@@ -28,6 +28,9 @@ # print hello world
   movw $message, %si
   call print
 
+  # TODO:
+  # - activate A20 gate
+
   # reset bootdrive
 reset:
   movb $0x00, %ah
@@ -62,9 +65,20 @@ xor %ax, %ax
   mov %ax, %ds
   mov %ax, %es
 
+  # - load global descriptor table and far jump into protected mode
+  lgdt (GDT_DESCRIPTOR)
+
+  mov %cr0, %eax
+  or $1, %eax
+  mov %eax, %cr0
+
+  ljmp $0x8, $protected
+
+.code32
+protected:
+
+
   # TODO:
-  # - load global descriptor table and far jump into protected mode
-  # - activate A20 gate
   # - jump to second stage code
 
 
@@ -72,6 +86,7 @@ # loop forever
 loop:
   jmp loop
 
+.code16
 
   # ############################################
   # print
@@ -98,6 +113,10 @@ .ascii "Hello World!"
   .byte 13
   .byte 10
   .byte 0
+
+GDT_DESCRIPTOR:
+  .int GDT
+  .word 0x23
 
 end:
   .=510

@@ -3,3 +3,12 @@
 .PHONY: build
 build: boot.s
 > $(GCC_PREFIX)as -o $(BUILD_DIR)/boot.o boot.s
+
+.PHONY: clear
+clear:
+> @rm build/*.* 2> /dev/null; true
+
+.PHONY: rebuild
+rebuild:
+> $(MAKE) clear
+> $(MAKE) build

@@ -2,9 +2,11 @@ .RECIPEPREFIX = >
 
 export CURRENT_DIR		= $(shell pwd)
 export BUILD_DIR		= $(CURRENT_DIR)/build
+export INCLUDE_DIR		= $(CURRENT_DIR)/include
+export DEBUG_DIR		= $(CURRENT_DIR)/debug
 
 export GCC_PREFIX		= $(HOME)/opt/cross/i686-elf-/bin/i686-elf-
-export GCC_OPTIONS		= -O0 -std=c++0x -Wno-write-strings -Wall -Wextra -fno-exceptions -fno-rtti -ffreestanding
+export GCC_OPTIONS		= -O0 -Wno-write-strings -Wall -Wextra -fno-exceptions -nostdlib -nostartfiles -ffreestanding
 
 # OBJ_FILES = $(wildcard obj/asm/*.o) $(wildcard obj/cpp/*.o)
 
@@ -12,11 +14,13 @@ .PHONY: build
 build:
 > $(MAKE) -C boot build
 > $(MAKE) -C second_stage build
-> $(GCC_PREFIX)ld -T link.txt -Map=mapfile.txt -o $(BUILD_DIR)/base.img --oformat binary
+> $(GCC_PREFIX)ld -T link.txt -Map=$(DEBUG_DIR)/mapfile.txt -o $(BUILD_DIR)/base.img --oformat binary
 
 .PHONY: clear
 clear:
 > @rm $(BUILD_DIR)/*.* 2> /dev/null; true
+> @$(MAKE) -C boot clear 2> /dev/null; true
+> @$(MAKE) -C second_stage clear 2> /dev/null; true
 
 .PHONY: run
 run:

@@ -1,8 +1,10 @@
 .section .text
-start:
-# loop:
-#   jmp loop
+.global _start
+_start:
+loop:
+  jmp loop
 
+.section .data
 low_kernel_welcome:
   .ascii "Welcome to the low kernel!"
   .byte 13

@@ -0,0 +1,23 @@
+#include "gdt.h"
+
+#define GDT_MAKE_ENTRY(base, limit, access, flags) { \
+        (uint8_t)(limit >> 0), \
+        (uint8_t)(limit >> 8), \
+        (uint8_t)(base >> 0), \
+        (uint8_t)(base >> 8), \
+        (uint8_t)(base >> 16), \
+        (uint8_t)(access), \
+        (uint8_t)(((limit >> 16) & 0x0F) | ((flags << 4) & 0xF0)), \
+        (uint8_t)(base >> 24), \
+    }
+
+GDT_ENTRY GDT[3] = {
+    // null descriptor
+    GDT_MAKE_ENTRY(0x00000000, 0x00000000, 0x00, 0x0),
+
+    // identity mapping (code)
+    GDT_MAKE_ENTRY(0x00000000, 0x000FFFFF, 0x9A, 0xC),
+
+    // identity mapping (data)
+    GDT_MAKE_ENTRY(0x00000000, 0x000FFFFF, 0x92, 0xC)
+};

@@ -0,0 +1,27 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include "stdint.h"
+
+typedef struct {
+    uint8_t limit_0;
+    uint8_t limit_8;
+    uint8_t base_0;
+    uint8_t base_8;
+    uint8_t base_16;
+    uint8_t access;
+    uint8_t limit_and_flags;
+    uint8_t base_24;
+} __attribute__((packed)) GDT_ENTRY;
+
+GDT_ENTRY GDT[3];
+
+/*struct {
+    uint32_t gdt_offset;
+    uint16_t gdt_size;
+} GDT_DESCRIPTOR = {
+    (uint32_t)GDT,
+    (uint16_t)(sizeof GDT)
+};*/
+
+#endif

@@ -0,0 +1,19 @@
+INPUT(build/entry.o build/gdt.o)
+OUTPUT_FORMAT(elf32-i386)
+OUTPUT_ARCH(i386)
+ENTRY(_start)
+
+SECTIONS
+{
+  .text : 
+  {
+      build/entry.o(.text)
+      build/gdt.o(.text)
+  }
+
+  .data :
+  {
+      build/entry.o(.data)
+      build/gdt.o(.data)
+  }
+}

@@ -1,8 +1,20 @@
 .RECIPEPREFIX = >
 
 .PHONY: build
-build: build/entry.o
-> $(GCC_PREFIX)ld -i build/entry.o -o $(BUILD_DIR)/second_stage.o --oformat elf32-i386
+build: build/entry.o build/gdt.o
+> $(GCC_PREFIX)ld -T link.txt -o $(BUILD_DIR)/second_stage.o --oformat elf32-i386
+
+.PHONY: clear
+clear:
+> @rm build/*.* 2> /dev/null; true
+
+.PHONY: rebuild
+rebuild:
+> $(MAKE) clear
+> $(MAKE) build
 
 build/entry.o: entry.s
-> $(GCC_PREFIX)as -o $@ $?+> $(GCC_PREFIX)as -o $@ $<
+
+build/gdt.o: gdt.c gdt.h
+> $(GCC_PREFIX)gcc -I$(INCLUDE_DIR) --prefix=$(GCC_PREFIX) $(GCC_OPTIONS) -o $@ $<