Re: [PATCH] x86/oprof: fix !HVM && !PV32 build

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.04.2021 12:51, Andrew Cooper wrote:
> On 23/04/2021 10:50, Roger Pau Monné wrote:
>> On Fri, Apr 16, 2021 at 04:20:59PM +0200, Jan Beulich wrote:
>>> On 16.04.2021 15:41, Andrew Cooper wrote:
>>>> On 16/04/2021 09:16, Jan Beulich wrote:
>>>>> clang, at the very least, doesn't like unused inline functions, unless
>>>>> their definitions live in a header.
>>>>>
>>>>> Fixes: d23d792478 ("x86: avoid building COMPAT code when !HVM && !PV32")
>>>>> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>> I agree this will fix the build.  However, looking at the code, I'm not
>>>> sure the original CONFIG_COMPAT was correct.  In particular, ...
>>>>
>>>>> --- a/xen/arch/x86/oprofile/backtrace.c
>>>>> +++ b/xen/arch/x86/oprofile/backtrace.c
>>>>> @@ -43,6 +43,7 @@ dump_hypervisor_backtrace(struct vcpu *v
>>>>>      return head->ebp;
>>>>>  }
>>>>>  
>>>>> +#ifdef CONFIG_COMPAT
>>>>>  static inline int is_32bit_vcpu(struct vcpu *vcpu)
>>>>>  {
>>>>>      if (is_hvm_vcpu(vcpu))
>>>> ... this chunk of logic demonstrates that what oprofile is doing isn't
>>>> related to the Xen ABI in the slightest.
>>>>
>>>> I think OProfile is misusing the guest handle infrastructure, and
>>>> shouldn't be using it for this task.
>>> I'm afraid I consider this something for another day. Both the
>>> original #ifdef and the one getting added here are merely
>>> measures to get things to build.
>> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>
>> Without entering on the debate whether CONFIG_COMPAT is the correct
>> conditional to use it's not making the issue any worse, and it will
>> allow to unblock the build. We can discuss about the CONFIG_COMPAT
>> stuff later.
> 
> I disagree.  Fixing this less effort than the time wasted arguing about
> fixing it.
> 
> But if you are going to insist on not fixing it, and putting in a patch
> like this, then at a minimum, it needs to include a TODO comment stating
> that the use of CONFIG_COMPAT is bogus and needs fixing.

I disagree: It is (for now) just you saying this is bogus. The (ab)use
of the handle infrastructure was there before. You could have sent a
fix long ago, therefore, if you were thinking this needs fixing. I can
see that you have good intentions, but orthogonal issues shouldn't be
used to block necessary adjustments (and this applies to other pending
build fixes as well).

Jan