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Re: [PATCH v9] common: honor CONFIG_CC_SPLIT_SECTIONS also for assembly functions
- To: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 13 Feb 2026 09:12:59 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 13 Feb 2026 08:13:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.02.2026 19:29, Alejandro Vallejo wrote:
> On Wed Jan 28, 2026 at 3:35 PM CET, Jason Andryuk wrote:
>> On 2025-04-01 06:58, Jan Beulich wrote:
>>> Leverage the new infrastructure in xen/linkage.h to also switch to per-
>>> function sections (when configured), deriving the specific name from the
>>> "base" section in use at the time FUNC() is invoked.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx> # arm
>
> I don't seem to have the original patch in my inbox, so I'll just answer here.
>
> About the assembly modifications on the exception entry points:
>
> With split sections the linker is free to reorder all of them as it sees fit,
> which probably means we want int3 after every jump to prevent straight-line
> speculation from allocating an XSA number for us. It's possible the linker
> might
> inject them, but it might also not. Better to err on the side of caution.
We're lacking such INT3 elsewhere, hence why this is the topic of separate
(existing) work. See how, for example, we're also not using -mharden-sls=all.
See e.g. [1] for a very old posting. Even in my outbox I can't find newer
postings covering more stuff. Intermediately some of this was posted to
security@ only, but there clearly was the plan to have all of this in public.
> Though more generally, I'd just keep all exception entry points in the same
> section. They'd never get GC'ed anyway and we're paying an extra branch in the
> #PF path for no reason.
Inserting a branch there was, iirc, asked for by someone independent of this
work. But yes, suppressing too fine grained section splits is an option.
Jan
[1] https://lists.xenproject.org/archives/html/xen-devel/2020-11/msg01542.html
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