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 #ifndef ART_DEX2OAT_LINKER_INDEX_BSS_MAPPING_ENCODER_H_
18 #define ART_DEX2OAT_LINKER_INDEX_BSS_MAPPING_ENCODER_H_
19 
20 #include <android-base/logging.h>
21 
22 #include "base/bit_utils.h"
23 #include "base/bit_vector-inl.h"
24 #include "index_bss_mapping.h"
25 
26 namespace art {
27 namespace linker {
28 
29 // Helper class for encoding compressed IndexBssMapping.
30 class IndexBssMappingEncoder {
31  public:
IndexBssMappingEncoder(size_t number_of_indexes,size_t slot_size)32   IndexBssMappingEncoder(size_t number_of_indexes, size_t slot_size)
33       : index_bits_(IndexBssMappingEntry::IndexBits(number_of_indexes)),
34         slot_size_(slot_size) {
35     entry_.index_and_mask = static_cast<uint32_t>(-1);
36     entry_.bss_offset = static_cast<uint32_t>(-1);
37     DCHECK_NE(number_of_indexes, 0u);
38   }
39 
40   // Try to merge the next index -> bss_offset mapping into the current entry.
41   // Return true on success, false on failure.
TryMerge(uint32_t index,uint32_t bss_offset)42   bool TryMerge(uint32_t index, uint32_t bss_offset) {
43     DCHECK_LE(MinimumBitsToStore(index), index_bits_);
44     DCHECK_NE(index, entry_.GetIndex(index_bits_));
45     if (entry_.bss_offset + slot_size_ != bss_offset) {
46       return false;
47     }
48     uint32_t diff = index - entry_.GetIndex(index_bits_);
49     if (diff > 32u - index_bits_) {
50       return false;
51     }
52     uint32_t mask = entry_.GetMask(index_bits_);
53     if ((mask & ~(static_cast<uint32_t>(-1) << diff)) != 0u) {
54       return false;
55     }
56     // Insert the bit indicating the index we've just overwritten
57     // and shift bits indicating indexes before that.
58     mask = ((mask << index_bits_) >> diff) | (static_cast<uint32_t>(1u) << (32 - diff));
59     entry_.index_and_mask = mask | index;
60     entry_.bss_offset = bss_offset;
61     return true;
62   }
63 
Reset(uint32_t method_index,uint32_t bss_offset)64   void Reset(uint32_t method_index, uint32_t bss_offset) {
65     DCHECK_LE(MinimumBitsToStore(method_index), index_bits_);
66     entry_.index_and_mask = method_index;  // Mask bits set to 0.
67     entry_.bss_offset = bss_offset;
68   }
69 
GetEntry()70   IndexBssMappingEntry GetEntry() {
71     return entry_;
72   }
73 
GetIndexBits()74   size_t GetIndexBits() const {
75     return index_bits_;
76   }
77 
78  private:
79   const size_t index_bits_;
80   const size_t slot_size_;
81   IndexBssMappingEntry entry_;
82 };
83 
84 }  // namespace linker
85 }  // namespace art
86 
87 #endif  // ART_DEX2OAT_LINKER_INDEX_BSS_MAPPING_ENCODER_H_
88