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Add comments about the bogus zeroing of the drive number for floppies

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and the bogus dummy partition table.
This commit is contained in:
Bruce Evans 1995-09-16 13:51:20 +00:00
parent 45c7e5044d
commit 72b3459d61
1 changed files with 17 additions and 3 deletions
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20
sys/i386/boot/biosboot/start.S
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@ -24,7 +24,7 @@
* the rights to redistribute these changes.
*
* from: Mach, Revision 2.2 92/04/04 11:36:29 rpd
* $Id: start.S,v 1.4 1994/10/02 05:18:26 rgrimes Exp $
* $Id: start.S,v 1.5 1994/10/06 09:41:05 rgrimes Exp $
*/
/*
@ -51,7 +51,7 @@ WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include "asm.h"
.file "start.s"
.file "start.S"
SIGNATURE= 0xaa55
LOADSZ= 15 /* size of unix boot */
@ -99,7 +99,14 @@ start:
jae hd
fd:
/*
* XXX some bootstraps don't pass the drive number in %dl.
* This is a problem mainly when we are block 0 on a floppy.
* Force drive 0 for floppies.
* XXX %dl was assumed valid in the test that led here.
*/
mov $0x0, %dl
/* reset the disk system */
#ifdef DEBUG
data32
@ -274,7 +281,14 @@ seven: String "7\r\n\0"
eread: String "Read error\r\n\0"
enoboot: String "No bootable partition\r\n\0"
endofcode:
/* throw in a partition in case we are block0 as well */
/*
* Dummy partition table in case we are block 0. The ending c/h/s values
* of the non-null partition are almost arbitary. The length of this
* partition is bogus for backwards compatibility and as a signature.
* A real partition table shouldn't be as weird and broken as this one,
* and the isa slice initialization routine interprets this table as
* saying that the whole disk is used for FreeBSD.
*/
/* flag, head, sec, cyl, typ, ehead, esect, ecyl, start, len */
. = EXT(boot1) + PARTSTART
.byte 0x0,0,0,0,0,0,0,0