From: Michael Tokarev <mjt@tls.msk.ru>
Date:   Wed Jun 6 22:21:57 2012 +0400
Subject: resurrect extboot

This patch restores extboot functionality of qemu-kvm
which was removed for 1.0 version.  It partially reverts
commit
   2a06024dc1b1e27b1be0266379af397e61b4a9ad qemu-kvm: Remove extboot support
and modifies commit
  841280b6c224ea2c6edc2f5afc2add513c85181d qemu-kvm: Deprecate drive parameter boot=on|off
in qemu-kvm git tree.
    
I want to keep it for some more time to let users to migrate --
e.g. from bootable scsi drives - to something else.  One possible
alternative is to use ahci (sata).

It will definitely go away after wheezy.

diff --git a/Makefile.target b/Makefile.target
index eda8637..4e4bd23 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -226,6 +226,7 @@ obj-i386-y += apic_common.o apic.o kvmvapic.o
 obj-i386-y += sga.o ioapic_common.o ioapic.o piix_pci.o
 obj-i386-y += vmport.o
 obj-i386-y += pci-hotplug.o smbios.o wdt_ib700.o
+obj-i386-y += extboot.o
 obj-i386-y += debugcon.o multiboot.o
 obj-i386-y += pc_piix.o
 obj-i386-y += pc_sysfw.o
diff --git a/blockdev.c b/blockdev.c
index 0d20460..63c384e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -20,6 +20,8 @@
 #include "trace.h"
 #include "arch_init.h"
 
+DriveInfo *extboot_drive = NULL;
+
 static QTAILQ_HEAD(drivelist, DriveInfo) drives = QTAILQ_HEAD_INITIALIZER(drives);
 
 static const char *const if_name[IF_COUNT] = {
@@ -293,6 +295,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
     int on_read_error, on_write_error;
     const char *devaddr;
     DriveInfo *dinfo;
+    int is_extboot = 0;
     BlockIOLimit io_limits;
     int snapshot = 0;
     bool copy_on_read;
@@ -435,11 +438,17 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
     }
 
     if (qemu_opt_get(opts, "boot") != NULL) {
-        fprintf(stderr, "qemu-kvm: boot=on|off is deprecated and will be "
-                "ignored. Future versions will reject this parameter. Please "
+        fprintf(stderr, "qemu-kvm: WARNING: boot=on|off is deprecated and does not exist upstream. "
+                "Please "
                 "update your scripts.\n");
     }
 
+    is_extboot = qemu_opt_get_bool(opts, "boot", 0);
+    if (is_extboot && extboot_drive) {
+        fprintf(stderr, "qemu: two bootable drives specified\n");
+        return NULL;
+    }
+
     on_write_error = BLOCK_ERR_STOP_ENOSPC;
     if ((buf = qemu_opt_get(opts, "werror")) != NULL) {
         if (type != IF_IDE && type != IF_SCSI && type != IF_VIRTIO && type != IF_NONE) {
@@ -546,6 +555,10 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
     }
     QTAILQ_INSERT_TAIL(&drives, dinfo, next);
 
+    if (is_extboot) {
+        extboot_drive = dinfo;
+    }
+
     bdrv_set_on_error(dinfo->bdrv, on_read_error, on_write_error);
 
     /* disk I/O throttling */
diff --git a/blockdev.h b/blockdev.h
index 260e16b..0b593f4 100644
--- a/blockdev.h
+++ b/blockdev.h
@@ -54,6 +54,8 @@ QemuOpts *drive_add(BlockInterfaceType type, int index, const char *file,
                     const char *optstr);
 DriveInfo *drive_init(QemuOpts *arg, int default_to_scsi);
 
+extern DriveInfo *extboot_drive;
+
 /* device-hotplug */
 
 DriveInfo *add_init_drive(const char *opts);
diff --git a/hw/extboot.c b/hw/extboot.c
new file mode 100644
index 0000000..d517834
--- /dev/null
+++ b/hw/extboot.c
@@ -0,0 +1,123 @@
+/*
+ * Extended boot option ROM support.
+ *
+ * Copyright IBM, Corp. 2007
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "hw.h"
+#include "pc.h"
+#include "isa.h"
+#include "block.h"
+
+/* Extended Boot ROM suport */
+
+union extboot_cmd
+{
+    uint16_t type;
+    struct {
+	uint16_t type;
+	uint16_t cylinders;
+	uint16_t heads;
+	uint16_t sectors;
+	uint64_t nb_sectors;
+    } query_geometry;
+    struct {
+	uint16_t type;
+	uint16_t nb_sectors;
+	uint16_t segment;
+	uint16_t offset;
+	uint64_t sector;
+    } xfer;
+};
+
+static void get_translated_chs(BlockDriverState *bs, int *c, int *h, int *s)
+{
+    bdrv_get_geometry_hint(bs, c, h, s);
+
+    if (*c <= 1024) {
+	*c >>= 0;
+	*h <<= 0;
+    } else if (*c <= 2048) {
+	*c >>= 1;
+	*h <<= 1;
+    } else if (*c <= 4096) {
+	*c >>= 2;
+	*h <<= 2;
+    } else if (*c <= 8192) {
+	*c >>= 3;
+	*h <<= 3;
+    } else {
+	*c >>= 4;
+	*h <<= 4;
+    }
+
+    /* what is the correct algorithm for this?? */
+    if (*h == 256) {
+	*h = 255;
+	*c = *c + 1;
+    }
+}
+
+static void extboot_write_cmd(void *opaque, uint32_t addr, uint32_t value)
+{
+    union extboot_cmd cmd;
+    BlockDriverState *bs = opaque;
+    int cylinders, heads, sectors, err;
+    uint64_t nb_sectors;
+    target_phys_addr_t pa = 0;
+    int blen = 0;
+    void *buf = NULL;
+
+    cpu_physical_memory_read((value & 0xFFFF) << 4, (uint8_t *)&cmd,
+                             sizeof(cmd));
+
+    if (cmd.type == 0x01 || cmd.type == 0x02) {
+	pa = cmd.xfer.segment * 16 + cmd.xfer.offset;
+        blen = cmd.xfer.nb_sectors * 512;
+        buf = qemu_memalign(512, blen);
+    }
+
+    switch (cmd.type) {
+    case 0x00:
+        get_translated_chs(bs, &cylinders, &heads, &sectors);
+	bdrv_get_geometry(bs, &nb_sectors);
+	cmd.query_geometry.cylinders = cylinders;
+	cmd.query_geometry.heads = heads;
+	cmd.query_geometry.sectors = sectors;
+	cmd.query_geometry.nb_sectors = nb_sectors;
+	break;
+    case 0x01:
+	err = bdrv_read(bs, cmd.xfer.sector, buf, cmd.xfer.nb_sectors);
+	if (err)
+	    printf("Read failed\n");
+
+        cpu_physical_memory_write(pa, buf, blen);
+
+	break;
+    case 0x02:
+        cpu_physical_memory_read(pa, buf, blen);
+
+	err = bdrv_write(bs, cmd.xfer.sector, buf, cmd.xfer.nb_sectors);
+	if (err)
+	    printf("Write failed\n");
+
+	break;
+    }
+
+    cpu_physical_memory_write((value & 0xFFFF) << 4, (uint8_t *)&cmd,
+                              sizeof(cmd));
+    if (buf)
+        free(buf);
+}
+
+void extboot_init(BlockDriverState *bs)
+{
+    register_ioport_write(0x405, 1, 2, extboot_write_cmd, bs);
+}
diff --git a/hw/pc.c b/hw/pc.c
index dc31933..b4111d8 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -1021,6 +1021,12 @@ void pc_memory_init(MemoryRegion *system_memory,
     /* Initialize PC system firmware */
     pc_system_firmware_init(rom_memory);
 
+    if (extboot_drive) {
+        option_rom[nb_option_roms].name = "extboot.bin";
+        option_rom[nb_option_roms].bootindex = 0;
+        nb_option_roms++;
+    }
+
     option_rom_mr = g_malloc(sizeof(*option_rom_mr));
     memory_region_init_ram(option_rom_mr, "pc.rom", PC_ROM_SIZE);
     vmstate_register_ram_global(option_rom_mr);
@@ -1190,4 +1196,16 @@ void pc_pci_device_init(PCIBus *pci_bus)
     for (bus = 0; bus <= max_bus; bus++) {
         pci_create_simple(pci_bus, -1, "lsi53c895a");
     }
+
+    if (extboot_drive) {
+        DriveInfo *info = extboot_drive;
+        int cyls, heads, secs;
+
+        if (info->type != IF_IDE && info->type != IF_VIRTIO) {
+            bdrv_guess_geometry(info->bdrv, &cyls, &heads, &secs);
+            bdrv_set_geometry_hint(info->bdrv, cyls, heads, secs);
+        }
+
+        extboot_init(info->bdrv);
+    }
 }
diff --git a/hw/pc.h b/hw/pc.h
index 8ccf202..d8744ef 100644
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -225,6 +225,10 @@ static inline bool isa_ne2000_init(ISABus *bus, int base, int irq, NICInfo *nd)
 /* pc_sysfw.c */
 void pc_system_firmware_init(MemoryRegion *rom_memory);
 
+/* extboot.c */
+
+void extboot_init(BlockDriverState *bs);
+
 /* e820 types */
 #define E820_RAM        1
 #define E820_RESERVED   2
diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile
index 57d8bd0..ef2e9de 100644
--- a/pc-bios/optionrom/Makefile
+++ b/pc-bios/optionrom/Makefile
@@ -14,7 +14,7 @@ CFLAGS += -I$(SRC_PATH)
 CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector)
 QEMU_CFLAGS = $(CFLAGS)
 
-build-all: multiboot.bin linuxboot.bin kvmvapic.bin
+build-all: multiboot.bin linuxboot.bin kvmvapic.bin extboot.bin
 
 # suppress auto-removal of intermediate files
 .SECONDARY:
diff --git a/pc-bios/optionrom/extboot.S b/pc-bios/optionrom/extboot.S
new file mode 100644
index 0000000..db6c2b6
--- /dev/null
+++ b/pc-bios/optionrom/extboot.S
@@ -0,0 +1,691 @@
+/*
+ * Extended Boot Option ROM
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Copyright IBM Corporation, 2007
+ *   Authors: Anthony Liguori <aliguori@us.ibm.com>
+ */
+
+#define OLD_INT19	(0x80 * 4)	/* re-use INT 0x80 BASIC vector */
+#define OLD_INT13	(0x81 * 4)	/* re-use INT 0x81 BASIC vector */
+
+.code16
+.text
+	.global _start
+_start:
+	.short 0xaa55
+	.byte (_end - _start) / 512
+	push %eax
+	push %ds
+
+	/* setup ds so we can access the IVT */
+	xor %ax, %ax
+	mov %ax, %ds
+
+	/* there is one more bootable HD */
+	incb 0x0475
+
+	/* save old int 19 */
+	mov (0x19*4), %eax
+	mov %eax, (OLD_INT19)
+
+	/* install out int 19 handler */
+	movw $int19_handler, (0x19*4)
+	mov %cs, (0x19*4+2)
+
+	pop %ds
+	pop %eax
+	lret
+
+int19_handler:
+	push %eax /* reserve space for lret */
+	push %eax
+	push %bx
+	push %cx
+	push %dx
+	push %ds
+
+	/* setup ds to access IVT */
+	xor %ax, %ax
+	mov %ax, %ds
+
+	/* save old int 13 to int 2c */
+	mov (0x13*4), %eax
+	mov %eax, (OLD_INT13)
+
+	/* install our int 13 handler */
+	movw $int13_handler, (0x13*4)
+	mov %cs, (0x13*4+2)
+
+	/* restore previous int $0x19 handler */
+	mov (OLD_INT19),%eax
+	mov %eax,(0x19*4)
+
+	/* write old handler as return address onto stack */
+	push %bp
+	mov %sp, %bp
+	mov %eax, 14(%bp)
+	pop %bp
+
+	pop %ds
+	pop %dx
+	pop %cx
+	pop %bx
+	pop %eax
+	lret
+
+#define FLAGS_CF	0x01
+
+/* The two macro below clear/set the carry flag to indicate the status
+ * of the interrupt execution. It is not enough to issue a clc/stc instruction,
+ * since the value of the flags register will be overwritten by whatever is
+ * in the stack frame
+ */
+.macro clc_stack
+	push %bp
+	mov %sp, %bp
+	/* 8 = 2 (bp, just pushed) + 2 (ip) + 3 (real mode interrupt frame) */
+	and $(~FLAGS_CF), 8(%bp)
+	pop %bp
+.endm
+
+.macro stc_stack
+	push %bp
+	/* 8 = 2 (bp, just pushed) + 2 (ip) + 3 (real mode interrupt frame) */
+	or $(FLAGS_CF), 8(%bp)
+	pop %bp
+.endm
+
+/* we clobber %bx */
+.macro alloca size
+	push %ds
+	push %bp
+	mov %sp, %bp  /* remember the current stack position */
+
+	mov %ss, %bx
+	mov %bx, %ds
+
+	sub \size, %sp
+	and $(~0x0F), %sp
+	mov %sp, %bx
+
+	push %bp
+	mov 0(%bp), %bp
+.endm
+
+/* we clobber %bp */
+.macro allocbpa size
+	mov %sp, %bp  /* remember the current stack position */
+	sub \size, %sp
+	and $(~0x0F), %sp
+	push %bp
+	mov %sp, %bp
+	add $2, %bp
+.endm
+
+.macro freea
+	pop %sp
+	add $2, %sp
+	pop %ds
+.endm
+
+.macro freebpa
+	pop %sp
+.endm
+
+.macro dump reg
+	push %ax
+	push %dx
+
+	mov \reg, %ax
+	mov $0x406, %dx
+	outw %ax, %dx
+
+	pop %dx
+	pop %ax
+.endm
+
+.macro callout value
+	push %bp
+	push %bx
+	mov %sp, %bp
+	alloca $16
+	push %ax
+	push %dx
+
+	mov %ax, 0(%bx)     /* ax */
+	mov 0(%bp), %ax     /* bx */
+	mov %ax, 2(%bx)
+	mov %cx, 4(%bx)     /* cx */
+	mov %dx, 6(%bx)     /* dx */
+	mov %si, 8(%bx)     /* si */
+	mov %ds, 10(%bx)    /* ds */
+	mov %es, 12(%bx)    /* ds */
+	movw \value, 14(%bx) /* value */
+
+	mov %bx, %ax
+	shr $4, %ax
+	mov %ds, %dx
+	add %dx, %ax
+
+	mov $0x407, %dx
+	outw %ax, %dx
+
+	pop %dx
+	pop %ax
+	freea
+	pop %bx
+	pop %bp
+.endm
+
+send_command:
+	push %bp
+	mov %sp, %bp
+	push %ax
+	push %bx
+	push %dx
+
+	mov 4(%bp), %ax
+	shr $4, %ax
+	and $0x0FFF, %ax
+	mov %ss, %bx
+	add %bx, %ax
+
+	mov $0x405, %dx
+	outw %ax, %dx
+
+	pop %dx
+	pop %bx
+	pop %ax
+	pop %bp
+
+	push %ax
+	mov 2(%bx), %ax
+	pop %ax
+
+	ret
+
+add32:  /* lo, hi, lo, hi */
+	push %bp
+	mov %sp, %bp
+
+	movw 4(%bp), %cx  /* hi */
+	movw 6(%bp), %dx  /* lo */
+
+	add  10(%bp), %dx
+	jnc 1f
+	add $1, %cx
+1:	add 8(%bp), %cx
+
+	pop %bp
+	ret
+
+mul32:  /* lo,      hi,     lo,     hi */
+	/* 10(%bp), 8(%bp), 6(%bp), 4(%bp) */
+	push %bp
+	mov %sp, %bp
+	push %ax
+	push %bx
+
+	xor %cx, %cx
+	xor %dx, %dx
+
+	/* for (i = 0; i < 16;) */
+	xor %bx, %bx
+0:
+	cmp $16, %bx
+	jge 2f
+
+	mov 6(%bp), %ax
+	and $1, %ax
+	cmp $1, %ax
+	jne 1f
+	push 10(%bp)
+	push 8(%bp)
+	push %dx
+	push %cx
+	call add32
+	add $8, %sp
+1:
+	shlw $1, 8(%bp)
+	movw 10(%bp), %ax
+	and $0x8000, %ax
+	cmp $0x8000, %ax
+	jne 1f
+	orw $1, 8(%bp)
+1:
+	shlw $1, 10(%bp)
+	shrw $1, 6(%bp)
+
+	/* i++) { */
+	add $1, %bx
+	jmp 0b
+
+2:
+	pop %bx
+	pop %ax
+	pop %bp
+	ret
+
+disk_reset:
+	movb $0, %ah
+	clc_stack
+	ret
+
+/* this really should be a function, not a macro but i'm lazy */
+.macro read_write_disk_sectors cmd
+	push %ax
+	push %bx
+	push %cx
+	push %dx
+	push %si
+
+	push %bp
+	sub $10, %sp
+	mov %sp, %bp
+
+	/* save nb_sectors */
+	mov %al, 6(%bp)
+	movb $0, 7(%bp)
+
+	/* save buffer */
+	mov %bx, 8(%bp)
+
+	/* cylinders */
+	xor %ax, %ax
+	mov %cl, %al
+	shl $2, %ax
+	and $0x300, %ax
+	mov %ch, %al
+	mov %ax, 0(%bp)
+
+	/* heads */
+	xor %ax, %ax
+	mov %dh, %al
+	mov %ax, 2(%bp)
+
+	/* sectors - 1 */
+	xor %ax, %ax
+	mov %cl, %al
+	and $0x3F, %al
+	sub $1, %ax
+	mov %ax, 4(%bp)
+
+	alloca $16
+
+	movw $0, 0(%bx) /* read c,h,s */
+	push %bx
+	call send_command
+	add $2, %sp
+
+	mov 6(%bx), %ax /* total_sectors */
+	mov 2(%bp), %si /* *= heads */
+	mul %si
+	add 4(%bp), %ax /* += sectors - 1 */
+
+	push 4(%bx) /* total_heads */
+	push $0
+	push 6(%bx) /* total_sectors */
+	push $0
+	call mul32
+	add $8, %sp
+
+	push 0(%bp) /* cylinders */
+	push $0
+	push %dx
+	push %cx
+	call mul32
+	add $8, %sp
+
+	add %ax, %dx
+	jnc 1f
+	add $1, %cx
+1:
+	freea
+
+	alloca $16
+
+	movw \cmd, 0(%bx) /* read */
+	movw 6(%bp), %ax /* nb_sectors */
+	movw %ax, 2(%bx)
+	movw %es, 4(%bx) /* segment */
+	movw 8(%bp), %ax /* offset */
+	mov %ax, 6(%bx)
+	movw %dx, 8(%bx) /* sector */
+	movw %cx, 10(%bx)
+	movw $0, 12(%bx)
+	movw $0, 14(%bx)
+
+	push %bx
+	call send_command
+	add $2, %sp
+
+	freea
+
+	add $10, %sp
+	pop %bp
+
+	pop %si
+	pop %dx
+	pop %cx
+	pop %bx
+	pop %ax
+
+	mov $0, %ah
+	clc_stack
+	ret
+.endm
+
+read_disk_sectors:
+	read_write_disk_sectors $0x01
+
+write_disk_sectors:
+	read_write_disk_sectors $0x02
+
+read_disk_drive_parameters:
+	push %bx
+
+	/* allocate memory for packet, pointer gets returned in bx */
+	alloca $16
+
+	/* issue command */
+	movw $0, 0(%bx) /* cmd = 0, read c,h,s */
+	push %bx
+	call send_command
+	add $2, %sp
+
+	/* normalize sector value */
+	movb 6(%bx), %cl
+	andb $0x3F, %cl
+	movb %cl, 6(%bx)
+
+	/* normalize cylinders */
+	subw $2, 2(%bx)
+
+	/* normalize heads */
+	subw $1, 4(%bx)
+
+	/* return code */
+	mov $0, %ah
+
+	/* cylinders */
+	movb 2(%bx), %ch
+	movb 3(%bx), %cl
+	shlb $6, %cl
+	andb $0xC0, %cl
+
+	/* sectors */
+	orb 6(%bx), %cl
+
+	/* heads */
+	movb 4(%bx), %dh
+
+	/* drives */
+	movb $1, %dl
+
+	/* status */
+	mov $0, %ah
+
+	freea
+
+	pop %bx
+
+	/* do this last since it's the most sensitive */
+	clc_stack
+	ret
+
+alternate_disk_reset:
+	movb $0, %ah
+	clc_stack
+	ret
+
+read_disk_drive_size:
+	push %bx
+	alloca $16
+
+	movw $0, 0(%bx) /* cmd = 0, read c,h,s */
+	push %bx
+	call send_command
+	add $2, %sp
+
+	/* cylinders - 1 to cx:dx */
+	mov 2(%bx), %dx
+	xor %cx, %cx
+	sub $1, %dx
+
+	/* heads */
+	push 4(%bx)
+	push $0
+	push %dx
+	push %cx
+	call mul32
+	add $8, %sp
+
+	/* sectors */
+	push 6(%bx)
+	push $0
+	push %dx
+	push %cx
+	call mul32
+	add $8, %sp
+
+	/* status */
+	mov $3, %ah
+
+	freea
+	pop %bx
+
+	clc_stack
+	ret
+
+check_if_extensions_present:
+	mov $0x30, %ah
+	mov $0xAA55, %bx
+	mov $0x07, %cx
+	clc_stack
+	ret
+
+.macro extended_read_write_sectors cmd
+	cmpb $10, 0(%si)
+	jg 1f
+	mov $1, %ah
+	stc_stack
+	ret
+1:
+	push %ax
+	push %bp
+	allocbpa $16
+
+	movw \cmd, 0(%bp) /* read */
+	movw 2(%si), %ax   /* nb_sectors */
+	movw %ax, 2(%bp)
+	movw 4(%si), %ax   /* offset */
+	movw %ax, 6(%bp)
+	movw 6(%si), %ax   /* segment */
+	movw %ax, 4(%bp)
+	movw 8(%si), %ax   /* block */
+	movw %ax, 8(%bp)
+	movw 10(%si), %ax
+	movw %ax, 10(%bp)
+	movw 12(%si), %ax
+	movw %ax, 12(%bp)
+	movw 14(%si), %ax
+	movw %ax, 14(%bp)
+
+	push %bp
+	call send_command
+	add $2, %sp
+
+	freebpa
+	pop %bp
+	pop %ax
+
+	mov $0, %ah
+	clc_stack
+	ret
+.endm
+
+extended_read_sectors:
+	extended_read_write_sectors $0x01
+
+extended_write_sectors:
+	extended_read_write_sectors $0x02
+
+get_extended_drive_parameters:
+	push %ax
+	push %bp
+	push %cx
+	push %dx
+
+	allocbpa $16
+
+	movw $0, 0(%bp) /* read c,h,s */
+	push %bp
+	call send_command
+	add $2, %sp
+
+	/* write size */
+	movw $26, 0(%si)
+
+	/* set flags to 2 */
+	movw $2, 2(%si)
+
+	/* cylinders */
+	mov 2(%bp), %ax
+	mov %ax, 4(%si)
+	xor %ax, %ax
+	mov %ax, 6(%si)
+
+	/* heads */
+	mov 4(%bp), %ax
+	mov %ax, 8(%si)
+	xor %ax, %ax
+	mov %ax, 10(%si)
+
+	/* sectors */
+	mov 6(%bp), %ax
+	mov %ax, 12(%si)
+	xor %ax, %ax
+	mov %ax, 14(%si)
+
+	/* set total number of sectors */
+	mov 8(%bp), %ax
+	mov %ax, 16(%si)
+	mov 10(%bp), %ax
+	mov %ax, 18(%si)
+	mov 12(%bp), %ax
+	mov %ax, 20(%si)
+	mov 14(%bp), %ax
+	mov %ax, 22(%si)
+
+	/* number of bytes per sector */
+	movw $512, 24(%si)
+
+	freebpa
+
+	pop %dx
+	pop %cx
+	pop %bp
+	pop %ax
+
+	mov $0, %ah
+	clc_stack
+	ret
+
+terminate_disk_emulation:
+	mov $1, %ah
+	stc_stack
+	ret
+
+int13_handler:
+	cmp $0x80, %dl
+	je 1f
+
+	/* write old handler as return address onto stack */
+	push %eax
+	push %eax
+	push %ds
+	push %bp
+	mov %sp, %bp
+	xor %ax, %ax
+	mov %ax, %ds
+	mov (OLD_INT13), %eax
+	mov %eax, 8(%bp)
+	pop %bp
+	pop %ds
+	pop %eax
+	lret
+1:
+	cmp $0x0, %ah
+	jne 1f
+	call disk_reset
+	iret
+1:
+	cmp $0x2, %ah
+	jne 1f
+	call read_disk_sectors
+	iret
+1:
+	cmp $0x8, %ah
+	jne 1f
+	call read_disk_drive_parameters
+	iret
+1:
+	cmp $0x15, %ah
+	jne 1f
+	call read_disk_drive_size
+	iret
+1:
+	cmp $0x41, %ah
+	jne 1f
+	call check_if_extensions_present
+	iret
+1:
+	cmp $0x42, %ah
+	jne 1f
+	call extended_read_sectors
+	iret
+1:
+	cmp $0x48, %ah
+	jne 1f
+	call get_extended_drive_parameters
+	iret
+1:
+	cmp $0x4b, %ah
+	jne 1f
+	call terminate_disk_emulation
+	iret
+1:
+	cmp $0x0d, %ah
+	jne 1f
+	call alternate_disk_reset
+	iret
+1:
+	cmp $0x03, %ah
+	jne 1f
+	call write_disk_sectors
+	iret
+1:
+	cmp $0x43, %ah
+	jne 1f
+	call extended_write_sectors
+	iret
+1:
+	int $0x18  /* boot failed */
+	iret
+
+.align 512, 0
+_end: