>    Stopped at if_slowtimo+0x24: movw 0x2e(%ebx),%ax
> 
> This looks like a size inconsistency between registers.  ebx is 4 bytes, ax is
> 2 bytes.  Source and destination of mov commands must be same size.  Or is my
> interpretation of the error message wrong?

Your interpretation is incorrect. 

the x86 instruction:

	movw 0x2e(%ebx),%ax

means:

	add 0x2e and the contents of %ebx to form a 32-bit effective address.
	move a 16 bit quantity) from memory at that effective address
		into %ax (the low-order 16 bits of %eax)

					- Bill