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      1 /*
      2  * Copyright (C) 2011 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 #ifndef ART_RUNTIME_VMAP_TABLE_H_
     18 #define ART_RUNTIME_VMAP_TABLE_H_
     19 
     20 #include "base/logging.h"
     21 #include "leb128.h"
     22 #include "stack.h"
     23 
     24 namespace art {
     25 
     26 class VmapTable {
     27  public:
     28   explicit VmapTable(const uint8_t* table) : table_(table) {
     29   }
     30 
     31   // Look up nth entry, not called from performance critical code.
     32   uint16_t operator[](size_t n) const {
     33     const uint8_t* table = table_;
     34     size_t size = DecodeUnsignedLeb128(&table);
     35     CHECK_LT(n, size);
     36     uint16_t entry = DecodeUnsignedLeb128(&table);
     37     for (size_t i = 0; i < n; ++i) {
     38       entry = DecodeUnsignedLeb128(&table);
     39     }
     40     return entry;
     41   }
     42 
     43   size_t Size() const {
     44     const uint8_t* table = table_;
     45     return DecodeUnsignedLeb128(&table);
     46   }
     47 
     48   // Is the dex register 'vreg' in the context or on the stack? Should not be called when the
     49   // 'kind' is unknown or constant.
     50   bool IsInContext(size_t vreg, VRegKind kind, uint32_t* vmap_offset) const {
     51     DCHECK(kind == kReferenceVReg || kind == kIntVReg || kind == kFloatVReg ||
     52            kind == kLongLoVReg || kind == kLongHiVReg || kind == kDoubleLoVReg ||
     53            kind == kDoubleHiVReg || kind == kImpreciseConstant);
     54     *vmap_offset = 0xEBAD0FF5;
     55     // TODO: take advantage of the registers being ordered
     56     // TODO: we treat kImpreciseConstant as an integer below, need to ensure that such values
     57     //       are never promoted to floating point registers.
     58     bool is_float = (kind == kFloatVReg) || (kind == kDoubleLoVReg) || (kind == kDoubleHiVReg);
     59     bool in_floats = false;
     60     const uint8_t* table = table_;
     61     size_t end = DecodeUnsignedLeb128(&table);
     62     for (size_t i = 0; i < end; ++i) {
     63       // Stop if we find what we are are looking for.
     64       uint16_t entry = DecodeUnsignedLeb128(&table);
     65       if ((entry == vreg) && (in_floats == is_float)) {
     66         *vmap_offset = i;
     67         return true;
     68       }
     69       // 0xffff is the marker for LR (return PC on x86), following it are spilled float registers.
     70       if (entry == 0xffff) {
     71         in_floats = true;
     72       }
     73     }
     74     return false;
     75   }
     76 
     77   // Compute the register number that corresponds to the entry in the vmap (vmap_offset, computed
     78   // by IsInContext above). If the kind is floating point then the result will be a floating point
     79   // register number, otherwise it will be an integer register number.
     80   uint32_t ComputeRegister(uint32_t spill_mask, uint32_t vmap_offset, VRegKind kind) const {
     81     // Compute the register we need to load from the context.
     82     DCHECK(kind == kReferenceVReg || kind == kIntVReg || kind == kFloatVReg ||
     83            kind == kLongLoVReg || kind == kLongHiVReg || kind == kDoubleLoVReg ||
     84            kind == kDoubleHiVReg || kind == kImpreciseConstant);
     85     // TODO: we treat kImpreciseConstant as an integer below, need to ensure that such values
     86     //       are never promoted to floating point registers.
     87     bool is_float = (kind == kFloatVReg) || (kind == kDoubleLoVReg) || (kind == kDoubleHiVReg);
     88     uint32_t matches = 0;
     89     if (UNLIKELY(is_float)) {
     90       const uint8_t* table = table_;
     91       DecodeUnsignedLeb128(&table);  // Skip size.
     92       while (DecodeUnsignedLeb128(&table) != 0xffff) {
     93         matches++;
     94       }
     95       matches++;
     96     }
     97     CHECK_LT(vmap_offset - matches, static_cast<uint32_t>(__builtin_popcount(spill_mask)));
     98     uint32_t spill_shifts = 0;
     99     while (matches != (vmap_offset + 1)) {
    100       DCHECK_NE(spill_mask, 0u);
    101       matches += spill_mask & 1;  // Add 1 if the low bit is set
    102       spill_mask >>= 1;
    103       spill_shifts++;
    104     }
    105     spill_shifts--;  // wind back one as we want the last match
    106     return spill_shifts;
    107   }
    108 
    109  private:
    110   const uint8_t* const table_;
    111 };
    112 
    113 }  // namespace art
    114 
    115 #endif  // ART_RUNTIME_VMAP_TABLE_H_
    116