The don't. Both alpha and sparc64 use 64-bit values in struct stat.
What sparc64 kernel are you running? ;-)
No seriously, do you present a 64-bit struct stat in the glibc headers
and then swizzle between that and what the kernel speaks in? Because
at least as of right now, both alpha and sparc64 kernels have 32-bit
values in the native struct stat, so only in the presence of glibc
swizzling can I see your statement as making sense.