Re: [Xen-devel] [PATCH] x86/vmx: fix build with clang 3.8.0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.02.17 at 14:42, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 09/02/17 13:14, Jan Beulich wrote:
>>>>> On 09.02.17 at 14:05, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 09/02/17 13:01, Jan Beulich wrote:
>>>>>>> On 09.02.17 at 13:49, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>> On 09/02/17 11:33, Roger Pau Monne wrote:
>>>>>> --- a/xen/include/asm-x86/hvm/vmx/vmx.h
>>>>>> +++ b/xen/include/asm-x86/hvm/vmx/vmx.h
>>>>>> @@ -602,15 +602,16 @@ void vmx_pi_hooks_assign(struct domain *d);
>>>>>>  void vmx_pi_hooks_deassign(struct domain *d);
>>>>>>  
>>>>>>  /* EPT violation qualifications definitions */
>>>>>> -typedef union __transparent__ ept_qual {
>>>>>> +typedef union ept_qual {
>>>>> Please can we use
>>>>>
>>>>> typedef __transparent__ union ept_qual {
>>>>>
>>>>> which clang is happy with, and will help avoid problems such as the
>>>>> cper_mce_record issue in c/s f8be76e2fe
>>>> Would clang also be happy with it moved near the end of that
>>>> line
>>>>
>>>> typedef union ept_qual __transparent__ {
>>>>
>>>> Having the attribute ahead of "union" is, I think, strictly speaking
>>>> undefined behavior, as it then may as well apply to "typedef".
>>> No.  The result is
>>>
>>> /local/xen.git/xen/include/asm/hvm/vmx/vmx.h:605:40: error: expected
>>> identifier or '('
>>> typedef union ept_qual __transparent__ {
>>>                                        ^
>>> /local/xen.git/xen/include/asm/hvm/vmx/vmx.h:614:3: error: type
>>> specifier missing, defaults to 'int' [-Werror,-Wimplicit-int]
>>> } ept_qual_t;
>>>   ^~~~~~~~~~
>>> 2 errors generated.
>>>
>>> In which case the original patch as proposed will probably do.  It turns
>>> out the presence of ept_qual_t does cause a compiler error if
>>> __transparent__ is missing from scope.
>> But then the question is what the attribute applies to in the original
>> version - the union, or just the typedef? The placement would
>> suggest the latter, so I'd again be afraid of undefined behavior. Can
>> it be moved ahead on that line?
> 
> You mean this?
> 
> } __transparent__ ept_qual_t;

Yes.

> Clang is happy with that.

Good.

Jan


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