Re: [RFC 0/5] Introduce dynamic tracer using Livepatch

[Ryo Takakura <takakura@xxxxxxxxxxxxx>]

On Tue, 27 Oct 2026 10:18:44 +0000, Andrew Cooper wrote:
>On 27/10/2026 4:37 am, Ryo Takakura wrote:
>>> You are also going to need a GCC_PATCHABLE_FUNCTION_ENTRY_BROKEN symbol,
>>> because of https://godbolt.org/z/sde4faxaz.  See the ASM_GOTO_OUTPUT for
>>> another example of this pattern.  Just use a plain version check rather
>>> than tying it to XEN_IBT; this is a new feature and people wanting to
>>> use it can use a new enough compiler, and it avoids variability
>>> depending on other options.
>> I didn't know about the compiler behaviour. Thank you for the detail.
>> I'll make sure to check the acceptable compiler version and add a version
>> check as you suggest.
>
>https://maskray.me/blog/fpatchable-function-entry seems to have a
>blow-by-blow of the bugs.

Interesting!

>The ordering with respect to ENDBR instructions is the only issue which
>will affect Xen, I think.  We don't use COMDAT, or BTI on ARM yet.
>
>Clang support seems to have been mostly correct at the point of being
>added, which is rather more than can be said for the GCC side.

I see. Thank you for the advise.
I follow them when preparing the check.

>>> Separately, you have a number of MISRA violations which you're
>>> introducing in your series.  I see you've got cf_check, which suggests
>>> you have built in GitlabCI.  Have you also run Eclair?
>> Thank you for pointing this out.
>> My apologies for the violations. I wasn't aware of the tests
>> and haven't run either of them. I added the cf_check following
>> the existing code that I referred to when preparing this series.
>> I'll make sure to run those tests before sending next version.
>
>Do you have an account on Gitlab to run the CI testing?  If not, reach
>out on Matrix.

I don't have an account yet.
Ok, I'll ask on Matrix.

Sincerely,
Ryo Takakura