gdt: add and setup a global descriptor table

Makefile

@@ -30,7 +30,13 @@ ASM_OBJ=$(subst src/, build/, ${ASM_SRC:.asm=.o})
 all: $(KERNEL)
 
 run: $(ISO)
-	@qemu-system-x86_64 -drive format=raw,file=$(ISO) -serial stdio
+	@qemu-system-i386 -drive format=raw,file=$(ISO) -serial stdio
+
+rund: $(ISO)
+	@qemu-system-i386 -drive format=raw,file=$(ISO) -serial stdio -d int
+
+rundd: $(ISO)
+	@qemu-system-i386 -drive format=raw,file=$(ISO) -serial stdio -d int -s -S
 
 iso: $(ISO)
 

src/arch/i686/gdt.asm

@@ -0,0 +1,17 @@
+global _gdt_flush
+extern _gp
+
+_gdt_flush:
+	lgdt [_gp]
+
+	mov ax, 0x10
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
+
+	jmp 0x08:complete_flush
+
+complete_flush:
+	ret

src/elsos.rs

@@ -11,6 +11,7 @@ mod keyboard;
 mod tty;
 mod multiboot;
 mod serial;
+mod gdt;
 
 use core::panic::PanicInfo;
 
@@ -34,6 +35,8 @@ pub static mut SETTINGS: Settings = Settings
 #[no_mangle]
 pub extern "C" fn kernel_main(magic: u32, address: u32)
 {
+
+	gdt::init_gdt();
 	init_vga();
 	vga::cursor::Cursor::init(0, 15);
 	if multiboot::check_magic(magic) && multiboot::parse(address)

src/gdt.rs

@@ -0,0 +1,123 @@
+use core::mem::size_of;
+
+#[repr(C, packed)]
+struct gdt_ptr
+{
+    limit: u16,
+    base: u32
+}
+
+#[repr(C, packed)]
+struct gdt_entry
+{
+    limit0: u16,
+    base0: u16,
+    base1: u8,
+    access_byte: u8,
+    limit1_flags: u8,
+    base2: u8
+}
+
+#[repr(C, packed)]
+struct gdt
+{
+    null: gdt_entry,
+    kernel_code: gdt_entry,
+    kernel_data: gdt_entry,
+	kernel_stack: gdt_entry,
+    user_code: gdt_entry,
+    user_data: gdt_entry,
+	user_stack: gdt_entry,
+}
+
+static mut GDT_TABLE: gdt = gdt
+{
+    null: gdt_entry
+    {
+        limit0: 0,
+        base0: 0,
+        base1: 0,
+        access_byte: 0x00,
+        limit1_flags: 0x00,
+        base2: 0
+    },
+    kernel_code: gdt_entry
+    {
+        limit0: 0xffff,
+        base0: 0,
+        base1: 0,
+        access_byte: 0x9a,
+        limit1_flags: 0xcf,
+        base2: 0
+    },
+    kernel_data: gdt_entry
+    {
+        limit0: 0xffff,
+        base0: 0,
+        base1: 0,
+        access_byte: 0x92,
+        limit1_flags: 0xcf,
+        base2: 0
+    },
+	kernel_stack: gdt_entry
+	{
+		limit0: 0xffff,
+		base0: 0,
+		base1: 0,
+		access_byte: 0x92,
+		limit1_flags: 0xcf,
+		base2: 0
+	},
+    user_code: gdt_entry
+    {
+        limit0: 0xffff,
+        base0: 0,
+        base1: 0,
+        access_byte: 0x9a,
+        limit1_flags: 0xcf,
+        base2: 0
+    },
+    user_data: gdt_entry
+    {
+        limit0: 0xffff,
+        base0: 0,
+        base1: 0,
+        access_byte: 0x92,
+        limit1_flags: 0xcf,
+        base2: 0
+    },
+    user_stack: gdt_entry
+    {
+        limit0: 0xffff,
+        base0: 0,
+        base1: 0,
+        access_byte: 0x92,
+        limit1_flags: 0xcf,
+        base2: 0
+    },
+};
+
+extern "C"
+{
+    fn _gdt_flush();
+    fn memcpy(dst: *const u8, src: *const u8, size: usize);
+}
+
+#[no_mangle]
+static mut _gp: gdt_ptr = gdt_ptr
+{
+    limit: 0,
+    base: 0x800
+};
+
+pub fn init_gdt()
+{
+    let size = size_of::<gdt>() - 1;
+    unsafe
+    {
+        memcpy(0x800 as *const u8, (&GDT_TABLE as *const _) as *const u8, size);
+        _gp.limit = size as u16;
+        _gdt_flush();
+    }
+}
+