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 R_ARM_RELATIVE relocations into a more compact form. 6 // 7 // Applies two packing strategies. The first is run-length encoding, which 8 // turns a large set of R_ARM_RELATIVE relocations into a much smaller set 9 // of delta-count pairs, prefixed with a two-word header comprising the 10 // count of pairs and the initial relocation offset. The second is LEB128 11 // encoding, which compacts the result of run-length encoding. 12 // 13 // Once packed, data is prefixed by an identifier that allows for any later 14 // versioning of packing strategies. 15 // 16 // A complete packed stream might look something like: 17 // 18 // "APR1" pairs init_offset count1 delta1 count2 delta2 ... 19 // 41505231 f2b003 b08ac716 e001 04 01 10 ... 20 21 #ifndef TOOLS_RELOCATION_PACKER_SRC_PACKER_H_ 22 #define TOOLS_RELOCATION_PACKER_SRC_PACKER_H_ 23 24 #include <stdint.h> 25 #include <string.h> 26 #include <vector> 27 28 #include "elf.h" 29 30 namespace relocation_packer { 31 32 // A RelocationPacker packs vectors of R_ARM_RELATIVE relocations into more 33 // compact forms, and unpacks them to reproduce the pre-packed data. 34 class RelocationPacker { 35 public: 36 // Pack R_ARM_RELATIVE relocations into a more compact form. 37 // |relocations| is a vector of R_ARM_RELATIVE relocation structs. 38 // |packed| is the vector of packed bytes into which relocations are packed. 39 static void PackRelativeRelocations(const std::vector<Elf32_Rel>& relocations, 40 std::vector<uint8_t>* packed); 41 42 // Unpack R_ARM_RELATIVE relocations from their more compact form. 43 // |packed| is the vector of packed relocations. 44 // |relocations| is a vector of unpacked R_ARM_RELATIVE relocation structs. 45 static void UnpackRelativeRelocations(const std::vector<uint8_t>& packed, 46 std::vector<Elf32_Rel>* relocations); 47 }; 48 49 } // namespace relocation_packer 50 51 #endif // TOOLS_RELOCATION_PACKER_SRC_PACKER_H_ 52