Add a bootstrap chainloading API, and include a sample program for it.syslinux-2.08-pre5

1 files changed, 58 insertions, 33 deletions

diff --git a/bootsect.inc b/bootsect.inc
index 24ebab6e..f0dc260f 100644
--- a/bootsect.inc
+++ b/bootsect.inc
@@ -27,81 +27,106 @@
 is_bootsector:
 %if IS_SYSLINUX || IS_MDSLINUX
 		; Transfer zero bytes
-		xor cx,cx
+		mov byte [CopySuper],0
 		jmp short load_bootsec
+
 is_bss_sector:
 		; Transfer the superblock
-		mov cx,superblock_len
-load_bootsec:
-		push cx
+		mov byte [CopySuper],superblock_len
 %endif
+load_bootsec:
 		xchg dx,ax
 		shl eax,16
 		xchg dx,ax		; Now EAX = file length
 		mov edi, 100000h
+		push edi		; Save load address
 		call load_high
 		call crlf
 
-%if IS_SYSLINUX || IS_MDSLINUX
-		pop cx
-%endif
-
 		sub edi,100000h
 		push edi		; Save length
 
 %if IS_SYSLINUX || IS_MDSLINUX
+		movzx ecx,byte [CopySuper]
 		jcxz .not_bss
 
 		; For a BSS boot sector we have to patch.
 		mov esi,superblock
 		mov edi,100000h+(superblock-bootsec)
-		movzx ecx,cx
 		call bcopy
 
 .not_bss:
 %endif
-;
-; Prepare for shutting down
-;
-		call vgaclearmode
+
 		xor edx,edx
-		xor eax,eax
+		xor esi,esi
 %if IS_SYSLINUX || IS_MDSLINUX
-		mov dl,[bsDriveNumber]
+		; Restore original FDC table
+		mov eax,[OrigFDCTabPtr]
+		mov [fdctab],eax
 
-		mov si,PartInfo
+		mov dl,[bsDriveNumber]
+		mov si,PartInfo		; Partition info buffer
 		mov di,800h-18		; Put partition info here
 		push di
 		mov cx,8		; 16 bytes
+		xor ax,ax
 		rep movsw
 		pop si			; DS:SI points to partition info
 %elif IS_ISOLINUX
 		mov dl,[DriveNo]
 %elif IS_PXELINUX
-		; Close the UDP stack so the PXE stack is in a known state for
-		; the new NBP
+		mov byte [KeepPXE],1	; Chainloading another NBP
 		call reset_pxe
 %endif
+		xor bx,bx
 
-		pop ecx			; Byte count to copy
+; 
+; Entrypoint for "shut down and replace bootstrap" -- also invoked by
+; the COMBOOT API.  This routine expects two dword on the stack:
+; linear address and length.  Additionally, the values of ESI and EDX
+; are passed on to the new bootstrap; the value of BX becomes the new
+; DS.
+; 
+replace_bootstrap:
+
+		;
+		; Prepare for shutting down
+		;
+		call vgaclearmode
+
+		;
+		; Set up initial stack frame (not used by PXE if keeppxe is set)
+		;
+		xor ax,ax
+		mov ds,ax
+		mov es,ax		
 
-		cli
-		xor ebx,ebx
-		mov ds,bx
-		mov es,bx
 %if IS_PXELINUX
-		lss sp,[InitStack]	; Reset stack to PXE original
-%else
-		mov esp,7C00h
-		pushfd
-		pushad
-		push bx	; ds
-		push bx ; es
-		push bx ; fs
-		push bx	; gs
+		test byte [KeepPXE],01h
+		jz .stdstack
+		les di,[InitStack]	; Reset stack to PXE original
+		jmp .stackok
 %endif
+.stdstack:
+		mov di,7C00h-44
+		push di
+		mov cx,22		; 44 bytes
+		rep stosw
+		pop di
+.stackok:
+
+		mov [es:di+28],edx
+		mov [es:di+12],esi
+		mov [es:di+6],bx
 
-		mov esi,100000h		; Copy from...
+		pop ecx			; Byte count to copy
+		pop esi			; Copy from...
+
+		cli
+		mov ax,es
+		mov ss,ax
+		movzx esp,di
 		mov edi,7C00h		; Copy to...
 
 		jmp bcopy_over_self