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 @@ public:
     }
 
 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)
 	}