Re: [PATCH] restore floppy boot image

[Timothy Miller]

Joshua wrote:

> +enter:

You get a segment number here into AX...

> +	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

Then you clobber it here....

> +	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

And then you use the clobbered value here.  (Unless the low byte of SS 
is supposed to be zero.)

> +	mov	%ax, %ss
> +	mov	$0xFFF0, %sp	/* Plenty heap */
> +	ljmp	$KS_LOAD + 0x20, $0

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