isohybrid: support booting from partition; fix CBIOS booting

Fix CBIOS in isohybrid mode.  Also allow an isohybrid image to be
booted from a partition.  Unfortunately this breaks compatibility
between differing versions of isohybrid and isolinux.bin.

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

6 files changed, 86 insertions, 39 deletions

diff --git a/core/isolinux.asm b/core/isolinux.asm
index cc97f479..b85ecd36 100644
--- a/core/isolinux.asm
+++ b/core/isolinux.asm
@@ -112,6 +112,8 @@ DiskError	resb 1			; Error code for disk I/O
 DriveNumber	resb 1			; CD-ROM BIOS drive number
 ISOFlags	resb 1			; Flags for ISO directory search
 RetryCount      resb 1			; Used for disk access retries
+		alignb 8
+bsHidden	resq 1			; Used in hybrid mode
 bsSecPerTrack	resw 1			; Used in hybrid mode
 bsHeads		resw 1			; Used in hybrid mode
 
@@ -222,26 +224,31 @@ bi_end:
 		; Custom entry point for the hybrid-mode disk.
 		; The following values will have been pushed onto the
 		; entry stack:
-		;	- CBIOS Heads
-		;	- CBIOS Sectors
-		;	- EBIOS flag
-		;	- DX (including drive number)
-		;	- DI
 		;	- ES
+		;	- DI
+		;	- DX (including drive number)
+		;	- partition offset (qword)
+		;	- EBIOS flag
+		;	- CBIOS Sectors
+		;	- CBIOS Heads
 		;       (top of stack)
+		;
 %ifndef DEBUG_MESSAGES
 _hybrid_signature:
-		dd 0x7078c0fb			; An arbitrary number...
-
+		dd 0x0defe3f7
 _start_hybrid:
+		pop word [cs:bsHeads]
+		pop word [cs:bsSecPerTrack]
+
 		pop ax
 		mov si,bios_cbios
 		and ax,ax
 		jz .cbios
 		mov si,bios_ebios
 .cbios:
-		pop word [cs:bsSecPerTrack]
-		pop word [cs:bsHeads]
+
+		pop dword [cs:bsHidden]
+		pop dword [cs:bsHidden+4]
 
 		pop dx
 		pop di
@@ -745,6 +752,8 @@ getlinsec_ebios:
 		xor edx,edx
 		shld edx,eax,2
 		shl eax,2			; Convert to HDD sectors
+		add eax,[bsHidden]
+		adc edx,[bsHidden+4]
 		shl bp,2
 
 .loop:
@@ -814,7 +823,9 @@ getlinsec_ebios:
 ; getlinsec implementation for legacy CBIOS
 ;
 getlinsec_cbios:
+		xor edx,edx
 		shl eax,2			; Convert to HDD sectors
+		add eax,[bsHidden]
 		shl bp,2
 
 .loop:
diff --git a/mbr/Makefile b/mbr/Makefile
index 3140132a..c3eb97a7 100644
--- a/mbr/Makefile
+++ b/mbr/Makefile
@@ -18,11 +18,10 @@
 topdir = ..
 include $(topdir)/MCONFIG.embedded
 
-all:	mbr.bin   altmbr.bin   gptmbr.bin   isohdpfx.bin   \
-	mbr_c.bin altmbr_c.bin gptmbr_c.bin isohdpfx_c.bin \
-	mbr_f.bin altmbr_f.bin gptmbr_f.bin isohdpfx_f.bin
+all:	mbr.bin   altmbr.bin   gptmbr.bin   isohdpfx.bin   isohdppx.bin \
+	mbr_c.bin altmbr_c.bin gptmbr_c.bin isohdpfx_c.bin isohdppx_c.bin \
+	mbr_f.bin altmbr_f.bin gptmbr_f.bin isohdpfx_f.bin isohdppx_f.bin
 
-.PRECIOUS: %.o
 %.o: %.S
 	$(CC) $(MAKEDEPS) $(SFLAGS) -Wa,-a=$*.lst -c -o $@ $<
 
@@ -50,3 +49,5 @@ clean: tidy
 
 spotless: clean
 	rm -f *.bin
+
+-include .*.d
diff --git a/mbr/checksize.pl b/mbr/checksize.pl
index 4648c95c..7d61bdfd 100755
--- a/mbr/checksize.pl
+++ b/mbr/checksize.pl
@@ -27,7 +27,7 @@ if (!defined($maxsize)) {
 	$maxsize = $padsize = 440;
     } elsif ($file =~ /^gptmbr[^0-9a-z]/) {
 	$maxsize = $padsize = 424;
-    } elsif ($file =~ /^isohdpfx[^0-9a-z]/) {
+    } elsif ($file =~ /^isohdp[fp]x[^0-9a-z]/) {
 	$maxsize = $padsize = 432;
     } elsif ($file =~ /^altmbr[^0-9a-z]/) {
 	$maxsize = 439; $padsize = 440;
diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S
index f42b4b5b..53e1ed6b 100644
--- a/mbr/isohdpfx.S
+++ b/mbr/isohdpfx.S
@@ -39,7 +39,7 @@
 	.code16
 	.text
 
-HYBRID_MAGIC			= 0x7078c0fb
+HYBRID_MAGIC			= 0x0defe3f7
 isolinux_hybrid_signature	= 0x7c00+64
 isolinux_start_hybrid		= 0x7c00+64+4
 
@@ -47,10 +47,11 @@ isolinux_start_hybrid		= 0x7c00+64+4
 /* Important: the top 6 words on the stack are passed to isolinux.bin */
 stack		= 0x7c00
 driveno		= (stack-6)
-ebios_flag	= (stack-8)
-sectors		= (stack-10)
-heads		= (stack-12)
-secpercyl	= (stack-16)
+partoffset	= (stack-14)
+ebios_flag	= (stack-16)
+sectors		= (stack-18)
+heads		= (stack-20)
+secpercyl	= (stack-24)
 
 BIOS_kbdflags	= 0x417
 BIOS_page	= 0x462
@@ -66,18 +67,47 @@ bootsec:
 _start:
 
 	cli
-	xorw	%ax, %ax
-	movw	%ax, %ds
-	movw	%ax, %ss
+	xorw	%bx, %bx
+	movw	%bx, %ds
+	movw	%bx, %ss
 	movw	$stack, %sp
-	movw	%sp, %si
-	pushw	%es		/* es:di -> $PnP header */
+	pushw	%es			/* -4: es:di -> $PnP header */
 	pushw	%di
-	movw	%ax, %es
+	movw	%bx, %es
 	sti
 	cld
 
+	ADJUST_DRIVE
+	pushw	%dx			/* -6: dl -> drive number */
+
+	/* Check to see if we have a partition table entry */
+#ifdef PARTITION_SUPPORT
+	andw	%si, %si		/* %si == 0 -> no partition data */
+	jz	1f
+	testb	$0x7f, (%si)		/* Invalid active flag field? */
+	jnz	1f
+	cmpl	$0x58504721, %eax	/* !GPT signature in EAX? */
+	jne	2f
+	cmpb	$0xee, 4(%si)		/* EFI partition type? */
+	jne	2f
+	/* We have GPT partition information */
+	pushl	(36+16)(%si)		/* -10: partoffset_hi */
+	pushl	(32+16)(%si)		/* -14: partoffset_lo */
+	jmp	3f
+2:
+	/* We have non-GPT partition information */
+	pushl	$0			/* -10: partoffset_hi */
+	pushl	8(%si)			/* -14: partoffset_lo */
+	jmp	3f
+#endif
+1:
+	/* We have no partition information */
+	pushl	$0			/* -10: partoffset_hi */
+	pushl	$0			/* -14: partoffset_lo */
+3:
+	
 	/* Copy down to 0:0x600 */
+	movw	$0x7c00, %si
 	movw	$_start, %di
 	movw	$(512/2), %cx
 	rep; movsw
@@ -85,9 +115,6 @@ _start:
 	ljmpw	$0, $next
 next:
 
-	ADJUST_DRIVE
-	pushw	%dx		/* dl -> drive number */
-
 	/* Check to see if we have EBIOS */
 	pushw	%dx		/* drive number */
 	movb	$0x41, %ah	/* %al == 0 already */
@@ -106,24 +133,24 @@ next:
 	   read_sector_cbios: movb $0x42, %ah ;  jmp read_common */
 	movl	$0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
 		(read_sector_cbios)
-
+	jmp	1f
 1:
 	popw	%dx
-	pushw	%cx		/* Save EBIOS flag */
+	pushw	%cx		/* -16: Save EBIOS flag */
 
 	/* Get (C)HS geometry */
 	movb	$0x08, %ah
 	int	$0x13
 	andw	$0x3f, %cx	/* Sector count */
-	pushw	%cx		/* Save sectors on the stack */
+	pushw	%cx		/* -18: Save sectors on the stack */
 	movzbw	%dh, %ax	/* dh = max head */
 	incw	%ax		/* From 0-based max to count */
-	pushw	%ax		/* Save heads on the stack */
+	pushw	%ax		/* -20: Save heads on the stack */
 	mulw	%cx		/* Heads*sectors -> sectors per cylinder */
 
 	/* Save sectors/cylinder on the stack */
-	pushw	%dx		/* High word */
-	pushw	%ax		/* Low word */
+	pushw	%dx		/* -22: High word */
+	pushw	%ax		/* -24: Low word */
 
 	/*
 	 * Load sectors.  We do this one at a time mostly to avoid
@@ -169,6 +196,8 @@ bad_signature:
 read_sector:
 	pushal
 	xorl	%edx, %edx
+	addl	(partoffset), %eax
+	adcl	(partoffset+4), %edx
 	pushl	%edx	/* MSW of LBA */
 	pushl	%eax	/* LSW of LBA */
 	pushw	%es	/* Buffer segment */
diff --git a/utils/Makefile b/utils/Makefile
index 7670bef6..9df9595a 100644
--- a/utils/Makefile
+++ b/utils/Makefile
@@ -23,7 +23,8 @@ LDFLAGS  = -O2 -s
 TARGETS	 = mkdiskimage isohybrid gethostip
 ASIS     = keytab-lilo lss16toppm md5pass ppmtolss16 sha1pass syslinux2ansi
 
-ISOHDPFX = ../mbr/isohdpfx.bin ../mbr/isohdpfx_f.bin ../mbr/isohdpfx_c.bin
+ISOHDPFX = ../mbr/isohdpfx.bin ../mbr/isohdpfx_f.bin ../mbr/isohdpfx_c.bin \
+	   ../mbr/isohdppx.bin ../mbr/isohdppx_f.bin ../mbr/isohdppx_c.bin
 
 all: $(TARGETS)
 
diff --git a/utils/isohybrid.in b/utils/isohybrid.in
index 2bbaada4..b3a502bc 100644
--- a/utils/isohybrid.in
+++ b/utils/isohybrid.in
@@ -43,6 +43,7 @@ use Fcntl;
     'type'   => [0, 255],
     'id'     => [0, 0xffffffff],
     'hd0'    => [0, 2],
+    'partok' => [0, 1],
 );
 
 # Boolean options just set other options
@@ -50,6 +51,8 @@ use Fcntl;
     'nohd0'    => ['hd0', 0],
     'forcehd0' => ['hd0', 1],
     'ctrlhd0'  => ['hd0', 2],
+    'nopartok' => ['partok', 0],
+    'partok'   => ['partok', 1],
 );
 
 sub usage() {
@@ -63,6 +66,7 @@ sub usage() {
     "  -id         Specify MBR ID (default random)\n",
     "  -forcehd0   Always assume we are loaded as disk ID 0\n",
     "  -ctrlhd0    Assume disk ID 0 if the Ctrl key is pressed\n",
+    "  -partok     Allow booting from within a partition\n";
     exit 1;
 }
 
@@ -161,9 +165,10 @@ if ($de_boot != 0x88 || $de_media != 0 ||
 # Now $de_lba should contain the CD sector number for isolinux.bin
 seek(FILE, $de_lba*2048+0x40, SEEK_SET) or die "$0: $file: $!\n";
 read(FILE, $ibsig, 4);
-if ($ibsig ne "\xfb\xc0\x78\x70") {
-    die "$0: $file: bootloader is missing isolinux.bin hybrid signature\n".
-	"Note: isolinux-debug.bin does not support hybrid booting\n";
+if ($ibsig ne "\xf7\xe3\xef\x0d") {
+    die "$0: $file: bootloader is missing current (3.81+) isolinux.bin\n".
+	"        hybrid signature; Note that isolinux-debug.bin does not\n".
+	"        support hybrid booting.\n";
 }
 
 # Get the total size of the image
@@ -202,7 +207,7 @@ if (defined($opt{'id'})) {
 # Print the MBR and partition table
 seek(FILE, 0, SEEK_SET) or die "$0: $file: $!\n";
 
-for ($i = 0; $i <= $opt{'hd0'}; $i++) {
+for ($i = 0; $i <= $opt{'hd0'}+3*$opt{'partok'}; $i++) {
     $mbr = get_hex_data();
 }
 if ( length($mbr) > 432 ) {