From 2cca21750c022e22720a3a8a475848ff89945620 Mon Sep 17 00:00:00 2001
From: pantonshire <tom@tomandtally.co.uk>
Date: Sat, 6 Jul 2024 22:36:04 +0100
Subject: [PATCH] load stage 2 partition start and end

---
 boot0.s | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/boot0.s b/boot0.s
index 7a631ea..8ce7140 100644
--- a/boot0.s
+++ b/boot0.s
@@ -203,8 +203,31 @@ bits 16
   jmp .loop_find_stage2
 
 .found_stage2:
-  ; TODO: we've found the right entry, now we need to parse it, load the sector and jump to it
   push ax ; address of the GPT entry for stage 2
+  mov si, ax
+
+  ; Load partition LBA start.
+  mov eax, [si + 0x20]
+  mov ebx, [si + 0x24]
+  ; Ensure it fits in 16 bits.
+  or ebx, ebx
+  jnz .panic
+  cmp ebx, 0xffff
+  ja .panic
+  ; Load partition LBA end.
+  mov ecx, [si + 0x28]
+  mov edx, [si + 0x2c]
+  ; Assert that the end LBA is greater than the start LBA, so we have at least one sector to load.
+  ; TODO: is the end LBA inclusive?
+  or edx, edx
+  jnz .stage2_end_lba_ok
+  cmp eax, ecx
+  jae .panic
+.stage2_end_lba_ok:
+
+  mov bx, 0x8200
+  call .read_lba
+  ; TODO: jump to the sector we just read
 
   mov al, [0x7e00]
   mov byte fs:[0x0000], al