Re: [PATCH 3/6] x86/mem-paging: use guest handle for XENMEM_paging_op_prep

[Julien Grall <julien@xxxxxxx>]

On 20/04/2020 13:35, Jan Beulich wrote:
> On 20.04.2020 14:31, Jan Beulich wrote:
> > On 20.04.2020 14:20, Julien Grall wrote:
> > > On 20/04/2020 13:12, Jan Beulich wrote:
> > > > On 20.04.2020 14:08, Julien Grall wrote:
> > > > Are the unions plain ones? I could see room for behavior like
> > > > the one you describe with transparent unions, albeit still
> > > > not quite like you describe it. Getting handle types to be
> > > > properly type-checked by the compiler is pretty imperative imo.
> > > It looks like x86 is using structure, but arm is using plain union:
> > >
> > > #define ___DEFINE_XEN_GUEST_HANDLE(name, type)                  \
> > >      typedef union { type *p; unsigned long q; }                 \
> > >          __guest_handle_ ## name;                                \
> > >      typedef union { type *p; uint64_aligned_t q; }              \
> > >          __guest_handle_64_ ## name
> > I don't see how this would make a difference, and hence ...
> >
> > > I will look at introducing a union on Arm.
> > ... how this would help. I must be missing something, or there
> > must be a very curious bug in only the Arm gcc.
> Compiling this (for x86) properly raises two errors:
>
> union u1 { void *p; unsigned long v; };
> union u2 { void *p; unsigned long v; };
>
> void test(union u1 u1, union u2 u2) {
>         test(u1, u1);
>         test(u2, u2);
> }
You are right. It is just me not compiling properly. Sorry for the noise :(

Cheers,

--
Julien Grall