From 9a30df58affaa1c00ebdc77693ffe6004e507230 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 11 Nov 2025 00:02:58 -0500
Subject: mbr: Transfer to C in protected mode

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 mbr/stage1.asm | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

(limited to 'mbr/stage1.asm')

diff --git a/mbr/stage1.asm b/mbr/stage1.asm
index ea51f22..d0299e4 100644
--- a/mbr/stage1.asm
+++ b/mbr/stage1.asm
@@ -17,9 +17,39 @@ _start:
     call enable_a20
     call disk_load
 
-    jmp 0x0000:0x8000
-    hlt
-    jmp $
+    ;; Enable protected mode
+    mov eax, cr0
+    or al, 1
+    mov cr0, eax
+
+    lgdt [GDTR]
+    jmp 0x8:0x8000
+
+GDT32:
+.null_desc:
+    dw 0x0000
+    dw 0x0000
+    db 0x00
+    db 0b00000000
+    db 0b00000000
+    db 0x00
+.code_desc:
+    dw 0xFFFF
+    dw 0x0000
+    db 0x00
+    db 0b10011010
+    db 0b11001111
+    db 0x00
+.data_desc:
+    dw 0xFFFF
+    dw 0x0000
+    db 0x00
+    db 0b10010010
+    db 0b11001111
+    db 0x00
+GDTR:
+    dw $ - GDT32 - 1
+    dd GDT32
 
 ;;
 ;; Write a string to the screen
-- 
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