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Re: [PATCH v5 1/2] xen: Allow lib-y targets to also be .init.o
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Fri, 23 Jan 2026 13:53:31 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- Delivery-date: Fri, 23 Jan 2026 12:54:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 23/01/2026 12:37, Jan Beulich wrote:
> On 23.01.2026 11:56, Orzel, Michal wrote:
>> On 22/01/2026 11:01, Jan Beulich wrote:
>>> On 22.01.2026 10:49, Jan Beulich wrote:
>>>> On 21.01.2026 16:47, Alejandro Vallejo wrote:
>>>>> There's some assumptions as to which targets may be init-only. But
>>>>> there's little reason to preclude libraries from being init-only.
>>>>>
>>>>> Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
>>>>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>
>>>> I can't tell (yet) what it is, but as per CI something's clearly wrong
>>>> with this
>>>> change. Both xilinx-smoke-dom0less-arm64-* and qemu-smoke-dom0*-debug*
>>>> fail with
>>>> it in place. qemu-smoke-dom0-arm64-gcc (no "debug") was fine, suggesting
>>>> it may
>>>> be an early assertion triggering.
>>>
>>> Or an early UBSAN failure. I think ...
>> I did a test and it looks like the problem is division by zero in
>> generic_muldiv64. At this point, time is not yet initialized on Arm, so
>> cpu_khz
>> is 0 in ticks_to_ns.
>
> And division by 0 is otherwise benign on Arm64? (On x86 it raises an exception
> and hence would be a problem also without UBSAN.)
>From the ARM ARM spec:
"A division by zero results in a zero being written to the destination register,
without any indication that the division by
zero occurred."
~Michal
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