1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // Pack relative relocations into a more compact form. 6 // 7 // 8 // For relative relocations without addends (32 bit platforms) 9 // ----------------------------------------------------------- 10 // 11 // Applies two packing strategies. The first is run-length encoding, which 12 // turns a large set of relative relocations into a much smaller set 13 // of delta-count pairs, prefixed with a two-word header comprising the 14 // count of pairs and the initial relocation offset. The second is LEB128 15 // encoding, which compresses the result of run-length encoding. 16 // 17 // Once packed, data is prefixed by an identifier that allows for any later 18 // versioning of packing strategies. 19 // 20 // A complete packed stream of relocations without addends might look 21 // something like: 22 // 23 // "APR1" pairs init_offset count1 delta1 count2 delta2 ... 24 // 41505231 f2b003 b08ac716 e001 04 01 10 ... 25 // 26 // 27 // For relative relocations with addends (64 bit platforms) 28 // -------------------------------------------------------- 29 // 30 // Applies two packing strategies. The first is delta encoding, which 31 // turns a large set of relative relocations into a smaller set 32 // of offset and addend delta pairs, prefixed with a header indicating the 33 // count of pairs. The second is signed LEB128 encoding, which compacts 34 // the result of delta encoding. 35 // 36 // Once packed, data is prefixed by an identifier that allows for any later 37 // versioning of packing strategies. 38 // 39 // A complete packed stream might look something like: 40 // 41 // "APA1" pairs offset_d1 addend_d1 offset_d2 addend_d2 ... 42 // 41505232 f2b018 04 28 08 9f01 ... 43 44 #ifndef TOOLS_RELOCATION_PACKER_SRC_PACKER_H_ 45 #define TOOLS_RELOCATION_PACKER_SRC_PACKER_H_ 46 47 #include <stdint.h> 48 #include <vector> 49 50 #include "elf.h" 51 #include "elf_traits.h" 52 53 namespace relocation_packer { 54 55 // A RelocationPacker packs vectors of relative relocations into more 56 // compact forms, and unpacks them to reproduce the pre-packed data. 57 class RelocationPacker { 58 public: 59 // Pack relative relocations into a more compact form. 60 // |relocations| is a vector of relative relocation structs. 61 // |packed| is the vector of packed bytes into which relocations are packed. 62 static void PackRelativeRelocations(const std::vector<ELF::Rel>& relocations, 63 std::vector<uint8_t>* packed); 64 static void PackRelativeRelocations(const std::vector<ELF::Rela>& relocations, 65 std::vector<uint8_t>* packed); 66 67 // Unpack relative relocations from their more compact form. 68 // |packed| is the vector of packed relocations. 69 // |relocations| is a vector of unpacked relative relocation structs. 70 static void UnpackRelativeRelocations(const std::vector<uint8_t>& packed, 71 std::vector<ELF::Rel>* relocations); 72 static void UnpackRelativeRelocations(const std::vector<uint8_t>& packed, 73 std::vector<ELF::Rela>* relocations); 74 }; 75 76 } // namespace relocation_packer 77 78 #endif // TOOLS_RELOCATION_PACKER_SRC_PACKER_H_ 79
