Re: [Xen-devel] [PATCH ARM v6 07/14] mini-os: arm: boot code

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-07-17 at 10:37 +0100, Thomas Leonard wrote:

> >> +irq_handler:
> >> +       ldr     sp, =irqstack_end
> >> +       push    {r0 - r12, r14}
> >> +
> >> +       ldr     r0, IRQ_handler
> >> +       cmp     r0, #0
> >> +       .word   0x07f000f0      @ undeq - panic if no handler
> >
> >
> > Hrmmm, I didn't spot this earlier. How can this work? You unconditionally
> > called an undefined encoding.
> 
> Here, the leading "0" is EQ, so it's only executed if IRQ_handler is
> unset ("undEQ").

ARMv7 ARM A8.8.247 says that UDF isn't conditional,so you probably odn't
want to rely on that.

Ian.



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