Add observations of the Linux98 and Grub/98 boot loaders. These

observations lead me to believe that the convetion for pc98 boot
loaders is to have a jump unstruction, followed by a string, followed
by code.  The jump usually doesn't have a nop after it and usually the
string is NUL terminated, but Grub/98 breaks both of these rules.

# I looked for, but failed to find the Minux boot blocks for PC-9801 port.

1 files changed, 15 insertions, 5 deletions

diff --git a/sys/geom/geom_pc98.c b/sys/geom/geom_pc98.c
index 0b24690..f30cb9d 100644
--- a/sys/geom/geom_pc98.c
+++ b/sys/geom/geom_pc98.c
@@ -84,11 +84,21 @@ g_pc98_modify(struct g_geom *gp, struct g_pc98_softc *ms, u_char *sec)
 
 #if 0
 	/*
-	 * FreeBSD's boot0 IPL uses the name IPL1.  This test initially was
-	 * based on that observation.  However, other boot loaders have use
-	 * different names.  A likely good test would be to test if the first
-	 * 4 bytes are a jump to location 11 (or greater?) as well as the next
-	 * 7 bytes being printable or with trailing NUL's.
+	 * By convetion, it seems that the ipl program has a jump at location
+	 * 0 to the real start of the boot loader.  By convetion, it appears
+	 * that after this jump, there's a string, terminated by at last one,
+	 * if not more, zeros, followed by the target of the jump.  FreeBSD's
+	 * pc98 boot0 uses 'IPL1' followed by 3 zeros here, likely for
+	 * compatibility with some older boot loader.  Linux98's boot loader
+	 * appears to use 'Linux 98' followed by only two.  GRUB/98 appears to
+	 * use 'GRUB/98 ' followed by none.  These last two appear to be
+	 * ported from the ia32 versions, but appear to show similar
+	 * convention.  Grub/98 has an additional NOP after the jmp, which
+	 * isn't present in others.
+	 *
+	 * The following test was inspired by looking only at partitions
+	 * with FreeBSD's boot0 (or one that it is compatible with).  As
+	 * such, if failed when other IPL programs were used.
 	 */
 	if (sec[4] != 'I' || sec[5] != 'P' || sec[6] != 'L' || sec[7] != '1')
 		return (EBUSY);