Kernel: Removing hardcoded offsets from Memory Manager

Now the kernel page directory and the page tables are located at a
safe address, to prevent from paging data colliding with garbage.

Kernel/Arch/i386/Boot/boot.S

@@ -31,6 +31,11 @@ stack_bottom:
 .skip 32768
 stack_top:
 
+.section .page_tables
+.align 4096
+page_tables_start:
+.skip 4096*3
+
 .section .text
 
 .global start
@@ -52,7 +57,9 @@ start:
 
  mov %ebx, multiboot_info_ptr
 
+ pushl $page_tables_start
  call init
+ add $4, %esp
 
  pushl $exit_message
  call kprintf

Kernel/VM/MemoryManager.cpp

@@ -20,13 +20,11 @@ MemoryManager& MM
  return *s_the;
 }
 
-MemoryManager::MemoryManager()
+MemoryManager::MemoryManager(u32 physical_address_for_kernel_page_tables)
 {
- // FIXME: Hard-coding these is stupid. Find a better way.
- m_kernel_page_directory = PageDirectory::create_at_fixed_address(PhysicalAddress(0x4000));
- m_page_table_zero = (PageTableEntry*)0x6000;
- m_page_table_one = (PageTableEntry*)0x7000;
-
+ m_kernel_page_directory = PageDirectory::create_at_fixed_address(PhysicalAddress(physical_address_for_kernel_page_tables));
+ m_page_table_zero = (PageTableEntry*)(physical_address_for_kernel_page_tables + PAGE_SIZE);
+ m_page_table_one = (PageTableEntry*)(physical_address_for_kernel_page_tables + PAGE_SIZE * 2);
  initialize_paging();
 
  kprintf("MM initialized.\n");
@@ -262,9 +260,9 @@ void MemoryManager::create_identity_mapping(PageDirectory& page_directory, Virtu
  }
 }
 
-void MemoryManager::initialize()
+void MemoryManager::initialize(u32 physical_address_for_kernel_page_tables)
 {
- s_the = new MemoryManager;
+ s_the = new MemoryManager(physical_address_for_kernel_page_tables);
 }
 
 Region* MemoryManager::kernel_region_from_vaddr(VirtualAddress vaddr)

Kernel/VM/MemoryManager.h

@@ -38,7 +38,7 @@ class MemoryManager {
 public:
  static MemoryManager& the();
 
- static void initialize();
+ static void initialize(u32 physical_address_for_kernel_page_tables);
 
  PageFaultResponse handle_page_fault(const PageFault&);
 
@@ -79,7 +79,7 @@ class MemoryManager {
  }
 
 private:
- MemoryManager();
+ MemoryManager(u32 physical_address_for_kernel_page_tables);
  ~MemoryManager();
 
  void register_vmo(VMObject&);

Kernel/init.cpp

@@ -206,7 +206,7 @@ extern "C" int __cxa_atexit ( void (*)(void *), void *, void *)
  return 0;
 }
 
-extern "C" [[noreturn]] void init()
+extern "C" [[noreturn]] void init(u32 physical_address_for_kernel_page_tables)
 {
  // this is only used one time, directly below here. we can't use this part
  // of libc at this point in the boot process, or we'd just pull strstr in
@@ -268,7 +268,7 @@ extern "C" [[noreturn]] void init()
 
  kprintf("Starting Serenity Operating System...\n");
 
- MemoryManager::initialize();
+ MemoryManager::initialize(physical_address_for_kernel_page_tables);
 
  if (APIC::init())
  APIC::enable(0);

Kernel/linker.ld

@@ -8,6 +8,7 @@ SECTIONS
  {
  Arch/i386/Boot/boot.ao
  *(.multiboot)
+ *(.page_tables)
  *(.text)
  *(.text.startup)
  }