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>

3 files changed, 55 insertions, 25 deletions

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 */