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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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;

Clang is happy with that.

~Andrew

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