delta_encoder.cc revision 5f1c94371a64b3196d4be9466099bb892df9b88e
15f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// Copyright 2014 The Chromium Authors. All rights reserved. 25f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// found in the LICENSE file. 45f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 55f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)#include "delta_encoder.h" 65f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 75f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)#include <vector> 85f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 95f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)#include "debug.h" 105f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)#include "elf_traits.h" 115f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 125f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)namespace relocation_packer { 135f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 145f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// Encode relative relocations with addends into a delta encoded (packed) 155f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// representation. Represented as simple r_offset and r_addend delta pairs, 165f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// with an implicit neutral element at the start. 175f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)void RelocationDeltaCodec::Encode(const std::vector<ELF::Rela>& relocations, 185f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) std::vector<ELF::Sxword>* packed) { 195f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // One relocation is sufficient for delta encoding. 205f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) if (relocations.size() < 1) 215f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) return; 225f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 235f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // Start with the element count, then append the delta pairs. 245f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) packed->push_back(relocations.size()); 255f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 265f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) ELF::Addr offset = 0; 275f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) ELF::Sxword addend = 0; 285f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 295f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) for (size_t i = 0; i < relocations.size(); ++i) { 305f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) const ELF::Rela* relocation = &relocations[i]; 315f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) CHECK(ELF_R_TYPE(relocation->r_info) == ELF::kRelativeRelocationCode); 325f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 335f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) packed->push_back(relocation->r_offset - offset); 345f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) offset = relocation->r_offset; 355f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) packed->push_back(relocation->r_addend - addend); 365f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) addend = relocation->r_addend; 375f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) } 385f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)} 395f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 405f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// Decode relative relocations with addends from a delta encoded (packed) 415f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)// representation. 425f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)void RelocationDeltaCodec::Decode(const std::vector<ELF::Sxword>& packed, 435f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) std::vector<ELF::Rela>* relocations) { 445f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // We need at least one packed pair after the packed pair count to be 455f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // able to unpack. 465f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) if (packed.size() < 3) 475f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) return; 485f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 495f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // Ensure that the packed data offers enough pairs. There may be zero 505f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // padding on it that we ignore. 515f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) CHECK(static_cast<size_t>(packed[0]) <= (packed.size() - 1) >> 1); 525f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 535f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) ELF::Addr offset = 0; 545f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) ELF::Sxword addend = 0; 555f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 565f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // The first packed vector element is the pairs count. Start uncondensing 575f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // pairs at the second, and finish at the end of the pairs data. 585f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) const size_t pairs_count = packed[0]; 595f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) for (size_t i = 1; i < 1 + (pairs_count << 1); i += 2) { 605f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) offset += packed[i]; 615f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) addend += packed[i + 1]; 625f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 635f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) // Generate a relocation for this offset and addend pair. 645f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) ELF::Rela relocation; 655f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) relocation.r_offset = offset; 665f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) relocation.r_info = ELF_R_INFO(0, ELF::kRelativeRelocationCode); 675f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) relocation.r_addend = addend; 685f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) relocations->push_back(relocation); 695f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) } 705f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)} 715f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles) 725f1c94371a64b3196d4be9466099bb892df9b88eTorne (Richard Coles)} // namespace relocation_packer 73