#include <array>
#include <cstdint>

extern void kernel_main();

struct multiboot2
{
    static constexpr std::uint32_t MAGIC    = 0xE85250D6;
    static constexpr std::uint32_t FLAGS    = 0;
    static constexpr std::uint32_t LENGTH   = 16;
    static constexpr std::uint32_t CHECKSUM = -(MAGIC + FLAGS + LENGTH);

    alignas(8)
    std::uint32_t magic = MAGIC;
    std::uint32_t flags = FLAGS;
    std::uint32_t length = LENGTH;
    std::uint32_t checksum = CHECKSUM;
} __attribute__((packed));

struct multiboot2_tag
{
    alignas(8)
    std::uint16_t id;
    std::uint16_t flags;
    std::uint32_t length;
    std::uint32_t data[];
} __attribute__((packed));

__attribute__((section(".multiboot2")))
multiboot2 multibootHeader;

__attribute__((section(".multiboot2")))
multiboot2_tag multibootTagInfoRequest = { 
    1, 0, sizeof(multiboot2_tag) + sizeof(std::uint32_t),
    {4}
};

__attribute__((section(".multiboot2")))
multiboot2_tag multibootTagEnd = { 
    0, 0, sizeof(multiboot2_tag), {}
};

alignas(16)
std::array<std::uint8_t, 16384> stack;

extern "C"
__attribute__((naked))
void _start()
{
    asm volatile(R"(
        mov %%eax, multiboot_magic
        mov %%ebx, multiboot_ptr
        mov %0, %%esp
    )" :: "i" (stack.data() + stack.size()));

    extern std::uint32_t __init_array_start;
    extern std::uint32_t __init_array_end;

    auto it = &__init_array_start;
    while (it < &__init_array_end) {
        auto fn = reinterpret_cast<void (*)()>(*it);
        fn();
        ++it;
    }

    kernel_main();

    asm volatile("cli");
    for (;;)
        asm volatile("hlt");
}