Yet another snapshot. Now we can actually compile the sucker...

6 files changed, 462 insertions, 165 deletions

diff --git a/memdisk/Makefile b/memdisk/Makefile
index 52b33f71..9e81685c 100644
--- a/memdisk/Makefile
+++ b/memdisk/Makefile
@@ -12,16 +12,21 @@
 ## -----------------------------------------------------------------------
 
 CC      = gcc
-CFLAGS  = -g -O2 -fomit-frame-pointer -march=i386 -malign-functions=0 -malign-jumps=0 -malign-loops=0
+CFLAGS  = -g -O2 -fomit-frame-pointer -march=i386 \
+	  -malign-functions=0 -malign-jumps=0 -malign-loops=0
 LDFLAGS = 
 AS      = as
 LD	= ld
 NASM    = nasm
+OBJCOPY = objcopy
 
-all: e820func.o16 msetup.o16 e820test memdisk.bin
+# Important: init.o16 must be first!!
+OBJS    = init.o16 setup.o16 msetup.o16 e820func.o16 memdisk.o
+
+all: memdisk e820test
 
 clean:
-	rm -f *.o *.s *.o16 *.s16 *.bin *.lst e820test
+	rm -f *.o *.s *.o16 *.s16 *.bin *.lst *.elf e820test memdisk
 
 %.o16: %.s16
 	$(AS) -o $@ $<
@@ -29,15 +34,30 @@ clean:
 %.s16: %.s
 	echo '.code16' | cat - $< > $@
 
+%.s: %.S
+	$(CC) -x c $(CFLAGS) -Wp,-traditional -E -o $@ $<
+
+%.s16: %.S16
+	$(CC) -x c $(CFLAGS) -Wp,-traditional -E -o $@ $<
+
 %.s: %.c
 	$(CC) $(CFLAGS) -S -o $@ $<
 
+%.i: %.c
+	$(CC) $(CFLAGS) -E -o $@ $<
+
 %.o: %.c
 	$(CC) $(CFLAGS) -c -o $@ $<
 
 %.bin: %.asm
 	$(NASM) -f bin -o $@ -l $*.lst $<
 
+memdisk.elf: $(OBJS)
+	$(LD) -Ttext 0 -o $@ $^
+
+memdisk: memdisk.elf
+	$(OBJCOPY) -O binary $< $@
+
 e820test: e820func.o msetup.o e820test.o memdisk.o
 	$(CC) $(LDFLAGS) -o $@ $^
 
diff --git a/memdisk/e820.h b/memdisk/e820.h
index ec261d7f..7f064c43 100644
--- a/memdisk/e820.h
+++ b/memdisk/e820.h
@@ -26,5 +26,8 @@ struct e820range {
 
 extern struct e820range ranges[];
 extern int nranges;
+extern uint32_t dos_mem, low_mem, high_mem;
 
 extern void insertrange(uint64_t, uint64_t, uint32_t);
+extern void get_mem(void);
+extern void parse_mem(void);
diff --git a/memdisk/init.S16 b/memdisk/init.S16
new file mode 100644
index 00000000..0231d8f7
--- /dev/null
+++ b/memdisk/init.S16
@@ -0,0 +1,150 @@
+/* $Id$ */
+/* ----------------------------------------------------------------------- *
+ *   
+ *   Copyright 2001 H. Peter Anvin - All Rights Reserved
+ *
+ *   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, Inc., 53 Temple Place Ste 330,
+ *   Bostom MA 02111-1307, USA; either version 2 of the License, or
+ *   (at your option) any later version; incorporated herein by reference.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * init.S
+ *
+ * memdisk initialization code
+ *
+ * This module *MUST* get linked first into the image
+ */
+
+		.section ".text", "ax"
+		.code16
+
+/*
+ * The header derives directly from the Linux kernel and must be first
+ * in the binary, hence section .init
+ */
+		.org 497
+setup_sects:	.byte 0			# Filled in later
+root_flags:	.word 0
+syssize:	.word 0
+swap_dev:	.word 0
+ram_size:	.word 0
+vid_mode:	.word 0
+root_dev:	.word 0
+boot_flag:	.word 0xAA55
+
+		.globl _start
+_start:
+		jmp	start
+
+# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
+	
+		.ascii	"HdrS"		# header signature
+		.word	0x0203		# header version number (>= 0x0105)
+					# or else old loadlin-1.5 will fail)
+realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
+start_sys_seg:	.word	0
+		.word	kernel_version	# pointing to kernel version string
+					# above section of header is compatible
+					# with loadlin-1.5 (header v1.5).
+
+type_of_loader:	.byte	0		# = 0, old one (LILO, Loadlin,
+					#      Bootlin, SYSLX, bootsect...)
+					# See Documentation/i386/boot.txt for
+					# assigned ids
+	
+# flags, unused bits must be zero (RFU) bit within loadflags
+loadflags:
+LOADED_HIGH	= 1			# If set, the kernel is loaded high
+CAN_USE_HEAP	= 0x80			# If set, the loader also has set
+					# heap_end_ptr to tell how much
+					# space behind setup.S can be used for
+					# heap purposes.
+					# Only the loader knows what is free
+
+		.byte	LOADED_HIGH	# Dont force the loader to move 
+					# us to 0x90000
+
+setup_move_size: .word  0		# Unused
+
+code32_start:				# here loaders can put a different
+					# start address for 32-bit code.
+#ifndef __BIG_KERNEL__
+		.long	0x1000		#   0x1000 = default for zImage
+#else
+		.long	0x100000	# 0x100000 = default for big kernel
+#endif
+
+ramdisk_image:	.long	0		# address of loaded ramdisk image
+					# Here the loader puts the 32-bit
+					# address where it loaded the image.
+					# This only will be read by the kernel.
+
+ramdisk_size:	.long	0		# its size in bytes
+
+bootsect_kludge:
+		.word  0, 0
+
+heap_end_ptr:	.word  0		# (Header version 0x0201 or later)
+					# space from here (exclusive) down to
+					# end of setup code can be used by setup
+					# for local heap purposes.
+
+pad1:		.word 0
+cmd_line_ptr:	.long 0			# (Header version 0x0202 or later)
+					# If nonzero, a 32-bit pointer
+					# to the kernel command line.
+					# The command line should be
+					# located between the start of
+					# setup and the end of low
+					# memory (0xa0000), or it may
+					# get overwritten before it
+					# gets read.  If this field is
+					# used, there is no longer
+					# anything magical about the
+					# 0x90000 segment; the setup
+					# can be located anywhere in
+					# low memory 0x10000 or higher.
+
+ramdisk_max:	.long 0xffffffff	# Load ramdisk as high as
+					# absolutely possible
+
+/* ------------------- End of setup header --------------------------- */
+
+/*
+ * Canonicalize CS to match the other segments; also, the C
+ * code uses 32-bit registers to make sure the high part of
+ * %esp is zero.
+ */
+start:
+		.byte 0x66,0x0f,0xb7,0xe4	# movzwl %sp,%esp
+		pushw %ds
+		pushw $main
+		lret
+
+main:
+		sti
+		call setup		# Call the C code
+		# The setup function returns the drive number,
+		# which should be returned in %dl
+		movw %ax,%dx
+
+		# If the C code returns, we are good to go, and the
+		# new boot sector is already loaded
+		cli
+		movw $0x7c00,%sp
+		xorw %si,%si		# Not a partition BS - SI <- 0
+		movw %si,%ds
+		movw %si,%es
+		movw %si,%fs
+		movw %si,%gs
+		movw %si,%ss
+		ljmp $0,$0x7c00		# Entrypoint at 0000:7C00
+
+		.section ".rodata", "a"
+kernel_version:	.ascii "MEMDISK ..."
+		.byte 0
+
diff --git a/memdisk/memdisk.asm b/memdisk/memdisk.asm
index 46e19236..3c9513dd 100644
--- a/memdisk/memdisk.asm
+++ b/memdisk/memdisk.asm
@@ -127,8 +127,16 @@ GetDriveType:
 		pop ax			; Drop return address
 		mov ah,[DriveNo]
 		shr ah,7
+		pushf
 		or ah,02h		; CF = 0
 		mov P_AH,ah
+		popf
+		jz .floppy
+		mov ax,[DiskSize]	; For hard disk return the size
+		mov P_DX,ax
+		mov ax,[DiskSize+2]
+		mov P_CX,ax
+.floppy:
 		mov [LastStatus],byte 0	; Success, but AH returns a value
 		jmp short DoneWeird
 
@@ -402,15 +410,12 @@ Mover_dst1:	db 0, 0, 0		; Low 24 bits of target addy
 		db 00h			; Extended access rights
 Mover_dst2:	db 0			; High 8 bits of source addy
 
+LastStatus	db 0			; Last return status
+
 		section .bss
 		alignb 4
 PatchArea	equ $			; This gets filled in by the installer
 
-DriveNo		resb 1			; Our drive number
-DriveType	resb 1			; Our drive type (floppies)
-LastStatus	resb 1			; Last return status
-		resb 1			; pad
-
 Cylinders	resw 1			; Cylinder count
 Heads		resw 1			; Head count
 Sectors		resd 1			; Sector count (zero-extended)
@@ -425,6 +430,11 @@ MemInt1588	resd 1			; 1MB-65MB memory amount (1K)
 OldInt13	resd 1			; INT 13h in chain
 OldInt15	resd 1			; INT 15h in chain
 
+OldDosMem	resw 1			; Old position of DOS mem end
+
+DriveNo		resb 1			; Our drive number
+DriveType	resb 1			; Our drive type (floppies)
+
 		; End patch area
 
 Stack		resd 2			; Saved SS:ESP on invocation
diff --git a/memdisk/msetup.c b/memdisk/msetup.c
index 713f368f..c37169be 100644
--- a/memdisk/msetup.c
+++ b/memdisk/msetup.c
@@ -181,160 +181,3 @@ void parse_mem(void)
     }
   }
 }
-
-extern const char _binary_memdisk_bin_start[], _binary_memdisk_bin_end[];
-extern const char _binary_memdisk_bin_size[]; /* Weird, I know */
-struct memdisk_header {
-  uint16_t int13_offs;
-  uint16_t int15_offs;
-  uint16_t patch_offs;
-  uint16_t total_size;
-};
-struct patch_area {
-  uint8_t  driveno;
-  uint8_t  drivetype;
-  uint8_t  laststatus;
-  uint8_t  _pad1;
-
-  uint16_t cylinders;
-  uint16_t heads;
-  uint32_t sectors;
-  uint32_t disksize;
-  uint32_t diskbuf;
-
-  uint32_t e820table;
-  uint32_t mem1mb;
-  uint32_t mem16mb;
-  uint32_t memint1588;
-
-  uint32_t oldint13;
-  uint32_t oldint15;
-  uint16_t olddosmem;
-};
-
-/* Access to objects in the zero page */
-static inline void
-wrz_8(uint32_t addr, uint8_t data)
-{
-  asm volatile("movb %0,%%fs:%1" :: "ri" (data), "m" (*(uint8_t *)addr));
-}
-static inline void
-wrz_16(uint32_t addr, uint16_t data)
-{
-  asm volatile("movw %0,%%fs:%1" :: "ri" (data), "m" (*(uint16_t *)addr));
-}
-static inline void
-wrz_32(uint32_t addr, uint16_t data)
-{
-  asm volatile("movl %0,%%fs:%1" :: "ri" (data), "m" (*(uint32_t *)addr));
-}
-static inline uint8_t
-rdz_8(uint32_t addr)
-{
-  uint8_t data;
-  asm volatile("movb %%fs:%1,%0" : "=r" (data) : "m" (*(uint8_t *)addr));
-  return data;
-}
-static inline uint16_t
-rdz_16(uint32_t addr)
-{
-  uint16_t data;
-  asm volatile("movw %%fs:%1,%0" : "=r" (data) : "m" (*(uint16_t *)addr));
-  return data;
-}
-static inline uint8_t
-rdz_32(uint32_t addr)
-{
-  uint32_t data;
-  asm volatile("movl %%fs:%1,%0" : "=r" (data) : "m" (*(uint32_t *)addr));
-  return data;
-}
-
-/* Addresses in the zero page */
-#define BIOS_INT13	(0x13*4) /* INT 13h vector */
-#define BIOS_INT15	(0x15*4) /* INT 13h vector */
-#define BIOS_BASEMEM	0x413	 /* Amount of DOS memory */
-
-void setup(void)
-{
-  unsigned int size = (int) &_binary_memdisk_bin_size;
-  struct memdisk_header *hptr;
-  struct patch_area *pptr;
-  uint16_t driverseg;
-  uint32_t driverptr, driveraddr;
-  uint8_t driveno = 0;
-  uint8_t status;
-  uint16_t exitcode;
-
-  /* Point %fs to the zero page */
-  asm volatile("movw %0,%%fs" :: "r" (0));
-
-  get_mem();
-  parse_mem();
-
-  /* Figure out where it needs to go */
-  hptr = (struct memdisk_header *) &_binary_memdisk_bin_start;
-  pptr = (struct patch_area *)(_binary_memdisk_bin_start + hptr->patch_offs);
-
-  if ( hptr->total_size > dos_mem ) {
-    /* Badness... */
-  }
-
-  pptr->olddosmem = rdz_16(BIOS_BASEMEM);
-
-  driveraddr  = dos_mem - hptr->total_size;
-  driveraddr &= ~0x3FF;
-
-  /* Reserve this range of memory */
-  insertrange(driveraddr, dos_mem-driveraddr, 2);
-  parse_mem();
-
-  pptr->mem1mb     = low_mem  >> 10;
-  pptr->mem16mb    = high_mem >> 16;
-  pptr->memint1588 = (low_mem == 0xf00000)
-    ? ((high_mem > 0x30ffc00) ? 0xffff : (high_mem >> 10)+0x3c00)
-    : (low_mem >> 10);
-
-  driverseg = driveraddr >> 4;
-  driverptr = driverseg  << 16;
-
-  pptr->oldint13 = rdz_32(BIOS_INT13);
-  pptr->oldint15 = rdz_32(BIOS_INT15);
-
-  /* Claim the memory and copy the driver into place */
-  wrz_16(BIOS_BASEMEM, dos_mem >> 10);
-
-  asm volatile("pushw %%es ; "
-	       "movw %0,%%es ; "
-	       "rep ; movsl %%ds:(%%si), %%es:(%%di) ; "
-	       "popw %%es"
-	       :: "r" (driverseg),
-	       "c" (size >> 2),
-	       "S" (&_binary_memdisk_bin_start),
-	       "D" (0));
-
-  /* Install the interrupt handlers */
-  wrz_32(BIOS_INT13, driverptr+hptr->int13_offs);
-  wrz_32(BIOS_INT15, driverptr+hptr->int15_offs);
-
-  /* Reboot into the new "disk" */
-  asm volatile("pushw %%es ; "
-	       "xorw %%cx,%%cx ; "
-	       "movw %%cx,%%es ; "
-	       "incw %%cx ; "
-	       "movw $0x0201,%%ax ; "
-	       "movw $0x7c00,%%bx ; "
-	       "int $0x13 ; "
-	       "setc %0 ; "
-	       "popw %%es"
-	       : "=r" (status), "=a" (exitcode)
-	       : "d" ((uint16_t)driveno)
-	       : "ebx", "ecx", "edx", "esi", "edi", "ebp");
-
-  if ( status ) {
-    /* Badness... */
-  }
-  
-  /* On return the assembly code will jump to the boot vector */
-}
-
diff --git a/memdisk/setup.c b/memdisk/setup.c
new file mode 100644
index 00000000..d40f21bb
--- /dev/null
+++ b/memdisk/setup.c
@@ -0,0 +1,271 @@
+#ident "$Id$"
+/* ----------------------------------------------------------------------- *
+ *   
+ *   Copyright 2001 H. Peter Anvin - All Rights Reserved
+ *
+ *   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, Inc., 53 Temple Place Ste 330,
+ *   Bostom MA 02111-1307, USA; either version 2 of the License, or
+ *   (at your option) any later version; incorporated herein by reference.
+ *
+ * ----------------------------------------------------------------------- */
+
+#include <stdint.h>
+#include "e820.h"
+
+extern const char _binary_memdisk_bin_start[], _binary_memdisk_bin_end[];
+extern const char _binary_memdisk_bin_size[]; /* Weird, I know */
+
+struct memdisk_header {
+  uint16_t int13_offs;
+  uint16_t int15_offs;
+  uint16_t patch_offs;
+  uint16_t total_size;
+};
+
+struct patch_area {
+  uint16_t cylinders;
+  uint16_t heads;
+  uint32_t sectors;
+  uint32_t disksize;
+  uint32_t diskbuf;
+
+  uint32_t e820table;
+  uint32_t mem1mb;
+  uint32_t mem16mb;
+  uint32_t memint1588;
+
+  uint32_t oldint13;
+  uint32_t oldint15;
+
+  uint16_t olddosmem;
+
+  uint8_t  driveno;
+  uint8_t  drivetype;
+};
+
+/* This is the header in the boot sector/setup area */
+struct setup_header {
+  uint8_t dummy[0x1f1];		/* Boot sector */
+  uint8_t setup_secs;
+  uint16_t syssize;
+  uint16_t swap_dev;
+  uint16_t ram_size;
+  uint16_t vid_mode;
+  uint16_t root_dev;
+  uint16_t boot_flag;
+  uint16_t jump;
+  char header[4];
+  uint16_t version;
+  uint32_t realmode_swtch;
+  uint32_t start_sys;
+  uint8_t type_of_loader;
+  uint8_t loadflags;
+  uint16_t setup_move_size;
+  uint32_t code32_start;
+  uint32_t ramdisk_image;
+  uint32_t ramdisk_size;
+  uint32_t bootsect_kludge;
+  uint16_t head_end_ptr;
+  uint16_t pad1;
+  uint32_t cmd_line_ptr;
+  uint32_t initrd_addr_max;
+};
+
+const struct setup_header * const shdr = (struct setup_header *)0;
+
+/* Access to objects in the zero page */
+static inline void
+wrz_8(uint32_t addr, uint8_t data)
+{
+  asm volatile("movb %0,%%fs:%1" :: "ri" (data), "m" (*(uint8_t *)addr));
+}
+static inline void
+wrz_16(uint32_t addr, uint16_t data)
+{
+  asm volatile("movw %0,%%fs:%1" :: "ri" (data), "m" (*(uint16_t *)addr));
+}
+static inline void
+wrz_32(uint32_t addr, uint16_t data)
+{
+  asm volatile("movl %0,%%fs:%1" :: "ri" (data), "m" (*(uint32_t *)addr));
+}
+static inline uint8_t
+rdz_8(uint32_t addr)
+{
+  uint8_t data;
+  asm volatile("movb %%fs:%1,%0" : "=r" (data) : "m" (*(uint8_t *)addr));
+  return data;
+}
+static inline uint16_t
+rdz_16(uint32_t addr)
+{
+  uint16_t data;
+  asm volatile("movw %%fs:%1,%0" : "=r" (data) : "m" (*(uint16_t *)addr));
+  return data;
+}
+static inline uint8_t
+rdz_32(uint32_t addr)
+{
+  uint32_t data;
+  asm volatile("movl %%fs:%1,%0" : "=r" (data) : "m" (*(uint32_t *)addr));
+  return data;
+}
+
+/* Addresses in the zero page */
+#define BIOS_INT13	(0x13*4) /* INT 13h vector */
+#define BIOS_INT15	(0x15*4) /* INT 13h vector */
+#define BIOS_BASEMEM	0x413	 /* Amount of DOS memory */
+
+/*
+ * Figure out the "geometry" of the disk in question
+ */
+struct geometry {
+  uint32_t size;		/* Size in bytes */
+  uint32_t sectors;		/* 512-byte sector limit */
+  uint32_t c, h, s;		/* C/H/S geometry */
+  uint8_t type;		        /* Type byte for INT 13h AH=08h */
+  uint8_t driveno;		/* Drive no */
+};
+
+static const uint32_t image_sizes[] =
+{  360*1024,
+   720*1024,
+  1200*1024,
+  1440*1024,
+  2880*1024,
+  0 };
+static const struct geometry geometries[] =
+{ {  360*1024,  720, 40,  2,  9, 0x01, 0 },
+  {  720*1024, 1440, 80,  2,  9, 0x03, 0 },
+  { 1200*1024, 2400, 80,  2, 15, 0x02, 0 },
+  { 1440*1024, 2880, 80,  2, 18, 0x04, 0 },
+  { 2880*1024, 5760, 80,  2, 36, 0x06, 0 } };
+#define known_geometries (sizeof(geometries)/sizeof(struct geometry))
+
+const struct geometry *get_disk_image_geometry(uint32_t where, uint32_t size)
+{
+  static struct geometry hd_geometry;
+  int i;
+
+  for ( i = 0 ; i < known_geometries ; i++ ) {
+    if ( size == geometries[i].size ) {
+      return &geometries[i];
+    }
+  }
+
+  /* No match, must be a hard disk image */
+  /* Need to examine the partition table for geometry */
+
+  /* For now, though, just use a simple standard geometry CHS = Nx16x63 */
+
+  hd_geometry.size    = size & ~0x1FF;
+  hd_geometry.sectors = size >> 9;
+  hd_geometry.c       = size/(16*63*512);
+  hd_geometry.h       = 16;
+  hd_geometry.s       = 63;
+  hd_geometry.type    = 0;
+  hd_geometry.driveno = 0x80;	/* Hard drive */
+
+  return &hd_geometry;
+}
+
+/*
+ * Actual setup routine
+ * Returns the drive number (which is then passed in %dl to the
+ * called routine.)
+ */
+uint32_t setup(void)
+{
+  unsigned int size = (int) &_binary_memdisk_bin_size;
+  struct memdisk_header *hptr;
+  struct patch_area *pptr;
+  uint16_t driverseg;
+  uint32_t driverptr, driveraddr;
+  uint8_t driveno = 0;
+  uint8_t status;
+  uint16_t exitcode;
+  const struct geometry *geometry;
+
+  /* Point %fs to the zero page */
+  asm volatile("movw %0,%%fs" :: "r" (0));
+
+  geometry = get_disk_image_geometry(shdr->ramdisk_image, shdr->ramdisk_size);
+
+  get_mem();
+  parse_mem();
+
+  /* Figure out where it needs to go */
+  hptr = (struct memdisk_header *) &_binary_memdisk_bin_start;
+  pptr = (struct patch_area *)(_binary_memdisk_bin_start + hptr->patch_offs);
+
+  if ( hptr->total_size > dos_mem ) {
+    /* Badness... */
+  }
+
+  pptr->olddosmem = rdz_16(BIOS_BASEMEM);
+  pptr->driveno   = geometry->driveno;
+  pptr->drivetype = geometry->type;
+  pptr->cylinders = geometry->c;
+  pptr->heads     = geometry->h;
+  pptr->sectors   = geometry->s;
+  pptr->disksize  = geometry->sectors;
+  pptr->diskbuf   = shdr->ramdisk_image;
+
+  driveraddr  = dos_mem - hptr->total_size;
+  driveraddr &= ~0x3FF;
+
+  /* Reserve this range of memory */
+  insertrange(driveraddr, dos_mem-driveraddr, 2);
+  parse_mem();
+
+  pptr->mem1mb     = low_mem  >> 10;
+  pptr->mem16mb    = high_mem >> 16;
+  pptr->memint1588 = (low_mem == 0xf00000)
+    ? ((high_mem > 0x30ffc00) ? 0xffff : (high_mem >> 10)+0x3c00)
+    : (low_mem >> 10);
+
+  driverseg = driveraddr >> 4;
+  driverptr = driverseg  << 16;
+
+  pptr->oldint13 = rdz_32(BIOS_INT13);
+  pptr->oldint15 = rdz_32(BIOS_INT15);
+
+  /* Claim the memory and copy the driver into place */
+  wrz_16(BIOS_BASEMEM, dos_mem >> 10);
+
+  asm volatile("pushw %%es ; "
+	       "movw %0,%%es ; "
+	       "rep ; movsl %%ds:(%%si), %%es:(%%di) ; "
+	       "popw %%es"
+	       :: "r" (driverseg),
+	       "c" (size >> 2),
+	       "S" (&_binary_memdisk_bin_start),
+	       "D" (0));
+
+  /* Install the interrupt handlers */
+  wrz_32(BIOS_INT13, driverptr+hptr->int13_offs);
+  wrz_32(BIOS_INT15, driverptr+hptr->int15_offs);
+
+  /* Reboot into the new "disk" */
+  asm volatile("pushw %%es ; "
+	       "xorw %%cx,%%cx ; "
+	       "movw %%cx,%%es ; "
+	       "incw %%cx ; "
+	       "movw $0x0201,%%ax ; "
+	       "movw $0x7c00,%%bx ; "
+	       "int $0x13 ; "
+	       "setc %0 ; "
+	       "popw %%es"
+	       : "=r" (status), "=a" (exitcode)
+	       : "d" ((uint16_t)driveno)
+	       : "ebx", "ecx", "edx", "esi", "edi", "ebp");
+
+  if ( status ) {
+    /* Badness... */
+  }
+  
+  /* On return the assembly code will jump to the boot vector */
+  return driveno;
+}