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Re: [XEN][PATCH] x86/hvm: vlapic: move vlapic_set_ppr/apicv_write() under CONFIG_INTEL_VMX
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 23 Oct 2025 17:37:49 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Grygorii Strashko <grygorii_strashko@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 23 Oct 2025 15:37:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 23.10.2025 17:30, Andrew Cooper wrote:
> On 23/10/2025 4:20 pm, Grygorii Strashko wrote:
>> From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
>>
>> Functions:
>> - vlapic_apicv_write()
>> - vlapic_set_ppr()
>> are used by Intel VMX code only, so move them under CONFIG_INTEL_VMX ifdef.
>>
>> Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
>
> Yes and no. Yes right now, but this is needed for AMD AVIC, which I
> understand is one one of the plans.
>
> Throwing #ifdef's around like this in common files is fragile and will
> lead to a randconfig nightmare.
>
> There is an alternative which ought to work. Turning on
> -ffunction-sections (we already have this for livepatching), and
> implementing link time --gc-sections (new work).
>
> That way, the compiler/linker simply drops functions that are not
> referenced in the final binary.
>
> Personally I think it will be far nicer and more scalable than the
> #ifdefary, (not to mention far easier - it gets rid of everything
> unreferenced with one fell swoop).
>
> Thoughts?
We'd need to have Misra buy-off on such an approach. I'm not sure if Eclair's
scanning would take --gc-sections effects into account.
Jan
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