this extends commit 5a105f19, removing
timer[fd]_settime and timer[fd]_gettime. the timerfd ones are likely
to have been used in software that started using them before it could
rely on libc exposing functions.

this extends commit 5a105f19, removing
clock_settime, clock_getres, clock_nanosleep, and settimeofday.

some nontrivial number of applications have historically performed
direct syscalls for these operations rather than using the public
functions. such usage is invalid now that time_t is 64-bit and these
syscalls no longer match the types they are used with, and it was
already harmful before (by suppressing use of vdso).

since syscall() has no type safety, incorrect usage of these syscalls
can't be caught at compile-time. so, without manually inspecting or
running additional tools to check sources, the risk of such errors
slipping through is high.

this patch renames the syscalls on 32-bit archs to clock_gettime32 and
gettimeofday_time32, so that applications using the original names
will fail to build without being fixed.

note that there are a number of other syscalls that may also be unsafe
to use directly after the time64 switchover, but (1) these are the
main two that seem to be in widespread use, and (2) most of the others
continue to have valid usage with a null timeval/timespec argument, as
the argument is an optional timeout or similar.

the definitions of SO_TIMESTAMP* changed on 32-bit archs in commit
38143339 to the new versions that
provide 64-bit versions of timeval/timespec structure in control
message payload. socket options, being state attached to the socket
rather than function calls, are not trivial to implement as fallbacks
on ENOSYS, and support for them was initially omitted on the
assumption that the ioctl-based polling alternatives (SIOCGSTAMP*)
could be used instead by applications if setsockopt fails.

unfortunately, it turns out that SO_TIMESTAMP is sufficiently old and
widely supported that a number of applications assume it's available
and treat errors as fatal.

this patch introduces emulation of SO_TIMESTAMP[NS] on pre-time64
kernels by falling back to setting the "_OLD" (time32) versions of the
options if the time64 ones are not recognized, and performing
translation of the SCM_TIMESTAMP[NS] control messages in recvmsg.
since recvmsg does not know whether its caller is legacy time32 code
or time64, it performs translation for any SCM_TIMESTAMP[NS]_OLD
control messages it sees, leaving the original time32 timestamp as-is
(it can't be rewritten in-place anyway, and memmove would be mildly
expensive) and appending the converted time64 control message at the
end of the buffer. legacy time32 callers will see the converted one as
a spurious control message of unknown type; time64 callers running on
pre-time64 kernels will see the original one as a spurious control
message of unknown type. a time64 caller running on a kernel with
native time64 support will only see the time64 version of the control
message.

emulation of SO_TIMESTAMPING is not included at this time since (1)
applications which use it seem to be prepared for the possibility that
it's not present or working, and (2) it can also be used in sendmsg
control messages, in a manner that looks complex to emulate
completely, and costly even when running on a time64-supporting
kernel.

corresponding changes in recvmmsg are not made at this time; they will
be done separately.

without this, the SIOCGSTAMP and SIOCGSTAMPNS ioctl commands, for
obtaining timestamps, would stop working on pre-5.1 kernels after
time_t is switched to 64-bit and their values are changed to the new
time64 versions.

new code is written such that it's statically unreachable on 64-bit
archs, and on existing 32-bit archs until the macro values are changed
to activate 64-bit time_t.

without this, the SO_RCVTIMEO and SO_SNDTIMEO socket options would
stop working on pre-5.1 kernels after time_t is switched to 64-bit and
their values are changed to the new time64 versions.

new code is written such that it's statically unreachable on 64-bit
archs, and on existing 32-bit archs until the macro values are changed
to activate 64-bit time_t.

the __socketcall and __socketcall_cp macros are remnants from a really
old version of the syscall-mechanism infrastructure, and don't follow
the pattern that the "__" version of the macro returns the raw negated
error number rather than setting errno and returning -1.

for time64 purposes, some socket syscalls will need to operate on the
error value rather than returning immediately, so fix this up so they
can use it.

this commit has no effect whatsoever right now, but is in preparation
for a future riscv32 port and other future 32-bit archs that will be
"time64-only" from the start on the kernel side.

together with the previous x32 changes, this commit ensures that
syscall call points that don't care about time (passing null timeouts,
etc.) can continue to do so without having to special-case time64-only
archs, and allows code using the time64 syscalls to uniformly test for
the need to fallback with SYS_foo != SYS_foo_time64, rather than
needing to check defined(SYS_foo) && SYS_foo != SYS_foo_time64.

commit 788d5e24 noted that we could
add this if needed, and in fact it is needed, but not for one of the
archs documented as having a 7th syscall arg register. rather, it's
needed for mips (o32), where all but the first 4 arguments are passed
on the stack, and the stack can accommodate a 7th.

the weak version of __syscall_cp_c was using a tail call to __syscall
to avoid duplicating the 6-argument syscall code inline in small
static-linked programs, but now that __syscall no longer exists, the
inline expansion is no longer duplication.

the syscall.h machinery suppported up to 7 syscall arguments, only via
an external __syscall function, but we presently have no syscall call
points that actually make use of that many, and the kernel only
defines 7-argument calling conventions for arm, powerpc (32-bit), and
sh. if it turns out we need them in the future, they can easily be
added.

as originally published, the C99 syntax only allowed static index
parameter declarators when a gratuitous parameter name was included.
gcc 3, which some projects use for bootstrapping, is a supported C99
compiler, but does not have the fix to the standard incorporated, so
edit the affected declaration to conform to the earlier buggy C99
syntax.

libc.h was intended to be a header for access to global libc state and
related interfaces, but ended up included all over the place because
it was the way to get the weak_alias macro. most of the inclusions
removed here are places where weak_alias was needed. a few were
recently introduced for hidden. some go all the way back to when
libc.h defined CANCELPT_BEGIN and _END, and all (wrongly implemented)
cancellation points had to include it.

remaining spurious users are mostly callers of the LOCK/UNLOCK macros
and files that use the LFS64 macro to define the awful *64 aliases.

in a few places, new inclusion of libc.h is added because several
internal headers no longer implicitly include libc.h.

declarations for __lockfile and __unlockfile are moved from libc.h to
stdio_impl.h so that the latter does not need libc.h. putting them in
libc.h made no sense at all, since the macros in stdio_impl.h are
needed to use them correctly anyway.

syscall.h was chosen as the header to declare it, since its intended
usage is alongside syscalls as a fallback for operations the direct
syscall does not support.

this cleans up what had become widespread direct inline use of "GNU C"
style attributes directly in the source, and lowers the barrier to
increased use of hidden visibility, which will be useful to recovering
some of the efficiency lost when the protected visibility hack was
dropped in commit dc2f368e, especially
on archs where the PLT ABI is costly.

despite sh not generally using register-pair alignment for 64-bit
syscall arguments, there are arch-specific versions of the syscall
entry points for pread and pwrite which include a dummy argument for
alignment before the 64-bit offset argument.

only use SYS_socketcall if SYSCALL_USE_SOCKETCALL is defined
internally, otherwise use direct syscalls.

this commit does not change the current behaviour, it is
preparation for adding direct syscall numbers for i386.

this is the first and simplest stage of removal of the SHARED macro,
which will eventually allow libc.a and libc.so to be produced from the
same object files.

the original motivation for these #ifdefs which are now being removed
was to allow building a static-only libc using a compiler that does
not support visibility. however, SHARED was the wrong condition to
test for this anyway; various assembly-language sources refer to
hidden symbols and declare them with the .hidden directive, making it
wrong to define the referenced symbols as non-hidden. if there is a
need in the future to build libc using compilers that lack visibility,
support could be moved to the build system or perhaps the __PIC__
macro could be checked instead of SHARED.

x86_64 syscall.h defined some musl internal syscall names and made
them public. These defines were already moved to src/internal/syscall.h
(except for SYS_fadvise which is added now) so the cruft in x86_64
syscall.h is not needed.

except powerpc, which still lacks inline syscalls simply because
nobody has written the code, these are all fallbacks used to work
around a clang bug that probably does not exist in versions of clang
that can compile musl. however, it's useful to have the generic
non-inline code anyway, as it eases the task of porting to new archs:
writing inline syscall code is now optional. this approach could also
help support compilers which don't understand inline asm or lack
support for the needed register constraints.

mips could not be unified because it has special fixup code for broken
layout of the kernel's struct stat.

On 32 bit mips the kernel uses -1UL/2 to mark RLIM_INFINITY (and
this is the definition in the userspace api), but since it is in
the middle of the valid range of limits and limits are often
compared with relational operators, various kernel side logic is
broken if larger than -1UL/2 limits are used. So we truncate the
limits to -1UL/2 in get/setrlimit and prlimit.

Even if the kernel side logic consistently treated -1UL/2 as greater
than any other limit value, there wouldn't be any clean workaround
that allowed using large limits:
* using -1UL/2 as RLIM_INFINITY in userspace would mean different
infinity value for get/setrlimt and prlimit (where infinity is always
-1ULL) and userspace logic could break easily (just like the kernel
is broken now) and more special case code would be needed for mips.
* translating -1UL/2 kernel side value to -1ULL in userspace would
mean that -1UL/2 limit cannot be set (eg. -1UL/2+1 had to be passed
to the kernel instead).

using the existence of SYS_stat64 as the condition for remapping other
related syscalls is no longer valid, since new archs that omit the old
syscalls will not have SYS_stat or SYS_stat64, but still potentially
need SYS_fstat and others remapped. it would probably be possible to
get by with just one or two extra conditionals, but just breaking them
all down into separate conditions is robust and not significantly
heavier for the preprocessor.

somehow the remapping of this syscall to the 64-bit version was
overlooked. the issue was found, and patch provided, by Stefan
Kristiansson. presumably the reason this bug was not caught earlier is
that the syscall takes a pointer to off_t rather than a value, so on
little-endian systems, everything appears to work as long as the
offset value fits in the low 31 bits. on big-endian systems, though,
sendfile was presumably completely non-functional.

this was messed up during a recent commit when the socketcall macros
were moved to the common internal/syscall.h, and the following commit
expanded the problem by adding more new content outside the guard.

open is handled specially because it is used from so many places, in
so many variants (2 or 3 arguments, setting errno or not, and
cancellable or not). trying to do it as a function would not only
increase bloat, but would also risk subtle breakage.

this is the first step towards supporting "new" archs where linux
lacks "old" syscalls.

the use of visibility at all is purely an optimization to avoid the
need for the caller to load the GOT register or similar to prepare for
a call via the PLT. there is no reason for these symbols to be
externally visible, so hidden works just as well as protected, and
using protected visibility is undesirable due to toolchain bugs and
the lack of testing it receives.

in particular, GCC's microblaze target is known to generate symbolic
relocations in the GOT for functions with protected visibility. this
in turn results in a dynamic linker which crashes under any nontrivial
usage that requires making a syscall before symbolic relocations are
processed.

some 32-on-64 archs require that the actual syscall args be long long.
in that case syscall_arch.h can define syscall_arg_t to whatever it needs
and syscall.h picks it up.
all other archs just use long as usual.

this allows syscall_arch.h to define the macro __scc if special
casting is needed, as is the case for x32, where the actual syscall
arguments are 64bit, but, in case of pointers, would get sign-extended
and thus become invalid.

for 0-argument syscalls (1 argument to the macro, the syscall number),
the __SYSCALL_NARGS_X macro's ... argument was not satisfied. newer
compilers seem to care about this.

on x86 and some other archs, functions which make function calls which
might go through a PLT incur a significant overhead cost loading the
GOT register prior to making the call. this load is utterly useless in
musl, since all calls are bound at library-creation time using
-Bsymbolic-functions, but the compiler has no way of knowing this, and
attempts to set the default visibility to protected have failed due to
bugs in GCC and binutils.

this commit simply manually assigns hidden/protected visibility, as
appropriate, to a few internal-use-only functions which have many
callers, or which have callers that are hot paths like getc/putc. it
shaves about 5k off the i386 libc.so with -Os. many of the
improvements are in syscall wrappers, where the benefit is just size
and performance improvement is unmeasurable noise amid the syscall
overhead. however, stdio may be measurably faster.

if in the future there are toolchains that can do the same thing
globally without introducing linking bugs, it might be worth
considering removing these workarounds.

no syscalls actually use that many arguments; the issue is that some
syscalls with 64-bit arguments have them ordered badly so that
breaking them into aligned 32-bit half-arguments wastes slots with
padding, and a 7th slot is needed for the last argument.

now public syscall.h only exposes __NR_* and SYS_* constants and the
variadic syscall function. no macros or inline functions, no
__syscall_ret or other internal details, no 16-/32-bit legacy syscall
renaming, etc. this logic has all been moved to src/internal/syscall.h
with the arch-specific parts in arch/$(ARCH)/syscall_arch.h, and the
amount of arch-specific stuff has been reduced to a minimum.

changes still need to be reviewed/double-checked. minimal testing on
i386 and mips has already been performed.

with this patch, musl compiles and mostly works with pcc 1.0.0. a few
tests are still failing and i'm uncertain whether they are due to
portability problems in musl, or bugs in pcc, but i suspect the
latter.

this patch improves the correctness, simplicity, and size of
cancellation-related code. modulo any small errors, it should now be
completely conformant, safe, and resource-leak free.

the notion of entering and exiting cancellation-point context has been
completely eliminated and replaced with alternative syscall assembly
code for cancellable syscalls. the assembly is responsible for setting
up execution context information (stack pointer and address of the
syscall instruction) which the cancellation signal handler can use to
determine whether the interrupted code was in a cancellable state.

these changes eliminate race conditions in the previous generation of
cancellation handling code (whereby a cancellation request received
just prior to the syscall would not be processed, leaving the syscall
to block, potentially indefinitely), and remedy an issue where
non-cancellable syscalls made from signal handlers became cancellable
if the signal handler interrupted a cancellation point.

x86_64 asm is untested and may need a second try to get it right.