From 358837ed690ec5da3325c963acff4366f83869bb Mon Sep 17 00:00:00 2001
From: "Justin C. Miller" <justin@devjustinian.com>
Date: Sat, 28 Apr 2018 02:17:17 -0700
Subject: [PATCH] Implement first-pass simple virtual memory manager

---
 src/kernel/main.cpp         |  4 ++++
 src/kernel/memory.cpp       | 47 ++++++++++++++++++++++++++++++++++---
 src/kernel/memory.h         | 27 +++++++++++++++++++--
 src/kernel/memory_pages.cpp | 13 ++++++++++
 4 files changed, 86 insertions(+), 5 deletions(-)

diff --git a/src/kernel/main.cpp b/src/kernel/main.cpp
index c33848e..44d8669 100644
--- a/src/kernel/main.cpp
+++ b/src/kernel/main.cpp
@@ -54,6 +54,10 @@ kernel_main(popcorn_data *header)
 			header->memory_map_length,
 			header->memory_map_desc_size);
 
+	size_t n = 5000;
+	void *p = kalloc(n);
+	g_console.printf("kalloc'd %d bytes at %lx\n", n, p);
+
 	interrupts_init();
 	interrupts_enable();
 
diff --git a/src/kernel/memory.cpp b/src/kernel/memory.cpp
index 2a99900..6ef373c 100644
--- a/src/kernel/memory.cpp
+++ b/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
 }
diff --git a/src/kernel/memory.h b/src/kernel/memory.h
index 0df400d..7a94286 100644
--- a/src/kernel/memory.h
+++ b/src/kernel/memory.h
@@ -3,21 +3,44 @@
 /// The block memory manager and related definitions.
 
 #include <stddef.h>
+#include <stdint.h>
+
+struct memory_block_node;
 
 /// Manager for allocation of virtual memory.
 class memory_manager
 {
 public:
 	memory_manager();
+	memory_manager(void *start, size_t length);
 
-	memory_manager(const memory_manager &) = delete;
+	/// Allocate memory from the area managed.
+	/// \arg length  The amount of memory to allocate, in bytes
+	/// \returns     A pointer to the allocated memory, or nullptr if
+	///              allocation failed.
+	void * allocate(size_t length);
+
+	/// Free a previous allocation.
+	/// \arg p  A pointer previously retuned by allocate()
+	void free(void *p);
 
 private:
 	friend class page_manager;
+
+	// Simple incrementing pointer.
+	void *m_start;
+	size_t m_length;
+
+	memory_manager(const memory_manager &) = delete;
 };
 
-extern memory_manager g_memory_manager;
+extern memory_manager g_kernel_memory_manager;
 
 /// Bootstrap the memory managers.
 void memory_initialize_managers(const void *memory_map, size_t map_length, size_t desc_length);
 
+/// Allocate kernel space memory.
+/// \arg length  The amount of memory to allocate, in bytes
+/// \returns     A pointer to the allocated memory, or nullptr if
+///              allocation failed.
+inline void * kalloc(size_t length) { return g_kernel_memory_manager.allocate(length); }
diff --git a/src/kernel/memory_pages.cpp b/src/kernel/memory_pages.cpp
index 2a41642..00e19ff 100644
--- a/src/kernel/memory_pages.cpp
+++ b/src/kernel/memory_pages.cpp
@@ -2,6 +2,7 @@
 
 #include "assert.h"
 #include "console.h"
+#include "memory.h"
 #include "memory_pages.h"
 
 page_manager g_page_manager;
@@ -224,6 +225,18 @@ page_manager::init(
 	page_block::dump(m_used, "used", true);
 	page_block::dump(m_free, "free", true);
 
+	// Initialize the kernel memory manager
+	addr_t end = 0;
+	for (page_block *b = m_used; b; b = b->next) {
+		if (b->virtual_address < page_offset)
+			end = b->virtual_end();
+		else
+			break;
+
+	}
+	new (&g_kernel_memory_manager) memory_manager(
+			reinterpret_cast<void *>(end),
+			page_offset - end);
 }
 
 void