From fbdbbc5345749cb1527928227100f79d21783bf4 Mon Sep 17 00:00:00 2001
From: pantonshire <tom@tomandtally.co.uk>
Date: Sun, 7 Jul 2024 18:07:18 +0100
Subject: [PATCH] jump to stage 2 bootloader

---
 boot0.s | 39 +++++++--------------------------------
 1 file changed, 7 insertions(+), 32 deletions(-)

diff --git a/boot0.s b/boot0.s
index 92523d0..dc01ff5 100644
--- a/boot0.s
+++ b/boot0.s
@@ -222,7 +222,7 @@ STAGE2_GPT_ENTRY_ADDR  equ 0x1a
 
   ; Compare entry GUID to our stage 2 partition GUID.
   mov cx, GUID_LEN
-  mov si, guid_linux
+  mov si, guid_stage2
   mov di, ax
   repe cmpsb
   je .found_stage2
@@ -257,22 +257,13 @@ STAGE2_GPT_ENTRY_ADDR  equ 0x1a
 
   mov bx, 0x8200
   call .read_lba
-  ; TODO: jump to the sector we just read
-
-  mov al, [0x7e00]
-  mov byte fs:[0x0000], al
-
-  mov al, [0x8000]
-  mov byte fs:[0x0002], al
-
-  hlt
+  jmp bx
 
   ; Load a single boot disk sector. Panic on failure.
   ; Inputs:
   ; - ax: LBA to load
   ; - bx: address to read sector to
-  ; Clobber: ax, cx, dx. Possibly bx? TODO: double check
-  ; ngl probably best to assume everything is clobbered because it's a bios interrupt
+  ; Clobber: ax, cx, dx
 .read_lba:
   ; sector - 1 = LBA  % sectors_per_track
   ; temp       = LBA  / sectors_per_track
@@ -305,29 +296,13 @@ STAGE2_GPT_ENTRY_ADDR  equ 0x1a
   mov word fs:[0x0000], 0x4f21
   hlt
 
-  ; TODO: enable A20
-
-  ; TODO: load a second stage
-
-  ; TODO: grab all the info we can from bios interrupts and deliver it to ths OS nicely
-  ; e.g. in a fixed memory location
-
-  ; TODO:
-  ; - Generate GPT in justfile
-  ; - Parse global parition table
-  ; - Load second stage from GPT partition with a particular UUID / name like GRUB does
-  ;   (it's Hah!IdontNeedEFI in GRUB)
-  ;   - https://en.wikipedia.org/wiki/BIOS_boot_partition
-  ; - Future work:
-  ;   - Boot from UEFI
-  ;   - Boot on non-GPT partitioned disk
-
 gpt_magic     db "EFI PART"
 GPT_MAGIC_LEN equ $ - gpt_magic
 
-guid_linux db 0xaf, 0x3d, 0xc6, 0x0f, 0x83, 0x84, 0x72, 0x47, \
-              0x8e, 0x79, 0x3d, 0x69, 0xd8, 0x47, 0x7d, 0xe4
-GUID_LEN   equ $ - guid_linux
+; Our stage2 guid: fdffea69-3651-442f-a11d-88a09bf372dd
+guid_stage2 db 0x69, 0xea, 0xff, 0xfd, 0x51, 0x36, 0x2f, 0x44, \
+               0xa1, 0x1d, 0x88, 0xa0, 0x9b, 0xf3, 0x72, 0xdd
+GUID_LEN   equ $ - guid_stage2
 
   ; MBR bootstrap field is 440 bytes long
   %if ($ - $$) > 440