wrote a basic bootloader

2025-02-25 01:14:52 +00:00
commit 012b0454ed
36 changed files with 1667 additions and 0 deletions
@@ -0,0 +1,55 @@
+[BITS 16]
+[ORG 0x7c00]
+start:
+    mov ah,0x00 ; set mode
+    mov al,0x03 ; set vga text buffer mode (80x25)
+    int 0x10    ; call bios
+
+    cli
+
+    in al, 0x92
+    or al, 2
+    out 0x92, al
+
+    xor ax, ax
+    mov ds, ax
+
+    lgdt [GDT_PTR]
+
+    mov eax, 0x11
+    mov cr0, eax
+    jmp GDT_BOOT_CS-GDT:protmode
+
+[BITS 32]
+protmode:
+    mov ax, GDT_BOOT_DS-GDT
+    mov ds, ax
+    mov ss, ax
+    mov es, ax
+    mov esp, 0x90000 ; temporary stack
+
+    mov edi, 0xb8000
+    mov eax, "P R "
+    stosd
+
+hang:
+    pause
+    jmp hang
+
+GDT_PTR:
+    dw GDT_END-GDT-1
+    dd GDT
+
+
+align 16
+GDT:
+
+    GDT_NULL: dq 0 ; segment zero cannot be used
+    GDT_BOOT_DS: dq 0X00CF92000000FFFF
+    GDT_BOOT_CS: dq 0X00CF9A000000FFFF
+
+    GDT_END:
+
+times 510-$+start db 0;
+db 0x55;
+db 0xaa;