Master boot record for GPT partition tables

Beginnings of a master boot record for GPT partition tables.

2 files changed, 292 insertions, 1 deletions

diff --git a/mbr/Makefile b/mbr/Makefile
index a64869b1..ed33aedf 100644
--- a/mbr/Makefile
+++ b/mbr/Makefile
@@ -29,7 +29,7 @@ PERL	   = perl
 
 .SUFFIXES: .S .s .o .elf
 
-all:	mbr.bin
+all:	mbr.bin gptmbr.bin
 
 .PRECIOUS: %.o
 %.o: %.S
@@ -42,6 +42,13 @@ mbr.bin: mbr.elf checksize.pl
 	$(OBJCOPY) -O binary $< $@
 	$(PERL) checksize.pl mbr.bin 440
 
+gptmbr.elf: gptmbr.o mbr.ld
+	$(LD) -T mbr.ld -e _start -o $@ $<
+
+gptmbr.bin: gptmbr.elf checksize.pl
+	$(OBJCOPY) -O binary $< $@
+	$(PERL) checksize.pl gptmbr.bin 424
+
 tidy:
 	rm -f *.o *.elf *.lst
 
diff --git a/mbr/gptmbr.S b/mbr/gptmbr.S
new file mode 100644
index 00000000..a6b2607e
--- /dev/null
+++ b/mbr/gptmbr.S
@@ -0,0 +1,284 @@
+/* -----------------------------------------------------------------------
+ *
+ *   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.
+ *
+ * ----------------------------------------------------------------------- */
+
+	.code16
+	.text
+
+	.globl	bootsec
+stack		= 0x7c00
+driveno		= (stack-6)
+sectors		= (stack-8)
+secpercyl	= (stack-12)
+
+/* Partition table header here */
+phdr		= _start + 512
+/* Partition table sector here */
+/* To handle > 32K we need to play segment tricks... */
+psec		= 0x8000	/* Above the boot sector and stack */
+
+/* BootGUID */
+bootguid	= _start + 0x1a8
+/* Where we put DS:SI */
+dssi_out	= _start + 0x1be
+
+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 */
+	mulw	%cx		/* Heads*sectors -> sectors per cylinder */
+
+	/* Save sectors/cylinder on the stack */
+	pushw	%dx		/* High word */
+	pushw	%ax		/* Low word */
+
+	/* Load partition table header */
+	xorl	%eax,%eax
+	xorl	%edx,%edx
+	incl	%eax
+	movw	$phdr,%bx
+	call	read_sector
+
+	/* Number of partition sectors */
+	/* We assume the partition table is 32K or less, and that
+	   the sector size is 512. */
+	movw	(phdr+0x80),%cx		/* NumberOfPartitionEntries */
+	movw	(phdr+0x84),%ax		/* SizeOfPartitionEntry */
+	pushw	%ax
+	pushw	%cx
+	mulw	%cx
+	shrw	$9,%ax
+	xchgw	%ax,%cx
+	incw	%cx
+
+	/* Starting LBA of partition array */
+	movl	(phdr+0x72),%eax
+	movl	(phdr+0x76),%edx
+
+	movw	$psec,%bx
+	pushw	%bx
+get_ptab:
+	call	read_sector
+	addw	$512,%bx
+	call	inc64
+	loopw	get_ptab
+
+	/* Find the boot partition */
+	popw	%si			/* Partition table in memory */
+	popw	%cx			/* NumberOfPartitionEntries */
+	popw	%ax			/* SizeOfPartitionEntry */
+find_part:
+	pushw	%cx
+	pushw	%si
+	addw	$16,%si
+	movw	$bootguid,%di
+	movw	$8,%cx
+	rep; cmpsw
+	popw	%si
+	popw	%cx
+	je found_part
+	addw	%ax,%si
+	loopw	find_part
+
+	call	error
+	.ascii	"Boot partition not found\r\n"
+
+found_part:
+	movw	$dssi_out+16,%di
+	movw	%ax,%cx
+	rep; movsb
+	movw	$dssi_out,%si
+	movw	%si,%di
+	/* 80 00 00 00 ee 00 00 00
+	   - bootable partition, type EFI (EE), no CHS information */
+	xorl	%eax,%eax
+	movb	$0x80,%al
+	stosl
+	movb	$0xee,%al
+	stosl
+	movl	(40+16)(%si),%eax
+	movl	(48+16)(%si),%edx
+	pushl	%eax
+	pushl	%edx
+	call	saturate_stosl		/* Partition start */
+
+	subl	(32+16)(%si),%eax
+	sbbl	(36+16)(%si),%edx
+	call	inc64
+	call	saturate_stosl		/* Partition length */
+
+/*
+ * boot: invoke the actual bootstrap. (%si) points to the
+ * partition information in memory, and the block offset is
+ * on the stack.
+ */
+boot:
+	popl	%edx
+	popl	%eax
+	call	read_sector
+	cmpw	$0xaa55, (bootsec+510)
+	jne	missing_os	/* Not a valid boot sector */
+	movw	$driveno, %sp	/* driveno == bootsec-6 */
+	popw	%dx		/* dl -> drive number */
+	popw	%di		/* es:di -> $PnP vector */
+	popw	%es
+	cli
+	jmpw	*%sp		/* %sp == bootsec */
+
+missing_os:
+	call	error
+	.ascii	"Operating system not bootable\r\n"
+
+saturate_stosl:
+	pushl	%eax
+	andl	%edx,%edx
+	jz 1f
+	orl	$-1,%eax
+1:	stosl
+	popl	%eax
+	ret
+
+inc64:
+	addl	$1,%eax
+	adcl	$0,%edx
+	ret
+
+/*
+ * read_sector: read a single sector pointed to by %edx:%eax to
+ * %es:%bx.  CF is set on error.  All registers saved.
+ */
+read_sector:
+	pushal
+	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 %es:%bx or %edx:%eax before this chunk! */
+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
+	jc	disk_error
+	ret
+
+disk_error:
+	call	error
+	.ascii	"Disk error on boot\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