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