[Xen-devel] Re: non-ANSI Unions

[Anthony Liguori <aliguori@xxxxxxxxxx>]

PUCCETTI Armand wrote:
> Many "unions' are present in the code, but are non-ANSI!
Anonymous unions/structs are a rather common C extension.  They are much 
preferred to using a named union for the syntactical convenience of writing:
page_info.list

vs writing:

page_info.u.list

Also, this is not the only C extension that Xen utilizes.  If your 
analysis tool doesn't support the various GCC extensions, then it's not 
going to be much help.
Regards,

Anthony Liguori

> For instance, I see:
>
> struct page_info
> {
>    /* Each frame can be threaded onto a doubly-linked list. */
>    union {
>        struct list_head list;
>        /* Shadow uses this field as an up-pointer in lower-level shadows */
>        paddr_t up;
>    };
>    /* Reference count and various PGC_xxx flags and fields. */
>    u32 count_info;
> ...}
>
> which should be written properly:
>
> struct page_info
> {
>    /* Each frame can be threaded onto a doubly-linked list. */
>    union {
>        struct list_head list;
>        /* Shadow uses this field as an up-pointer in lower-level shadows */
>        paddr_t up;
>    } foo;
>
>    /* Reference count and various PGC_xxx flags and fields. */
>    u32 count_info;
> ...}
>
> Is there any good reason to do so? Is it possible to change that, to 
> comply with the standard
> (and therefore with analysis tools too) ?
>
> Armand

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