correctDeltas(1);
 133     }
 134
 135     void putByte(int value)
 136     {
 137         flushIfNoSpaceFor(1);
 138         AssemblerBuffer::putByte(value);
 139         correctDeltas(1);
 140     }
 141
 142     void putShortUnchecked(int value)
 143     {
 144         AssemblerBuffer::putShortUnchecked(value);
 145         correctDeltas(2);
 146     }
 147
 148     void putShort(int value)
 149     {
 150         flushIfNoSpaceFor(2);
 151         AssemblerBuffer::putShort(value);
 152         correctDeltas(2);
 153     }
 154
 155     void putIntUnchecked(int value)
 156     {
 157         AssemblerBuffer::putIntUnchecked(value);
 158         correctDeltas(4);
 159     }
 160
 161     void putInt(int value)
 162     {
 163         flushIfNoSpaceFor(4);
 164         AssemblerBuffer::putInt(value);
 165         correctDeltas(4);
 166     }
 167
 168     void putInt64Unchecked(int64_t value)
 169     {
 170         AssemblerBuffer::putInt64Unchecked(value);
 171         correctDeltas(8);
 172     }
 173
 174     int size()
 175     {
 176         flushIfNoSpaceFor(maxInstructionSize, sizeof(uint64_t));
 177         return AssemblerBuffer::size();
 178     }
 179
 180     int uncheckedSize()
 181     {
 182         return AssemblerBuffer::size();
 183     }
 184
 185     void* executableCopy(ExecutablePool* allocator)
 186     {
 187         flushConstantPool(false);
 188         return AssemblerBuffer::executableCopy(allocator);
 189     }
 190
 191     void putIntWithConstantInt(uint32_t insn, uint32_t constant, bool isReusable = false)
 192     {
 193         flushIfNoSpaceFor(4, 4);
 194
 195         m_loadOffsets.append(AssemblerBuffer::size());
 196         if (isReusable)
 197             for (int i = 0; i < m_numConsts; ++i) {
 198                 if (m_mask[i] == ReusableConst && m_pool[i] == constant) {
 199                     AssemblerBuffer::putInt(AssemblerType::patchConstantPoolLoad(insn, i));
 200                     correctDeltas(4);
 201                     return;
 202                 }
 203             }
 204
 205         m_pool[m_numConsts] = constant;
 206         m_mask[m_numConsts] = static_cast<char>(isReusable ? ReusableConst : UniqueConst);
 207
 208         AssemblerBuffer::putInt(AssemblerType::patchConstantPoolLoad(insn, m_numConsts));
 209         ++m_numConsts;
 210
 211         correctDeltas(4, 4);
 212     }
 213
 214     // This flushing mechanism can be called after any unconditional jumps.
 215     void flushWithoutBarrier(bool isForced = false)
 216     {
 217         // Flush if constant pool is more than 60% full to avoid overuse of this function.
 218         if (isForced || 5 * m_numConsts > 3 * maxPoolSize / sizeof(uint32_t))
 219             flushConstantPool(false);
 220     }
 221
 222     uint32_t* poolAddress()
 223     {
 224         return m_pool;
 225     }
 226
 227     int sizeOfConstantPool()
 228     {
 229         return m_numConsts;
 230     }
 231
 232 private:
 233     void correctDeltas(int insnSize)
 234     {
 235         m_maxDistance -= insnSize;
 236         m_lastConstDelta -= insnSize;
 237         if (m_lastConstDelta < 0)
 238             m_lastConstDelta = 0;
 239     }
 240
 241     void correctDeltas(int insnSize, int constSize)
 242     {
 243         correctDeltas(insnSize);
 244
 245         m_maxDistance -= m_lastConstDelta;
 246         m_lastConstDelta = constSize;
 247     }
 248
 249     void flushConstantPool(bool useBarrier = true)
 250     {
 251         if (m_numConsts == 0)
 252             return;
 253         int alignPool = (AssemblerBuffer::size() + (useBarrier ? barrierSize : 0)) & (sizeof(uint64_t) - 1);
 254
 255         if (alignPool)
 256             alignPool = sizeof(uint64_t) - alignPool;
 257
 258         // Callback to protect the constant pool from execution
 259         if (useBarrier)
 260             AssemblerBuffer::putInt(AssemblerType::placeConstantPoolBarrier(m_numConsts * sizeof(uint32_t) + alignPool));
 261
 262         if (alignPool) {
 263             if (alignPool & 1)
 264                 AssemblerBuffer::putByte(AssemblerType::padForAlign8);
 265             if (alignPool & 2)
 266                 AssemblerBuffer::putShort(AssemblerType::padForAlign16);
 267             if (alignPool & 4)
 268                 AssemblerBuffer::putInt(AssemblerType::padForAlign32);
 269         }
 270
 271         int constPoolOffset = AssemblerBuffer::size();
 272         append(reinterpret_cast<char*>(m_pool), m_numConsts * sizeof(uint32_t));
 273
 274         // Patch each PC relative load
 275         for (LoadOffsets::Iterator iter = m_loadOffsets.begin(); iter != m_loadOffsets.end(); ++iter) {
 276             void* loadAddr = reinterpret_cast<void*>(m_buffer + *iter);
 277             AssemblerType::patchConstantPoolLoad(loadAddr, reinterpret_cast<void*>(m_buffer + constPoolOffset));
 278         }
 279
 280         m_loadOffsets.clear();
 281         m_numConsts = 0;
 282         m_maxDistance = maxPoolSize;
 283     }
 284
 285     void flushIfNoSpaceFor(int nextInsnSize)
 286     {
 287         if (m_numConsts == 0)
 288             return;
 289         int lastConstDelta = m_lastConstDelta > nextInsnSize ? m_lastConstDelta - nextInsnSize : 0;
 290         if ((m_maxDistance < nextInsnSize + lastConstDelta + barrierSize + (int)sizeof(uint32_t)))
 291             flushConstantPool();
 292     }
 293
 294     void flushIfNoSpaceFor(int nextInsnSize, int nextConstSize)
 295     {
 296         if (m_numConsts == 0)
 297             return;
 298         if ((m_maxDistance < nextInsnSize + m_lastConstDelta + nextConstSize + barrierSize + (int)sizeof(uint32_t)) ||
 299             (m_numConsts * sizeof(uint32_t) + nextConstSize >= maxPoolSize))
 300             flushConstantPool();
 301     }
 302
 303     uint32_t* m_pool;
 304     char* m_mask;
 305     LoadOffsets m_loadOffsets;
 306
 307     int m_numConsts;
 308     int m_maxDistance;
 309     int m_lastConstDelta;
 310 };
 311
 312 } // namespace JSC
 313
 314 #endif // ENABLE(ASSEMBLER)
 315
 316 #endif // AssemblerBufferWithConstantPool_h