125 lines
3.8 KiB
C++
125 lines
3.8 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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#include "packer.h"
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#include <vector>
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#include "debug.h"
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#include "delta_encoder.h"
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#include "elf_traits.h"
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#include "leb128.h"
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#include "run_length_encoder.h"
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#include "sleb128.h"
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namespace relocation_packer {
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// Pack relative relocations into a run-length encoded packed
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// representation.
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void RelocationPacker::PackRelativeRelocations(
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const std::vector<ELF::Rel>& relocations,
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std::vector<uint8_t>* packed) {
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// Run-length encode.
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std::vector<ELF::Xword> packed_words;
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RelocationRunLengthCodec codec;
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codec.Encode(relocations, &packed_words);
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// If insufficient data to run-length encode, do nothing.
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if (packed_words.empty())
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return;
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// LEB128 encode, with "APR1" prefix.
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Leb128Encoder encoder;
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encoder.Enqueue('A');
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encoder.Enqueue('P');
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encoder.Enqueue('R');
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encoder.Enqueue('1');
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encoder.EnqueueAll(packed_words);
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encoder.GetEncoding(packed);
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// Pad packed to a whole number of words. This padding will decode as
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// LEB128 zeroes. Run-length decoding ignores it because encoding
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// embeds the pairs count in the stream itself.
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while (packed->size() % sizeof(ELF::Word))
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packed->push_back(0);
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}
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// Unpack relative relocations from a run-length encoded packed
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// representation.
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void RelocationPacker::UnpackRelativeRelocations(
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const std::vector<uint8_t>& packed,
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std::vector<ELF::Rel>* relocations) {
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// LEB128 decode, after checking and stripping "APR1" prefix.
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std::vector<ELF::Xword> packed_words;
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Leb128Decoder decoder(packed);
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CHECK(decoder.Dequeue() == 'A' &&
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decoder.Dequeue() == 'P' &&
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decoder.Dequeue() == 'R' &&
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decoder.Dequeue() == '1');
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decoder.DequeueAll(&packed_words);
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// Run-length decode.
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RelocationRunLengthCodec codec;
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codec.Decode(packed_words, relocations);
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}
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// Pack relative relocations with addends into a delta encoded packed
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// representation.
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void RelocationPacker::PackRelativeRelocations(
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const std::vector<ELF::Rela>& relocations,
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std::vector<uint8_t>* packed) {
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// Delta encode.
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std::vector<ELF::Sxword> packed_words;
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RelocationDeltaCodec codec;
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codec.Encode(relocations, &packed_words);
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// If insufficient data to delta encode, do nothing.
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if (packed_words.empty())
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return;
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// Signed LEB128 encode, with "APA1" prefix. ASCII does not encode as
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// itself under signed LEB128, so we have to treat it specially.
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Sleb128Encoder encoder;
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encoder.EnqueueAll(packed_words);
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std::vector<uint8_t> encoded;
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encoder.GetEncoding(&encoded);
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packed->push_back('A');
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packed->push_back('P');
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packed->push_back('A');
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packed->push_back('1');
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packed->insert(packed->end(), encoded.begin(), encoded.end());
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// Pad packed to a whole number of words. This padding will decode as
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// signed LEB128 zeroes. Delta decoding ignores it because encoding
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// embeds the pairs count in the stream itself.
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while (packed->size() % sizeof(ELF::Word))
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packed->push_back(0);
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}
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// Unpack relative relocations with addends from a delta encoded
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// packed representation.
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void RelocationPacker::UnpackRelativeRelocations(
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const std::vector<uint8_t>& packed,
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std::vector<ELF::Rela>* relocations) {
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// Check "APA1" prefix.
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CHECK(packed.at(0) == 'A' &&
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packed.at(1) == 'P' &&
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packed.at(2) == 'A' &&
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packed.at(3) == '1');
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// Signed LEB128 decode, after stripping "APA1" prefix.
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std::vector<ELF::Sxword> packed_words;
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std::vector<uint8_t> stripped(packed.begin() + 4, packed.end());
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Sleb128Decoder decoder(stripped);
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decoder.DequeueAll(&packed_words);
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// Delta decode.
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RelocationDeltaCodec codec;
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codec.Decode(packed_words, relocations);
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}
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} // namespace relocation_packer
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