On Wed, Jul 24, 2024 at 10:41:43AM +0200, Jan Beulich wrote:
> On 24.07.2024 10:28, Roger Pau Monné wrote:
> > The only way I've found to cope with this is to use something like:
> >
> > #define ALT_CALL_ARG(arg, n) \
> > union { \
> > typeof(arg) e[(sizeof(long) + sizeof(arg) - 1) / sizeof(arg)]; \
> > unsigned long r; \
> > } a ## n ## __ = { \
> > .e[0] = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); })\
> > }; \
> > register unsigned long a ## n ## _ asm ( ALT_CALL_arg ## n ) = \
> > a ## n ## __.r
> >
> > An oversized array that ensures all the space of the long is covered
> > by the array, but then we need an extra variable, as we would
> > otherwise require modifying ALT_CALL{0..6}_OUT to use aX_.r instead of
> > aX_.
>
> I don't think we need to over-size the array. It just gets yet a little
> more complex then:
>
> #define ALT_CALL_ARG(arg, n) \
> register union { \
> struct { \
> typeof(arg) e; \
> char pad[sizeof(long) - sizeof(arg)]; \
> } s; \
> unsigned long r; \
> } a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \
> .s.e = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); }) \
> }
We could even simplify this, there's no need for the union anymore,
since struct size == sizeof(long) already:
#define ALT_CALL_ARG(arg, n) \
register struct { \
typeof(arg) e; \
char pad[sizeof(long) - sizeof(arg)]; \
} a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \
.e = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); }) \
}
The above seems to work for both the original issue and the new one.
Thanks, Roger.
