Add in a hack to support IBM "El Torito" CD-ROM booting BIOS's which expect

the first sector of the emulated floppy to contain a valid MS-DOS BPB that
it can modify.  Since boot1 is the first sector of boot.flp, this resulted
in the BIOS overwriting part of boot1: specifically the function used to
read in sectors from the disk.

Submitted by:	Mark Peek <mark@whistle.com>
Submitted by:	Doug Ambrisko <ambrisko@ambrisko.com>
PR:		i386/26382
Obtained from:	NetBSD, OpenBSD (the example BPB)
MFC after:	1 month

sys/boot/i386/boot2/Makefile

@@ -6,9 +6,11 @@ STRIP=
 BINDIR?=	/boot
 BINMODE=	444
 CLEANFILES+=	boot1 boot1.out boot1.o \
-		boot2.ldr boot2.bin boot2.ld boot2.out boot2.o \
+		boot2.ldr boot2.bin boot2.ld boot2.out boot2.o boot2.h \
 		sio.o
 
+NM?=		nm
+
 # A value of 0x80 enables LBA support.
 B1FLAGS=	0x80
 
@@ -46,6 +48,11 @@ boot1.out: boot1.o
 boot1.o: boot1.s
 	${AS} ${AFLAGS} --defsym FLAGS=${B1FLAGS} ${.IMPSRC} -o ${.TARGET}
 
+boot2.h: boot1.out
+	${NM} -t d ${.ALLSRC} | awk '/([0-9])+ T xread/ \
+	 	{ x = $$1 - ORG1; printf("#define XREADORG 0x7%x\n", x) }' \
+	 	ORG1=`printf "%d" ${ORG1}` > boot2.h
+
 boot2: boot2.ldr boot2.bin ${BTX}/btx/btx
 	btxld -v -E ${ORG2} -f bin -b ${BTX}/btx/btx -l boot2.ldr \
 		-o boot2.ld -P 1 boot2.bin
@@ -63,6 +70,8 @@ boot2.out: boot2.o sio.o
 	${LD} ${LDFLAGS} -Ttext ${ORG2} -o ${.TARGET} \
 		${BTX}/lib/crt0.o boot2.o sio.o
 
+boot2.o: boot2.h
+
 sio.o: sio.s
 	${AS} ${AFLAGS} --defsym SIOPRT=${BOOT_COMCONSOLE_PORT} \
 		--defsym SIOFMT=${B2SIOFMT} \

sys/boot/i386/boot2/boot1.S

@@ -43,7 +43,40 @@
 
 start:		jmp main			# Start recognizably
 
-		.org 0x4,0x90
+# This is the start of a standard BIOS Parameter Block (BPB). Most bootable
+# FAT disks have this at the start of their MBR. While normal BIOS's will
+# work fine without this section, IBM's El Torito emulation "fixes" up the
+# BPB by writing into the memory copy of the MBR. Rather than have data
+# written into our xread routine, we'll define a BPB to work around it.
+# The data marked with (T) indicates a field required for a ThinkPad to
+# recognize the disk and (W) indicates fields written from IBM BIOS code.
+# The use of the BPB is based on what OpenBSD and NetBSD implemented in
+# their boot code but the required fields were determined by trial and error.
+#
+# Note: If additional space is needed in boot1, one solution would be to
+# move the "prompt" message data (below) to replace the OEM ID.
+
+		.org 0x03, 0x00
+oemid:		.space 0x08, 0x00	# OEM ID
+
+		.org 0x0b, 0x00
+bpb:		.word   512		# sector size (T)
+		.byte	0		# sectors/clustor
+		.word	0		# reserved sectors
+		.byte	0		# number of FATs
+		.word	0		# root entries
+		.word	0		# small sectors
+		.byte	0		# media type (W)
+		.word	0		# sectors/fat
+		.word	18		# sectors per track (T)
+		.word	2		# number of heads (T)
+		.long	0		# hidden sectors (W)
+		.long	0		# large sectors
+
+		.org 0x24, 0x00
+ebpb:		.byte	0		# BIOS physical drive number (W)
+
+		.org 0x25,0x90
 # 
 # Trampoline used by boot2 to call read to read data from the disk via
 # the BIOS.  Call with:

sys/boot/i386/boot2/boot1.s

@@ -43,7 +43,40 @@
 
 start:		jmp main			# Start recognizably
 
-		.org 0x4,0x90
+# This is the start of a standard BIOS Parameter Block (BPB). Most bootable
+# FAT disks have this at the start of their MBR. While normal BIOS's will
+# work fine without this section, IBM's El Torito emulation "fixes" up the
+# BPB by writing into the memory copy of the MBR. Rather than have data
+# written into our xread routine, we'll define a BPB to work around it.
+# The data marked with (T) indicates a field required for a ThinkPad to
+# recognize the disk and (W) indicates fields written from IBM BIOS code.
+# The use of the BPB is based on what OpenBSD and NetBSD implemented in
+# their boot code but the required fields were determined by trial and error.
+#
+# Note: If additional space is needed in boot1, one solution would be to
+# move the "prompt" message data (below) to replace the OEM ID.
+
+		.org 0x03, 0x00
+oemid:		.space 0x08, 0x00	# OEM ID
+
+		.org 0x0b, 0x00
+bpb:		.word   512		# sector size (T)
+		.byte	0		# sectors/clustor
+		.word	0		# reserved sectors
+		.byte	0		# number of FATs
+		.word	0		# root entries
+		.word	0		# small sectors
+		.byte	0		# media type (W)
+		.word	0		# sectors/fat
+		.word	18		# sectors per track (T)
+		.word	2		# number of heads (T)
+		.long	0		# hidden sectors (W)
+		.long	0		# large sectors
+
+		.org 0x24, 0x00
+ebpb:		.byte	0		# BIOS physical drive number (W)
+
+		.org 0x25,0x90
 # 
 # Trampoline used by boot2 to call read to read data from the disk via
 # the BIOS.  Call with:

sys/boot/i386/boot2/boot2.c

@@ -34,6 +34,7 @@
 
 #include <btxv86.h>
 
+#include "boot2.h"
 #include "lib.h"
 
 #define RBX_ASKNAME	0x0	/* -a */
@@ -739,7 +740,7 @@ drvread(void *buf, unsigned lba, unsigned nblk)
 
     printf("%c\b", c = c << 8 | c >> 24);
     v86.ctl = V86_ADDR | V86_CALLF | V86_FLAGS;
-    v86.addr = 0x704;		/* call to xread in boot1 */
+    v86.addr = XREADORG;		/* call to xread in boot1 */
     v86.es = VTOPSEG(buf);
     v86.eax = lba;
     v86.ebx = VTOPOFF(buf);

sys/boot/i386/gptboot/Makefile

@@ -6,9 +6,11 @@ STRIP=
 BINDIR?=	/boot
 BINMODE=	444
 CLEANFILES+=	boot1 boot1.out boot1.o \
-		boot2.ldr boot2.bin boot2.ld boot2.out boot2.o \
+		boot2.ldr boot2.bin boot2.ld boot2.out boot2.o boot2.h \
 		sio.o
 
+NM?=		nm
+
 # A value of 0x80 enables LBA support.
 B1FLAGS=	0x80
 
@@ -46,6 +48,11 @@ boot1.out: boot1.o
 boot1.o: boot1.s
 	${AS} ${AFLAGS} --defsym FLAGS=${B1FLAGS} ${.IMPSRC} -o ${.TARGET}
 
+boot2.h: boot1.out
+	${NM} -t d ${.ALLSRC} | awk '/([0-9])+ T xread/ \
+	 	{ x = $$1 - ORG1; printf("#define XREADORG 0x7%x\n", x) }' \
+	 	ORG1=`printf "%d" ${ORG1}` > boot2.h
+
 boot2: boot2.ldr boot2.bin ${BTX}/btx/btx
 	btxld -v -E ${ORG2} -f bin -b ${BTX}/btx/btx -l boot2.ldr \
 		-o boot2.ld -P 1 boot2.bin
@@ -63,6 +70,8 @@ boot2.out: boot2.o sio.o
 	${LD} ${LDFLAGS} -Ttext ${ORG2} -o ${.TARGET} \
 		${BTX}/lib/crt0.o boot2.o sio.o
 
+boot2.o: boot2.h
+
 sio.o: sio.s
 	${AS} ${AFLAGS} --defsym SIOPRT=${BOOT_COMCONSOLE_PORT} \
 		--defsym SIOFMT=${B2SIOFMT} \

sys/boot/i386/gptboot/gptboot.c

@@ -34,6 +34,7 @@
 
 #include <btxv86.h>
 
+#include "boot2.h"
 #include "lib.h"
 
 #define RBX_ASKNAME	0x0	/* -a */
@@ -739,7 +740,7 @@ drvread(void *buf, unsigned lba, unsigned nblk)
 
     printf("%c\b", c = c << 8 | c >> 24);
     v86.ctl = V86_ADDR | V86_CALLF | V86_FLAGS;
-    v86.addr = 0x704;		/* call to xread in boot1 */
+    v86.addr = XREADORG;		/* call to xread in boot1 */
     v86.es = VTOPSEG(buf);
     v86.eax = lba;
     v86.ebx = VTOPOFF(buf);