Aren/NetBSD
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Fix from Chris Demetriou to modify the way in which arm32 filecore

Browse Source 
checksums are calculated paying attention to the fact that the way
the checksum works a sectors filled with a single byte value will
always checksum correctly.
This commit is contained in:
mark 1998-06-07 20:33:22 +00:00
parent 74b990a7b4
commit e7424be3c9
1 changed files with 56 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

82
sbin/disklabel/disklabel.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: disklabel.c,v 1.54 1998/03/26 01:37:49 cgd Exp $ */
/* $NetBSD: disklabel.c,v 1.55 1998/06/07 20:33:22 mark Exp $ */
/*
* Copyright (c) 1987, 1993
@ -47,7 +47,7 @@ __COPYRIGHT("@(#) Copyright (c) 1987, 1993\n\
static char sccsid[] = "@(#)disklabel.c 8.4 (Berkeley) 5/4/95";
/* from static char sccsid[] = "@(#)disklabel.c 1.2 (Symmetric) 11/28/85"; */
#else
__RCSID("$NetBSD: disklabel.c,v 1.54 1998/03/26 01:37:49 cgd Exp $");
__RCSID("$NetBSD: disklabel.c,v 1.55 1998/06/07 20:33:22 mark Exp $");
#endif
#endif /* not lint */
@ -144,7 +144,7 @@ static char mbrsig[2] = {0x55, 0xaa};
#ifdef __arm32__
static u_int filecore_partition_offset;
static u_int get_filecore_partition __P((int));
static u_int filecore_checksum __P((u_char *));
static int filecore_checksum __P((u_char *));
#endif /* __arm32__ */
#if defined(__i386__) || (defined(__arm32__) && defined(notyet))
static void confirm __P((const char *));
@ -646,42 +646,72 @@ readmbr(f)
#ifdef __arm32__
/*
* static u_int filecore_checksum(u_char *bootblock)
* static int filecore_checksum(u_char *bootblock)
*
* Calculates the filecore boot block checksum. This is used to validate
* a filecore boot block on the disc. If a boot block is validated then
* a filecore boot block on the disk. If a boot block is validated then
* it is used to locate the partition table. If the boot block is not
* validated, it is assumed that the whole disc is NetBSD.
* validated, it is assumed that the whole disk is NetBSD.
*
* The basic algorithm is:
*
* for (each byte in block, excluding checksum) {
* sum += byte;
* if (sum > 255)
* sum -= 255;
* }
*
* That's equivalent to summing all of the bytes in the block
* (excluding the checksum byte, of course), then calculating the
* checksum as "cksum = sum - ((sum - 1) / 255) * 255)". That
* expression may or may not yield a faster checksum function,
* but it's easier to reason about.
*
* Note that if you have a block filled with bytes of a single
* value "X" (regardless of that value!) and calculate the cksum
* of the block (excluding the checksum byte), you will _always_
* end up with a checksum of X. (Do the math; that can be derived
* from the checksum calculation function!) That means that
* blocks which contain bytes which all have the same value will
* always checksum properly. That's a _very_ unlikely occurence
* (probably impossible, actually) for a valid filecore boot block,
* so we treat such blocks as invalid.
*/
/*
* This can be coded better using add with carry but as it is used rarely
* there is not much point writing it in assembly.
*/
static u_int
static int
filecore_checksum(bootblock)
u_char *bootblock;
{
u_char byte0, accum_diff;
u_int sum;
u_int loop;
int i;
sum = 0;
accum_diff = 0;
byte0 = bootblock[0];
for (loop = 0; loop < 512; ++loop)
sum += bootblock[loop];
if (sum == 0) return(0xffff);
sum = 0;
for (loop = 0; loop < 511; ++loop) {
sum += bootblock[loop];
if (sum > 255)
sum -= 255;
/*
* Sum the contents of the block, keeping track of whether
* or not all bytes are the same. If 'accum_diff' ends up
* being zero, all of the bytes are, in fact, the same.
*/
for (i = 0; i < 511; ++i) {
sum += bootblock[i];
accum_diff |= bootblock[i] ^ byte0;
}
return(sum);
/*
* Check to see if the checksum byte is the same as the
* rest of the bytes, too. (Note that if all of the bytes
* are the same except the checksum, a checksum compare
* won't succeed, but that's not our problem.)
*/
accum_diff |= bootblock[i] ^ byte0;
/* All bytes in block are the same; call it invalid. */
if (accum_diff == 0)
return (-1);
return (sum - ((sum - 1) / 255) * 255);
}
/*