| /* |
| * Copyright (C) 2015 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #ifndef ART_COMPILER_LINKER_ELF_BUILDER_H_ |
| #define ART_COMPILER_LINKER_ELF_BUILDER_H_ |
| |
| #include <vector> |
| |
| #include "arch/instruction_set.h" |
| #include "arch/mips/instruction_set_features_mips.h" |
| #include "base/array_ref.h" |
| #include "base/bit_utils.h" |
| #include "base/casts.h" |
| #include "base/leb128.h" |
| #include "base/unix_file/fd_file.h" |
| #include "elf_utils.h" |
| #include "linker/error_delaying_output_stream.h" |
| |
| namespace art { |
| namespace linker { |
| |
| // Writes ELF file. |
| // |
| // The basic layout of the elf file: |
| // Elf_Ehdr - The ELF header. |
| // Elf_Phdr[] - Program headers for the linker. |
| // .note.gnu.build-id - Optional build ID section (SHA-1 digest). |
| // .rodata - Oat metadata. |
| // .text - Compiled code. |
| // .bss - Zero-initialized writeable section. |
| // .dex - Reserved NOBITS space for dex-related data. |
| // .MIPS.abiflags - MIPS specific section. |
| // .dynstr - Names for .dynsym. |
| // .dynsym - A few oat-specific dynamic symbols. |
| // .hash - Hash-table for .dynsym. |
| // .dynamic - Tags which let the linker locate .dynsym. |
| // .strtab - Names for .symtab. |
| // .symtab - Debug symbols. |
| // .eh_frame - Unwind information (CFI). |
| // .eh_frame_hdr - Index of .eh_frame. |
| // .debug_frame - Unwind information (CFI). |
| // .debug_frame.oat_patches - Addresses for relocation. |
| // .debug_info - Debug information. |
| // .debug_info.oat_patches - Addresses for relocation. |
| // .debug_abbrev - Decoding information for .debug_info. |
| // .debug_str - Strings for .debug_info. |
| // .debug_line - Line number tables. |
| // .debug_line.oat_patches - Addresses for relocation. |
| // .text.oat_patches - Addresses for relocation. |
| // .shstrtab - Names of ELF sections. |
| // Elf_Shdr[] - Section headers. |
| // |
| // Some section are optional (the debug sections in particular). |
| // |
| // We try write the section data directly into the file without much |
| // in-memory buffering. This means we generally write sections based on the |
| // dependency order (e.g. .dynamic points to .dynsym which points to .text). |
| // |
| // In the cases where we need to buffer, we write the larger section first |
| // and buffer the smaller one (e.g. .strtab is bigger than .symtab). |
| // |
| // The debug sections are written last for easier stripping. |
| // |
| template <typename ElfTypes> |
| class ElfBuilder FINAL { |
| public: |
| static constexpr size_t kMaxProgramHeaders = 16; |
| // SHA-1 digest. Not using SHA_DIGEST_LENGTH from openssl/sha.h to avoid |
| // spreading this header dependency for just this single constant. |
| static constexpr size_t kBuildIdLen = 20; |
| |
| using Elf_Addr = typename ElfTypes::Addr; |
| using Elf_Off = typename ElfTypes::Off; |
| using Elf_Word = typename ElfTypes::Word; |
| using Elf_Sword = typename ElfTypes::Sword; |
| using Elf_Ehdr = typename ElfTypes::Ehdr; |
| using Elf_Shdr = typename ElfTypes::Shdr; |
| using Elf_Sym = typename ElfTypes::Sym; |
| using Elf_Phdr = typename ElfTypes::Phdr; |
| using Elf_Dyn = typename ElfTypes::Dyn; |
| |
| // Base class of all sections. |
| class Section : public OutputStream { |
| public: |
| Section(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word type, |
| Elf_Word flags, |
| const Section* link, |
| Elf_Word info, |
| Elf_Word align, |
| Elf_Word entsize) |
| : OutputStream(name), |
| owner_(owner), |
| header_(), |
| section_index_(0), |
| name_(name), |
| link_(link), |
| phdr_flags_(PF_R), |
| phdr_type_(0) { |
| DCHECK_GE(align, 1u); |
| header_.sh_type = type; |
| header_.sh_flags = flags; |
| header_.sh_info = info; |
| header_.sh_addralign = align; |
| header_.sh_entsize = entsize; |
| } |
| |
| // Allocate chunk of virtual memory for this section from the owning ElfBuilder. |
| // This must be done at the start for all SHF_ALLOC sections (i.e. mmaped by linker). |
| // It is fine to allocate section but never call Start/End() (e.g. the .bss section). |
| void AllocateVirtualMemory(Elf_Word size) { |
| AllocateVirtualMemory(owner_->virtual_address_, size); |
| } |
| |
| void AllocateVirtualMemory(Elf_Addr addr, Elf_Word size) { |
| CHECK_NE(header_.sh_flags & SHF_ALLOC, 0u); |
| Elf_Word align = AddSection(); |
| CHECK_EQ(header_.sh_addr, 0u); |
| header_.sh_addr = RoundUp(addr, align); |
| CHECK(header_.sh_size == 0u || header_.sh_size == size); |
| header_.sh_size = size; |
| CHECK_LE(owner_->virtual_address_, header_.sh_addr); |
| owner_->virtual_address_ = header_.sh_addr + header_.sh_size; |
| } |
| |
| // Start writing file data of this section. |
| void Start() { |
| CHECK(owner_->current_section_ == nullptr); |
| Elf_Word align = AddSection(); |
| CHECK_EQ(header_.sh_offset, 0u); |
| header_.sh_offset = owner_->AlignFileOffset(align); |
| owner_->current_section_ = this; |
| } |
| |
| // Finish writing file data of this section. |
| void End() { |
| CHECK(owner_->current_section_ == this); |
| Elf_Word position = GetPosition(); |
| CHECK(header_.sh_size == 0u || header_.sh_size == position); |
| header_.sh_size = position; |
| owner_->current_section_ = nullptr; |
| } |
| |
| // Get the number of bytes written so far. |
| // Only valid while writing the section. |
| Elf_Word GetPosition() const { |
| CHECK(owner_->current_section_ == this); |
| off_t file_offset = owner_->stream_.Seek(0, kSeekCurrent); |
| DCHECK_GE(file_offset, (off_t)header_.sh_offset); |
| return file_offset - header_.sh_offset; |
| } |
| |
| // Get the location of this section in virtual memory. |
| Elf_Addr GetAddress() const { |
| DCHECK_NE(header_.sh_flags & SHF_ALLOC, 0u); |
| DCHECK_NE(header_.sh_addr, 0u); |
| return header_.sh_addr; |
| } |
| |
| // This function always succeeds to simplify code. |
| // Use builder's Good() to check the actual status. |
| bool WriteFully(const void* buffer, size_t byte_count) OVERRIDE { |
| CHECK(owner_->current_section_ == this); |
| return owner_->stream_.WriteFully(buffer, byte_count); |
| } |
| |
| // This function always succeeds to simplify code. |
| // Use builder's Good() to check the actual status. |
| off_t Seek(off_t offset, Whence whence) OVERRIDE { |
| // Forward the seek as-is and trust the caller to use it reasonably. |
| return owner_->stream_.Seek(offset, whence); |
| } |
| |
| // This function flushes the output and returns whether it succeeded. |
| // If there was a previous failure, this does nothing and returns false, i.e. failed. |
| bool Flush() OVERRIDE { |
| return owner_->stream_.Flush(); |
| } |
| |
| Elf_Word GetSectionIndex() const { |
| DCHECK_NE(section_index_, 0u); |
| return section_index_; |
| } |
| |
| // Returns true if this section has been added. |
| bool Exists() const { |
| return section_index_ != 0; |
| } |
| |
| protected: |
| // Add this section to the list of generated ELF sections (if not there already). |
| // It also ensures the alignment is sufficient to generate valid program headers, |
| // since that depends on the previous section. It returns the required alignment. |
| Elf_Word AddSection() { |
| if (section_index_ == 0) { |
| std::vector<Section*>& sections = owner_->sections_; |
| Elf_Word last = sections.empty() ? PF_R : sections.back()->phdr_flags_; |
| if (phdr_flags_ != last) { |
| header_.sh_addralign = kPageSize; // Page-align if R/W/X flags changed. |
| } |
| sections.push_back(this); |
| section_index_ = sections.size(); // First ELF section has index 1. |
| } |
| return owner_->write_program_headers_ ? header_.sh_addralign : 1; |
| } |
| |
| ElfBuilder<ElfTypes>* owner_; |
| Elf_Shdr header_; |
| Elf_Word section_index_; |
| const std::string name_; |
| const Section* const link_; |
| Elf_Word phdr_flags_; |
| Elf_Word phdr_type_; |
| |
| friend class ElfBuilder; |
| |
| DISALLOW_COPY_AND_ASSIGN(Section); |
| }; |
| |
| class CachedSection : public Section { |
| public: |
| CachedSection(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word type, |
| Elf_Word flags, |
| const Section* link, |
| Elf_Word info, |
| Elf_Word align, |
| Elf_Word entsize) |
| : Section(owner, name, type, flags, link, info, align, entsize), cache_() { } |
| |
| Elf_Word Add(const void* data, size_t length) { |
| Elf_Word offset = cache_.size(); |
| const uint8_t* d = reinterpret_cast<const uint8_t*>(data); |
| cache_.insert(cache_.end(), d, d + length); |
| return offset; |
| } |
| |
| Elf_Word GetCacheSize() { |
| return cache_.size(); |
| } |
| |
| void Write() { |
| this->WriteFully(cache_.data(), cache_.size()); |
| cache_.clear(); |
| cache_.shrink_to_fit(); |
| } |
| |
| void WriteCachedSection() { |
| this->Start(); |
| Write(); |
| this->End(); |
| } |
| |
| private: |
| std::vector<uint8_t> cache_; |
| }; |
| |
| // Writer of .dynstr section. |
| class CachedStringSection FINAL : public CachedSection { |
| public: |
| CachedStringSection(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word flags, |
| Elf_Word align) |
| : CachedSection(owner, |
| name, |
| SHT_STRTAB, |
| flags, |
| /* link */ nullptr, |
| /* info */ 0, |
| align, |
| /* entsize */ 0) { } |
| |
| Elf_Word Add(const std::string& name) { |
| if (CachedSection::GetCacheSize() == 0u) { |
| DCHECK(name.empty()); |
| } |
| return CachedSection::Add(name.c_str(), name.length() + 1); |
| } |
| }; |
| |
| // Writer of .strtab and .shstrtab sections. |
| class StringSection FINAL : public Section { |
| public: |
| StringSection(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word flags, |
| Elf_Word align) |
| : Section(owner, |
| name, |
| SHT_STRTAB, |
| flags, |
| /* link */ nullptr, |
| /* info */ 0, |
| align, |
| /* entsize */ 0) { |
| Reset(); |
| } |
| |
| void Reset() { |
| current_offset_ = 0; |
| last_name_ = ""; |
| last_offset_ = 0; |
| } |
| |
| Elf_Word Write(const std::string& name) { |
| if (current_offset_ == 0) { |
| DCHECK(name.empty()); |
| } else if (name == last_name_) { |
| return last_offset_; // Very simple string de-duplication. |
| } |
| last_name_ = name; |
| last_offset_ = current_offset_; |
| this->WriteFully(name.c_str(), name.length() + 1); |
| current_offset_ += name.length() + 1; |
| return last_offset_; |
| } |
| |
| private: |
| Elf_Word current_offset_; |
| std::string last_name_; |
| Elf_Word last_offset_; |
| }; |
| |
| // Writer of .dynsym and .symtab sections. |
| class SymbolSection FINAL : public Section { |
| public: |
| SymbolSection(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word type, |
| Elf_Word flags, |
| Section* strtab) |
| : Section(owner, |
| name, |
| type, |
| flags, |
| strtab, |
| /* info */ 1, |
| sizeof(Elf_Off), |
| sizeof(Elf_Sym)) { |
| syms_.push_back(Elf_Sym()); // The symbol table always has to start with NULL symbol. |
| } |
| |
| // Buffer symbol for this section. It will be written later. |
| // If the symbol's section is null, it will be considered absolute (SHN_ABS). |
| // (we use this in JIT to reference code which is stored outside the debug ELF file) |
| void Add(Elf_Word name, |
| const Section* section, |
| Elf_Addr addr, |
| Elf_Word size, |
| uint8_t binding, |
| uint8_t type) { |
| Elf_Word section_index; |
| if (section != nullptr) { |
| DCHECK_LE(section->GetAddress(), addr); |
| DCHECK_LE(addr, section->GetAddress() + section->header_.sh_size); |
| section_index = section->GetSectionIndex(); |
| } else { |
| section_index = static_cast<Elf_Word>(SHN_ABS); |
| } |
| Add(name, section_index, addr, size, binding, type); |
| } |
| |
| // Buffer symbol for this section. It will be written later. |
| void Add(Elf_Word name, |
| Elf_Word section_index, |
| Elf_Addr addr, |
| Elf_Word size, |
| uint8_t binding, |
| uint8_t type) { |
| Elf_Sym sym = Elf_Sym(); |
| sym.st_name = name; |
| sym.st_value = addr; |
| sym.st_size = size; |
| sym.st_other = 0; |
| sym.st_shndx = section_index; |
| sym.st_info = (binding << 4) + (type & 0xf); |
| syms_.push_back(sym); |
| |
| // The sh_info file must be set to index one-past the last local symbol. |
| if (binding == STB_LOCAL) { |
| this->header_.sh_info = syms_.size(); |
| } |
| } |
| |
| Elf_Word GetCacheSize() { return syms_.size() * sizeof(Elf_Sym); } |
| |
| void WriteCachedSection() { |
| this->Start(); |
| this->WriteFully(syms_.data(), syms_.size() * sizeof(Elf_Sym)); |
| this->End(); |
| } |
| |
| private: |
| std::vector<Elf_Sym> syms_; // Buffered/cached content of the whole section. |
| }; |
| |
| class AbiflagsSection FINAL : public Section { |
| public: |
| // Section with Mips abiflag info. |
| static constexpr uint8_t MIPS_AFL_REG_NONE = 0; // no registers |
| static constexpr uint8_t MIPS_AFL_REG_32 = 1; // 32-bit registers |
| static constexpr uint8_t MIPS_AFL_REG_64 = 2; // 64-bit registers |
| static constexpr uint32_t MIPS_AFL_FLAGS1_ODDSPREG = 1; // Uses odd single-prec fp regs |
| static constexpr uint8_t MIPS_ABI_FP_DOUBLE = 1; // -mdouble-float |
| static constexpr uint8_t MIPS_ABI_FP_XX = 5; // -mfpxx |
| static constexpr uint8_t MIPS_ABI_FP_64A = 7; // -mips32r* -mfp64 -mno-odd-spreg |
| |
| AbiflagsSection(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word type, |
| Elf_Word flags, |
| const Section* link, |
| Elf_Word info, |
| Elf_Word align, |
| Elf_Word entsize, |
| InstructionSet isa, |
| const InstructionSetFeatures* features) |
| : Section(owner, name, type, flags, link, info, align, entsize) { |
| if (isa == InstructionSet::kMips || isa == InstructionSet::kMips64) { |
| bool fpu32 = false; // assume mips64 values |
| uint8_t isa_rev = 6; // assume mips64 values |
| if (isa == InstructionSet::kMips) { |
| // adjust for mips32 values |
| fpu32 = features->AsMipsInstructionSetFeatures()->Is32BitFloatingPoint(); |
| isa_rev = features->AsMipsInstructionSetFeatures()->IsR6() |
| ? 6 |
| : features->AsMipsInstructionSetFeatures()->IsMipsIsaRevGreaterThanEqual2() |
| ? (fpu32 ? 2 : 5) |
| : 1; |
| } |
| abiflags_.version = 0; // version of flags structure |
| abiflags_.isa_level = (isa == InstructionSet::kMips) ? 32 : 64; |
| abiflags_.isa_rev = isa_rev; |
| abiflags_.gpr_size = (isa == InstructionSet::kMips) ? MIPS_AFL_REG_32 : MIPS_AFL_REG_64; |
| abiflags_.cpr1_size = fpu32 ? MIPS_AFL_REG_32 : MIPS_AFL_REG_64; |
| abiflags_.cpr2_size = MIPS_AFL_REG_NONE; |
| // Set the fp_abi to MIPS_ABI_FP_64A for mips32 with 64-bit FPUs (ie: mips32 R5 and R6). |
| // Otherwise set to MIPS_ABI_FP_DOUBLE. |
| abiflags_.fp_abi = |
| (isa == InstructionSet::kMips && !fpu32) ? MIPS_ABI_FP_64A : MIPS_ABI_FP_DOUBLE; |
| abiflags_.isa_ext = 0; |
| abiflags_.ases = 0; |
| // To keep the code simple, we are not using odd FP reg for single floats for both |
| // mips32 and mips64 ART. Therefore we are not setting the MIPS_AFL_FLAGS1_ODDSPREG bit. |
| abiflags_.flags1 = 0; |
| abiflags_.flags2 = 0; |
| } |
| } |
| |
| Elf_Word GetSize() const { |
| return sizeof(abiflags_); |
| } |
| |
| void Write() { |
| this->WriteFully(&abiflags_, sizeof(abiflags_)); |
| } |
| |
| private: |
| struct { |
| uint16_t version; // version of this structure |
| uint8_t isa_level, isa_rev, gpr_size, cpr1_size, cpr2_size; |
| uint8_t fp_abi; |
| uint32_t isa_ext, ases, flags1, flags2; |
| } abiflags_; |
| }; |
| |
| class BuildIdSection FINAL : public Section { |
| public: |
| BuildIdSection(ElfBuilder<ElfTypes>* owner, |
| const std::string& name, |
| Elf_Word type, |
| Elf_Word flags, |
| const Section* link, |
| Elf_Word info, |
| Elf_Word align, |
| Elf_Word entsize) |
| : Section(owner, name, type, flags, link, info, align, entsize), |
| digest_start_(-1) { |
| } |
| |
| Elf_Word GetSize() { |
| return 16 + kBuildIdLen; |
| } |
| |
| void Write() { |
| // The size fields are 32-bit on both 32-bit and 64-bit systems, confirmed |
| // with the 64-bit linker and libbfd code. The size of name and desc must |
| // be a multiple of 4 and it currently is. |
| this->WriteUint32(4); // namesz. |
| this->WriteUint32(kBuildIdLen); // descsz. |
| this->WriteUint32(3); // type = NT_GNU_BUILD_ID. |
| this->WriteFully("GNU", 4); // name. |
| digest_start_ = this->Seek(0, kSeekCurrent); |
| static_assert(kBuildIdLen % 4 == 0, "expecting a mutliple of 4 for build ID length"); |
| this->WriteFully(std::string(kBuildIdLen, '\0').c_str(), kBuildIdLen); // desc. |
| DCHECK_EQ(this->GetPosition(), GetSize()); |
| } |
| |
| off_t GetDigestStart() { |
| CHECK_GT(digest_start_, 0); |
| return digest_start_; |
| } |
| |
| private: |
| bool WriteUint32(uint32_t v) { |
| return this->WriteFully(&v, sizeof(v)); |
| } |
| |
| // File offset where the build ID digest starts. |
| // Populated with zeros first, then updated with the actual value as the |
| // very last thing in the output file creation. |
| off_t digest_start_; |
| }; |
| |
| ElfBuilder(InstructionSet isa, const InstructionSetFeatures* features, OutputStream* output) |
| : isa_(isa), |
| features_(features), |
| stream_(output), |
| rodata_(this, ".rodata", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), |
| text_(this, ".text", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR, nullptr, 0, kPageSize, 0), |
| data_bimg_rel_ro_( |
| this, ".data.bimg.rel.ro", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), |
| bss_(this, ".bss", SHT_NOBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), |
| dex_(this, ".dex", SHT_NOBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), |
| dynstr_(this, ".dynstr", SHF_ALLOC, kPageSize), |
| dynsym_(this, ".dynsym", SHT_DYNSYM, SHF_ALLOC, &dynstr_), |
| hash_(this, ".hash", SHT_HASH, SHF_ALLOC, &dynsym_, 0, sizeof(Elf_Word), sizeof(Elf_Word)), |
| dynamic_(this, ".dynamic", SHT_DYNAMIC, SHF_ALLOC, &dynstr_, 0, kPageSize, sizeof(Elf_Dyn)), |
| eh_frame_(this, ".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0), |
| eh_frame_hdr_(this, ".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0), |
| strtab_(this, ".strtab", 0, 1), |
| symtab_(this, ".symtab", SHT_SYMTAB, 0, &strtab_), |
| debug_frame_(this, ".debug_frame", SHT_PROGBITS, 0, nullptr, 0, sizeof(Elf_Addr), 0), |
| debug_info_(this, ".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0), |
| debug_line_(this, ".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0), |
| shstrtab_(this, ".shstrtab", 0, 1), |
| abiflags_(this, ".MIPS.abiflags", SHT_MIPS_ABIFLAGS, SHF_ALLOC, nullptr, 0, kPageSize, 0, |
| isa, features), |
| build_id_(this, ".note.gnu.build-id", SHT_NOTE, SHF_ALLOC, nullptr, 0, 4, 0), |
| current_section_(nullptr), |
| started_(false), |
| finished_(false), |
| write_program_headers_(false), |
| loaded_size_(0u), |
| virtual_address_(0) { |
| text_.phdr_flags_ = PF_R | PF_X; |
| data_bimg_rel_ro_.phdr_flags_ = PF_R | PF_W; // Shall be made read-only at run time. |
| bss_.phdr_flags_ = PF_R | PF_W; |
| dex_.phdr_flags_ = PF_R; |
| dynamic_.phdr_flags_ = PF_R | PF_W; |
| dynamic_.phdr_type_ = PT_DYNAMIC; |
| eh_frame_hdr_.phdr_type_ = PT_GNU_EH_FRAME; |
| abiflags_.phdr_type_ = PT_MIPS_ABIFLAGS; |
| build_id_.phdr_type_ = PT_NOTE; |
| } |
| ~ElfBuilder() {} |
| |
| InstructionSet GetIsa() { return isa_; } |
| BuildIdSection* GetBuildId() { return &build_id_; } |
| Section* GetRoData() { return &rodata_; } |
| Section* GetText() { return &text_; } |
| Section* GetDataBimgRelRo() { return &data_bimg_rel_ro_; } |
| Section* GetBss() { return &bss_; } |
| Section* GetDex() { return &dex_; } |
| StringSection* GetStrTab() { return &strtab_; } |
| SymbolSection* GetSymTab() { return &symtab_; } |
| Section* GetEhFrame() { return &eh_frame_; } |
| Section* GetEhFrameHdr() { return &eh_frame_hdr_; } |
| Section* GetDebugFrame() { return &debug_frame_; } |
| Section* GetDebugInfo() { return &debug_info_; } |
| Section* GetDebugLine() { return &debug_line_; } |
| |
| // Encode patch locations as LEB128 list of deltas between consecutive addresses. |
| // (exposed publicly for tests) |
| static void EncodeOatPatches(const ArrayRef<const uintptr_t>& locations, |
| std::vector<uint8_t>* buffer) { |
| buffer->reserve(buffer->size() + locations.size() * 2); // guess 2 bytes per ULEB128. |
| uintptr_t address = 0; // relative to start of section. |
| for (uintptr_t location : locations) { |
| DCHECK_GE(location, address) << "Patch locations are not in sorted order"; |
| EncodeUnsignedLeb128(buffer, dchecked_integral_cast<uint32_t>(location - address)); |
| address = location; |
| } |
| } |
| |
| void WritePatches(const char* name, const ArrayRef<const uintptr_t>& patch_locations) { |
| std::vector<uint8_t> buffer; |
| EncodeOatPatches(patch_locations, &buffer); |
| std::unique_ptr<Section> s(new Section(this, name, SHT_OAT_PATCH, 0, nullptr, 0, 1, 0)); |
| s->Start(); |
| s->WriteFully(buffer.data(), buffer.size()); |
| s->End(); |
| other_sections_.push_back(std::move(s)); |
| } |
| |
| void WriteSection(const char* name, const std::vector<uint8_t>* buffer) { |
| std::unique_ptr<Section> s(new Section(this, name, SHT_PROGBITS, 0, nullptr, 0, 1, 0)); |
| s->Start(); |
| s->WriteFully(buffer->data(), buffer->size()); |
| s->End(); |
| other_sections_.push_back(std::move(s)); |
| } |
| |
| // Reserve space for ELF header and program headers. |
| // We do not know the number of headers until later, so |
| // it is easiest to just reserve a fixed amount of space. |
| // Program headers are required for loading by the linker. |
| // It is possible to omit them for ELF files used for debugging. |
| void Start(bool write_program_headers = true) { |
| int size = sizeof(Elf_Ehdr); |
| if (write_program_headers) { |
| size += sizeof(Elf_Phdr) * kMaxProgramHeaders; |
| } |
| stream_.Seek(size, kSeekSet); |
| started_ = true; |
| virtual_address_ += size; |
| write_program_headers_ = write_program_headers; |
| } |
| |
| off_t End() { |
| DCHECK(started_); |
| DCHECK(!finished_); |
| finished_ = true; |
| |
| // Note: loaded_size_ == 0 for tests that don't write .rodata, .text, .bss, |
| // .dynstr, dynsym, .hash and .dynamic. These tests should not read loaded_size_. |
| // TODO: Either refactor the .eh_frame creation so that it counts towards loaded_size_, |
| // or remove all support for .eh_frame. (The currently unused .eh_frame counts towards |
| // the virtual_address_ but we don't consider it for loaded_size_.) |
| CHECK(loaded_size_ == 0 || loaded_size_ == RoundUp(virtual_address_, kPageSize)) |
| << loaded_size_ << " " << virtual_address_; |
| |
| // Write section names and finish the section headers. |
| shstrtab_.Start(); |
| shstrtab_.Write(""); |
| for (auto* section : sections_) { |
| section->header_.sh_name = shstrtab_.Write(section->name_); |
| if (section->link_ != nullptr) { |
| section->header_.sh_link = section->link_->GetSectionIndex(); |
| } |
| if (section->header_.sh_offset == 0) { |
| section->header_.sh_type = SHT_NOBITS; |
| } |
| } |
| shstrtab_.End(); |
| |
| // Write section headers at the end of the ELF file. |
| std::vector<Elf_Shdr> shdrs; |
| shdrs.reserve(1u + sections_.size()); |
| shdrs.push_back(Elf_Shdr()); // NULL at index 0. |
| for (auto* section : sections_) { |
| shdrs.push_back(section->header_); |
| } |
| Elf_Off section_headers_offset; |
| section_headers_offset = AlignFileOffset(sizeof(Elf_Off)); |
| stream_.WriteFully(shdrs.data(), shdrs.size() * sizeof(shdrs[0])); |
| off_t file_size = stream_.Seek(0, kSeekCurrent); |
| |
| // Flush everything else before writing the program headers. This should prevent |
| // the OS from reordering writes, so that we don't end up with valid headers |
| // and partially written data if we suddenly lose power, for example. |
| stream_.Flush(); |
| |
| // The main ELF header. |
| Elf_Ehdr elf_header = MakeElfHeader(isa_, features_); |
| elf_header.e_shoff = section_headers_offset; |
| elf_header.e_shnum = shdrs.size(); |
| elf_header.e_shstrndx = shstrtab_.GetSectionIndex(); |
| |
| // Program headers (i.e. mmap instructions). |
| std::vector<Elf_Phdr> phdrs; |
| if (write_program_headers_) { |
| phdrs = MakeProgramHeaders(); |
| CHECK_LE(phdrs.size(), kMaxProgramHeaders); |
| elf_header.e_phoff = sizeof(Elf_Ehdr); |
| elf_header.e_phnum = phdrs.size(); |
| } |
| |
| stream_.Seek(0, kSeekSet); |
| stream_.WriteFully(&elf_header, sizeof(elf_header)); |
| stream_.WriteFully(phdrs.data(), phdrs.size() * sizeof(phdrs[0])); |
| stream_.Flush(); |
| |
| return file_size; |
| } |
| |
| // This has the same effect as running the "strip" command line tool. |
| // It removes all debugging sections (but it keeps mini-debug-info). |
| // It returns the ELF file size (as the caller needs to truncate it). |
| off_t Strip() { |
| DCHECK(finished_); |
| finished_ = false; |
| Elf_Off end = 0; |
| std::vector<Section*> non_debug_sections; |
| for (Section* section : sections_) { |
| if (section == &shstrtab_ || // Section names will be recreated. |
| section == &symtab_ || |
| section == &strtab_ || |
| section->name_.find(".debug_") == 0) { |
| section->header_.sh_offset = 0; |
| section->header_.sh_size = 0; |
| section->section_index_ = 0; |
| } else { |
| if (section->header_.sh_type != SHT_NOBITS) { |
| DCHECK_LE(section->header_.sh_offset, end + kPageSize) << "Large gap between sections"; |
| end = std::max<off_t>(end, section->header_.sh_offset + section->header_.sh_size); |
| } |
| non_debug_sections.push_back(section); |
| } |
| } |
| shstrtab_.Reset(); |
| // Write the non-debug section headers, program headers, and ELF header again. |
| sections_ = std::move(non_debug_sections); |
| stream_.Seek(end, kSeekSet); |
| return End(); |
| } |
| |
| // The running program does not have access to section headers |
| // and the loader is not supposed to use them either. |
| // The dynamic sections therefore replicates some of the layout |
| // information like the address and size of .rodata and .text. |
| // It also contains other metadata like the SONAME. |
| // The .dynamic section is found using the PT_DYNAMIC program header. |
| void PrepareDynamicSection(const std::string& elf_file_path, |
| Elf_Word rodata_size, |
| Elf_Word text_size, |
| Elf_Word data_bimg_rel_ro_size, |
| Elf_Word bss_size, |
| Elf_Word bss_methods_offset, |
| Elf_Word bss_roots_offset, |
| Elf_Word dex_size) { |
| std::string soname(elf_file_path); |
| size_t directory_separator_pos = soname.rfind('/'); |
| if (directory_separator_pos != std::string::npos) { |
| soname = soname.substr(directory_separator_pos + 1); |
| } |
| |
| // Allocate all pre-dynamic sections. |
| rodata_.AllocateVirtualMemory(rodata_size); |
| text_.AllocateVirtualMemory(text_size); |
| if (data_bimg_rel_ro_size != 0) { |
| data_bimg_rel_ro_.AllocateVirtualMemory(data_bimg_rel_ro_size); |
| } |
| if (bss_size != 0) { |
| bss_.AllocateVirtualMemory(bss_size); |
| } |
| if (dex_size != 0) { |
| dex_.AllocateVirtualMemory(dex_size); |
| } |
| if (isa_ == InstructionSet::kMips || isa_ == InstructionSet::kMips64) { |
| abiflags_.AllocateVirtualMemory(abiflags_.GetSize()); |
| } |
| |
| // Cache .dynstr, .dynsym and .hash data. |
| dynstr_.Add(""); // dynstr should start with empty string. |
| Elf_Word oatdata = dynstr_.Add("oatdata"); |
| dynsym_.Add(oatdata, &rodata_, rodata_.GetAddress(), rodata_size, STB_GLOBAL, STT_OBJECT); |
| if (text_size != 0u) { |
| // The runtime does not care about the size of this symbol (it uses the "lastword" symbol). |
| // We use size 0 (meaning "unknown size" in ELF) to prevent overlap with the debug symbols. |
| Elf_Word oatexec = dynstr_.Add("oatexec"); |
| dynsym_.Add(oatexec, &text_, text_.GetAddress(), /* size */ 0, STB_GLOBAL, STT_OBJECT); |
| Elf_Word oatlastword = dynstr_.Add("oatlastword"); |
| Elf_Word oatlastword_address = text_.GetAddress() + text_size - 4; |
| dynsym_.Add(oatlastword, &text_, oatlastword_address, 4, STB_GLOBAL, STT_OBJECT); |
| } else if (rodata_size != 0) { |
| // rodata_ can be size 0 for dwarf_test. |
| Elf_Word oatlastword = dynstr_.Add("oatlastword"); |
| Elf_Word oatlastword_address = rodata_.GetAddress() + rodata_size - 4; |
| dynsym_.Add(oatlastword, &rodata_, oatlastword_address, 4, STB_GLOBAL, STT_OBJECT); |
| } |
| if (data_bimg_rel_ro_size != 0u) { |
| Elf_Word oatdatabimgrelro = dynstr_.Add("oatdatabimgrelro"); |
| dynsym_.Add(oatdatabimgrelro, |
| &data_bimg_rel_ro_, |
| data_bimg_rel_ro_.GetAddress(), |
| data_bimg_rel_ro_size, |
| STB_GLOBAL, |
| STT_OBJECT); |
| Elf_Word oatdatabimgrelrolastword = dynstr_.Add("oatdatabimgrelrolastword"); |
| Elf_Word oatdatabimgrelrolastword_address = |
| data_bimg_rel_ro_.GetAddress() + data_bimg_rel_ro_size - 4; |
| dynsym_.Add(oatdatabimgrelrolastword, |
| &data_bimg_rel_ro_, |
| oatdatabimgrelrolastword_address, |
| 4, |
| STB_GLOBAL, |
| STT_OBJECT); |
| } |
| DCHECK_LE(bss_roots_offset, bss_size); |
| if (bss_size != 0u) { |
| Elf_Word oatbss = dynstr_.Add("oatbss"); |
| dynsym_.Add(oatbss, &bss_, bss_.GetAddress(), bss_roots_offset, STB_GLOBAL, STT_OBJECT); |
| DCHECK_LE(bss_methods_offset, bss_roots_offset); |
| DCHECK_LE(bss_roots_offset, bss_size); |
| // Add a symbol marking the start of the methods part of the .bss, if not empty. |
| if (bss_methods_offset != bss_roots_offset) { |
| Elf_Word bss_methods_address = bss_.GetAddress() + bss_methods_offset; |
| Elf_Word bss_methods_size = bss_roots_offset - bss_methods_offset; |
| Elf_Word oatbssroots = dynstr_.Add("oatbssmethods"); |
| dynsym_.Add( |
| oatbssroots, &bss_, bss_methods_address, bss_methods_size, STB_GLOBAL, STT_OBJECT); |
| } |
| // Add a symbol marking the start of the GC roots part of the .bss, if not empty. |
| if (bss_roots_offset != bss_size) { |
| Elf_Word bss_roots_address = bss_.GetAddress() + bss_roots_offset; |
| Elf_Word bss_roots_size = bss_size - bss_roots_offset; |
| Elf_Word oatbssroots = dynstr_.Add("oatbssroots"); |
| dynsym_.Add( |
| oatbssroots, &bss_, bss_roots_address, bss_roots_size, STB_GLOBAL, STT_OBJECT); |
| } |
| Elf_Word oatbsslastword = dynstr_.Add("oatbsslastword"); |
| Elf_Word bsslastword_address = bss_.GetAddress() + bss_size - 4; |
| dynsym_.Add(oatbsslastword, &bss_, bsslastword_address, 4, STB_GLOBAL, STT_OBJECT); |
| } |
| if (dex_size != 0u) { |
| Elf_Word oatdex = dynstr_.Add("oatdex"); |
| dynsym_.Add(oatdex, &dex_, dex_.GetAddress(), /* size */ 0, STB_GLOBAL, STT_OBJECT); |
| Elf_Word oatdexlastword = dynstr_.Add("oatdexlastword"); |
| Elf_Word oatdexlastword_address = dex_.GetAddress() + dex_size - 4; |
| dynsym_.Add(oatdexlastword, &dex_, oatdexlastword_address, 4, STB_GLOBAL, STT_OBJECT); |
| } |
| |
| Elf_Word soname_offset = dynstr_.Add(soname); |
| |
| // We do not really need a hash-table since there is so few entries. |
| // However, the hash-table is the only way the linker can actually |
| // determine the number of symbols in .dynsym so it is required. |
| int count = dynsym_.GetCacheSize() / sizeof(Elf_Sym); // Includes NULL. |
| std::vector<Elf_Word> hash; |
| hash.push_back(1); // Number of buckets. |
| hash.push_back(count); // Number of chains. |
| // Buckets. Having just one makes it linear search. |
| hash.push_back(1); // Point to first non-NULL symbol. |
| // Chains. This creates linked list of symbols. |
| hash.push_back(0); // Dummy entry for the NULL symbol. |
| for (int i = 1; i < count - 1; i++) { |
| hash.push_back(i + 1); // Each symbol points to the next one. |
| } |
| hash.push_back(0); // Last symbol terminates the chain. |
| hash_.Add(hash.data(), hash.size() * sizeof(hash[0])); |
| |
| // Allocate all remaining sections. |
| dynstr_.AllocateVirtualMemory(dynstr_.GetCacheSize()); |
| dynsym_.AllocateVirtualMemory(dynsym_.GetCacheSize()); |
| hash_.AllocateVirtualMemory(hash_.GetCacheSize()); |
| |
| Elf_Dyn dyns[] = { |
| { DT_HASH, { hash_.GetAddress() } }, |
| { DT_STRTAB, { dynstr_.GetAddress() } }, |
| { DT_SYMTAB, { dynsym_.GetAddress() } }, |
| { DT_SYMENT, { sizeof(Elf_Sym) } }, |
| { DT_STRSZ, { dynstr_.GetCacheSize() } }, |
| { DT_SONAME, { soname_offset } }, |
| { DT_NULL, { 0 } }, |
| }; |
| dynamic_.Add(&dyns, sizeof(dyns)); |
| dynamic_.AllocateVirtualMemory(dynamic_.GetCacheSize()); |
| |
| loaded_size_ = RoundUp(virtual_address_, kPageSize); |
| } |
| |
| void WriteDynamicSection() { |
| dynstr_.WriteCachedSection(); |
| dynsym_.WriteCachedSection(); |
| hash_.WriteCachedSection(); |
| dynamic_.WriteCachedSection(); |
| } |
| |
| Elf_Word GetLoadedSize() { |
| CHECK_NE(loaded_size_, 0u); |
| return loaded_size_; |
| } |
| |
| void WriteMIPSabiflagsSection() { |
| abiflags_.Start(); |
| abiflags_.Write(); |
| abiflags_.End(); |
| } |
| |
| void WriteBuildIdSection() { |
| build_id_.Start(); |
| build_id_.Write(); |
| build_id_.End(); |
| } |
| |
| void WriteBuildId(uint8_t build_id[kBuildIdLen]) { |
| stream_.Seek(build_id_.GetDigestStart(), kSeekSet); |
| stream_.WriteFully(build_id, kBuildIdLen); |
| stream_.Flush(); |
| } |
| |
| // Returns true if all writes and seeks on the output stream succeeded. |
| bool Good() { |
| return stream_.Good(); |
| } |
| |
| // Returns the builder's internal stream. |
| OutputStream* GetStream() { |
| return &stream_; |
| } |
| |
| off_t AlignFileOffset(size_t alignment) { |
| return stream_.Seek(RoundUp(stream_.Seek(0, kSeekCurrent), alignment), kSeekSet); |
| } |
| |
| private: |
| static Elf_Ehdr MakeElfHeader(InstructionSet isa, const InstructionSetFeatures* features) { |
| Elf_Ehdr elf_header = Elf_Ehdr(); |
| switch (isa) { |
| case InstructionSet::kArm: |
| // Fall through. |
| case InstructionSet::kThumb2: { |
| elf_header.e_machine = EM_ARM; |
| elf_header.e_flags = EF_ARM_EABI_VER5; |
| break; |
| } |
| case InstructionSet::kArm64: { |
| elf_header.e_machine = EM_AARCH64; |
| elf_header.e_flags = 0; |
| break; |
| } |
| case InstructionSet::kX86: { |
| elf_header.e_machine = EM_386; |
| elf_header.e_flags = 0; |
| break; |
| } |
| case InstructionSet::kX86_64: { |
| elf_header.e_machine = EM_X86_64; |
| elf_header.e_flags = 0; |
| break; |
| } |
| case InstructionSet::kMips: { |
| elf_header.e_machine = EM_MIPS; |
| elf_header.e_flags = (EF_MIPS_NOREORDER | |
| EF_MIPS_PIC | |
| EF_MIPS_CPIC | |
| EF_MIPS_ABI_O32 | |
| (features->AsMipsInstructionSetFeatures()->IsR6() |
| ? EF_MIPS_ARCH_32R6 |
| : EF_MIPS_ARCH_32R2)); |
| break; |
| } |
| case InstructionSet::kMips64: { |
| elf_header.e_machine = EM_MIPS; |
| elf_header.e_flags = (EF_MIPS_NOREORDER | |
| EF_MIPS_PIC | |
| EF_MIPS_CPIC | |
| EF_MIPS_ARCH_64R6); |
| break; |
| } |
| case InstructionSet::kNone: { |
| LOG(FATAL) << "No instruction set"; |
| break; |
| } |
| default: { |
| LOG(FATAL) << "Unknown instruction set " << isa; |
| } |
| } |
| |
| elf_header.e_ident[EI_MAG0] = ELFMAG0; |
| elf_header.e_ident[EI_MAG1] = ELFMAG1; |
| elf_header.e_ident[EI_MAG2] = ELFMAG2; |
| elf_header.e_ident[EI_MAG3] = ELFMAG3; |
| elf_header.e_ident[EI_CLASS] = (sizeof(Elf_Addr) == sizeof(Elf32_Addr)) |
| ? ELFCLASS32 : ELFCLASS64; |
| elf_header.e_ident[EI_DATA] = ELFDATA2LSB; |
| elf_header.e_ident[EI_VERSION] = EV_CURRENT; |
| elf_header.e_ident[EI_OSABI] = ELFOSABI_LINUX; |
| elf_header.e_ident[EI_ABIVERSION] = 0; |
| elf_header.e_type = ET_DYN; |
| elf_header.e_version = 1; |
| elf_header.e_entry = 0; |
| elf_header.e_ehsize = sizeof(Elf_Ehdr); |
| elf_header.e_phentsize = sizeof(Elf_Phdr); |
| elf_header.e_shentsize = sizeof(Elf_Shdr); |
| return elf_header; |
| } |
| |
| // Create program headers based on written sections. |
| std::vector<Elf_Phdr> MakeProgramHeaders() { |
| CHECK(!sections_.empty()); |
| std::vector<Elf_Phdr> phdrs; |
| { |
| // The program headers must start with PT_PHDR which is used in |
| // loaded process to determine the number of program headers. |
| Elf_Phdr phdr = Elf_Phdr(); |
| phdr.p_type = PT_PHDR; |
| phdr.p_flags = PF_R; |
| phdr.p_offset = phdr.p_vaddr = phdr.p_paddr = sizeof(Elf_Ehdr); |
| phdr.p_filesz = phdr.p_memsz = 0; // We need to fill this later. |
| phdr.p_align = sizeof(Elf_Off); |
| phdrs.push_back(phdr); |
| // Tell the linker to mmap the start of file to memory. |
| Elf_Phdr load = Elf_Phdr(); |
| load.p_type = PT_LOAD; |
| load.p_flags = PF_R; |
| load.p_offset = load.p_vaddr = load.p_paddr = 0; |
| load.p_filesz = load.p_memsz = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * kMaxProgramHeaders; |
| load.p_align = kPageSize; |
| phdrs.push_back(load); |
| } |
| // Create program headers for sections. |
| for (auto* section : sections_) { |
| const Elf_Shdr& shdr = section->header_; |
| if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { |
| DCHECK(shdr.sh_addr != 0u) << "Allocate virtual memory for the section"; |
| // PT_LOAD tells the linker to mmap part of the file. |
| // The linker can only mmap page-aligned sections. |
| // Single PT_LOAD may contain several ELF sections. |
| Elf_Phdr& prev = phdrs.back(); |
| Elf_Phdr load = Elf_Phdr(); |
| load.p_type = PT_LOAD; |
| load.p_flags = section->phdr_flags_; |
| load.p_offset = shdr.sh_offset; |
| load.p_vaddr = load.p_paddr = shdr.sh_addr; |
| load.p_filesz = (shdr.sh_type != SHT_NOBITS ? shdr.sh_size : 0u); |
| load.p_memsz = shdr.sh_size; |
| load.p_align = shdr.sh_addralign; |
| if (prev.p_type == load.p_type && |
| prev.p_flags == load.p_flags && |
| prev.p_filesz == prev.p_memsz && // Do not merge .bss |
| load.p_filesz == load.p_memsz) { // Do not merge .bss |
| // Merge this PT_LOAD with the previous one. |
| Elf_Word size = shdr.sh_offset + shdr.sh_size - prev.p_offset; |
| prev.p_filesz = size; |
| prev.p_memsz = size; |
| } else { |
| // If we are adding new load, it must be aligned. |
| CHECK_EQ(shdr.sh_addralign, (Elf_Word)kPageSize); |
| phdrs.push_back(load); |
| } |
| } |
| } |
| for (auto* section : sections_) { |
| const Elf_Shdr& shdr = section->header_; |
| if ((shdr.sh_flags & SHF_ALLOC) != 0 && shdr.sh_size != 0) { |
| // Other PT_* types allow the program to locate interesting |
| // parts of memory at runtime. They must overlap with PT_LOAD. |
| if (section->phdr_type_ != 0) { |
| Elf_Phdr phdr = Elf_Phdr(); |
| phdr.p_type = section->phdr_type_; |
| phdr.p_flags = section->phdr_flags_; |
| phdr.p_offset = shdr.sh_offset; |
| phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr; |
| phdr.p_filesz = phdr.p_memsz = shdr.sh_size; |
| phdr.p_align = shdr.sh_addralign; |
| phdrs.push_back(phdr); |
| } |
| } |
| } |
| // Set the size of the initial PT_PHDR. |
| CHECK_EQ(phdrs[0].p_type, (Elf_Word)PT_PHDR); |
| phdrs[0].p_filesz = phdrs[0].p_memsz = phdrs.size() * sizeof(Elf_Phdr); |
| |
| return phdrs; |
| } |
| |
| InstructionSet isa_; |
| const InstructionSetFeatures* features_; |
| |
| ErrorDelayingOutputStream stream_; |
| |
| Section rodata_; |
| Section text_; |
| Section data_bimg_rel_ro_; |
| Section bss_; |
| Section dex_; |
| CachedStringSection dynstr_; |
| SymbolSection dynsym_; |
| CachedSection hash_; |
| CachedSection dynamic_; |
| Section eh_frame_; |
| Section eh_frame_hdr_; |
| StringSection strtab_; |
| SymbolSection symtab_; |
| Section debug_frame_; |
| Section debug_info_; |
| Section debug_line_; |
| StringSection shstrtab_; |
| AbiflagsSection abiflags_; |
| BuildIdSection build_id_; |
| std::vector<std::unique_ptr<Section>> other_sections_; |
| |
| // List of used section in the order in which they were written. |
| std::vector<Section*> sections_; |
| Section* current_section_; // The section which is currently being written. |
| |
| bool started_; |
| bool finished_; |
| bool write_program_headers_; |
| |
| // The size of the memory taken by the ELF file when loaded. |
| size_t loaded_size_; |
| |
| // Used for allocation of virtual address space. |
| Elf_Addr virtual_address_; |
| |
| DISALLOW_COPY_AND_ASSIGN(ElfBuilder); |
| }; |
| |
| } // namespace linker |
| } // namespace art |
| |
| #endif // ART_COMPILER_LINKER_ELF_BUILDER_H_ |