Implement first-pass simple virtual memory manager

src/kernel/memory.cpp

@@ -3,9 +3,50 @@
 #include "memory.h"
 #include "memory_pages.h"
 
-memory_manager g_memory_manager;
+memory_manager g_kernel_memory_manager;
 
-memory_manager::memory_manager()
+struct memory_allocation_header
+{
+	uint64_t pages;
+	uint64_t reserved;
+	uint8_t data[0];
+} __attribute__ ((packed));
+
+memory_manager::memory_manager() :
+	m_start(nullptr),
+	m_length(0)
 {
-	kassert(this == &g_memory_manager, "Attempt to create another memory_manager.");
+}
+
+memory_manager::memory_manager(void *start, size_t length) :
+	m_start(start),
+	m_length(length)
+{
+}
+
+void *
+memory_manager::allocate(size_t length)
+{
+	length = page_align(length + sizeof(memory_allocation_header));
+
+	if (length > m_length) return nullptr;
+
+	m_length -= length;
+	memory_allocation_header *header =
+		reinterpret_cast<memory_allocation_header *>(m_start);
+	m_start = reinterpret_cast<uint8_t *>(m_start) + length;
+
+	size_t pages = length / page_manager::page_size;
+	g_page_manager.map_pages(
+			reinterpret_cast<page_manager::addr_t>(header),
+			pages);
+
+	header->pages = pages;
+	return &header->data;
+}
+
+void
+memory_manager::free(void *p)
+{
+	// In this simple version, we don't care about freed pointers
 }