Luna/kernel/src/thread/ThreadImage.cpp

#include "thread/ThreadImage.h"
#include "memory/MemoryManager.h"
#include "thread/Thread.h"
#include <luna/Alignment.h>
#include <luna/CString.h>

static constexpr usize DEFAULT_USER_STACK_PAGES = 6;
static constexpr usize DEFAULT_USER_STACK_SIZE = DEFAULT_USER_STACK_PAGES * ARCH_PAGE_SIZE;

static Result<void> create_stacks(Stack& user_stack, Stack& kernel_stack, UserVM* vm)
{
    const u64 THREAD_STACK_BASE = 0x10000;

    if (!TRY(vm->test_and_alloc_region(THREAD_STACK_BASE, DEFAULT_USER_STACK_PAGES, true))) return err(ENOMEM);

    TRY(MemoryManager::alloc_at_zeroed(THREAD_STACK_BASE, DEFAULT_USER_STACK_PAGES,
                                       MMU::ReadWrite | MMU::NoExecute | MMU::User));

    auto guard = make_scope_guard([&] { MemoryManager::unmap_owned(THREAD_STACK_BASE, 4); });

    const u64 kernel_stack_base = TRY(MemoryManager::alloc_for_kernel(4, MMU::ReadWrite | MMU::NoExecute));

    guard.deactivate();

    user_stack = { THREAD_STACK_BASE, DEFAULT_USER_STACK_SIZE };
    kernel_stack = { kernel_stack_base, 4 * ARCH_PAGE_SIZE };

    return {};
}

Result<OwnedPtr<ThreadImage>> ThreadImage::try_load_from_elf(SharedPtr<VFS::Inode> inode)
{
    auto image = TRY(make_owned<ThreadImage>());

    auto vm_allocator = TRY(UserVM::try_create());

    auto old_directory = MMU::get_page_directory();

    MMU::switch_page_directory(vm_allocator->page_directory());

    auto guard = make_scope_guard([=] { MMU::switch_page_directory(old_directory); });

    const ELFData data = TRY(ELFLoader::load(inode, vm_allocator.ptr()));

    Stack user_stack;
    Stack kernel_stack;
    TRY(create_stacks(user_stack, kernel_stack, vm_allocator.ptr()));

    guard.deactivate();

    image->m_kernel_stack = kernel_stack;
    image->m_user_stack = user_stack;
    image->m_loaded_image_data = data;
    image->m_vm_allocator = move(vm_allocator);
    image->m_sp = user_stack.top();

    return image;
}

Result<OwnedPtr<ThreadImage>> ThreadImage::clone_from_thread(Thread* parent)
{
    auto image = TRY(make_owned<ThreadImage>());

    auto vm_allocator = TRY(parent->vm_allocator->clone());

    const ELFData data = { .entry = parent->ip() };

    const u64 kernel_stack_base = TRY(MemoryManager::alloc_for_kernel(4, MMU::ReadWrite | MMU::NoExecute));
    Stack kernel_stack { kernel_stack_base, 4 * ARCH_PAGE_SIZE };

    image->m_kernel_stack = kernel_stack;
    image->m_user_stack = parent->stack;
    image->m_loaded_image_data = data;
    image->m_vm_allocator = move(vm_allocator);
    image->m_sp = parent->sp();

    return image;
}

Result<u64> ThreadImage::push_mem_on_stack(const u8* mem, usize size)
{
    if ((m_sp - size) < m_user_stack.bottom()) return err(E2BIG);

    if (!MemoryManager::validate_user_write((void*)(m_sp - size), size)) return err(EFAULT);

    m_sp -= size;

    memcpy((void*)m_sp, mem, size);

    return m_sp;
}

Result<u64> ThreadImage::push_string_vector_on_stack(const Vector<String>& vec)
{
    Vector<u64> user_vec;
    for (const auto& item : vec)
    {
        // Copy each individual string and retrieve a userspace pointer to said copy
        u64 addr = TRY(push_mem_on_stack((const u8*)item.chars(), item.length() + 1));
        TRY(user_vec.try_append(addr));
    }

    TRY(user_vec.try_append((u64) nullptr));
    // Copy the actual vector of userspace pointers to the stack
    return TRY(push_mem_on_stack((u8*)user_vec.data(), user_vec.size() * sizeof(u64)));
}

void ThreadImage::apply(Thread* thread)
{
    thread->init_regs_user();

    thread->set_ip(m_loaded_image_data.entry);

    thread->kernel_stack = m_kernel_stack;
    thread->stack = m_user_stack;
    thread->set_sp(align_down<16>(m_sp));

    thread->active_directory = m_vm_allocator->page_directory();

    thread->vm_allocator = move(m_vm_allocator);
}