under _GNU_SOURCE for namespace cleanliness, analogous to other archs.
the original placement in sys/reg.h seems not to have been motivated;
such a header isn't even present on other implementations.

This patch adds an explicit cast to the int arguments passed to the
inline asm used in the RISC-V's implementation of `a_cas`, to ensure
that they are properly sign extended to 64 bits. They aren't
automatically sign extended by Clang, and GCC technically also doesn't
guarantee that they will be sign extended.

the syscall number is reserved on all targets, but it is not wired up
on all targets, see

  linux commit 8f6ccf6159aed1f04c6d179f61f6fb2691261e84
  Merge tag 'clone3-v5.3' of ... brauner/linux

  linux commit 8f3220a806545442f6f26195bc491520f5276e7c
  arch: wire-up clone3() syscall

  linux commit 7f192e3cd316ba58c88dfa26796cf77789dd9872
  fork: add clone3

see

  linux commit 7615d9e1780e26e0178c93c55b73309a5dc093d7
  arch: wire-up pidfd_open()

  linux commit 32fcb426ec001cb6d5a4a195091a8486ea77e2df
  pid: add pidfd_open()

now that all 32-bit archs have 64-bit time_t (and suseconds_t), the
arch-provided _Int64 macro (long or long long, as appropriate) can be
used to define them, and arch-specific definitions are no longer
needed.

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.

policy has long been that these definitions are purely a function of
whether long/pointer is 32- or 64-bit, and that they are not allowed
to vary per-arch. move the definition to the shared alltypes.h.in
fragment, using integer constant expressions in terms of sizeof to
vary the array dimensions appropriately. I'm not sure whether this is
more or less ugly than using preprocessor conditionals and two sets of
definitions here, but either way is a lot less ugly than repeating the
same thing for every arch.

LLONG_MAX is uniform for all archs we support and plenty of header and
code level logic assumes it is, so it does not make sense for limits.h
bits mechanism to pretend it's variable.

LONG_BIT can be defined in terms of LONG_MAX; there's no reason to put
it in bits.

by moving LONG_MAX definition to __LONG_MAX in alltypes.h and moving
LLONG_MAX out of bits, there are now no plain-C limits that are
defined in the bits header, so the bits header only needs to be
included in the POSIX or extended profiles. this allows the feature
test macro logic to be removed from the bits header, facilitating a
long-term goal of getting such logic out of bits.

having __LONG_MAX in alltypes.h will allow further generalization of
headers.

archs without a constant PAGESIZE no longer need bits/limits.h at all.

building on commit 97d35a55,
__BYTE_ORDER is now available wherever alltypes.h is included.
endian.h should not be used since, in the future, it will expose
identifiers that are not in the reserved namespace for the headers
which were previously using it.

this change is motivated by the intersection of several factors.
presently, despite being a nonstandard header, endian.h is exposing
the unprefixed byte order macros and functions only if _BSD_SOURCE or
_GNU_SOURCE is defined. this is to accommodate use of endian.h from
other headers, including bits headers, which need to define structure
layout in terms of endianness. with time64 switch-over, even more
headers will need to do this.

at the same time, the resolution of Austin Group issue 162 makes
endian.h a standard header for POSIX-future, requiring that it expose
the unprefixed macros and the functions even in standards-conforming
profiles. changes to meet this new requirement would break existing
internal usage of endian.h by causing it to violate namespace where
it's used.

instead, have the arch's alltypes.h define __BYTE_ORDER, either as a
fixed constant or depending on the right arch-specific predefined
macros for determining endianness. explicit literals 1234 and 4321 are
used instead of __LITTLE_ENDIAN and __BIG_ENDIAN so that there's no
danger of getting the wrong result if a macro is undefined and
implicitly evaluates to 0 at the preprocessor level.

the powerpc (32-bit) bits/endian.h being removed had logic for varying
endianness, but our powerpc arch has never supported that and has
always been big-endian-only. this logic is not carried over to the new
__BYTE_ORDER definition in alltypes.h.

now that commit f7f10797 removed the
legacy i386 conditional definition, va_list is in no way
arch-specific, and has no reason to be in the future. move it to the
shared part of alltypes.h.in

commit ab3eb89a removed it as part of
correcting the mcontext_t definition, but there is still code using
struct sigcontext and expecting the member names present in it, most
notably libgcc_eh. almost all such usage is incorrect, but bring back
struct sigcontext at least for now so as not to introduce regressions.

in order for sys/procfs.h (provided by sys/user.h) to be useful, it
needs to match the API its consumers (gdb, etc.) expect, including the
member names established by glibc.

this partly reverts commit 29e8737f,
which partly reverted d493206d,
eliminating struct user_fpregs_struct which seems to have had no
precedent and using union __riscv_mc_fp_state for elf_fpregset_t. this
requires indirect inclusion of signal.h to make union
__riscv_mc_fp_state visible, but being that these are nonstandard
"junk" headers with no official restrictions on what they can pull in,
that's no big deal.

split off and expanded from patch by Khem Raj.

the top-level mcontext_t member names were namespace-violating in
standards profiles before, and nested-level member names (some of them
single-letter) were egregiously bad namespace impositions even in
non-strict profiles. moreover, they mismatched those used in the
public API first defined in glibc, breaking any code making use of
them.

unlike most archs, the public API used in glibc for riscv mcontext_t
members was designed to be namespace-safe, so we can and should expose
the members regardless of feature test macros. only the typedefs for
greg_t, gregset_t, and fpregset_t need to be protected behind FTMs.

the struct tags for mcontext_t and ucontext_t are also changed. for
mcontext_t this is necessary to make the common definition across
profiles namespace-safe. for ucontext_t, it's just a matter of
matching the tag from the glibc-defined API.

these changes are split off and expanded from a patch by Khem Raj.

The operand sepcifiers in a_cas and a_cas_p for riscv64 were incorrect:
there's a backwards branch in the routine, so despite tmp being written
at the end of the assembly fragment it cannot be allocated in one of the
input registers because the input values may be needed for another trip
around the loop.

For code that follows the guaranteed forward progress requirements, the
backwards branch is rarely taken: SiFive's hardware only fails a store
conditional on execptional cases (ie, instruction cache misses inside
the loop), and until recently a bug in QEMU allowed back-to-back
store conditionals to succeed.  The bug has been fixed in the latest
QEMU release, but it turns out that the fix caused this latent bug in
musl to manifest.

new mount api syscalls were added, same numers on all targets, see

  linux commit a07b20004793d8926f78d63eb5980559f7813404
  vfs: syscall: Add open_tree(2) to reference or clone a mount

  linux commit 2db154b3ea8e14b04fee23e3fdfd5e9d17fbc6ae
  vfs: syscall: Add move_mount(2) to move mounts around

  linux commit 24dcb3d90a1f67fe08c68a004af37df059d74005
  vfs: syscall: Add fsopen() to prepare for superblock creation

  linux commit ecdab150fddb42fe6a739335257949220033b782
  vfs: syscall: Add fsconfig() for configuring and managing a context

  linux commit 93766fbd2696c2c4453dd8e1070977e9cd4e6b6d
  vfs: syscall: Add fsmount() to create a mount for a superblock

  linux commit cf3cba4a429be43e5527a3f78859b1bfd9ebc5fb
  vfs: syscall: Add fspick() to select a superblock for reconfiguration

  linux commit 9c8ad7a2ff0bfe58f019ec0abc1fb965114dde7d
  uapi, x86: Fix the syscall numbering of the mount API syscalls [ver #2]

  linux commit d8076bdb56af5e5918376cd1573a6b0007fc1a89
  uapi: Wire up the mount API syscalls on non-x86 arches [ver #2]

d493206d deleted all the content of
user.h, but sys/procfs.h expects this from sys/user.h
threfore we retain the non conflicting parts

the contents conflicted with asm/ptrace.h. glibc does not provide
anything in user.h for riscv, so software cannot be depending on it.

simplified from patch submitted by Baruch Siach.

Rename user registers struct definitions to avoid conflict with the
asm/ptrace.h kernel header that defines the same structs. Use the
__riscv_mc prefix as glibc does.

commit f3f96f2d added these for the
rest of the archs, but the patch it corresponded to missed riscv64
since riscv64 was not yet upstream at the time. this caused commit
dfc81828 to break riscv64 build, due
to a wrong assumption that SYS_statx was unconditionally defined.

these differ from generic only in using endian-matched padding with a
short __ipc_perm_seq field in place of the int field in generic. this
is not a documented public interface anyway, and the original intent
was to use int here. some ports just inadvertently slipped in the
kernel short+padding form.

the definition of the IPC_64 macro controls the interface between libc
and the kernel through syscalls; it's not a public API. the meaning is
rather obscure. long ago, Linux's sysvipc *id_ds structures used
16-bit uids/gids and wrong types for a few other fields. this was in
the libc5 era, before glibc. the IPC_64 flag (64 is a misnomer; it's
more like 32) tells the kernel to use the modern[-ish] versions of the
structures.

the definition of IPC_64 has nothing to do with whether the arch is
32- or 64-bit. rather, due to either historical accident or
intentional obnoxiousness, the kernel only accepts and masks off the
0x100 IPC_64 flag conditional on CONFIG_ARCH_WANT_IPC_PARSE_VERSION,
i.e. for archs that want to provide, or that accidentally provided,
both. for archs which don't define this option, no masking is
performed and commands with the 0x100 bit set will fail as invalid. so
ultimately, the definition is just a matter of matching an arbitrary
switch defined per-arch in the kernel.

some of these were not exact duplicates, but had gratuitously
different naming for padding, or omitted the endian checks because the
arch is fixed-endian.

various padding fields in the generic bits/sem.h were defined in terms
of time_t as a cheap hack standing in for "kernel long", to allow x32
to use the generic version of the file. this was a really bad idea, as
it ended up getting copied into lots of arch-specific versions of the
bits file, and is a blocker to changing time_t to 64-bit on 32-bit
archs.

this commit adds an x32-specific version of the header, and changes
padding type back from time_t to long (currently the same type on all
archs but x32) in the generic header and all the others the hack got
copied into.

presently, all archs/ABIs have struct stat matching the kernel
stat[64] type, except mips/mipsn32/mips64 which do conversion hacks in
syscall_arch.h to work around bugs in the kernel type. this patch
completely decouples them and adds a translation step to the success
path of fstatat. at present, this is just a gratuitous copying, but it
opens up multiple possibilities for future support for 64-bit time_t
on 32-bit archs and for cleaned-up/unified ABIs.

for clarity, the mips hacks are not yet removed in this commit, so the
mips kstat structs still correspond to the output of the hacks in
their syscall_arch.h files, not the raw kernel type. a subsequent
commit will fix this.

the "A" constraint is simply for an address expression that's a single
register, but it's not yet supported by clang, and has no advantage
here over just using a register operand for the address. the latter is
actually preferable in the a_cas_p case because it avoids aliasing an
lvalue onto the memory.

most egregious problem was the lack of memory clobber and lack of
volatile asm; this made the atomics memory barriers but not compiler
barriers. use of "+r" rather than "=r" for a clobbered temp was also
wrong, since the initial value is indeterminate.

having "+r"(a0) is redundant with "0"(a0) in syscalls with at least 1
arg, which is arguably a constraint violation (clang treats it as
such), and an invalid input with indeterminate value in the 0-arg
case. use the "=r"(a0) form instead.

this was apparently copied from x86_64; it's not part of the kernel
API for riscv64. this change eliminates the need for a
riscv64-specific bits header and lets it use the generic one.

Author: Alex Suykov <alex.suykov@gmail.com>
Author: Aric Belsito <lluixhi@gmail.com>
Author: Drew DeVault <sir@cmpwn.com>
Author: Michael Clark <mjc@sifive.com>
Author: Michael Forney <mforney@mforney.org>
Author: Stefan O'Rear <sorear2@gmail.com>

This port has involved the work of many people over several years. I
have tried to ensure that everyone with substantial contributions has
been credited above; if any omissions are found they will be noted
later in an update to the authors/contributors list in the COPYRIGHT
file.

The version committed here comes from the riscv/riscv-musl repo's
commit 3fe7e2c75df78eef42dcdc352a55757729f451e2, with minor changes by
me for issues found during final review:

- a_ll/a_sc atomics are removed (according to the ISA spec, lr/sc
  are not safe to use in separate inline asm fragments)

- a_cas[_p] is fixed to be a memory barrier

- the call from the _start assembly into the C part of crt1/ldso is
  changed to allow for the possibility that the linker does not place
  them nearby each other.

- DTP_OFFSET is defined correctly so that local-dynamic TLS works

- reloc.h LDSO_ARCH logic is simplified and made explicit.

- unused, non-functional crti/n asm files are removed.

- an empty .sdata section is added to crt1 so that the
  __global_pointer reference is resolvable.

- indentation style errors in some asm files are fixed.