new OS

bootloader/boot.asm

@@ -0,0 +1,67 @@
+[BITS 16]
+[ORG 0x7C00]
+
+start:
+    cli
+    xor ax, ax
+    mov ds, ax
+    mov es, ax
+    mov ss, ax
+    mov sp, 0x7C00
+
+    call enable_a20
+    call setup_gdt
+    call switch_to_pm
+
+; ----------------------
+; A20 Gate Enable (Fast method)
+enable_a20:
+    in al, 0x92
+    or al, 0x02
+    out 0x92, al
+    ret
+
+; ----------------------
+; Set up a minimal GDT
+gdt_start:
+    dq 0x0000000000000000          ; null descriptor
+    dq 0x00CF9A000000FFFF          ; code segment descriptor
+    dq 0x00CF92000000FFFF          ; data segment descriptor
+
+gdt_descriptor:
+    dw gdt_end - gdt_start - 1     ; size of GDT
+    dd gdt_start                   ; address of GDT
+
+gdt_end:
+
+setup_gdt:
+    lgdt [gdt_descriptor]
+    ret
+
+; ----------------------
+; Switch to Protected Mode
+switch_to_pm:
+    cli
+    mov eax, cr0
+    or eax, 1
+    mov cr0, eax
+    jmp 0x08:protected_mode_entry
+; ----------------------
+; 32-bit Protected Mode Entry Point
+[BITS 32]
+protected_mode_entry:
+    mov ax, 0x10       ; data segment selector
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+    mov esp, 0x90000
+
+    ; Kernel is assumed to be loaded at 0x100000
+    jmp 0x08:0x100000
+
+; ----------------------
+; Boot signature
+times 510 - ($ - $$) db 0
+dw 0xAA55

bootloader/linker.ld

@@ -0,0 +1,17 @@
+ENTRY(start)
+
+SECTIONS {
+    . = 1M;
+
+    .text : {
+        *(.multiboot)
+        *(.text*)
+    }
+
+    .rodata : { *(.rodata*) }
+    .data : { *(.data*) }
+    .bss : {
+        *(.bss*)
+        *(COMMON)
+    }
+}