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review.shift-gmbh.com / SHIFTPHONES / android_art / c6470621ad665c39a903469c519bfd328103fb94 / . / libelffile / elf / elf_builder.h
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/*
* 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_LIBELFFILE_ELF_ELF_BUILDER_H_
#define ART_LIBELFFILE_ELF_ELF_BUILDER_H_
#include <vector>
#include <deque>
#include "arch/instruction_set.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/elf_utils.h"
#include "stream/error_delaying_output_stream.h"
namespace art {
// 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.
// .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.
// .debug_frame - Unwind information (CFI).
// .debug_info - Debug information.
// .debug_abbrev - Decoding information for .debug_info.
// .debug_str - Strings for .debug_info.
// .debug_line - Line number tables.
// .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.
virtual 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.
virtual 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;
}
void Start() {
Section::Start();
Write(""); // ELF specification requires that the section starts with empty string.
}
Elf_Word Write(std::string_view 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.data(), name.length());
char null_terminator = '\0';
this->WriteFully(&null_terminator, sizeof(null_terminator));
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.
void Add(Elf_Word name,
const Section* section,
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_info = (binding << 4) + (type & 0xf);
Add(sym, section);
}
// Buffer symbol for this section. It will be written later.
void Add(Elf_Sym sym, const Section* section) {
if (section != nullptr) {
DCHECK_LE(section->GetAddress(), sym.st_value);
DCHECK_LE(sym.st_value, section->GetAddress() + section->header_.sh_size);
sym.st_shndx = section->GetSectionIndex();
} else {
sym.st_shndx = SHN_UNDEF;
}
syms_.push_back(sym);
}
Elf_Word GetCacheSize() { return syms_.size() * sizeof(Elf_Sym); }
void WriteCachedSection() {
auto is_local = [](const Elf_Sym& sym) { return ELF_ST_BIND(sym.st_info) == STB_LOCAL; };
auto less_then = [is_local](const Elf_Sym& a, const Elf_Sym b) {
auto tuple_a = std::make_tuple(!is_local(a), a.st_value, a.st_name);
auto tuple_b = std::make_tuple(!is_local(b), b.st_value, b.st_name);
return tuple_a < tuple_b; // Locals first, then sort by address and name offset.
};
if (!std::is_sorted(syms_.begin(), syms_.end(), less_then)) {
std::sort(syms_.begin(), syms_.end(), less_then);
}
auto locals_end = std::partition_point(syms_.begin(), syms_.end(), is_local);
this->header_.sh_info = locals_end - syms_.begin(); // Required by the spec.
this->Start();
for (; !syms_.empty(); syms_.pop_front()) {
this->WriteFully(&syms_.front(), sizeof(Elf_Sym));
}
this->End();
}
private:
std::deque<Elf_Sym> syms_; // Buffered/cached content of the whole section.
};
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, OutputStream* output)
: isa_(isa),
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)),
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_frame_hdr_(
this, ".debug_frame_hdr.android", 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),
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;
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* GetDebugFrame() { return &debug_frame_; }
Section* GetDebugFrameHdr() { return &debug_frame_hdr_; }
Section* GetDebugInfo() { return &debug_info_; }
Section* GetDebugLine() { return &debug_line_; }
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_.
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_);
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);
}
// 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); // Placeholder 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[] = {
{ .d_tag = DT_HASH, .d_un = { .d_ptr = hash_.GetAddress() }, },
{ .d_tag = DT_STRTAB, .d_un = { .d_ptr = dynstr_.GetAddress() }, },
{ .d_tag = DT_SYMTAB, .d_un = { .d_ptr = dynsym_.GetAddress() }, },
{ .d_tag = DT_SYMENT, .d_un = { .d_ptr = sizeof(Elf_Sym) }, },
{ .d_tag = DT_STRSZ, .d_un = { .d_ptr = dynstr_.GetCacheSize() }, },
{ .d_tag = DT_SONAME, .d_un = { .d_ptr = soname_offset }, },
{ .d_tag = DT_NULL, .d_un = { .d_ptr = 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 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);
}
static InstructionSet GetIsaFromHeader(const Elf_Ehdr& header) {
switch (header.e_machine) {
case EM_ARM:
return InstructionSet::kThumb2;
case EM_AARCH64:
return InstructionSet::kArm64;
case EM_386:
return InstructionSet::kX86;
case EM_X86_64:
return InstructionSet::kX86_64;
}
LOG(FATAL) << "Unknown architecture: " << header.e_machine;
UNREACHABLE();
}
private:
static Elf_Ehdr MakeElfHeader(InstructionSet isa) {
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::kNone: {
LOG(FATAL) << "No instruction set";
break;
}
default: {
LOG(FATAL) << "Unknown instruction set " << isa;
}
}
DCHECK_EQ(GetIsaFromHeader(elf_header),
(isa == InstructionSet::kArm) ? InstructionSet::kThumb2 : 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_;
ErrorDelayingOutputStream stream_;
Section rodata_;
Section text_;
Section data_bimg_rel_ro_;
Section bss_;
Section dex_;
CachedStringSection dynstr_;
SymbolSection dynsym_;
CachedSection hash_;
CachedSection dynamic_;
StringSection strtab_;
SymbolSection symtab_;
Section debug_frame_;
Section debug_frame_hdr_;
Section debug_info_;
Section debug_line_;
StringSection shstrtab_;
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 art
#endif // ART_LIBELFFILE_ELF_ELF_BUILDER_H_