prior to commit 685e40bb09, x86_64 was
correctly passing O_LARGEFILE to SYS_open; it was removed (defined to
0 in the public header, and changed to use the public definition) as
part of that change, probably out of a mistaken belief that it's not
needed.
however, on a mixed system with 32-bit and 64-bit binaries, it's
important that all files be opened with O_LARGEFILE, even if the
opening process is 64-bit, in case a descriptor is passed to a 32-bit
process. otherwise, attempts to access past 2GB in the 32-bit process
could produce EOVERFLOW.
most 64-bit archs added later got this right alread, except for
mips64. x32 was also affected. there are now fixed.
