elf.cpp

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#include <processes/elf.h>
#include <common/logger.h>
 
using namespace MaxOS;
using namespace MaxOS::processes;
using namespace MaxOS::memory;
 
 
 
ELF64::ELF64(uintptr_t elf_header_address)
: m_elf_header_address(elf_header_address)
{
}
 
ELF64::~ELF64() = default;
 
void ELF64::load() {
 
    if (!is_valid())
        return;
 
    load_program_headers();
 
}
 
elf_64_header_t* ELF64::header() const {
 
    return (elf_64_header_t*) m_elf_header_address;
}
 
elf_64_program_header_t* ELF64::get_program_header(size_t index) const {
 
    // Check bounds
    if (index >= header()->program_header_count)
        return nullptr;
 
    // Find the program headers and return the item
    auto* program_headers = (elf_64_program_header_t*) (m_elf_header_address + header()->program_header_offset);
    return &program_headers[index];
 
}
 
elf_64_section_header_t* ELF64::get_section_header(size_t index) const {
 
    // Check bound
    if (index >= header()->section_header_count)
        return nullptr;
 
    // Find the section headers and return the item
    auto* section_headers = (elf_64_section_header_t*) (m_elf_header_address + header()->section_header_offset);
    return &section_headers[index];
 
}
 
bool ELF64::is_valid() const {
 
    // Validate the magic number
    for (size_t i = 0; i < 4; i++)
        if (header()->identification[i] != ELF_MAGIC[i])
            return false;
 
    // Check if the elf is 64 bit
    if (header()->identification[(int) ELFIdentification::Class] != (int) ELFClass::Bits64)
        return false;
 
    // Check if the elf is little endian
    if (header()->identification[(int) ELFIdentification::Data] != (int) ELFData::LittleEndian)
        return false;
 
    // Check if the elf is version 1
    if (header()->identification[(int) ELFIdentification::Version] != (int) ELFVersion::Current)
        return false;
 
    // Check if the elf is for the MaxOS platform
    //  if(header() -> identification[OSABI] != MaxOSABI)
    //      return false;
 
    // Check if the elf is executable
    if (header()->type != (int) ELFType::Executable)
        return false;
 
    // Check if the elf is for the x86_64 platform
    if (header()->machine != (int) ELFMachine::x86_64)
        return false;
 
    // LGTM
    return true;
 
}
 
void ELF64::load_program_headers() const {
 
    for (size_t i = 0; i < header()->program_header_count; i++) {
 
        // Get the header information
        elf_64_program_header_t* program_header = get_program_header(i);
 
        // Only load headers that actually need loading
        if (program_header->type != (int) ELFProgramType::Load)
            continue;
 
        // Allocate space at the requested address
        void* address = MemoryManager::s_current_memory_manager->vmm()->allocate(program_header->virtual_address, program_header->memory_size, PRESENT | WRITE);
        ASSERT(address != nullptr, "Failed to allocate memory for program header\n");
 
        // Copy the program into memory at that address
        memcpy(address, (void*) (m_elf_header_address + program_header->offset), program_header->file_size);
 
        // Zero the rest of the memory if needed
        size_t zero_size = program_header->memory_size - program_header->file_size;
        memset((void*) ((uintptr_t) address + program_header->file_size), 0, zero_size);
 
        // Once the memory has been copied can now mark the pages as read only etc
        uint64_t flags = to_vmm_flags(program_header->flags);
        PhysicalMemoryManager::s_current_manager->change_page_flags(address, flags, MemoryManager::s_current_memory_manager->vmm()->pml4_root_address());
    }
}
 
uint64_t ELF64::to_vmm_flags(uint32_t type) {
 
    // Conversion
    // ELF   |   VMM
    // 0x0   |   Executable
    // 0x1   |   Write
    // 0x2   |   Read
 
    uint64_t flags = PRESENT | USER | NO_EXECUTE;
 
    // Enable write
    if (type & ELFWrite)
        flags |= WRITE;
 
    // Disable no execute
    if (type & ELFExecute)
        flags &= ~NO_EXECUTE;
 
    return flags;
}