From 78b194840bb929792b4954dc67b0762dbf2ba131 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Thu, 13 Dec 2007 13:55:21 -0800
Subject: [PATCH] Snapshot: initialize the default ADV for disk-based
 derivatives

For the disk-based derivatives, handle the default ADV that is part of
the image.
---
 adv.inc      | 36 ++++++++++++++++++++++++++----------
 extlinux.asm |  9 +++++++--
 2 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/adv.inc b/adv.inc
index 42b36b1..b84ae04 100644
--- a/adv.inc
+++ b/adv.inc
@@ -64,12 +64,25 @@ adv1:
 		; the intended location of the ADV
 		;
 adv_init:
-		cmp dword [ADVSec0],0
+		cmp byte [ADVDrive],-1
 		jne adv_read
 
-		; Here, poke the proper values of ADVSec0, 1
-		; based on the position of the syslinux file
-
+%if IS_SYSLINUX || IS_MDSLINUX || IS_EXTLINUX
+		;
+		; Update pointers to default ADVs...
+		;
+		mov bx,[LDLSectors]
+		shl bx,2
+		mov ecx,[bsHidden]
+		mov eax,[bx+SectorPtrs-8]
+		mov edx,[bx+SectorPtrs-4]
+		add eax,ecx
+		add edx,ecx
+		mov [ADVSec0],eax
+		mov [ADVSec1],edx
+		mov al,[DriveNumber]
+		mov [ADVDrive],al
+%endif
 		; ** fall through to adv_verify **
 
 		;
@@ -456,9 +469,12 @@ adv_read_write:
 
 		section .data
 		align 4, db 0
-ADVSec0		dd 1
-ADVSec1		dd 2
-ADVSecPerTrack	dw 0
-ADVHeads	dw 0
-ADVDrive	db 80h
-ADVOp		db 0
+ADVDrive	db -1			; No ADV defined
+
+		section .bss
+		alignb 4
+ADVSec0		resd 1
+ADVSec1		resd 1
+ADVSecPerTrack	resw 1
+ADVHeads	resw 1
+ADVOp		resb 1
diff --git a/extlinux.asm b/extlinux.asm
index 5e662d9..818d754 100644
--- a/extlinux.asm
+++ b/extlinux.asm
@@ -591,12 +591,17 @@ ldlinux_magic	dd LDLINUX_MAGIC
 ; LDLINUX_MAGIC, plus 8 bytes.
 ;
 patch_area:
-LDLDwords	dw 0		; Total dwords starting at ldlinux_sys
-LDLSectors	dw 0		; Number of sectors - (bootsec+this sec)
+LDLDwords	dw 0		; Total dwords starting at ldlinux_sys,
+				; not including ADVs
+LDLSectors	dw 0		; Number of sectors, not including
+				; bootsec & this sec, but including the two ADVs
 CheckSum	dd 0		; Checksum starting at ldlinux_sys
 				; value = LDLINUX_MAGIC - [sum of dwords]
 CurrentDir	dd 2		; "Current" directory inode number
 
+; Pointer to auxilliary data vector, for the benefit of the installer.
+ADVPtr		dw adv0
+
 ; Space for up to 64 sectors, the theoretical maximum
 SectorPtrs	times 64 dd 0
 
-- 
2.7.4