| // 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. |
| |
| // ELF shared object file updates handler. |
| // |
| // Provides functions to pack relocations in the .rel.dyn or .rela.dyn |
| // sections, and unpack to return the file to its pre-packed state. |
| // |
| // SetPadding() causes PackRelocations() to pad .rel.dyn or .rela.dyn with |
| // NONE-type entries rather than cutting a hole out of the shared object |
| // file. This keeps all load addresses and offsets constant, and enables |
| // easier debugging and testing. |
| // |
| // A packed shared object file is shorter than its non-packed original. |
| // Unpacking a packed file restores the file to its non-packed state. |
| |
| #ifndef TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ |
| #define TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ |
| |
| #include <string.h> |
| #include <vector> |
| |
| #include "elf.h" |
| #include "libelf.h" |
| #include "packer.h" |
| |
| namespace relocation_packer { |
| |
| // An ElfFile reads shared objects, and shuttles relative relocations |
| // between .rel.dyn or .rela.dyn and .android.rel.dyn or .android.rela.dyn |
| // sections. |
| template <typename ELF> |
| class ElfFile { |
| public: |
| explicit ElfFile(int fd) |
| : fd_(fd), is_padding_relocations_(false), elf_(NULL), |
| relocations_section_(NULL), dynamic_section_(NULL), |
| relocations_type_(NONE), has_android_relocations_(false) {} |
| ~ElfFile() {} |
| |
| // Set padding mode. When padding, PackRelocations() will not shrink |
| // the .rel.dyn or .rela.dyn section, but instead replace relative with |
| // NONE-type entries. |
| // |flag| is true to pad .rel.dyn or .rela.dyn, false to shrink it. |
| inline void SetPadding(bool flag) { is_padding_relocations_ = flag; } |
| |
| // Transfer relative relocations from .rel.dyn or .rela.dyn to a packed |
| // representation in .android.rel.dyn or .android.rela.dyn. Returns true |
| // on success. |
| bool PackRelocations(); |
| |
| // Transfer relative relocations from a packed representation in |
| // .android.rel.dyn or .android.rela.dyn to .rel.dyn or .rela.dyn. Returns |
| // true on success. |
| bool UnpackRelocations(); |
| |
| private: |
| enum relocations_type_t { |
| NONE = 0, REL, RELA |
| }; |
| |
| // Load a new ElfFile from a filedescriptor. If flushing, the file must |
| // be open for read/write. Returns true on successful ELF file load. |
| // |fd| is an open file descriptor for the shared object. |
| bool Load(); |
| |
| // Templated packer, helper for PackRelocations(). Rel type is one of |
| // ELF::Rel or ELF::Rela. |
| bool PackTypedRelocations(std::vector<typename ELF::Rela>* relocations); |
| |
| // Templated unpacker, helper for UnpackRelocations(). Rel type is one of |
| // ELF::Rel or ELF::Rela. |
| bool UnpackTypedRelocations(const std::vector<uint8_t>& packed); |
| |
| // Write ELF file changes. |
| void Flush(); |
| |
| void AdjustRelativeRelocationTargets(typename ELF::Off hole_start, |
| ssize_t hole_size, |
| std::vector<typename ELF::Rela>* relocations); |
| |
| static void ResizeSection(Elf* elf, Elf_Scn* section, size_t new_size, |
| typename ELF::Word new_sh_type, relocations_type_t relocations_type); |
| |
| static void AdjustDynamicSectionForHole(Elf_Scn* dynamic_section, |
| typename ELF::Off hole_start, |
| ssize_t hole_size, |
| relocations_type_t relocations_type); |
| |
| static void ConvertRelArrayToRelaVector(const typename ELF::Rel* rel_array, size_t rel_array_size, |
| std::vector<typename ELF::Rela>* rela_vector); |
| |
| static void ConvertRelaVectorToRelVector(const std::vector<typename ELF::Rela>& rela_vector, |
| std::vector<typename ELF::Rel>* rel_vector); |
| |
| |
| // File descriptor opened on the shared object. |
| int fd_; |
| |
| // If set, pad rather than shrink .rel.dyn or .rela.dyn. Primarily for |
| // debugging, allows packing to be checked without affecting load addresses. |
| bool is_padding_relocations_; |
| |
| // Libelf handle, assigned by Load(). |
| Elf* elf_; |
| |
| // Sections that we manipulate, assigned by Load(). |
| Elf_Scn* relocations_section_; |
| Elf_Scn* dynamic_section_; |
| |
| // Relocation type found, assigned by Load(). |
| relocations_type_t relocations_type_; |
| |
| // Elf-file has android relocations section |
| bool has_android_relocations_; |
| }; |
| |
| } // namespace relocation_packer |
| |
| #endif // TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ |