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Re: [PATCH] RFC: xen/x86: Enable --gc-sections
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 8 Dec 2025 09:46:06 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Grygorii Strashko <grygorii_strashko@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 08 Dec 2025 08:46:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05.12.2025 23:40, Andrew Cooper wrote:
> On 05/12/2025 10:28 pm, Jason Andryuk wrote:
>> When linking to create xen-syms, add --gc-sections to garbage collect
>> unused stuff. Relies on CONFIG_CC_SPLIT_SECTIONS
>>
>> We need to add KEEP() to the linker script in assorted places to retain
>> appropriate data - especially the arrays created therein.
>>
>> Something is off though. In a test where memory_add() is unreachable,
>> it is still included. I'm not sure, but I am wondering if it's the
>> alternatives somehow keeping a reference to it.
>
> Yes, .altinstructions contains relocations against the origin patch
> site, which will cause it to appear to be referenced. The same will be
> happening with a bunch of other sections.
We will need to derive helper section names from base section ones. See
e.g. HAVE_AS_SECTNAME_SUBST as introduced by "common: honor
CONFIG_CC_SPLIT_SECTIONS also for assembly functions", controlling the
use of the --sectname-subst asssembler option, to in turn be able to use
%S in section names (available from gas 2.26 onwards).
I'd like to point out though that for the purpose of "x86/alternatives:
allow replacement code snippets to be merged" we may want to avoid
extending this to .altinstr_replacement.
Jan
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