SplenkOS/kernel/src/PageFrameAllocator.cpp

#include "PageFrameAllocator.h"

uint64_t freeMemory;
uint64_t reservedMemory;
uint64_t usedMemory;
bool Initialized = false;

void PageFrameAllocator::ReadEFIMemoryMap(EFI_MEMORY_DESCRIPTOR* mMap, size_t mMapSize, size_t mMapDescSize){
    if (Initialized) return;

    Initialized = true;

    uint64_t mMapEntries = mMapSize / mMapDescSize;

    void* largestFreeMemSeg = NULL;
    size_t largestFreeMemSegSize = 0;

    for (int i = 0; i < mMapEntries; i++) {
        EFI_MEMORY_DESCRIPTOR* desc = (EFI_MEMORY_DESCRIPTOR*)((uint64_t)mMap + (i * mMapDescSize));
        if (desc->type == 7) {
            if (desc -> numPages * 4096 > largestFreeMemSegSize) {
                largestFreeMemSeg = desc-> physAddr;
                largestFreeMemSegSize = desc -> numPages * 4096;
            }
        }
    }

    uint64_t memorySize = GetMemorySize(mMap, mMapEntries, mMapDescSize);
    freeMemory = memorySize;
    uint64_t bitmapSize = memorySize / 4096 / 8 + 1;

    InitBitmap(bitmapSize, largestFreeMemSeg);

    //lock pages of bitmap
    //reserve pages of unsable/reserverd memory
}

void PageFrameAllocator::InitBitmap(size_t bitmapSize, void* bufferAddress){
    PageBitmap.Size = bitmapSize;
    PageBitmap.Buffer = (uint8_t*)bufferAddress;
    for (int i = 0; i < bitmapSize; i++){
        *(uint8_t*)(PageBitmap.Buffer + i) = 0; 
    }
}