feat(pfa): Add PageFrameAllocator class

kernel/src/Memory/PageFrameAllocator.cpp

@@ -0,0 +1,58 @@
+/*
+    * PageFrameAllocator.hpp
+    * Memory allocator for physical pages
+    * Copyright (c) 2025 Daniel Hammer
+*/
+
+#include "PageFrameAllocator.hpp"
+#include "HHDM.hpp"
+
+namespace Memory {
+    PageFrameAllocator::PageFrameAllocator(LargestSection section) {
+        /* we need the virtual address rather than the physical address, so we call the helper */
+        g_section = LargestSection{
+            .address = HHDM(section.address),
+            .size = section.size
+        };
+
+        head.next = (Page*)g_section.address;
+        head.next->size = section.size;
+        head.next->next = nullptr;
+    }
+
+    void* PageFrameAllocator::Allocate() {
+        Page* current = head.next;
+        Page* prev = &head;
+
+        while (current != nullptr) {
+            if (current->size >= 0x1000) {
+                uint64_t current_addr = (uint64_t)current;
+                uint64_t current_end_addr = current_addr + current->size;
+                uint64_t new_size = current->size - 0x1000;
+
+                if (new_size == 0) {
+                    prev->next = current->next;
+                    return (void*)current;
+                }
+                else
+                {
+                    current->size -= 0x1000;
+                    return (void*)current_end_addr - 0x1000;
+                }
+            }
+
+            prev = current;
+            current = current->next;
+        }
+
+        return nullptr;
+    }
+
+    void PageFrameAllocator::Free(void* ptr) {
+        auto prev_next = head.next;
+        head.next = (Page*)ptr;
+
+        head.next->next = prev_next;
+        head.next->size = 0x1000;
+    }
+};

kernel/src/Memory/PageFrameAllocator.hpp

@@ -0,0 +1,28 @@
+/*
+    * PageFrameAllocator.hpp
+    * Memory allocator for physical pages
+    * Copyright (c) 2025 Daniel Hammer
+*/
+
+#pragma once
+#include "Memmap.hpp"
+
+namespace Memory {
+    class PageFrameAllocator {
+        struct Page {
+            std::size_t size;
+            Page* next;
+        };
+
+        Page head{};
+
+        LargestSection g_section;
+public:
+        PageFrameAllocator(LargestSection section);
+
+        void* Allocate();
+        void Free(void* ptr);
+    };
+
+    extern PageFrameAllocator* g_pfa;
+};