Re: [Xen-devel] [PATCH 09/14] livepatch: Add per-function applied/reverted state tracking marker

["Wieczorkiewicz, Pawel" <wipawel@xxxxxxxxx>]

On 22. Aug 2019, at 12:07, Julien Grall <julien.grall@xxxxxxx> wrote:

Hi,

On 22/08/2019 08:44, Wieczorkiewicz, Pawel wrote:

…snip...

Is this going to break livepatch on Arm? If so, do you have any plan to fix it?

No, I do not think it is. But, I am unable to test on Arm (No access to HW and SW),
so I took the conservative approach here.

Arm provides decent free model (see FoundationModel) that you can use for basic testing. Alternatively, you QEMU also support virtualization extension.

Let me have a look at the code (I will answer separately) to see if I can spot anything.

[...]

diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index 2aec532ee2..a93126f631 100644
--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -117,7 +117,7 @@ int arch_livepatch_quiesce(void);
 void arch_livepatch_revive(void);
   void arch_livepatch_apply(struct livepatch_func *func);
-void arch_livepatch_revert(const struct livepatch_func *func);
+void arch_livepatch_revert(struct livepatch_func *func);

I doubt livepatch on Arm will compile after this change.

What would be you suggestion then?

Cross-compiler are nowadays widely available. So build testing your changes in common code would be the minimum.

I wish it was that simple. Nevertheless, I will try to prepare an environment to perform such builds.

In this case, as you dropped the const from the prototype, you will need to do the same in the declaration.

Yes, but I see 2 options here:

- Enable the feature also for Arm (I prefer that, but will not be able to test that in nearest future)

- Keep Arm excluded and sprinkle code with #ifdef CONFIG_X86

Shall I limit the change to X86 everywhere
 Or maybe drop the compilation flag completely?

I am a bit confused. Which compilation flag do you refer to?

CONFIG_X86

Cheers,

--
Julien Grall

Best Regards,
Pawel Wieczorkiewicz

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