Re: [Xen-devel] headers.chk failing under certain circumstances.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.12.11 at 14:38, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> To fix the current 32/64bit interaction errors with the kexec
> hypercalls, I need to use uint64_aligned_t as a datatype.  For the
> normal compile, this is all fine, but as header.chk does not define
> __XEN__ or __XEN_TOOLS__, the declaration of uint64_aligned_t is never
> made, leading to the check failing.
> 
> There are other hypercall interfaces which use these datatypes: domctl,
> sysctl and hvm_op, but these header files are explicitly filtered out
> from the prerequisites for header.chk.

This is really intentional for the domctl and sysctl cases - these are
"internal" interfaces (between the tools and the hypervisor), and
hence can be more relaxed in style.

Pretty much the same goes for the hvm op definitions - we simply
assume that users of this use a compiler capable of dealing with this
(I'm not fully convinced this is The Right Thing To Do, but it's the
status quo at least).

> Given that uint64_aligned_t is a
> sensible datatype to be using with the hypercall interface, fixing the
> check seems to be the correct solution.

Sensible or not, you would have to find a way to define such a type
in a compiler-independent (i.e. ANSI conforming) manner, and I'm
afraid you won't be able to.

> In your oppinion, which is the best course of action? To define __XEN__
> or __XEN_TOOLS__ as part of the check (this throws up other errors as
> part of the check process, suggesting that the header files are hiding
> ansi non-conformance in certain blocks), or dont predicate the
> definition of uint64_aligned_t on the presence of the above defines?

__XEN__ and __XEN_TOOLS__ must specifically not be defined for
these checks (and these symbols indeed get used to frame certain
definitions that are considered "internal" as outlined above - obviously,
by framing any definition this way we hide them from "foreign"
consumers *and* the [pointless in this case] style checking).

So bottom line is - no, you can't use uint64_aligned_t as much as any
other non-ANSI extension. Preventing anyone to try is what the
check was introduced for.

Jan


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