elf.cpp
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#undef NDEBUG
#include <cstring>
#include <assert.h>
#include "elfxx.h"
template <class endian, typename R, typename T>
void Elf_Ehdr_Traits::swap(T &t, R &r)
{
memcpy(r.e_ident, t.e_ident, sizeof(r.e_ident));
r.e_type = endian::swap(t.e_type);
r.e_machine = endian::swap(t.e_machine);
r.e_version = endian::swap(t.e_version);
r.e_entry = endian::swap(t.e_entry);
r.e_phoff = endian::swap(t.e_phoff);
r.e_shoff = endian::swap(t.e_shoff);
r.e_flags = endian::swap(t.e_flags);
r.e_ehsize = endian::swap(t.e_ehsize);
r.e_phentsize = endian::swap(t.e_phentsize);
r.e_phnum = endian::swap(t.e_phnum);
r.e_shentsize = endian::swap(t.e_shentsize);
r.e_shnum = endian::swap(t.e_shnum);
r.e_shstrndx = endian::swap(t.e_shstrndx);
}
template <class endian, typename R, typename T>
void Elf_Phdr_Traits::swap(T &t, R &r)
{
r.p_type = endian::swap(t.p_type);
r.p_offset = endian::swap(t.p_offset);
r.p_vaddr = endian::swap(t.p_vaddr);
r.p_paddr = endian::swap(t.p_paddr);
r.p_filesz = endian::swap(t.p_filesz);
r.p_memsz = endian::swap(t.p_memsz);
r.p_flags = endian::swap(t.p_flags);
r.p_align = endian::swap(t.p_align);
}
template <class endian, typename R, typename T>
void Elf_Shdr_Traits::swap(T &t, R &r)
{
r.sh_name = endian::swap(t.sh_name);
r.sh_type = endian::swap(t.sh_type);
r.sh_flags = endian::swap(t.sh_flags);
r.sh_addr = endian::swap(t.sh_addr);
r.sh_offset = endian::swap(t.sh_offset);
r.sh_size = endian::swap(t.sh_size);
r.sh_link = endian::swap(t.sh_link);
r.sh_info = endian::swap(t.sh_info);
r.sh_addralign = endian::swap(t.sh_addralign);
r.sh_entsize = endian::swap(t.sh_entsize);
}
template <class endian, typename R, typename T>
void Elf_Dyn_Traits::swap(T &t, R &r)
{
r.d_tag = endian::swap(t.d_tag);
r.d_un.d_val = endian::swap(t.d_un.d_val);
}
template <class endian, typename R, typename T>
void Elf_Sym_Traits::swap(T &t, R &r)
{
r.st_name = endian::swap(t.st_name);
r.st_value = endian::swap(t.st_value);
r.st_size = endian::swap(t.st_size);
r.st_info = t.st_info;
r.st_other = t.st_other;
r.st_shndx = endian::swap(t.st_shndx);
}
template <class endian>
struct _Rel_info {
static inline void swap(Elf32_Word &t, Elf32_Word &r) { r = endian::swap(t); }
static inline void swap(Elf64_Xword &t, Elf64_Xword &r) { r = endian::swap(t); }
static inline void swap(Elf64_Xword &t, Elf32_Word &r) {
r = endian::swap(ELF32_R_INFO(ELF64_R_SYM(t), ELF64_R_TYPE(t)));
}
static inline void swap(Elf32_Word &t, Elf64_Xword &r) {
r = endian::swap(ELF64_R_INFO(ELF32_R_SYM(t), ELF32_R_TYPE(t)));
}
};
template <class endian, typename R, typename T>
void Elf_Rel_Traits::swap(T &t, R &r)
{
r.r_offset = endian::swap(t.r_offset);
_Rel_info<endian>::swap(t.r_info, r.r_info);
}
template <class endian, typename R, typename T>
void Elf_Rela_Traits::swap(T &t, R &r)
{
r.r_offset = endian::swap(t.r_offset);
_Rel_info<endian>::swap(t.r_info, r.r_info);
r.r_addend = endian::swap(t.r_addend);
}
static const Elf32_Shdr null32_section =
{ 0, SHT_NULL, 0, 0, 0, 0, SHN_UNDEF, 0, 0, 0 };
Elf_Shdr null_section(null32_section);
Elf_Ehdr::Elf_Ehdr(std::ifstream &file, char ei_class, char ei_data)
: serializable<Elf_Ehdr_Traits>(file, ei_class, ei_data),
ElfSection(null_section, nullptr, nullptr)
{
shdr.sh_size = Elf_Ehdr::size(ei_class);
}
Elf::Elf(std::ifstream &file)
{
if (!file.is_open())
throw std::runtime_error("Error opening file");
file.exceptions(std::ifstream::eofbit | std::ifstream::failbit | std::ifstream::badbit);
// Read ELF magic number and identification information
char e_ident[EI_VERSION];
file.seekg(0);
file.read(e_ident, sizeof(e_ident));
file.seekg(0);
ehdr = new Elf_Ehdr(file, e_ident[EI_CLASS], e_ident[EI_DATA]);
// ELFOSABI_LINUX is kept unsupported because I haven't looked whether
// STB_GNU_UNIQUE or STT_GNU_IFUNC would need special casing.
if ((ehdr->e_ident[EI_OSABI] != ELFOSABI_NONE) && (ehdr->e_ident[EI_ABIVERSION] != 0))
throw std::runtime_error("unsupported ELF ABI");
if (ehdr->e_version != 1)
throw std::runtime_error("unsupported ELF version");
// Sanity checks
if (ehdr->e_shnum == 0)
throw std::runtime_error("sstripped ELF files aren't supported");
if (ehdr->e_ehsize != Elf_Ehdr::size(e_ident[EI_CLASS]))
throw std::runtime_error("unsupported ELF inconsistency: ehdr.e_ehsize != sizeof(ehdr)");
if (ehdr->e_shentsize != Elf_Shdr::size(e_ident[EI_CLASS]))
throw std::runtime_error("unsupported ELF inconsistency: ehdr.e_shentsize != sizeof(shdr)");
if (ehdr->e_phnum == 0) {
if (ehdr->e_phoff != 0)
throw std::runtime_error("unsupported ELF inconsistency: e_phnum == 0 && e_phoff != 0");
if (ehdr->e_phentsize != 0)
throw std::runtime_error("unsupported ELF inconsistency: e_phnum == 0 && e_phentsize != 0");
} else if (ehdr->e_phoff != ehdr->e_ehsize)
throw std::runtime_error("unsupported ELF inconsistency: ehdr->e_phoff != ehdr->e_ehsize");
else if (ehdr->e_phentsize != Elf_Phdr::size(e_ident[EI_CLASS]))
throw std::runtime_error("unsupported ELF inconsistency: ehdr->e_phentsize != sizeof(phdr)");
// Read section headers
Elf_Shdr **shdr = new Elf_Shdr *[ehdr->e_shnum];
file.seekg(ehdr->e_shoff);
for (int i = 0; i < ehdr->e_shnum; i++)
shdr[i] = new Elf_Shdr(file, e_ident[EI_CLASS], e_ident[EI_DATA]);
// Sanity check in section header for index 0
if ((shdr[0]->sh_name != 0) || (shdr[0]->sh_type != SHT_NULL) ||
(shdr[0]->sh_flags != 0) || (shdr[0]->sh_addr != 0) ||
(shdr[0]->sh_offset != 0) || (shdr[0]->sh_size != 0) ||
(shdr[0]->sh_link != SHN_UNDEF) || (shdr[0]->sh_info != 0) ||
(shdr[0]->sh_addralign != 0) || (shdr[0]->sh_entsize != 0))
throw std::runtime_error("Section header for index 0 contains unsupported values");
if ((shdr[ehdr->e_shstrndx]->sh_link != 0) || (shdr[ehdr->e_shstrndx]->sh_info != 0))
throw std::runtime_error("unsupported ELF content: string table with sh_link != 0 || sh_info != 0");
// Store these temporarily
tmp_shdr = shdr;
tmp_file = &file;
// Fill sections list
sections = new ElfSection *[ehdr->e_shnum];
for (int i = 0; i < ehdr->e_shnum; i++)
sections[i] = nullptr;
for (int i = 1; i < ehdr->e_shnum; i++) {
if (sections[i] != nullptr)
continue;
getSection(i);
}
Elf_Shdr s;
s.sh_name = 0;
s.sh_type = SHT_NULL;
s.sh_flags = 0;
s.sh_addr = 0;
s.sh_offset = ehdr->e_shoff;
s.sh_entsize = Elf_Shdr::size(e_ident[EI_CLASS]);
s.sh_size = s.sh_entsize * ehdr->e_shnum;
s.sh_link = 0;
s.sh_info = 0;
s.sh_addralign = (e_ident[EI_CLASS] == ELFCLASS32) ? 4 : 8;
shdr_section = new ElfSection(s, nullptr, nullptr);
// Fake section for program headers
s.sh_offset = ehdr->e_phoff;
s.sh_addr = ehdr->e_phoff;
s.sh_entsize = Elf_Phdr::size(e_ident[EI_CLASS]);
s.sh_size = s.sh_entsize * ehdr->e_phnum;
phdr_section = new ElfSection(s, nullptr, nullptr);
phdr_section->insertAfter(ehdr, false);
sections[1]->insertAfter(phdr_section, false);
for (int i = 2; i < ehdr->e_shnum; i++) {
// TODO: this should be done in a better way
if ((shdr_section->getPrevious() == nullptr) && (shdr[i]->sh_offset > ehdr->e_shoff)) {
shdr_section->insertAfter(sections[i - 1], false);
sections[i]->insertAfter(shdr_section, false);
} else
sections[i]->insertAfter(sections[i - 1], false);
}
if (shdr_section->getPrevious() == nullptr)
shdr_section->insertAfter(sections[ehdr->e_shnum - 1], false);
tmp_file = nullptr;
tmp_shdr = nullptr;
for (int i = 0; i < ehdr->e_shnum; i++)
delete shdr[i];
delete[] shdr;
eh_shstrndx = (ElfStrtab_Section *)sections[ehdr->e_shstrndx];
// Skip reading program headers if there aren't any
if (ehdr->e_phnum == 0)
return;
// Read program headers
file.seekg(ehdr->e_phoff);
for (int i = 0; i < ehdr->e_phnum; i++) {
Elf_Phdr phdr(file, e_ident[EI_CLASS], e_ident[EI_DATA]);
if (phdr.p_type == PT_LOAD) {
// Default alignment for PT_LOAD on x86-64 prevents elfhack from
// doing anything useful. However, the system doesn't actually
// require such a big alignment, so in order for elfhack to work
// efficiently, reduce alignment when it's originally the default
// one.
if ((ehdr->e_machine == EM_X86_64) && (phdr.p_align == 0x200000))
phdr.p_align = 0x1000;
}
ElfSegment *segment = new ElfSegment(&phdr);
// Some segments aren't entirely filled (if at all) by sections
// For those, we use fake sections
if ((phdr.p_type == PT_LOAD) && (phdr.p_offset == 0)) {
// Use a fake section for ehdr and phdr
ehdr->getShdr().sh_addr = phdr.p_vaddr;
phdr_section->getShdr().sh_addr += phdr.p_vaddr;
segment->addSection(ehdr);
segment->addSection(phdr_section);
}
if (phdr.p_type == PT_PHDR)
segment->addSection(phdr_section);
for (int j = 1; j < ehdr->e_shnum; j++)
if (phdr.contains(sections[j]))
segment->addSection(sections[j]);
// Make sure that our view of segments corresponds to the original
// ELF file.
assert(segment->getFileSize() == phdr.p_filesz);
// gold makes TLS segments end on an aligned virtual address, even
// when the underlying section ends before that, while bfd ld
// doesn't. It's fine if we don't keep that alignment.
unsigned int memsize = segment->getMemSize();
if (phdr.p_type == PT_TLS && memsize != phdr.p_memsz) {
unsigned int align = segment->getAlign();
memsize = (memsize + align - 1) & ~(align - 1);
}
assert(memsize == phdr.p_memsz);
segments.push_back(segment);
}
new (&eh_entry) ElfLocation(ehdr->e_entry, this);
}
Elf::~Elf()
{
for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++)
delete *seg;
delete[] sections;
ElfSection *section = ehdr;
while (section != nullptr) {
ElfSection *next = section->getNext();
delete section;
section = next;
}
}
// TODO: This shouldn't fail after inserting sections
ElfSection *Elf::getSection(int index)
{
if ((index < -1) || (index >= ehdr->e_shnum))
throw std::runtime_error("Section index out of bounds");
if (index == -1)
index = ehdr->e_shstrndx; // TODO: should be fixed to use the actual current number
// Special case: the section at index 0 is void
if (index == 0)
return nullptr;
// Infinite recursion guard
if (sections[index] == (ElfSection *)this)
return nullptr;
if (sections[index] == nullptr) {
sections[index] = (ElfSection *)this;
switch (tmp_shdr[index]->sh_type) {
case SHT_DYNAMIC:
sections[index] = new ElfDynamic_Section(*tmp_shdr[index], tmp_file, this);
break;
case SHT_REL:
sections[index] = new ElfRel_Section<Elf_Rel>(*tmp_shdr[index], tmp_file, this);
break;
case SHT_RELA:
sections[index] = new ElfRel_Section<Elf_Rela>(*tmp_shdr[index], tmp_file, this);
break;
case SHT_DYNSYM:
case SHT_SYMTAB:
sections[index] = new ElfSymtab_Section(*tmp_shdr[index], tmp_file, this);
break;
case SHT_STRTAB:
sections[index] = new ElfStrtab_Section(*tmp_shdr[index], tmp_file, this);
break;
default:
sections[index] = new ElfSection(*tmp_shdr[index], tmp_file, this);
}
}
return sections[index];
}
ElfSection *Elf::getSectionAt(unsigned int offset)
{
for (int i = 1; i < ehdr->e_shnum; i++) {
ElfSection *section = getSection(i);
if ((section != nullptr) && (section->getFlags() & SHF_ALLOC) && !(section->getFlags() & SHF_TLS) &&
(offset >= section->getAddr()) && (offset < section->getAddr() + section->getSize()))
return section;
}
return nullptr;
}
ElfSegment *Elf::getSegmentByType(unsigned int type, ElfSegment *last)
{
std::vector<ElfSegment *>::iterator seg;
if (last) {
seg = std::find(segments.begin(), segments.end(), last);
++seg;
} else
seg = segments.begin();
for (; seg != segments.end(); seg++)
if ((*seg)->getType() == type)
return *seg;
return nullptr;
}
void Elf::removeSegment(ElfSegment *segment)
{
if (!segment)
return;
std::vector<ElfSegment *>::iterator seg;
seg = std::find(segments.begin(), segments.end(), segment);
if (seg == segments.end())
return;
segment->clear();
segments.erase(seg);
}
ElfDynamic_Section *Elf::getDynSection()
{
for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++)
if (((*seg)->getType() == PT_DYNAMIC) && ((*seg)->getFirstSection() != nullptr) &&
(*seg)->getFirstSection()->getType() == SHT_DYNAMIC)
return (ElfDynamic_Section *)(*seg)->getFirstSection();
return nullptr;
}
void Elf::normalize()
{
// fixup section headers sh_name; TODO: that should be done by sections
// themselves
for (ElfSection *section = ehdr; section != nullptr; section = section->getNext()) {
if (section->getIndex() == 0)
continue;
else
ehdr->e_shnum = section->getIndex() + 1;
section->getShdr().sh_name = eh_shstrndx->getStrIndex(section->getName());
}
ehdr->markDirty();
// Check segments consistency
int i = 0;
for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++, i++) {
std::list<ElfSection *>::iterator it = (*seg)->begin();
for (ElfSection *last = *(it++); it != (*seg)->end(); last = *(it++)) {
if (((*it)->getType() != SHT_NOBITS) &&
((*it)->getAddr() - last->getAddr()) != ((*it)->getOffset() - last->getOffset())) {
throw std::runtime_error("Segments inconsistency");
}
}
}
// fixup ehdr before writing
if (ehdr->e_phnum != segments.size()) {
ehdr->e_phnum = segments.size();
phdr_section->getShdr().sh_size = segments.size() * Elf_Phdr::size(ehdr->e_ident[EI_CLASS]);
phdr_section->getNext()->markDirty();
}
// fixup shdr before writing
if (ehdr->e_shnum != shdr_section->getSize() / shdr_section->getEntSize())
shdr_section->getShdr().sh_size = ehdr->e_shnum * Elf_Shdr::size(ehdr->e_ident[EI_CLASS]);
ehdr->e_shoff = shdr_section->getOffset();
ehdr->e_entry = eh_entry.getValue();
ehdr->e_shstrndx = eh_shstrndx->getIndex();
}
void Elf::write(std::ofstream &file)
{
normalize();
for (ElfSection *section = ehdr;
section != nullptr; section = section->getNext()) {
file.seekp(section->getOffset());
if (section == phdr_section) {
for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++) {
Elf_Phdr phdr;
phdr.p_type = (*seg)->getType();
phdr.p_flags = (*seg)->getFlags();
phdr.p_offset = (*seg)->getOffset();
phdr.p_vaddr = (*seg)->getAddr();
phdr.p_paddr = phdr.p_vaddr + (*seg)->getVPDiff();
phdr.p_filesz = (*seg)->getFileSize();
phdr.p_memsz = (*seg)->getMemSize();
phdr.p_align = (*seg)->getAlign();
phdr.serialize(file, ehdr->e_ident[EI_CLASS], ehdr->e_ident[EI_DATA]);
}
} else if (section == shdr_section) {
null_section.serialize(file, ehdr->e_ident[EI_CLASS], ehdr->e_ident[EI_DATA]);
for (ElfSection *sec = ehdr; sec!= nullptr; sec = sec->getNext()) {
if (sec->getType() != SHT_NULL)
sec->getShdr().serialize(file, ehdr->e_ident[EI_CLASS], ehdr->e_ident[EI_DATA]);
}
} else
section->serialize(file, ehdr->e_ident[EI_CLASS], ehdr->e_ident[EI_DATA]);
}
}
ElfSection::ElfSection(Elf_Shdr &s, std::ifstream *file, Elf *parent)
: shdr(s),
link(shdr.sh_link == SHN_UNDEF ? nullptr : parent->getSection(shdr.sh_link)),
next(nullptr), previous(nullptr), index(-1)
{
if ((file == nullptr) || (shdr.sh_type == SHT_NULL) || (shdr.sh_type == SHT_NOBITS))
data = nullptr;
else {
data = new char[shdr.sh_size];
int pos = file->tellg();
file->seekg(shdr.sh_offset);
file->read(data, shdr.sh_size);
file->seekg(pos);
}
if (shdr.sh_name == 0)
name = nullptr;
else {
ElfStrtab_Section *strtab = (ElfStrtab_Section *) parent->getSection(-1);
// Special case (see elfgeneric.cpp): if strtab is nullptr, the
// section being created is the strtab.
if (strtab == nullptr)
name = &data[shdr.sh_name];
else
name = strtab->getStr(shdr.sh_name);
}
// Only SHT_REL/SHT_RELA sections use sh_info to store a section
// number.
if ((shdr.sh_type == SHT_REL) || (shdr.sh_type == SHT_RELA))
info.section = shdr.sh_info ? parent->getSection(shdr.sh_info) : nullptr;
else
info.index = shdr.sh_info;
}
unsigned int ElfSection::getAddr()
{
if (shdr.sh_addr != (Elf32_Word)-1)
return shdr.sh_addr;
// It should be safe to adjust sh_addr for all allocated sections that
// are neither SHT_NOBITS nor SHT_PROGBITS
if ((previous != nullptr) && isRelocatable()) {
unsigned int addr = previous->getAddr();
if (previous->getType() != SHT_NOBITS)
addr += previous->getSize();
if (addr & (getAddrAlign() - 1))
addr = (addr | (getAddrAlign() - 1)) + 1;
return (shdr.sh_addr = addr);
}
return shdr.sh_addr;
}
unsigned int ElfSection::getOffset()
{
if (shdr.sh_offset != (Elf32_Word)-1)
return shdr.sh_offset;
if (previous == nullptr)
return (shdr.sh_offset = 0);
unsigned int offset = previous->getOffset();
ElfSegment *ptload = getSegmentByType(PT_LOAD);
ElfSegment *prev_ptload = previous->getSegmentByType(PT_LOAD);
if (ptload && (ptload == prev_ptload)) {
offset += getAddr() - previous->getAddr();
return (shdr.sh_offset = offset);
}
if (previous->getType() != SHT_NOBITS)
offset += previous->getSize();
Elf32_Word align = 0x1000;
for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++)
align = std::max(align, (*seg)->getAlign());
Elf32_Word mask = align - 1;
// SHF_TLS is used for .tbss which is some kind of special case.
if (((getType() != SHT_NOBITS) || (getFlags() & SHF_TLS)) && (getFlags() & SHF_ALLOC)) {
if ((getAddr() & mask) < (offset & mask))
offset = (offset | mask) + (getAddr() & mask) + 1;
else
offset = (offset & ~mask) + (getAddr() & mask);
}
if ((getType() != SHT_NOBITS) && (offset & (getAddrAlign() - 1)))
offset = (offset | (getAddrAlign() - 1)) + 1;
// Two subsequent sections can't be mapped in the same page in memory
// if they aren't in the same 4K block on disk.
if ((getType() != SHT_NOBITS) && getAddr()) {
if (((offset >> 12) != (previous->getOffset() >> 12)) &&
((getAddr() >> 12) == (previous->getAddr() >> 12)))
throw std::runtime_error("Moving section would require overlapping segments");
}
return (shdr.sh_offset = offset);
}
int ElfSection::getIndex()
{
if (index != -1)
return index;
if (getType() == SHT_NULL)
return (index = 0);
ElfSection *reference;
for (reference = previous; (reference != nullptr) && (reference->getType() == SHT_NULL); reference = reference->getPrevious());
if (reference == nullptr)
return (index = 1);
return (index = reference->getIndex() + 1);
}
Elf_Shdr &ElfSection::getShdr()
{
getOffset();
if (shdr.sh_link == (Elf32_Word)-1)
shdr.sh_link = getLink() ? getLink()->getIndex() : 0;
if (shdr.sh_info == (Elf32_Word)-1)
shdr.sh_info = ((getType() == SHT_REL) || (getType() == SHT_RELA)) ?
(getInfo().section ? getInfo().section->getIndex() : 0) :
getInfo().index;
return shdr;
}
ElfSegment::ElfSegment(Elf_Phdr *phdr)
: type(phdr->p_type), v_p_diff(phdr->p_paddr - phdr->p_vaddr),
flags(phdr->p_flags), align(phdr->p_align), vaddr(phdr->p_vaddr),
filesz(phdr->p_filesz), memsz(phdr->p_memsz) {}
void ElfSegment::addSection(ElfSection *section)
{
// Make sure all sections in PT_GNU_RELRO won't be moved by elfhack
assert(!((type == PT_GNU_RELRO) && (section->isRelocatable())));
//TODO: Check overlapping sections
std::list<ElfSection *>::iterator i;
for (i = sections.begin(); i != sections.end(); ++i)
if ((*i)->getAddr() > section->getAddr())
break;
sections.insert(i, section);
section->addToSegment(this);
}
void ElfSegment::removeSection(ElfSection *section)
{
sections.remove(section);
section->removeFromSegment(this);
}
unsigned int ElfSegment::getFileSize()
{
if (type == PT_GNU_RELRO || isElfHackFillerSegment())
return filesz;
if (sections.empty())
return 0;
// Search the last section that is not SHT_NOBITS
std::list<ElfSection *>::reverse_iterator i;
for (i = sections.rbegin(); (i != sections.rend()) && ((*i)->getType() == SHT_NOBITS); ++i);
// All sections are SHT_NOBITS
if (i == sections.rend())
return 0;
unsigned int end = (*i)->getAddr() + (*i)->getSize();
return end - sections.front()->getAddr();
}
unsigned int ElfSegment::getMemSize()
{
if (type == PT_GNU_RELRO || isElfHackFillerSegment())
return memsz;
if (sections.empty())
return 0;
unsigned int end = sections.back()->getAddr() + sections.back()->getSize();
return end - sections.front()->getAddr();
}
unsigned int ElfSegment::getOffset()
{
if ((type == PT_GNU_RELRO) && !sections.empty() &&
(sections.front()->getAddr() != vaddr))
throw std::runtime_error("PT_GNU_RELRO segment doesn't start on a section start");
// Neither bionic nor glibc linkers seem to like when the offset of that segment is 0
if (isElfHackFillerSegment())
return vaddr;
return sections.empty() ? 0 : sections.front()->getOffset();
}
unsigned int ElfSegment::getAddr()
{
if ((type == PT_GNU_RELRO) && !sections.empty() &&
(sections.front()->getAddr() != vaddr))
throw std::runtime_error("PT_GNU_RELRO segment doesn't start on a section start");
if (isElfHackFillerSegment())
return vaddr;
return sections.empty() ? 0 : sections.front()->getAddr();
}
void ElfSegment::clear()
{
for (std::list<ElfSection *>::iterator i = sections.begin(); i != sections.end(); ++i)
(*i)->removeFromSegment(this);
sections.clear();
}
ElfValue *ElfDynamic_Section::getValueForType(unsigned int tag)
{
for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++)
if (dyns[i].tag == tag)
return dyns[i].value;
return nullptr;
}
ElfSection *ElfDynamic_Section::getSectionForType(unsigned int tag)
{
ElfValue *value = getValueForType(tag);
return value ? value->getSection() : nullptr;
}
bool ElfDynamic_Section::setValueForType(unsigned int tag, ElfValue *val)
{
unsigned int i;
unsigned int shnum = shdr.sh_size / shdr.sh_entsize;
for (i = 0; (i < shnum) && (dyns[i].tag != DT_NULL); i++)
if (dyns[i].tag == tag) {
delete dyns[i].value;
dyns[i].value = val;
return true;
}
// If we get here, this means we didn't match for the given tag
// Most of the time, there are a few DT_NULL entries, that we can
// use to add our value, but if we are on the last entry, we can't.
if (i >= shnum - 1)
return false;
dyns[i].tag = tag;
dyns[i].value = val;
return true;
}
ElfDynamic_Section::ElfDynamic_Section(Elf_Shdr &s, std::ifstream *file, Elf *parent)
: ElfSection(s, file, parent)
{
int pos = file->tellg();
dyns.resize(s.sh_size / s.sh_entsize);
file->seekg(shdr.sh_offset);
// Here we assume tags refer to only one section (e.g. DT_RELSZ accounts
// for .rel.dyn size)
for (unsigned int i = 0; i < s.sh_size / s.sh_entsize; i++) {
Elf_Dyn dyn(*file, parent->getClass(), parent->getData());
dyns[i].tag = dyn.d_tag;
switch (dyn.d_tag) {
case DT_NULL:
case DT_SYMBOLIC:
case DT_TEXTREL:
case DT_BIND_NOW:
dyns[i].value = new ElfValue();
break;
case DT_NEEDED:
case DT_SONAME:
case DT_RPATH:
case DT_PLTREL:
case DT_RUNPATH:
case DT_FLAGS:
case DT_RELACOUNT:
case DT_RELCOUNT:
case DT_VERDEFNUM:
case DT_VERNEEDNUM:
dyns[i].value = new ElfPlainValue(dyn.d_un.d_val);
break;
case DT_PLTGOT:
case DT_HASH:
case DT_STRTAB:
case DT_SYMTAB:
case DT_RELA:
case DT_INIT:
case DT_FINI:
case DT_REL:
case DT_JMPREL:
case DT_INIT_ARRAY:
case DT_FINI_ARRAY:
case DT_GNU_HASH:
case DT_VERSYM:
case DT_VERNEED:
case DT_VERDEF:
dyns[i].value = new ElfLocation(dyn.d_un.d_ptr, parent);
break;
default:
dyns[i].value = nullptr;
}
}
// Another loop to get the section sizes
for (unsigned int i = 0; i < s.sh_size / s.sh_entsize; i++)
switch (dyns[i].tag) {
case DT_PLTRELSZ:
dyns[i].value = new ElfSize(getSectionForType(DT_JMPREL));
break;
case DT_RELASZ:
dyns[i].value = new ElfSize(getSectionForType(DT_RELA));
break;
case DT_STRSZ:
dyns[i].value = new ElfSize(getSectionForType(DT_STRTAB));
break;
case DT_RELSZ:
dyns[i].value = new ElfSize(getSectionForType(DT_REL));
break;
case DT_INIT_ARRAYSZ:
dyns[i].value = new ElfSize(getSectionForType(DT_INIT_ARRAY));
break;
case DT_FINI_ARRAYSZ:
dyns[i].value = new ElfSize(getSectionForType(DT_FINI_ARRAY));
break;
case DT_RELAENT:
dyns[i].value = new ElfEntSize(getSectionForType(DT_RELA));
break;
case DT_SYMENT:
dyns[i].value = new ElfEntSize(getSectionForType(DT_SYMTAB));
break;
case DT_RELENT:
dyns[i].value = new ElfEntSize(getSectionForType(DT_REL));
break;
}
file->seekg(pos);
}
ElfDynamic_Section::~ElfDynamic_Section()
{
for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++)
delete dyns[i].value;
}
void ElfDynamic_Section::serialize(std::ofstream &file, char ei_class, char ei_data)
{
for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++) {
Elf_Dyn dyn;
dyn.d_tag = dyns[i].tag;
dyn.d_un.d_val = (dyns[i].value != nullptr) ? dyns[i].value->getValue() : 0;
dyn.serialize(file, ei_class, ei_data);
}
}
ElfSymtab_Section::ElfSymtab_Section(Elf_Shdr &s, std::ifstream *file, Elf *parent)
: ElfSection(s, file, parent)
{
int pos = file->tellg();
syms.resize(s.sh_size / s.sh_entsize);
ElfStrtab_Section *strtab = (ElfStrtab_Section *)getLink();
file->seekg(shdr.sh_offset);
for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++) {
Elf_Sym sym(*file, parent->getClass(), parent->getData());
syms[i].name = strtab->getStr(sym.st_name);
syms[i].info = sym.st_info;
syms[i].other = sym.st_other;
ElfSection *section = (sym.st_shndx == SHN_ABS) ? nullptr : parent->getSection(sym.st_shndx);
new (&syms[i].value) ElfLocation(section, sym.st_value, ElfLocation::ABSOLUTE);
syms[i].size = sym.st_size;
syms[i].defined = (sym.st_shndx != SHN_UNDEF);
}
file->seekg(pos);
}
void
ElfSymtab_Section::serialize(std::ofstream &file, char ei_class, char ei_data)
{
ElfStrtab_Section *strtab = (ElfStrtab_Section *)getLink();
for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++) {
Elf_Sym sym;
sym.st_name = strtab->getStrIndex(syms[i].name);
sym.st_info = syms[i].info;
sym.st_other = syms[i].other;
sym.st_value = syms[i].value.getValue();
ElfSection *section = syms[i].value.getSection();
if (syms[i].defined)
sym.st_shndx = section ? section->getIndex() : SHN_ABS;
else
sym.st_shndx = SHN_UNDEF;
sym.st_size = syms[i].size;
sym.serialize(file, ei_class, ei_data);
}
}
Elf_SymValue *
ElfSymtab_Section::lookup(const char *name, unsigned int type_filter)
{
for (std::vector<Elf_SymValue>::iterator sym = syms.begin();
sym != syms.end(); sym++) {
if ((type_filter & (1 << ELF32_ST_TYPE(sym->info))) &&
(strcmp(sym->name, name) == 0)) {
return &*sym;
}
}
return nullptr;
}
const char *
ElfStrtab_Section::getStr(unsigned int index)
{
for (std::vector<table_storage>::iterator t = table.begin();
t != table.end(); t++) {
if (index < t->used)
return t->buf + index;
index -= t->used;
}
assert(1 == 0);
return nullptr;
}
const char *
ElfStrtab_Section::getStr(const char *string)
{
if (string == nullptr)
return nullptr;
// If the given string is within the section, return it
for (std::vector<table_storage>::iterator t = table.begin();
t != table.end(); t++)
if ((string >= t->buf) && (string < t->buf + t->used))
return string;
// TODO: should scan in the section to find an existing string
// If not, we need to allocate the string in the section
size_t len = strlen(string) + 1;
if (table.back().size - table.back().used < len)
table.resize(table.size() + 1);
char *alloc_str = table.back().buf + table.back().used;
memcpy(alloc_str, string, len);
table.back().used += len;
shdr.sh_size += len;
markDirty();
return alloc_str;
}
unsigned int
ElfStrtab_Section::getStrIndex(const char *string)
{
if (string == nullptr)
return 0;
unsigned int index = 0;
string = getStr(string);
for (std::vector<table_storage>::iterator t = table.begin();
t != table.end(); t++) {
if ((string >= t->buf) && (string < t->buf + t->used))
return index + (string - t->buf);
index += t->used;
}
assert(1 == 0);
return 0;
}
void
ElfStrtab_Section::serialize(std::ofstream &file, char ei_class, char ei_data)
{
file.seekp(getOffset());
for (std::vector<table_storage>::iterator t = table.begin();
t != table.end(); t++)
file.write(t->buf, t->used);
}
