ISOLINUX: support for hybrid mode (CD-ROM/USB key)

Still a work in progress.

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

2 files changed, 219 insertions, 5 deletions

diff --git a/mbr/Makefile b/mbr/Makefile
index 7952e60b..a57b3946 100644
--- a/mbr/Makefile
+++ b/mbr/Makefile
@@ -17,23 +17,25 @@
 topdir = ..
 include $(topdir)/MCONFIG.embedded
 
-all:	mbr.bin gptmbr.bin
+all:	mbr.bin gptmbr.bin isohdpfx.bin
 
 .PRECIOUS: %.o
 %.o: %.S
 	$(CC) $(SFLAGS) -Wa,-a=$*.lst -c -o $@ $<
 
-mbr.elf: mbr.o mbr.ld
+.PRECIOUS: %.elf
+%.elf: %.o mbr.ld
 	$(LD) $(LDFLAGS) -T mbr.ld -e _start -o $@ $<
 
 mbr.bin: mbr.elf checksize.pl
 	$(OBJCOPY) -O binary $< $@
 	$(PERL) checksize.pl mbr.bin 440
 
-mbr_bin.c: mbr.bin
+isohdpfx.bin: isohdpfx.elf checksize.pl
+	$(OBJCOPY) -O binary $< $@
+	$(PERL) checksize.pl mbr.bin 432
 
-gptmbr.elf: gptmbr.o mbr.ld
-	$(LD) $(LDFLAGS) -T mbr.ld -e _start -o $@ $<
+mbr_bin.c: mbr.bin
 
 gptmbr.bin: gptmbr.elf checksize.pl
 	$(OBJCOPY) -O binary $< $@
diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S
new file mode 100644
index 00000000..f2bc7dc6
--- /dev/null
+++ b/mbr/isohdpfx.S
@@ -0,0 +1,212 @@
+/* -----------------------------------------------------------------------
+ *
+ *   Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
+ *
+ *   Permission is hereby granted, free of charge, to any person
+ *   obtaining a copy of this software and associated documentation
+ *   files (the "Software"), to deal in the Software without
+ *   restriction, including without limitation the rights to use,
+ *   copy, modify, merge, publish, distribute, sublicense, and/or
+ *   sell copies of the Software, and to permit persons to whom
+ *   the Software is furnished to do so, subject to the following
+ *   conditions:
+ *
+ *   The above copyright notice and this permission notice shall
+ *   be included in all copies or substantial portions of the Software.
+ *
+ *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ *   OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Modified MBR code used on an ISO image in hybrid mode.
+ *
+ * This doesn't follow the El Torito spec at all -- it is just a stub
+ * loader of a hard-coded offset, but that's good enough to load
+ * ISOLINUX.
+ */
+	
+	.code16
+	.text
+
+HYBRID_MAGIC			= 0x7078c0fb
+isolinux_hybrid_signature 	= 0x7c00+64
+isolinux_start_hybrid		= 0x7c00+64+4
+
+	.globl	bootsec
+/* Important: the top 6 words on the stack are passed to isolinux.bin */
+stack		= 0x7c00
+driveno		= (stack-6)
+sectors		= (stack-8)
+heads		= (stack-10)
+secpercyl	= (stack-14)
+
+BIOS_page = 0x462
+
+	/* gas/ld has issues with doing this as absolute addresses... */
+	.section ".bootsec", "a", @nobits
+	.globl	bootsec
+bootsec:
+	.space	512
+
+	.text
+	.globl	_start
+_start:
+
+	cli
+	xorw	%ax, %ax
+	movw	%ax, %ds
+	movw	%ax, %ss
+	movw	$stack, %sp
+	movw	%sp, %si
+	pushw	%es		/* es:di -> $PnP header */
+	pushw	%di
+	pushw	%dx		/* dl -> drive number */
+	movw	%ax, %es
+	sti
+	cld
+
+	/* Copy down to 0:0x600 */
+	movw	$_start, %di
+	movw	$(512/2), %cx
+	rep; movsw
+
+	ljmpw	$0, $next
+
+next:
+	/* Check to see if we have EBIOS */
+	pushw	%dx		/* drive number */
+	movb	$0x41, %ah	/* %al == 0 already */
+	movw	$0x55aa, %bx
+	xorw	%cx, %cx
+	xorb	%dh, %dh
+	stc
+	int	$0x13
+	jc	1f
+	cmpw	$0xaa55, %bx
+	jne	1f
+	shrw	%cx		/* Bit 0 = fixed disk subset */
+	jnc	1f
+
+	/* We have EBIOS; patch in the following code at
+	   read_sector_cbios: movb $0x42, %ah ;  jmp read_common */
+	movl	$0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
+		(read_sector_cbios)
+
+1:
+	popw	%dx
+
+	/* Get (C)HS geometry */
+	movb	$0x08, %ah
+	int	$0x13
+	andw	$0x3f, %cx	/* Sector count */
+	pushw	%cx		/* 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 */
+	mulw	%cx		/* Heads*sectors -> sectors per cylinder */
+
+	/* Save sectors/cylinder on the stack */
+	pushw	%dx		/* High word */
+	pushw	%ax		/* Low word */
+
+	/*
+	 * Load sectors.  We do this one at a time mostly to avoid
+	 * pitfalls and to share code with the stock MBR code.
+	 */
+	movw	$0x7c00, %bx
+	movw	$4, %cx		/* Sector count */
+	movl	(lba_offset), %eax
+
+2:
+	call	read_sector
+	jc	disk_error
+	incl	%eax
+	addw	$512, %bx
+	loopw	2b
+
+	/*
+	 * Okay, that actually worked... update the stack pointer
+	 * and jump into isolinux.bin...
+	 */
+	cmpl	$HYBRID_MAGIC,(isolinux_hybrid_signature)
+	jne	bad_signature
+	
+	cli
+	movw	$heads, %sp
+	jmp	isolinux_start_hybrid
+
+bad_signature:
+	call	error
+	.ascii	"isolinux.bin missing or corrupt.\r\n"
+
+/*
+ * read_sector: read a single sector pointed to by %eax to %es:%bx.
+ * CF is set on error.  All registers saved.
+ */
+read_sector:
+	pushal
+	xorl	%edx, %edx
+	pushl	%edx	/* MSW of LBA */
+	pushl	%eax	/* LSW of LBA */
+	pushw	%es	/* Buffer segment */
+	pushw	%bx	/* Buffer offset */
+	pushw	$1	/* Sector count */
+	pushw	$16	/* Size of packet */
+	movw	%sp, %si
+
+	/* This chunk is skipped if we have ebios */
+	/* Do not clobber %eax before this chunk! */
+	/* This also relies on %bx and %edx as set up above. */
+read_sector_cbios:
+	divl	(secpercyl)
+	shlb	$6, %ah
+	movb	%ah, %cl
+	movb	%al, %ch
+	xchgw	%dx, %ax
+	divb	(sectors)
+	movb	%al, %dh
+	orb	%ah, %cl
+	incw	%cx	/* Sectors are 1-based */
+	movw	$0x0201, %ax
+
+read_common:
+	movb	(driveno), %dl
+	int	$0x13
+	addw	$16, %sp	/* Drop DAPA */
+	popal
+	ret
+
+disk_error:
+	call	error
+	.ascii	"Operating system load error.\r\n"
+
+/*
+ * Print error messages.  This is invoked with "call", with the
+ * error message at the return address.
+ */
+error:
+	popw	%si
+2:
+	lodsb
+	movb	$0x0e, %ah
+	movb	(BIOS_page), %bh
+	movb	$0x07, %bl
+	int	$0x10		/* May destroy %bp */
+	cmpb	$10, %al	/* Newline? */
+	jne	2b
+
+	int	$0x18		/* Boot failure */
+die:
+	hlt
+	jmp	die
+
+	/* Address of pointer to isolinux.bin */
+lba_offset = _start+432