bootsect.inc: try to catch obvious .0 problems

A typical Linux kernel will be way, way too big for the low memory
bootstrap area, so throw an error message if we end up in the
bootstrap path with something that cannot possibly fit below 640K.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/core/bootsect.inc b/core/bootsect.inc
index 6c20409..9e47e1a 100644 (file)
--- a/core/bootsect.inc
+++ b/core/bootsect.inc
@@ -1,7 +1,7 @@
 ;; -----------------------------------------------------------------------
 ;;
 ;;   Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
-;;   Copyright 2009 Intel Corporation; author: H. Peter Anvin
+;;   Copyright 2009-2012 Intel Corporation; author: H. Peter Anvin
 ;;
 ;;   This program is free software; you can redistribute it and/or modify
 ;;   it under the terms of the GNU General Public License as published by
@@ -38,6 +38,7 @@ SuperSize     equ $+1
 load_bootsec:
                mov edi,free_high_memory
                mov [trackbuf+4],edi    ; Copy from this address
+               mov eax,0xA0000         ; Maximum load
                xor dx,dx               ; No padding
                mov bx,abort_check      ; Don't print dots, but allow abort
                call load_high
@@ -45,6 +46,9 @@ load_bootsec:
                sub edi,free_high_memory
                mov [trackbuf+8],edi    ; Save length
 
+               cmp edi,0xA0000-7C00h
+               ja bs_too_big
+
                mov eax,7C00h           ; Entry point
                mov [trackbuf],eax      ; Copy to this address
 
@@ -237,3 +241,13 @@ replace_stub:
 .csip          equ $-4
 
                section .text16
+bs_too_big:    
+               call close
+               mov si,err_bs_too_big
+               jmp abort_load
+
+               section .data16
+err_bs_too_big db "Too large for a bootstrap (need LINUX instead of KERNEL?)"
+               db CR, LF, 0
+
+               section .text16