Refactor memory code.

Break out some more bootstrap code into functions. Add the start of
some Doxygen doc comments to help organize my thoughts.

src/kernel/memory_pages.h

@@ -1,9 +1,12 @@
 #pragma once
+/// \file memory_pages.h
+/// Structures related to handling memory paging.
 
 #include <stdint.h>
 
 #include "kutil/enum_bitfields.h"
 
+/// Flags used by `page_block`.
 enum class page_block_flags : uint32_t
 {
 	// Not a flag value, but for comparison
@@ -22,6 +25,10 @@ enum class page_block_flags : uint32_t
 };
 IS_BITFIELD(page_block_flags);
 
+
+/// A block of contiguous pages. Each `page_block` represents contiguous
+/// physical pages with the same attributes. A `page_block *` is also a
+/// linked list of such structures.
 struct page_block
 {
 	uint64_t physical_address;
@@ -31,15 +38,23 @@ struct page_block
 	page_block *next;
 
 	bool has_flag(page_block_flags f) const { return bitfield_contains(flags, f); }
-	uint64_t end() const { return physical_address + (count * 0x1000); }
+	uint64_t physical_end() const { return physical_address + (count * 0x1000); }
+	uint64_t virtual_end() const { return virtual_address + (count * 0x1000); }
 
+	/// Traverse the list, joining adjacent blocks where possible.
+	/// \returns  A linked list of freed page_block structures.
 	page_block * list_consolidate();
+
+	/// Traverse the list, printing debug info on this list.
+	/// \arg name  [optional] String to print as the name of this list
 	void list_dump(const char *name = nullptr);
 };
 
+
+/// Helper struct for computing page table indices of a given address.
 struct page_table_indices
 {
-	page_table_indices(uint64_t v) :
+	page_table_indices(uint64_t v = 0) :
 		index{
 			(v >> 39) & 0x1ff,
 			(v >> 30) & 0x1ff,
@@ -47,8 +62,18 @@ struct page_table_indices
 			(v >> 12) & 0x1ff }
 	{}
 
+	/// Get the index for a given level of page table.
 	uint64_t & operator[](size_t i) { return index[i]; }
-	uint64_t index[4];
-
-	void dump();
+	uint64_t index[4]; ///< Indices for each level of tables.
 };
+
+/// Calculate a page-aligned address.
+/// \arg p    The address to align.
+/// \returns  The next page-aligned address _after_ `p`.
+template <typename T> inline T page_align(T p)       { return ((p - 1) & ~0xfffull) + 0x1000; }
+
+/// Calculate a page-table-aligned address. That is, an address that is
+/// page-aligned to the first page in a page table.
+/// \arg p    The address to align.
+/// \returns  The next page-table-aligned address _after_ `p`.
+template <typename T> inline T page_table_align(T p) { return ((p - 1) & ~0x1fffffull) + 0x200000; }