@item
The macros @code{UTIME_NOW} and @code{UTIME_OMIT} are missing on some
platforms.
+@item
+On some platforms, @code{struct stat} does not include @code{st_atim},
+@code{st_mtim}, or @code{st_ctim} members. Use the gnulib module
+@samp{stat-time} for accessors to portably get at subsecond resolution.
@end itemize
Portability problems not fixed by Gnulib: