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Re: [PATCH 1/2] livepatch: do not ignore sections with 0 size
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 17 Mar 2022 15:09:14 +0100
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- Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 17 Mar 2022 14:09:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.03.2022 15:00, Andrew Cooper wrote:
> On 17/03/2022 11:08, Roger Pau Monne wrote:
>> A side effect of ignoring such sections is that symbols belonging to
>> them won't be resolved, and that could make relocations belonging to
>> other sections that reference those symbols fail.
>>
>> For example it's likely to have an empty .altinstr_replacement with
>> symbols pointing to it, and marking the section as ignored will
>> prevent the symbols from being resolved, which in turn will cause any
>> relocations against them to fail.
>
> I agree this is a bug in livepatch handling, but it's also an error in
> the generated livepatch. We should not have relocations to an empty
> altinstr_replacement section in the first place.
I think having such relocations is quite natural, but ...
> This will probably be from the lfences, where the replacement in a nop
> and takes no space. I think I know how to fix this case.
... of course it's possible to eliminate them. Whether that's worthwhile
to add logic for I'm not sure.
Jan
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