Paging now works. Is initially bootstrapped by GRUB then later OS accessible.

Some memory maybe wasted on bootstrap page table?

kernel/arch/i386/boot.s

@@ -10,16 +10,53 @@
 .long FLAGS
 .long CHECKSUM
 
-.section .bss
+.section .bootstrap_stack, "aw", @nobits
 .align 16
 stack_bottom:
 .skip 16384 # 16 KiB
 stack_top:
 
+.section .bss, "aw", @nobits
+.align 4096
+boot_pagedir:
+	.skip 4096
+boot_pagetab1:
+	.skip 4096
+
 .section .text
 .global _start
 .type _start, @function
 _start:
+  mov $(boot_pagetab1 - 0xC0000000), %edi
+  mov $0, %esi
+  mov $1023, %ecx
+1:
+  cmp $(_kernel_start - 0xC0000000), %esi
+	jl 2f
+	cmp $(_kernel_end - 0xC0000000), %esi
+	jge 3f
+  mov %esi, %edx
+	or $0x003, %edx
+	mov %edx, (%edi)
+2:
+  add $4096, %esi
+  add $4, %edi
+  loop 1b
+3:
+	movl $(boot_pagetab1 - 0xC0000000 + 0x003), boot_pagedir - 0xC0000000 + 0
+	movl $(boot_pagetab1 - 0xC0000000 + 0x003), boot_pagedir - 0xC0000000 + 768 * 4
+	movl $(boot_pagedir - 0xC0000000), %ecx
+	mov %ecx, %cr3
+	mov %cr0, %ecx
+	or $0x80010000, %ecx
+	mov %ecx, %cr0
+	lea 4f, %ecx
+	jmp *%ecx
+
+4:
+	movl $0, boot_pagedir + 0
+	mov %cr3, %ecx
+	mov %ecx, %cr3
 	mov $stack_top, %esp
 	call kernel_main
 	cli

kernel/arch/i386/interrupts.nim

@@ -84,11 +84,11 @@ macro generateISR(code: static[int], isError: static[bool]): typed =
               newIdentNode("writeLine")
             ),
             newLit(code)
-          ),
-          nnkAsmStmt.newTree(
-            newEmptyNode(),
-            newLit((if isError: "" else: "push 0\x0A") & "push " & $code & "\x0A")
-          )
+          )#,
+          #nnkAsmStmt.newTree(
+          #  newEmptyNode(),
+          #  newLit((if isError: "" else: "push 0\x0A") & "push " & $code & "\x0A")
+          #)
         )
       )
     )

kernel/arch/i386/linker.ld

@@ -4,28 +4,29 @@ OUTPUT_FORMAT(elf32-i386)
 
 SECTIONS
 {
-	. = 0x00100000;
-
-	.text BLOCK(4K) : ALIGN(4K)
+	. = 0xC0100000;
+  _kernel_start = .;
+	.text ALIGN(4K) : AT(ADDR(.text) - 0xC0000000)
 	{
 		*(.multiboot)
 		*(.text)
 	}
 
-	.rodata BLOCK(4K) : ALIGN(4K)
+	.rodata ALIGN(4K) : AT(ADDR(.rodata) - 0xC0000000)
 	{
 		*(.rodata)
 	}
 
-	.data BLOCK(4K) : ALIGN(4K)
+	.data ALIGN(4K) : AT(ADDR(.data) - 0xC0000000)
 	{
 		*(.data)
 	}
 
-	.bss BLOCK(4K) : ALIGN(4K)
+	.bss ALIGN(4K) : AT(ADDR(.bss) - 0xC0000000)
 	{
 		*(COMMON)
 		*(.bss)
+    *(.bootstrap_stack)
 	}
-
+  _kernel_end = .;
 }

kernel/arch/i386/paging.nim

@@ -10,7 +10,7 @@ const
   blankPageDirectory: PageDirectoryEntry = 0x00000002
 
 var
-  pageDirectory{.exportc, codegenDecl: "$# $# __attribute__((aligned(0x1000)))".}: PageDirectory
+  pageDirectory: ptr PageDirectory
   pageTable0{.exportc, codegenDecl: "$# $# __attribute__((aligned(0x1000)))".}: PageTable
 
 proc createEntry(address: uint32, present: bool = false, readWrite: bool = false, userAccessible: bool = false, writeThrough: bool = false, disableCache: bool = false): uint32 =
@@ -31,19 +31,32 @@ proc loadPageDirectory(address: uint32){.inline.} =
   serial.writeLine("Loading paging data")
   asm """
     mov %%cr3, %%eax
-    mov %%eax, %%cr0
-    or $0x80000001, %%eax
-    mov %%cr0, %%eax
     ::"a"(`address`)
   """
 
+# Converts a physical to a virtual address for the kernel
+proc toVirtual(address: uint32): uint32 =
+  result = address + 0xC0000000'u32
+
+# Converts a physical to a virtual address for the kernel
+proc toPhysical(address: uint32): uint32 =
+  result = address - 0xC0000000'u32
+
+# Each page starts from a multiple of 0x400000  769
 proc init*() =
   serial.writeLine("Initialising paging tables and directories.")
-  for i in 0..1023:
-    pageDirectory[i] = blankPageDirectory
+  var pagingAddress: uint32 = 0
+  # Find the bootstrapped page directory
+  asm """
+    mov %%cr3, %%eax
+    :"=a"(`pagingAddress`)
+  """
+  pageDirectory = cast[ptr PageDirectory](toVirtual(pagingAddress))
+  for i in 0..767:
+    pageDirectory[][i] = blankPageDirectory
   for i in 0..1023:
     pageTable0[i] = createEntry(address = uint32(i) * 0x1000, readWrite = true, present = true)
-  pageDirectory[0] = createDirectory(address = cast[uint32](pageTable0), readWrite = true, present = true)
-  loadPageDirectory(cast[uint32](pageDirectory.addr))
-  serial.write("Paging setup complete at ")
-  serial.writeLine(cast[uint32](pageDirectory.addr))
+  pageDirectory[][768] = createDirectory(address = toPhysical(cast[uint32](pageTable0.addr)), readWrite = true, present = true)
+  for i in 769..1023:
+    pageDirectory[][i] = blankPageDirectory
+  loadPageDirectory(pagingAddress)

kernel/arch/i386/tty.nim

@@ -8,7 +8,7 @@ type
   VGAMemory = ptr array[0..(vgaWidth * vgaHeight - 1), VGADoubleByte]
 
 const
-  terminalBufferBaseAddress = 0xB8000
+  terminalBufferBaseAddress = 0xC00B8000
   vgaMem = cast[VGAMemory](terminalBufferBaseAddress)
 
 var

kernel/kernel.nim

@@ -25,16 +25,17 @@ proc getMemoryMap(mbd: multiboot_info) =
 
 #proc kernelMain(mbd: multiboot_info, magic: uint) {.exportc: "kernel_main"}=
 proc kernelMain() {.exportc: "kernel_main"}=
+  paging.init()
   serial.init()
   serial.writeLine("Version:" & (version))
   serial.writeLine("Booting OS")
   #getMemoryMap(mbd)
-  #paging.init()
   gdt.gdtInstall()
   serial.writeLine("GDT installed")
   interrupts.idtInstall()
   serial.writeLine("IDT installed")
   tty.init()
+  serial.writeLine("TTY initialised")
   tty.writeLine("Version:" & version)
   tty.writeLine("Hello World!")
   tty.write("MAX_INT:")