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#include "common/linux/synth_elf.h"
#include <assert.h>
#include <elf.h>
#include <stdio.h>
#include <string.h>
#include "common/using_std_string.h"
namespace google_breakpad {
namespace synth_elf {
#ifndef NT_GNU_BUILD_ID
#define NT_GNU_BUILD_ID 3
#endif
ELF::ELF(uint16_t machine,
uint8_t file_class,
Endianness endianness)
: Section(endianness),
addr_size_(file_class == ELFCLASS64 ? 8 : 4),
program_count_(0),
section_count_(0),
section_header_table_(endianness),
section_header_strings_(endianness) {
// Could add support for more machine types here if needed.
assert(machine == EM_386 ||
machine == EM_X86_64 ||
machine == EM_ARM);
assert(file_class == ELFCLASS32 || file_class == ELFCLASS64);
start() = 0;
// Add ELF header
// e_ident
// EI_MAG0...EI_MAG3
D8(ELFMAG0);
D8(ELFMAG1);
D8(ELFMAG2);
D8(ELFMAG3);
// EI_CLASS
D8(file_class);
// EI_DATA
D8(endianness == kLittleEndian ? ELFDATA2LSB : ELFDATA2MSB);
// EI_VERSION
D8(EV_CURRENT);
// EI_OSABI
D8(ELFOSABI_SYSV);
// EI_ABIVERSION
D8(0);
// EI_PAD
Append(7, 0);
assert(Size() == EI_NIDENT);
// e_type
D16(ET_EXEC); //TODO: allow passing ET_DYN?
// e_machine
D16(machine);
// e_version
D32(EV_CURRENT);
// e_entry
Append(endianness, addr_size_, 0);
// e_phoff
Append(endianness, addr_size_, program_header_label_);
// e_shoff
Append(endianness, addr_size_, section_header_label_);
// e_flags
D32(0);
// e_ehsize
D16(addr_size_ == 8 ? sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr));
// e_phentsize
D16(addr_size_ == 8 ? sizeof(Elf64_Phdr) : sizeof(Elf32_Phdr));
// e_phnum
D16(program_count_label_);
// e_shentsize
D16(addr_size_ == 8 ? sizeof(Elf64_Shdr) : sizeof(Elf32_Shdr));
// e_shnum
D16(section_count_label_);
// e_shstrndx
D16(section_header_string_index_);
// Add an empty section for SHN_UNDEF.
Section shn_undef;
AddSection("", shn_undef, SHT_NULL);
}
int ELF::AddSection(const string& name, const Section& section,
uint32_t type, uint32_t flags, uint64_t addr,
uint32_t link, uint64_t entsize, uint64_t offset) {
Label offset_label;
Label string_label(section_header_strings_.Add(name));
size_t size = section.Size();
int index = section_count_;
++section_count_;
section_header_table_
// sh_name
.D32(string_label)
// sh_type
.D32(type)
// sh_flags
.Append(endianness(), addr_size_, flags)
// sh_addr
.Append(endianness(), addr_size_, addr)
// sh_offset
.Append(endianness(), addr_size_, offset_label)
// sh_size
.Append(endianness(), addr_size_, size)
// sh_link
.D32(link)
// sh_info
.D32(0)
// sh_addralign
.Append(endianness(), addr_size_, 0)
// sh_entsize
.Append(endianness(), addr_size_, entsize);
sections_.push_back(ElfSection(section, type, offset, offset_label));
return index;
}
void ELF::AppendSection(ElfSection §ion) {
// NULL and NOBITS sections have no content, so they
// don't need to be written to the file.
if (section.type_ == SHT_NULL) {
section.offset_label_ = 0;
} else if (section.type_ == SHT_NOBITS) {
section.offset_label_ = section.offset_;
} else {
Mark(§ion.offset_label_);
Append(section);
Align(4);
}
}
void ELF::Finish() {
// Add the section header string table at the end.
section_header_string_index_ = section_count_;
//printf(".shstrtab size: %ld\n", section_header_strings_.Size());
AddSection(".shstrtab", section_header_strings_, SHT_STRTAB);
//printf("section_count_: %ld, sections_.size(): %ld\n",
// section_count_, sections_.size());
for (vector<ElfSection>::iterator it = sections_.begin();
it < sections_.end(); ++it) {
AppendSection(*it);
}
section_count_label_ = section_count_;
program_count_label_ = program_count_;
// TODO: allow adding entries to program header table
program_header_label_ = 0;
// Section header table starts here.
Mark(§ion_header_label_);
Append(section_header_table_);
}
SymbolTable::SymbolTable(Endianness endianness,
size_t addr_size,
StringTable& table) : Section(endianness),
addr_size_(addr_size),
table_(table) {
assert(addr_size_ == 4 || addr_size_ == 8);
}
void SymbolTable::AddSymbol(const string& name, uint32_t value,
uint32_t size, unsigned info, uint16_t shndx) {
assert(addr_size_ == 4);
D32(table_.Add(name));
D32(value);
D32(size);
D8(info);
D8(0); // other
D16(shndx);
}
void SymbolTable::AddSymbol(const string& name, uint64_t value,
uint64_t size, unsigned info, uint16_t shndx) {
assert(addr_size_ == 8);
D32(table_.Add(name));
D8(info);
D8(0); // other
D16(shndx);
D64(value);
D64(size);
}
BuildIDNote::BuildIDNote(const uint8_t* id_bytes,
size_t id_size,
Endianness endianness) : Section(endianness) {
const char kNoteName[] = "GNU";
// Elf32_Nhdr and Elf64_Nhdr are exactly the same.
Elf32_Nhdr note_header;
memset(¬e_header, 0, sizeof(note_header));
note_header.n_namesz = sizeof(kNoteName);
note_header.n_descsz = id_size;
note_header.n_type = NT_GNU_BUILD_ID;
Append(reinterpret_cast<const uint8_t*>(¬e_header),
sizeof(note_header));
AppendCString(kNoteName);
Append(id_bytes, id_size);
}
// static
void BuildIDNote::AppendSection(ELF& elf,
const uint8_t* id_bytes,
size_t id_size) {
const char kBuildIDSectionName[] = ".note.gnu.build-id";
BuildIDNote note(id_bytes, id_size, elf.endianness());
elf.AddSection(kBuildIDSectionName, note, SHT_NOTE);
}
} // namespace synth_elf
} // namespace google_breakpad
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