| // 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 "delta_encoder.h" |
| |
| #include <vector> |
| |
| #include "debug.h" |
| #include "elf_traits.h" |
| |
| namespace relocation_packer { |
| |
| // Encode relative relocations with addends into a delta encoded (packed) |
| // representation. Represented as simple r_offset and r_addend delta pairs, |
| // with an implicit neutral element at the start. |
| void RelocationDeltaCodec::Encode(const std::vector<ELF::Rela>& relocations, |
| std::vector<ELF::Sxword>* packed) { |
| // One relocation is sufficient for delta encoding. |
| if (relocations.size() < 1) |
| return; |
| |
| // Start with the element count, then append the delta pairs. |
| packed->push_back(relocations.size()); |
| |
| ELF::Addr offset = 0; |
| ELF::Sxword addend = 0; |
| |
| for (size_t i = 0; i < relocations.size(); ++i) { |
| const ELF::Rela* relocation = &relocations[i]; |
| CHECK(ELF_R_TYPE(relocation->r_info) == ELF::kRelativeRelocationCode); |
| |
| packed->push_back(relocation->r_offset - offset); |
| offset = relocation->r_offset; |
| packed->push_back(relocation->r_addend - addend); |
| addend = relocation->r_addend; |
| } |
| } |
| |
| // Decode relative relocations with addends from a delta encoded (packed) |
| // representation. |
| void RelocationDeltaCodec::Decode(const std::vector<ELF::Sxword>& packed, |
| std::vector<ELF::Rela>* relocations) { |
| // We need at least one packed pair after the packed pair count to be |
| // able to unpack. |
| if (packed.size() < 3) |
| return; |
| |
| // Ensure that the packed data offers enough pairs. There may be zero |
| // padding on it that we ignore. |
| CHECK(static_cast<size_t>(packed[0]) <= (packed.size() - 1) >> 1); |
| |
| ELF::Addr offset = 0; |
| ELF::Sxword addend = 0; |
| |
| // The first packed vector element is the pairs count. Start uncondensing |
| // pairs at the second, and finish at the end of the pairs data. |
| const size_t pairs_count = packed[0]; |
| for (size_t i = 1; i < 1 + (pairs_count << 1); i += 2) { |
| offset += packed[i]; |
| addend += packed[i + 1]; |
| |
| // Generate a relocation for this offset and addend pair. |
| ELF::Rela relocation; |
| relocation.r_offset = offset; |
| relocation.r_info = ELF_R_INFO(0, ELF::kRelativeRelocationCode); |
| relocation.r_addend = addend; |
| relocations->push_back(relocation); |
| } |
| } |
| |
| } // namespace relocation_packer |