Luna/kernel/src/sys/elf/ELFLoader.cpp

#define MODULE "elf"

#include "sys/elf/ELFLoader.h"
#include "fs/VFS.h"
#include "init/InitRD.h"
#include "log/Log.h"
#include "memory/MemoryManager.h"
#include "misc/utils.h"
#include "std/stdlib.h"
#include "std/string.h"
#include "sys/elf/ELF.h"

static const char* format_permissions(uint32_t flags)
{
    static char perms[4];
    perms[0] = (flags & 4) > 0 ? 'r' : '-';
    perms[1] = (flags & 2) > 0 ? 'w' : '-';
    perms[2] = (flags & 1) > 0 ? 'x' : '-';
    perms[3] = 0;
    return perms;
}

ELFImage* ELFLoader::load_elf_from_filesystem(const char* filename)
{
    VFS::Node* node = VFS::resolve_path(filename);

    if (!node)
    {
        kwarnln("Failed to open file %s for loading", filename);
        return 0;
    }

    if (node->type == VFS_DIRECTORY)
    {
        kwarnln("Failed to load %s: is a directory", filename);
        return 0;
    }

    void* file = kmalloc(node->length);
    if (VFS::read(node, 0, node->length, (char*)file) < 0)
    {
        kwarnln("Failed to read ELF image from file");
        kfree(file);
        return 0;
    }

    ELFImage* result =
        load_elf_from_address((uintptr_t)file); // FIXME: Read headers and sections as we go along the file, to avoid
                                                // loading the entire file at once into memory.

    kfree(file);

    return result;
}

ELFImage* ELFLoader::load_elf_from_address(uintptr_t addr)
{
    Elf64_Ehdr* elf_ehdr = (Elf64_Ehdr*)addr;
    if (strncmp((const char*)elf_ehdr->e_ident, ELFMAG, SELFMAG) != 0)
    {
        kwarnln("ELF file has invalid magic, skipping");
        return 0;
    }
    if (elf_ehdr->e_ident[EI_CLASS] != ELFCLASS64)
    {
        kwarnln("ELF file is not ELF64, skipping");
        return 0;
    }
    if (elf_ehdr->e_ident[EI_DATA] != ELFDATA2LSB)
    {
        kwarnln("ELF file is not little-endian, skipping");
        return 0;
    }
    if (elf_ehdr->e_type != ET_EXEC)
    {
        kwarnln("not supported: ELF file is not an executable");
        return 0;
    }
    if (elf_ehdr->e_machine != EM_MACH)
    {
        kwarnln("Unsupported target machine");
        return 0;
    }
    if (elf_ehdr->e_phnum == 0)
    {
        kwarnln("ELF file has no PHDRS");
        return 0;
    }
    ELFImage* image = (ELFImage*)kmalloc(sizeof(ELFImage) - sizeof(ELFSection));
    memset(image, 0, sizeof(ELFImage) - sizeof(ELFSection));
    image->entry = elf_ehdr->e_entry;
    int i;
    Elf64_Phdr* phdr;
    for (phdr = (Elf64_Phdr*)((uint64_t)addr + elf_ehdr->e_phoff), i = 0; i < elf_ehdr->e_phnum;
         i++, phdr = (Elf64_Phdr*)((uint8_t*)phdr + elf_ehdr->e_phentsize))
    {
        if (phdr->p_type == PT_LOAD)
        {
            kdbgln("Loading loadable segment at address %lx, file size %ld, mem size %ld, permissions %s",
                   phdr->p_vaddr, phdr->p_filesz, phdr->p_memsz, format_permissions(phdr->p_flags));
            if (!phdr->p_vaddr)
            {
                kerrorln("Address is NULL, this is invalid :(");
                return 0;
            }
            uint64_t pages = Utilities::get_blocks_from_size(PAGE_SIZE, (phdr->p_vaddr % PAGE_SIZE) + phdr->p_memsz);
            void* buffer = (void*)((uint64_t)MemoryManager::get_pages_at(
                                       Utilities::round_down_to_nearest_page(phdr->p_vaddr), pages,
                                       phdr->p_flags & 2 ? MAP_READ_WRITE | MAP_USER : MAP_USER) +
                                   (phdr->p_vaddr % PAGE_SIZE));
            memcpy(buffer, (void*)(addr + phdr->p_offset), phdr->p_filesz);
            memset((void*)((uint64_t)buffer + phdr->p_filesz), 0, phdr->p_memsz - phdr->p_filesz);
            image = (ELFImage*)krealloc(image, (sizeof(ELFImage) - sizeof(ELFSection)) +
                                                   (image->section_count + 1) * sizeof(ELFSection));
            ELFSection& section = image->sections[image->section_count];
            section.base = (uintptr_t)buffer;
            section.pages = pages;
            image->section_count++;
        }
        else { kdbgln("skipping non-loadable segment"); }
    }
    if (!image->section_count)
    {
        kfree(image);
        return 0;
    }
    return image;
}

void ELFLoader::release_elf_image(ELFImage* image)
{
    for (uint64_t i = 0; i < image->section_count; i++)
    {
        ELFSection& section = image->sections[i];
        kdbgln("Freeing up section %lx, was using %ld pages", section.base, section.pages);
        MemoryManager::release_pages((void*)Utilities::round_down_to_nearest_page(section.base), section.pages);
    }
    kfree(image);
}