Check to see if we've reached the end of the map before attempting to

skip past an empty region, otherwise we end up generating an infinitely
long e820 map.  (Yes, there *are* real systems that provide e820 maps
with a zero-length region at the end...)

src/arch/i386/firmware/pcbios/e820mangler.S

@@ -361,7 +361,12 @@ int15_e820:
 	pushl	%edx	
 	call	split_e820
 	pushfw
+	/* Skip empty region checking if we've reached the end of the
+	 * map or hit an error, to avoid a potential endless loop.
+	 */
 	jc	1f
+	testl	%ebx, %ebx
+	jz	1f
 	/* Check for an empty region */
 	pushl	%eax
 	movl	%es:8(%di), %eax