Re: [PATCH v5 1/2] xen: Allow lib-y targets to also be .init.o

[Jan Beulich <jbeulich@xxxxxxxx>]

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.)

Jan

> (XEN) [000000005019d0ee] UBSAN: Undefined behaviour in lib/muldiv64.c:23:21
> (XEN) [00000000501cfc11] division by zero
> (XEN) [0000000050211d11] Xen WARN at common/ubsan/ubsan.c:176
> (XEN) [000000005023b3ec] ----[ Xen-4.22-unstable  arm64  debug=y ubsan=y  Not
> tainted ]----
> (XEN) [0000000050afc964] Xen call trace:
> (XEN) [0000000050b0e4ec]    [<00000a000032ab44>]
> ubsan.c#ubsan_epilogue+0x14/0xec (PC)
> (XEN) [0000000050b2f1c1]    [<00000a000032b35c>]
> __ubsan_handle_divrem_overflow+0x114/0x1e4 (LR)
> (XEN) [0000000050b577dd]    [<00000a000032b35c>]
> __ubsan_handle_divrem_overflow+0x114/0x1e4
> (XEN) [0000000050b790fb]    [<00000a00003eb9d0>] generic_muldiv64+0x7c/0xbc
> (XEN) [0000000050b94539]    [<00000a00003bfb9c>] ticks_to_ns+0x24/0x2c
> (XEN) [0000000050bad89d]    [<00000a00003bfc04>] get_s_time+0x34/0x54
> (XEN) [0000000050bc731b]    [<00000a000032dec8>]
> console.c#printk_start_of_line+0x2bc/0x374
> (XEN) [0000000050be7987]    [<00000a000032ef3c>]
> console.c#vprintk_common+0x454/0x484
> (XEN) [0000000050c06033]    [<00000a000032ef94>] vprintk+0x28/0x30
> (XEN) [0000000050c1e4df]    [<00000a000032eff8>] printk+0x5c/0x64
> (XEN) [0000000050c3904b]    [<00000a00005548f8>] 
> end_boot_allocator+0x31c/0x548
> (XEN) [0000000050c55a86]    [<00000a0000585c58>] start_xen+0x150/0xe68
> (XEN) [0000000050c70232]    [<00000a00002001a4>] 
> head.o#primary_switched+0x4/0x24
> (XEN) [0000000050c8d2bf]
> 
> ~Michal