Revert "Kernel: Move Kernel mapping to 0xc0000000"

This reverts commit bd33c66273.

This broke the network card drivers, since they depended on kmalloc
addresses being identity-mapped.

Kernel/Arch/i386/Boot/boot.S

@@ -34,9 +34,9 @@ stack_top:
 .section .page_tables
 .align 4096
 page_tables_start:
-.skip 4096*5
+.skip 4096*3
 
-.section .text.boot
+.section .text
 
 .global start
 .type start, @function
@@ -51,79 +51,13 @@ start:
     cli
     cld
 
-    # We first save the multiboot_info_ptr so it doesn't get trampled
-    addl $0xc0000000, %ebx
-    movl %ebx, multiboot_info_ptr - 0xc0000000
-
-    # First, let's set up the first page table to map the the first 4MiB of memory. 
-    # This makes sure we don't crash after we set CR3 and enable paging
-    movl $0x200, %ecx
-    xor %ebx, %ebx
-    movl $((page_tables_start + (4096 * 1)) - 0xc0000000), %edx
-    call make_table
-
-    # Now we create the kernel mappings. The kernel maps 0MiB -> 8MiB into its address space at 
-    # v0xc0000000. 
-    movl $0x400, %ecx
-    movl $0x0, %ebx # ebx is the base pointer (kernel base is at physical address 0 in this case)
-    movl $((page_tables_start + (4096 * 2)) - 0xc0000000), %edx
-    call make_table
-
-    movl $0x400, %ecx
-    movl $0x400000, %ebx # ebx is the base pointer (kernel base is at physical address 0 in this case)
-    movl $((page_tables_start + (4096 * 3)) - 0xc0000000), %edx
-    call make_table
-        
-    
-    # Okay, so we have a page table that contains addresses of the first 4MiB of memory. Let's insert this into the 
-    # boot page directory. The index we need to insert it into is at vaddr >> 22, which is the page directory index.
-    # This reveals that we need to insert the page directory into 0xc0000000 >> 22 = 768
-    # An interesting quirk is that we must also identity map the first 4MiB too, as the next instruction after enabling
-    # paging is at a physical address, which cause a page fault. As we have no handler, this would cause a triple fault.
-    movl $((page_tables_start + (4096 * 1)) - 0xc0000000 + 0x003), page_tables_start - 0xc0000000 + 0
-    movl $((page_tables_start + (4096 * 2)) - 0xc0000000 + 0x003), page_tables_start - 0xc0000000 + 768 * 4
-    movl $((page_tables_start + (4096 * 3)) - 0xc0000000 + 0x003), page_tables_start - 0xc0000000 + 769 * 4
-
-    # Now let's load the CR3 register with our page directory
-    movl $(page_tables_start - 0xc0000000), %ecx
-    movl %ecx, %cr3
-
-    # Let's enable paging!
-    movl %cr0, %ecx
-    orl $0x80000001, %ecx
-    movl %ecx, %cr0 
-
-    lea high_address_space_start, %ecx
-    jmp *%ecx
-
-
-# Make a page table. This is called with the following arguments:
-# ebx = base pointer of mapping
-# edx = page table physical address
-# ecx = number of pages to map
-#
-# Registers used in function
-# eax = loop counter
-make_table:
-    xorl %eax, %eax
-    .loop:
-        pushl %ecx
-        movl %ebx, %ecx
-        orl $0x3, %ecx # addr | READ_WRITE | PAGE_PRESENT
-        movl %ecx, 0(%edx, %eax, 4)
-        addl $0x1000, %ebx
-        inc %eax
-        popl %ecx
-        loop .loop
-    ret
-
-# At this point, the CPU now starts reading instructions from (virtual) address 0xc00100000 
-high_address_space_start:
     mov $stack_top, %esp
 
     and $-16, %esp
 
-    pushl $(page_tables_start - 0xc0000000)
+    mov %ebx, multiboot_info_ptr
+
+    pushl $page_tables_start
     call init
     add $4, %esp
 

Kernel/Arch/i386/CPU.h

@@ -8,8 +8,6 @@
 #define PAGE_SIZE 4096
 #define PAGE_MASK 0xfffff000
 
-static const u32 kernel_virtual_base = 0xc0000000;
-
 class MemoryManager;
 class PageTableEntry;
 
@@ -91,7 +89,6 @@ class PageDirectoryEntry {
 
 public:
     PageTableEntry* page_table_base() { return reinterpret_cast<PageTableEntry*>(m_raw & 0xfffff000u); }
-    PageTableEntry* page_table_virtual_base() { return reinterpret_cast<PageTableEntry*>((m_raw + kernel_virtual_base) & 0xfffff000u); }
     void set_page_table_base(u32 value)
     {
         m_raw &= 0xfff;