+++ b/sys/compat/freebsd32/freebsd32.h
> > @@ -36,8 +36,17 @@
> > #include <sys/_ffcounter.h>
> > 
> > /*
> > - * i386 is the only arch with a 32-bit time_t
> > + * i386 is the only arch with a 32-bit time_t.
> > + * Also it is the only arch with (u)int64_t having 4-bytes alignment.
> >  */
> > +typedef struct {
> > +#ifdef __amd64__
> > + uint32_t val[2];
> > +#else
> > + uint64_t val;
> > +#endif
> > +} freebsd32_uint64_t;
> 
> Any reason not to use:
> 
>   typedef uint64_t freebsd32_uint64_t __aligned(4);
> 
> on amd64 (and normal typedef elsewhere)? Then you can just use the
> normal CP. See for example https://godbolt.org/z/svseWv7xo.
Yes, this way it uses only std C instead of the GNU extension, and not
depend on compiler properly handle unaligned types.

IMO it is better that way, and all machinery is hidden under the typedef+
the macro.