mingw.
@item
-This function returns 0 for dup2 (1, 1) on some platforms:
+This function returns 0 for @code{dup2 (1, 1)} on some platforms:
Cygwin 1.5.x.
@item
+This function may return @code{-EBADF} instead of @code{-1} on some platforms:
+Linux releases between July 2008 and May 2009 (versions 2.6.27 to 2.6.29).
+
+@item
+This function returns @code{EMFILE} instead of @code{EBADF} for
+extremely large targets, which interferes with using
+@code{dup2(fd,fd)==fd)} as the minimal @code{EBADF} filter:
+FreeBSD 6.1, Cygwin 1.5.
+
+@item
This function is missing on some older platforms.
@end itemize