tools/relocation_packer/src/packer.h

   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_