banan-os/bootloader/installer/ELF.cpp

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#include "ELF.h"
#include <LibELF/Values.h>
#include <cassert>
#include <cerrno>
#include <cstring>
#include <fcntl.h>
#include <iostream>
#include <sys/mman.h>
#include <unistd.h>
using namespace LibELF;
ELFFile::ELFFile(std::string_view path)
: m_path(path)
{
m_fd = open(m_path.c_str(), O_RDONLY);
if (m_fd == -1)
{
std::cerr << "Could not open '" << m_path << "': " << std::strerror(errno) << std::endl;
return;
}
if (fstat(m_fd, &m_stat) == -1)
{
std::cerr << "Could not stat '" << m_path << "': " << std::strerror(errno) << std::endl;
return;
}
void* mmap_addr = mmap(nullptr, m_stat.st_size, PROT_READ, MAP_PRIVATE, m_fd, 0);
if (mmap_addr == MAP_FAILED)
{
std::cerr << "Could not mmap '" << m_path << "': " << std::strerror(errno) << std::endl;
return;
}
m_mmap = reinterpret_cast<uint8_t*>(mmap_addr);
if (!validate_elf_header())
return;
m_success = true;
}
ELFFile::~ELFFile()
{
if (m_mmap)
munmap(m_mmap, m_stat.st_size);
m_mmap = nullptr;
if (m_fd != -1)
close(m_fd);
m_fd = -1;
}
const ElfNativeFileHeader& ELFFile::elf_header() const
{
return *reinterpret_cast<LibELF::ElfNativeFileHeader*>(m_mmap);
}
bool ELFFile::validate_elf_header() const
{
if (m_stat.st_size < sizeof(ElfNativeFileHeader))
{
std::cerr << m_path << " is too small to be a ELF executable" << std::endl;
return false;
}
const auto& elf_header = this->elf_header();
if (
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
)
{
std::cerr << m_path << " doesn't have an ELF magic number" << std::endl;
return false;
}
#if ARCH(x86_64)
if (elf_header.e_ident[EI_CLASS] != ELFCLASS64)
#elif ARCH(i686)
if (elf_header.e_ident[EI_CLASS] != ELFCLASS32)
#endif
{
std::cerr << m_path << " architecture doesn't match" << std::endl;
return false;
}
if (elf_header.e_ident[EI_DATA] != ELFDATA2LSB)
{
std::cerr << m_path << " is not in little endian format" << std::endl;
return false;
}
if (elf_header.e_ident[EI_VERSION] != EV_CURRENT)
{
std::cerr << m_path << " has unsupported version" << std::endl;
return false;
}
if (elf_header.e_type != ET_EXEC)
{
std::cerr << m_path << " is not an executable ELF file" << std::endl;
return false;
}
return true;
}
const ElfNativeSectionHeader& ELFFile::section_header(std::size_t index) const
{
const auto& elf_header = this->elf_header();
assert(index < elf_header.e_shnum);
const uint8_t* section_array_start = m_mmap + elf_header.e_shoff;
return *reinterpret_cast<const ElfNativeSectionHeader*>(section_array_start + index * elf_header.e_shentsize);
}
std::string_view ELFFile::section_name(const ElfNativeSectionHeader& section_header) const
{
const auto& elf_header = this->elf_header();
assert(elf_header.e_shstrndx != SHN_UNDEF);
const auto& section_string_table = this->section_header(elf_header.e_shstrndx);
const char* string_table_start = reinterpret_cast<const char*>(m_mmap + section_string_table.sh_offset);
return string_table_start + section_header.sh_name;
}
std::optional<std::span<const uint8_t>> ELFFile::find_section(std::string_view name) const
{
const auto& elf_header = this->elf_header();
for (std::size_t i = 0; i < elf_header.e_shnum; i++)
{
const auto& section_header = this->section_header(i);
auto section_name = this->section_name(section_header);
if (section_name != name)
continue;
return std::span<const uint8_t>(m_mmap + section_header.sh_offset, section_header.sh_size);
}
return {};
}