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Re: [PATCH RFC] Arm64: amend "xen/arm64: head: Add missing code symbol annotations"
- To: Julien Grall <julien@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 15 Jul 2024 11:11:50 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 15 Jul 2024 09:12:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10.07.2024 23:29, Julien Grall wrote:
> Hi Jan,
>
> On 10/06/2024 14:37, Jan Beulich wrote:
>> While the change[1] didn't go in yet, there is the intention for the ELF
>> metadata annotations from xen/linkage.h to also effect honoring of
>> CONFIG_CC_SPLIT_SECTIONS. In code that's placement / ordering sensitive,
>> these annotations therefore need using with some care.
>
> Looking at the code, I think the ordering only really matter for
> 'start'. The rest can be ordered in any way within the assembly file. So...
>
>>
>> [1] https://lists.xen.org/archives/html/xen-devel/2024-02/msg00470.html
>>
>> Fixes: fba250ae604e ("xen/arm64: head: Add missing code symbol annotations")
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> An alternative would be to use LABEL{,_LOCAL}() instead of FUNC{,_LOCAL}().
>> That would avoid the need for any override, but would also lose the type
>> information.
>
> ... I would suggest to only convert FUNC(start) to LABEL(start).
>
>> Question is whether the annotated ranges really are
>> "functions" in whichever wide or narrow sense.
>
> Everything but 'start' are functions.
Well, maybe, but that's not the only criteria here. Expressions like
.long _end - real_start /* SizeOfCode */
need to be possible for the assembler to resolve. Which requires both
symbols to live in the same section, or the subtrahend to live in the
current section. IOW I then also need to convert real_start to use
LABEL_LOCAL(). Is that going to be okay?
Jan
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