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