[PATCH] restore floppy boot image
From: Joshua (jhudson_at_cyberspace.org)
Date: 06/30/04
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Date: Wed, 30 Jun 2004 14:45:07 -0400 (EDT) To: linux-kernel@vger.kernel.org
After installing the 2.6.7 kernel a week ago, I had LILO problems
(lilo bombed on the kernel image). My first thought was to dd the kernel
to a floppy, and boot Windows so that I could get a new LILO (I have
a winmodem for dialup). My second thought was better check w/ hexdump
first.
I saw that "booting from floppy is no longer supported" message, and
thought "This won't do.
Rather than go back to the old version, I thought that I could do it
better. Maybe I did and maybe I didn't, but this time the bzImage loading
code fits into a single sector (no more need of bootsect_kludge).
Patch-signed-off-by: Joshua Hudson <jhudson@cyberspace.org>
diff -ru linux-2.6.7/arch/i386/boot/bootsect.S
linux-2.6.7c/arch/i386/boot/bootsect.S
--- linux-2.6.7/arch/i386/boot/bootsect.S Tue Jun 15 22:19:23 2004
+++ linux-2.6.7c/arch/i386/boot/bootsect.S Wed Jun 30 04:22:00 2004
@@ -5,6 +5,7 @@
* modified by Bruce Evans (bde)
* modified by Chris Noe (May 1999) (as86 -> gas)
* gutted by H. Peter Anvin (Jan 2003)
+ * rewritten by Joshua Hudson (June 2004)
*
* BIG FAT NOTE: We're in real mode using 64k segments. Therefore
segment
* addresses must be multiplied by 16 to obtain their respective linear
@@ -43,50 +44,320 @@
.global _start
_start:
- # Normalize the start address
- jmpl $BOOTSEG, $start2
+#define KS_LOAD 0x2000
-start2:
- movw %cs, %ax
- movw %ax, %ds
- movw %ax, %es
- movw %ax, %ss
- movw $0x7c00, %sp
- sti
- cld
+/*
+ * Actually, ld86 has no clue what is going on here.
+ * We are at 0000:7C00, not 7C0:0000
+ * Therefore, we correct it.
+ */
- movw $bugger_off_msg, %si
+ nop /* Place to insert debug trap */
+ ljmp $0x7C0, $6 /* Didn't assemble "realstart" */
+realstart:
+ xor %dx, %dx
+ mov %dx, %ss /* This is a 386 (I should hope)
*/
+ mov $0x7C00, %sp /* You don't need a cli first. */
+
+ /*
+ * Many BIOS's default disk parameter tables will not
+ * recognize multi-sector reads beyond the maximum sector number
+ * specified in the default diskette parameter tables - this may
+ * mean 7 sectors in some cases.
+ *
+ * Since single sector reads are slow and out of the question,
+ * we must take care of this by creating new parameter tables
+ * (for the first disk) in RAM. We will set the maximum sector
+ * count to 36 - the most we will encounter on an ED 2.88.
+ *
+ * High doesn't hurt. Low does.
+ *
+ * Previous versions copied the param table.
+ * We are just going to tweak it. It is in ram anyway
+ */
+ mov %dx, %ds
+ movb $36, 0x7C
+ mov $01, %ah
+ int $0x13
+
+ /* Now correct ds to normalized load position */
+ push %cs
+ pop %ds
+
+ /*
+ * Determine how many sectors we have. Since there is no call
+ * that will determine how many sectors (int 13h, ah=8h doesn't
+ * always work on floppies, probe it)
+ *
+ * We probe by determining what highest sector we can load.
+ * Never probe by trying to read X sectors. Some bioses will
+ * actually span tracks.
+ */
+ mov $dflags, %si
+ mov $KS_LOAD, %ax
+ mov %ax, %es
+ push %ax /* Remember this for later */
+ xor %bx, %bx
-msg_loop:
+ cld
+ mov $0, %ch
+ lodsb
+probe:
+ mov %al, %cl
+ mov $0x201, %ax
+ int $0x13
+ cmp $0, %ah
+ je probeok
lodsb
- andb %al, %al
- jz die
- movb $0xe, %ah
- movw $7, %bx
+ cmp $0, %al
+ jne probe
+ call errcode
+halt: jmp halt
+probeok:
+
+ /* Load first track */
+ xchg %al, %cl
+load1: mov $2, %ah
+ int $0x13
+ jnc load1ok
+ call errcode
+ jmp load1
+load1ok:
+
+ /*
+ * Print some innane message...
+ */
+ push %ax
+ mov $msg, %si
+ mov $0xE, %ah
+ mov $7, %bx
+ lodsb
+mloop: int $0x10
+ lodsb
+ cmp $0, %al
+ jne mloop
+ pop %ax
+
+ /*
+ * If the root device is set to FLOPPY (0), set to the
+ * appropriate kind of floppy. /dev/fd0 will correctly
+ * autodetect everything but /dev/fd0u1722 (2, 60).
+ */
+
+ push %ds
+ push %es
+ pop %ds
+ cmpw $0, root_dev
+ jne rootok
+ movb $0x2, root_dev + 1
+ cmp $21, %al
+ jne rootok
+ movb $60, root_dev
+rootok:
+ pop %ds
+
+ /*
+ * I would like to assume that setup is less than 9 sectors, but
+ * it is not. This is too much code.
+ */
+ movzx setup_sects, %si
+ or %si, %si /* If setup_sects is zero */
+ jnz sv_ok
+ mov $4, %si /* The real value is 4 */
+sv_ok: inc %si /* Tricky: count bootsect as setup
*/
+ jmp fix_setup
+
+more_setup:
+ call next_track
+load_setup:
+ int $0x13
+ cmp $0, %ah
+ je fix_setup
+ pusha
+ call errcode
+ popa
+ jmp load_setup
+
+fix_setup:
+ push %ax
+ shl $9, %ax /* ax *= 512 */
+ add %ax, %bx
+ pop %ax
+ sub %ax, %si
+ or %si, %si
+ jns more_setup
+
+ /*
+ * 3. Compute the slop, and load it high
+ */
+ neg %si /* How many sectors too many */
+ mov %ax, %bx
+ sub %si, %bx /* How many sectors to skip */
+ shl $5, %bx
+ add $KS_LOAD, %bx
+ mov syssize, %bp /* Get system size */
+ add $31, %bp /* Convert 16 byte clicks to sectors */
+ shr $5, %bp
+ mov %bx, %es /* New high memory ptr */
+ mov %bx, %ds
+ xor %bx, %bx
+
+ /*
+ * 4. Load the rest.
+ */
+ldr_ct:
+ call upload
+ sub %si, %bp
+ jna enter
+ call next_track
+loader:
+ mov $2, %ah
+ int $0x13
+ cmp $0, %ah
+ je ldr_ok
+ pusha
+ call errcode
+ popa
+ jmp loader
+ldr_ok:
+ mov %ax, %si
+ jmp ldr_ct
+
+ /*
+ * 5. Set up entry paramiters
+ */
+enter:
+ pop %ax /* Pointer to setup area */
+ mov %ax, %ds
+ mov %ax, %es
+ mov %ax, %fs
+ mov %ax, %gs
+ movb $0x20, 0x210 /* Tell setup.S that we are the bootsect
*/
+ orb $0x1, 0x211 /* Covert any zImage to bzImage (weird) */
+ movw $0x0, 0x214 /* This is where we loaded it */
+ movw $0x10, 0x216
+
+ /*
+ * This procedure turns off the floppy drive motor, so
+ * that we enter the kernel in a known state, and
+ * don't have to worry about it later.
+ *
+ * Actually, all this does is not annoy sysadmin, when he is
+ * forced to use this method of booting, because if the floppy
+ * is a demand-loaded module, the motor just won't turn off
+ * otherwise.
+ */
+
+ mov $0x3f2, %dx
+ mov $0, %al
+ /* outb */
+ .byte 0xEE /* I don't have time to figure out
+ * why this didn't assemble. */
+
+ /*
+ * Enter kernel with interrupts off, and at segment +20 from
+ * legacy bootsect location
+ */
+ cli
+ mov %ax, %ss
+ mov $0xFFF0, %sp /* Plenty heap */
+ ljmp $KS_LOAD + 0x20, $0
+
+/*
+ * This routine skips to next track.
+ */
+next_track:
+ test $1, %dh
+ jnz nt2
+ inc %dh
+ ret
+nt2: mov $0, %dh
+ inc %ch
+ ret
+
+/*
+ * Routine errcode prints a diagnostic to the screen
+ * Used for debugging and for printing BIOS error codes
+ */
+errcode:
+ mov %ah, %dh
+ mov $1, %cx
+print_hex:
+ mov $10, %ah
+ mov $7, %bx
+phl: mov %dh, %al
+ shr $4, %al
+ and 15, %al
+ add $0x90, %al
+ daa
+ add $0x40, %al
+ daa
+ int $0x10
+ shl $4, %dx
+ loop phl
+ mov $32, %al
+ int $0x10
+ ret
+
+/* Routine to upload memory into high region */
+upload:
+ pusha /* Remember registers */
+ push %si /* Prepare GDT */
+ mov $0xFF00, %di
+ push %di
+ mov $25, %cx
+ xor %ax, %ax
+ rep stosw
+ pop %si
+ pop %cx
+ dec %ax
+ mov %ax, 16(%si)
+ mov %ax, 24(%si)
+ movb $0x93, 21(%si)
+ movb $0x93, 29(%si)
+
+ mov %bx, 18(%si) /* Compute soruce */
+ mov %es, %ax
+ shl $4, %ax
+ add %ax, 18(%si)
+ pushf
+ mov %es, %ax
+ shr $12, %ax
+ popf
+ adc $0, %al
+ mov %al, 20(%si)
+
+ push %ds /* So that we can read dest ptr */
+ push %cs
+ pop %ds
+ mov hiptr, %ax /* Copy in dest */
+ shl $1, %cx
+ add %cx, hiptr /* Apply delta to dest */
+ pop %ds /* Restore old data segment */
+ mov %ax, 27(%si)
+
+ shl $7, %cx /* Number of words to upload */
+ mov $0x8700, %ax /* ??? */
+ int $0x15 /* Do upload */
+ jc uperr
+ /*
+ * Stuff has been loaded. Tick the delay bar.
+ */
+ mov $0x0E2E, %ax
+ mov $7, %bx
int $0x10
- jmp msg_loop
+ popa
+ ret
-die:
- # Allow the user to press a key, then reboot
- xorw %ax, %ax
- int $0x16
- int $0x19
-
- # int 0x19 should never return. In case it does anyway,
- # invoke the BIOS reset code...
- ljmp $0xf000,$0xfff0
-
-
-bugger_off_msg:
- .ascii "Direct booting from floppy is no longer supported.\r\n"
- .ascii "Please use a boot loader program instead.\r\n"
- .ascii "\n"
- .ascii "Remove disk and press any key to reboot . . .\r\n"
+uperr: call errcode
+hltx: jmp hltx
+
+hiptr: .word 0x1000
+dflags: .byte 36, 21, 18, 15, 9, 0
+msg: .ascii "Loading"
.byte 0
-
# Kernel attributes; used by setup
-
.org 497
setup_sects: .byte SETUPSECTS
root_flags: .word ROOT_RDONLY
-
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- Previous message: Matt Domsch: "Re: list digest / non-digest delivery problems?"
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- Reply: Brian Gerst: "Re: [PATCH] restore floppy boot image"
- Reply: Timothy Miller: "Re: [PATCH] restore floppy boot image"
- Reply: Timothy Miller: "Re: [PATCH] restore floppy boot image"
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