1 files changed, 52 insertions, 0 deletions
diff --git a/boot.s b/boot.s
new file mode 100644
index 0000000..daba41f
--- /dev/null
+++ b/boot.s
@@ -0,0 +1,52 @@
+.globl _start
+
+.code16
+_start:
+    cli
+
+    lgdt (gdtr_desc) # 3. Load the GDTR
+
+    mov %cr0, %eax
+    or $1, %al
+    mov %eax, %cr0
+
+    ljmp $0x8, $PModeMain
+
+.align 8
+gdt_start: # 1. Define the GDT table in memory
+    .quad 0x0000000000000000 # Null descriptor (required)
+gdt_code:
+    .word 0xFFFF     # Limit (low)
+    .word 0x0000     # Base (low)
+    .byte 0x00       # Base (middle)
+    .byte 0b10011010 # Access byte (code, ring 0)
+    .byte 0b11001111 # Flags + Limit (high)
+    .byte 0x00       # Base (high)
+gdt_data:
+    .word 0xFFFF
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10010010 # Access byte (data, ring 0)
+    .byte 0b11001111
+    .byte 0x00
+gdt_end:
+
+gdtr_desc: # 2. Define the GDTR descriptor (limit + base)
+    .word gdt_end - gdt_start - 1 # Limit: Size of GDT - 1
+    .long gdt_start  # Base: Linear address of GDT
+
+.code32
+PModeMain:
+    # 5. Load Data Segment Selector (Offset 0x10 in GDT)
+    mov $0x10, %ax
+    mov %ax, %ds
+    mov %ax, %ss
+    mov %ax, %es
+
+    movw $0x0F4A, 0xB8000       # Write 'J' to the top-left pixel
+
+    hang:
+        jmp hang
+
+.fill 510 - (. - _start), 1, 0 
+.word 0xAA55