now that all 32-bit archs have 64-bit time types, the values for the
time-related socket option macros can be treated as universal for
32-bit archs. the sys/socket.h mechanism for this predates
arch/generic and is instead in the top-level header.

x32, which does not use the new time64 values of the macros, already
has its own overrides, so this commit does not affect it.

this commit preserves ABI fully for existing interface boundaries
between libc and libc consumers (applications or libraries), by
retaining existing symbol names for the legacy 32-bit interfaces and
redirecting sources compiled against the new headers to alternate
symbol names. this does not necessarily, however, preserve the
pairwise ABI of libc consumers with one another; where they use
time_t-derived types in their interfaces with one another, it may be
necessary to synchronize updates with each other.

the intent is that ABI resulting from this commit already be stable
and permanent, but it will not be officially so until a release is
made. changes to some header-defined types that do not play any role
in the ABI between libc and its consumers may still be subject to
change.

mechanically, the changes made by this commit for each 32-bit arch are
as follows:

- _REDIR_TIME64 is defined to activate the symbol redirections in
  public headers

- COMPAT_SRC_DIRS is defined in arch.mak to activate build of ABI
  compat shims to serve as definitions for the original symbol names

- time_t and suseconds_t definitions are changed to long long (64-bit)

- IPC_STAT definition is changed to add the IPC_TIME64 bit (0x100),
  triggering conversion of semid_ds, shmid_ds, and msqid_ds split
  low/high time bits into new time_t members

- structs semid_ds, shmid_ds, msqid_ds, and stat are modified to add
  new 64-bit time_t/timespec members at the end, maintaining existing
  layout of other members.

- socket options (SO_*) and ioctl (sockios) command macros are
  redefined to use the kernel's "_NEW" values.

in addition, on archs where vdso clock_gettime is used, the
VDSO_CGT_SYM macro definition in syscall_arch.h is changed to use a
new time64 vdso function if available, and a new VDSO_CGT32_SYM macro
is added for use as fallback on kernels lacking time64.

these structures can now be defined generically in terms of endianness
and long size. previously, the 32-bit archs all shared a common
definition from the generic bits header, and each 64-bit arch had to
repeat the 64-bit version, with endian conditionals if the arch had
variants of each endianness.

I would prefer getting rid of the preprocessor conditionals for
padding and instead using unnamed bitfield members, like commit
9b2921be did for struct timespec.
however, at present sendmsg, recvmsg, and recvmmsg need access to the
padding members by name to zero them. this could perhaps be cleaned up
in the future.

adapted from patch by Matthias Schiffer.

based on patch submitted by Jaydeep Patil, with minor changes.

....to be somewhat consistent and easily comparable with asm/socket.h
Signed-off-by: NRoman Yeryomin <roman@ubnt.com>

Signed-off-by: NRoman Yeryomin <roman@ubnt.com>

SO_REUSEPORT implementation was merged in the linux kernel commit
c617f398edd4db2b8567a28e899a88f8f574798d 2013-01-23

although a number is reserved for it, this option is not implemented
on Linux and does not work. defining it causes some applications to
use it, and subsequently break due to its failure.

why does mips have to be gratuitously incompatible in every possible
imaginable way?

the kernel wrongly expects the cmsg length field to be size_t instead
of socklen_t. in order to work around the issue, we have to impose a
length limit and copy to a local buffer. the length limit should be
more than sufficient for any real-world use; these headers are only
used for passing file descriptors and permissions between processes
over unix sockets.

basically, this version of the code was obtained by starting with
rdp's work from his ellcc source tree, adapting it to musl's build
system and coding style, auditing the bits headers for discrepencies
with kernel definitions or glibc/LSB ABI or large file issues, fixing
up incompatibility with the old binutils from aboriginal linux, and
adding some new special cases to deal with the oddities of sigaction
and pipe syscall interfaces on mips.

at present, minimal test programs work, but some interfaces are broken
or missing. threaded programs probably will not link.

this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.

some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.

some program was undefining AF_NETLINK and thereby breaking AF_ROUTE...

after re-reading 2.2.2 of POSIX 2008, all of these are in the correct
reserved namespaces and do not need protection.

based on patch by nik

thanks to Peter Mazinger (psm) for pointing many of these issues out
and submitting a patch on which this commit is loosely based