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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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?

Jan


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