Re: [Xen-devel] Clang tools build

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.02.16 at 16:25, <andrew.cooper3@xxxxxxxxxx> wrote:
> Hello,
> 
> Now that Clang 3.5 can build the hypervisor, I was just preparing a
> patch to README, and encountered this:
> 
> In file included from xc_altp2m.c:23:
> In file included from ./xc_private.h:35:
> In file included from ./include/xenctrl.h:53:
> /local/xen.git/tools/libxc/../../tools/include/xen/foreign/x86_64.h:203:47:
> error: 'aligned' attribute ignored when parsing type
> [-Werror,-Wignored-attributes]
>     __align8__ uint64_t evtchn_pending[sizeof(__align8__ uint64_t) * 8];
>                                               ^~~~~~~~~~
> /local/xen.git/tools/libxc/../../tools/include/xen/foreign/x86_64.h:13:36:
> note: expanded from macro '__align8__'
> # define __align8__ __attribute__((aligned (8)))
>                                    ^~~~~~~~~~~
> /local/xen.git/tools/libxc/../../tools/include/xen/foreign/x86_64.h:204:44:
> error: 'aligned' attribute ignored when parsing type
> [-Werror,-Wignored-attributes]
>     __align8__ uint64_t evtchn_mask[sizeof(__align8__ uint64_t) * 8];
>                                            ^~~~~~~~~~
> /local/xen.git/tools/libxc/../../tools/include/xen/foreign/x86_64.h:13:36:
> note: expanded from macro '__align8__'
> # define __align8__ __attribute__((aligned (8)))
>                                    ^~~~~~~~~~~
> 2 errors generated.
> 
> In this case, Clang is complaining that the alignment attribute is wrong
> for uint64_t.  This is correct for 64bit compilations, but wrong for
> 32bit.

If it only complains about it when used as operand to sizeof() I
think it's correctly saying so.

>  On the other hand, I am not sure whether it is sensible to do a
> blanket disable of -Wignored-attributes.

I agree it's not ideal, but I see no alternative, and I'm not sure
there are many cases where a legitimately ignored attribute
would be a problem (leaving as a potential issue only cases
where the compiler wrongly ignores one).

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel