GDT and IDT now exist in locations that aren't hard coded. Paging currently breaks interrupts.

kernel/arch/i386/gdt.nim

@@ -13,18 +13,20 @@ type
     base: uint32 # GDT memory location
   AccessByte = uint8
   Flags = uint8
+  GDTEntries{.packed.} = array[0..2, GDTEntry]
   GDT{.packed.} = object
     descriptor: GDTPointer
-    entries: array[0..2, GDTEntry]
+    entries: GDTEntries
 
-const
-  gdtAddress: uint32 = 0x800
-  gdt = cast[ptr GDT](gdtAddress)
+var
+  address: uint32
+  gdt: GDT
 
 proc gdtFlush(){.inline,asmNoStackFrame.} =
   asm """
-    lgdt (0x800)
+    lgdt (%%eax)
     ret
+    ::"a"(`address`)
   """
 
 proc gdtSetGate(num: int, base: uint16, limit: uint32, access: AccessByte, flags: Flags) =
@@ -68,7 +70,8 @@ proc gdtInstall*() =
   #gdtSetGate(3, 0'u16, 0xFFFFFFFF'u32, 0xFA, createFlags(true, true));
 
   #gdtSetGate(4, 0'u16, 0xFFFFFFFF'u32, 0xF2, createFlags(true, true));
-  serial.write("GDT Address:")
-  serial.writeLine(gdt.descriptor.base)
   serial.writeLine("Flushing GDT.")
+  address = cast[uint32](gdt.addr)
+  serial.write("GDT Address:")
+  serial.writeLine(address)
   gdtFlush()

kernel/arch/i386/interrupts.nim

@@ -18,14 +18,15 @@ type
       int_no, err_code: uint32                       # Interrupt number and error code (if applicable)
       eip, cs, eflags, useresp, ss: uint32           # Pushed by the processor automatically. 
 
-const
-  idtAddress: uint32 = 0x00000000
-  idt = cast[ptr IDT](idtAddress)
+var
+  address: uint32
+  idt: IDT
 
 proc idtFlush(){.inline,asmNoStackFrame.} =
   asm """
-    lidtl (0x0)
+    lidt (%%eax)
     ret
+    ::"a"(`address`)
   """
 
 #[
@@ -175,4 +176,7 @@ proc idtInstall*() =
   idtSetGate(30, cast[uint32](isr30), selector, flags)
   idtSetGate(31, cast[uint32](isr31), selector, flags)
   serial.writeLine("Flushing IDT.")
+  address = cast[uint32](idt.addr)
+  serial.write("IDT Address:")
+  serial.writeLine(address)
   idtFlush()

kernel/arch/i386/linker.ld

@@ -4,7 +4,7 @@ OUTPUT_FORMAT(elf32-i386)
 
 SECTIONS
 {
-	. = 1M;
+	. = 0x00100000;
 
 	.text BLOCK(4K) : ALIGN(4K)
 	{

kernel/arch/i386/paging.nim

@@ -10,8 +10,8 @@ const
   blankPageDirectory: PageDirectoryEntry = 0x00000002
 
 var
-  pageDirectory: PageDirectory
-  pageTable: PageTable
+  pageDirectory{.exportc, codegenDecl: "$# $# __attribute__((aligned(0x1000)))".}: PageDirectory
+  pageTable0{.exportc, codegenDecl: "$# $# __attribute__((aligned(0x1000)))".}: PageTable
 
 proc createEntry(address: uint32, present: bool = false, readWrite: bool = false, userAccessible: bool = false, writeThrough: bool = false, disableCache: bool = false): uint32 =
   result = address and 0xFFFFF000'u32 # Set attributes section to zero
@@ -21,12 +21,20 @@ proc createEntry(address: uint32, present: bool = false, readWrite: bool = false
   if writeThrough: result = result or 0b1000
   if disableCache: result = result or 0b10000
 
-proc loadPageDirectory(address: uint32){.asmNoStackFrame.} = 
+proc createDirectory(address: uint32, present: bool = false, readWrite: bool = false, userAccessible: bool = false, writeThrough: bool = false, disableCache: bool = false, pageSize: bool = false): uint32 =
+  var checkAddress = address
+  if pageSize: checkAddress = checkAddress and 0xFFFF0000'u32
+  result = createEntry(address, present, readWrite, userAccessible, writeThrough, disableCache)
+  if pageSize: result = result or 0b10000000
+
+proc loadPageDirectory(address: uint32){.inline.} = 
+  serial.writeLine("Loading paging data")
   asm """
-    mov `address`, %cr3
-    mov %cr0, %eax
-    or $0x80000001, %eax
-    mov %eax, %cr0
+    mov %%cr3, %%eax
+    mov %%eax, %%cr0
+    or $0x80000001, %%eax
+    mov %%cr0, %%eax
+    ::"a"(`address`)
   """
 
 proc init*() =
@@ -34,6 +42,8 @@ proc init*() =
   for i in 0..1023:
     pageDirectory[i] = blankPageDirectory
   for i in 0..1023:
-    pageTable[i] = createEntry(address = uint32(i) * 0x1000, readWrite = true, present = true)
-  pageDirectory[0] = createEntry(address = cast[uint32](pageTable), readWrite = true, present = true)
-  loadPageDirectory(cast[uint32](pageDirectory.addr))
+    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))

kernel/kernel.nim

@@ -2,7 +2,7 @@
 {.passL: "-ffreestanding -target i386 -nostdlib -T arch/i386/linker.ld".}
 {.passC: "-ffreestanding -nostdlib --target=i386-pc-none-elf -march=i386".}
 
-import tty, gdt, interrupts, serial, multiboot
+import tty, gdt, interrupts, serial, multiboot, paging
 
 const version {.strdefine.} = "UNKNOWN"
 
@@ -23,11 +23,13 @@ proc memset*(dest: ByteAddress, value: char, count: int){.exportc.} =
 proc getMemoryMap(mbd: multiboot_info) =
   discard # Use this if we need to do anything with the GRUB memory map
 
-proc kernelMain(mbd: multiboot_info, magic: uint) {.exportc: "kernel_main"}=
+#proc kernelMain(mbd: multiboot_info, magic: uint) {.exportc: "kernel_main"}=
+proc kernelMain() {.exportc: "kernel_main"}=
   serial.init()
   serial.writeLine("Version:" & (version))
   serial.writeLine("Booting OS")
-  getMemoryMap(mbd)
+  #getMemoryMap(mbd)
+  #paging.init()
   gdt.gdtInstall()
   serial.writeLine("GDT installed")
   interrupts.idtInstall()
@@ -37,7 +39,7 @@ proc kernelMain(mbd: multiboot_info, magic: uint) {.exportc: "kernel_main"}=
   tty.writeLine("Hello World!")
   tty.write("MAX_INT:")
   tty.writeLine(high(int))
-  tty.write("LMIN_INT:")
+  tty.write("MIN_INT:")
   tty.writeLine((low(int)+1))
   tty.write("MAX_UINT:")
   tty.writeLine(high(uint32))