ELFLoader.cpp

#include "ELFLoader.h"
#include <iostream>
#include <string>
#include <fstream>

uint32_t ELFLoader::loadELF(const std::string& filename, Bus& bus)
{
    std::ifstream file(filename, std::ios::binary);
    if (!file) {
        throw std::runtime_error ("Failed to open ELF file.\n");
    }


    // Read ELF Header and compare magic
    Ehdr eheader;
    file.read((char*)&eheader, sizeof(eheader));


    //Checks 
    if (eheader.e_ident[0] != CHECKS::num || eheader.e_ident[1] != CHECKS::E 
        || eheader.e_ident[2] != CHECKS::L || eheader.e_ident[3] != CHECKS::F) 
    {
        std::cerr << "TYPE error\n";
        throw std::runtime_error("Not an ELF file.\n");
     }


    if (eheader.e_type != CHECKS::EXEC) { 
        std::cerr << "TYPE error\n";
        throw std::runtime_error("ELF file is not an executable.\n");
        
    }

    if (eheader.e_machine != CHECKS::RISCV) { 
        std::cerr << "TYPE error\n";
        throw std::runtime_error("ELF file is not for RISC-V.\n");
    }

    if (eheader.e_ident[4] != CHECKS::TYPE) {  
        std::cerr << "TYPE error\n";
        throw std::runtime_error("ELF file is not 32-bit.\n");
    }

    // read Program header files
    //use the offset to find the start of Program headers
    file.seekg(eheader.e_phoff, std::ios::beg);

    // for number of program headers loop through them
    for (int i = 0; i < eheader.e_phnum; ++i) {

        Phdr pheader;
        file.read((char*)&pheader, sizeof(pheader));

        //LOAD
        if (pheader.p_type != CHECKS::LOAD) continue;
            
            char* segment = new char[pheader.p_filesz];
            //Segment offset used to find where the segment begins 
            file.seekg(pheader.p_offset, std::ios::beg);
            file.read(segment, pheader.p_filesz);

            // put LOAD segment into memory
            for (size_t j = 0; j < pheader.p_filesz; ++j) {
                bus.storeInMem(pheader.p_vaddr + j, BYTE_SIZE, static_cast<uint8_t>(segment[j]));

            }

            // Zero out the rest of the memory if memsz > filesz
            if (pheader.p_memsz > pheader.p_filesz) {
                size_t remaining = pheader.p_memsz - pheader.p_filesz;
                for (size_t j = 0; j < remaining; ++j) {
                    bus.storeInMem(pheader.p_vaddr + pheader.p_filesz + j, BYTE_SIZE, 0);
                }
            }

            delete[] segment; 
        
    }


    return eheader.e_entry;
}