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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Pack relative relocations into a more compact form.
//
//
// For relative relocations without addends (32 bit platforms)
// -----------------------------------------------------------
//
// Applies two packing strategies. The first is run-length encoding, which
// turns a large set of relative relocations into a much smaller set
// of delta-count pairs, prefixed with a two-word header comprising the
// count of pairs and the initial relocation offset. The second is LEB128
// encoding, which compresses the result of run-length encoding.
//
// Once packed, data is prefixed by an identifier that allows for any later
// versioning of packing strategies.
//
// A complete packed stream of relocations without addends might look
// something like:
//
// "APR1" pairs init_offset count1 delta1 count2 delta2 ...
// 41505231 f2b003 b08ac716 e001 04 01 10 ...
//
//
// For relative relocations with addends (64 bit platforms)
// --------------------------------------------------------
//
// Applies two packing strategies. The first is delta encoding, which
// turns a large set of relative relocations into a smaller set
// of offset and addend delta pairs, prefixed with a header indicating the
// count of pairs. The second is signed LEB128 encoding, which compacts
// the result of delta encoding.
//
// Once packed, data is prefixed by an identifier that allows for any later
// versioning of packing strategies.
//
// A complete packed stream might look something like:
//
// "APA1" pairs offset_d1 addend_d1 offset_d2 addend_d2 ...
// 41505232 f2b018 04 28 08 9f01 ...
#ifndef TOOLS_RELOCATION_PACKER_SRC_PACKER_H_
#define TOOLS_RELOCATION_PACKER_SRC_PACKER_H_
#include <stdint.h>
#include <vector>
#include "elf.h"
namespace relocation_packer {
// A RelocationPacker packs vectors of relocations into more
// compact forms, and unpacks them to reproduce the pre-packed data.
template <typename ELF>
class RelocationPacker {
public:
// Pack relocations into a more compact form.
// |relocations| is a vector of relocation structs.
// |packed| is the vector of packed bytes into which relocations are packed.
static void PackRelocations(const std::vector<typename ELF::Rela>& relocations,
std::vector<uint8_t>* packed);
// Unpack relocations from their more compact form.
// |packed| is the vector of packed relocations.
// |relocations| is a vector of unpacked relocation structs.
static void UnpackRelocations(const std::vector<uint8_t>& packed,
std::vector<typename ELF::Rela>* relocations);
};
} // namespace relocation_packer
#endif // TOOLS_RELOCATION_PACKER_SRC_PACKER_H_
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