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

[Thomas Leonard <talex5@xxxxxxxxx>]

On 17 July 2014 10:46, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> 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.

Yes, just noticed that myself. Will replace it with a branch.


-- 
Dr Thomas Leonard        http://0install.net/
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