Inline assembly under FreeBSD

[Unga]

Hi all

I'm trying to execute following inline assembly code
in a C function under FreeBSD 7.0:

typedef unsigned char u8;
typedef unsigned short u16;

u8 devno= 0x80;

static int check_extensions(u8 devno)
{
	u16 ax, bx, cx, dx, di;

	ax = 0x4100;
	bx = 0x55AA;
	dx = devno;
	asm("pushfl; stc; int $0x13; setc %%al; popfl"
	    : "+a" (ax), "+b" (bx), "=c" (cx), "+d" (dx)
	    : : "esi", "edi");

	if ((u8)ax)
		return -1;	/* No extended information */
	else
		return 1;	/* Extended information available */
}

When it is executing the int $0x13, it crashes with
"Program received signal SIGBUS, Bus error."

Could you guys give me a helping hand to identify
what's the problem?

Input and return values are at:
http://en.wikipedia.org/wiki/INT_13

Thanks in advance.

Kind regards
Unga


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