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

[Jan Beulich <jbeulich@suse.com>]

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@citrix.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> 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.

Jan