bad_apple_os/targets/x86_64/src/kernel/startup.cpp

#include "boot.hpp"

#include <bit>
#include <cstdio>

#include "os/draw.hpp"
#include "os/serial.hpp"
#include "os/tty.hpp"
#include "./x86_64.hpp"

extern "C" int gKernelEnd;

namespace
{
void initHeapFromEfiMemoryMap(const EfiMemoryMap& memoryMap) noexcept
{
    const uint64_t minAddr = reinterpret_cast<uint64_t>(&gKernelEnd);
    for (const EFI_MEMORY_DESCRIPTOR& descriptor : memoryMap)
    {
        if (!isEfiMemoryTypeUsable(descriptor.Type))
        {
            continue;
        }

        uint64_t addr = descriptor.PhysicalStart;
        uint64_t len = descriptor.NumberOfPages * 4096; // TODO: is this the correct page size?
        // anything before the kernel we ignore
        if (addr < minAddr)
        {
            // if the entire entry is before the kernel, continue
            if (addr + len <= minAddr)
            {
                continue;
            }
            // otherwise shrink it and use the rest
            len -= (minAddr - addr);
            addr = minAddr;
        }
        __ba_registerAllocatableMemory(reinterpret_cast<void*>(addr), len);
    }
#if 0
    const uint64_t minAddr = reinterpret_cast<uint64_t>(&gKernelEnd);
    for (uint32_t addr = firstEntryAddr; addr < firstEntryAddr + bufferLength;)
    {
        multiboot_memory_map_t entry = *reinterpret_cast<multiboot_memory_map_t*>(addr);

        if(entry.type == MULTIBOOT_MEMORY_AVAILABLE)
        {
            std::printf("Start Addr: %X | Length: %b\n",
                        static_cast<unsigned>(entry.addr), static_cast<size_t>(entry.len));

            // anything before the kernel we ignore
            if (entry.addr < minAddr)
            {
                // if the entire entry is before the kernel, continue
                if (entry.addr + entry.len <= minAddr)
                {
                    addr += sizeof(entry.size) + entry.size;
                    continue;
                }
                // otherwise shrink it and use the rest
                entry.len -= (minAddr - entry.addr);
                entry.addr = minAddr;
            }
            __ba_registerAllocatableMemory(reinterpret_cast<void*>(entry.addr), entry.len);
        }
        addr += sizeof(entry.size) + entry.size;
    }
#endif
}

using initfunc_t = void *();
extern "C" initfunc_t* start_ctors;
extern "C" initfunc_t* end_ctors;

void initGlobals()
{
    for (initfunc_t** initFunc = &start_ctors; initFunc != &end_ctors; ++initFunc)
    {
        // TODO: this confuses me
        if (*initFunc == reinterpret_cast<initfunc_t*>(0xffffffffffffffff)) {
            break;
        }
        (*initFunc)();
    }
}

constinit std::array GDT alignas(16) = {
    SEGMENT_NULL,
    SEGMENT_KERNEL_CODE,
    SEGMENT_KERNEL_DATA,
    SEGMENT_USER_CODE,
    SEGMENT_USER_DATA
};

constinit std::array<InterruptDescriptor, 256> IDT alignas(16);
extern "C" void __setGDT(uint16_t limit, void* base);
extern "C" void __setIDT(uint16_t limit, void* base);

void setupInterrupt(std::uint8_t index, void* handler, std::uint8_t flags) noexcept
{
    const std::uint64_t offset = std::bit_cast<std::uint64_t>(handler);
    IDT[index] = InterruptDescriptor{
        .offsetLow = static_cast<unsigned>(offset & 0xFFFF),
        .selector = 1, // kernel code
        .interruptStackTable = 0,
        .gateType = InterruptGateType::INTERRUPT_GATE,
        .privilegeLevel = 0,
        .present = true,
        .offsetHigh = (offset >> 16)
    };
}
}

extern "C"
{
EfiBootInfo* gBootInfo;

void main();

void kernel_main()
{
    __setGDT(sizeof(GDT), &GDT);
    __setIDT(sizeof(IDT), &IDT);

    // done initializing OS stuff, enable interrupts
    __asm__ __volatile__("sti");

    initGlobals();

    // init the heap (required for the double buffer)
    // initHeapFromEfiMemoryMap(gBootInfo->memoryMap);

    // initialize the framebuffer
    draw::initializeDefaultFramebuffer({
        /* base   = */ static_cast<draw::Pixel*>(gBootInfo->displayInfo.frameBufferBase),
        /* width  = */ gBootInfo->displayInfo.frameBufferWidth,
        /* height = */ gBootInfo->displayInfo.frameBufferHeight,
        /* pitch  = */ gBootInfo->displayInfo.frameBufferPitch / 4
    });

	// initialize terminal interface
	tty::initialize();

    if (!initSerialPort(PORT_COM1))
    {
        tty::write("Error initializing serial port.\n");
        return;
    }
    serialWriteString(PORT_COM1, "\r\n\r\n"); // write newlines to separate from UEFI output

    std::puts("This is BadAppleOS and everything is fine!\n");

    main();
}
} // extern "C"