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.

POSIX mandates EOVERFLOW for this condition.

this commit has two major user-visible parts: zoneinfo-format time
zones are now supported, and overflow handling is intended to be
complete in the sense that all functions return a correct result if
and only if the result fits in the destination type, and otherwise
return an error. also, some noticable bugs in the way DST detection
and normalization worked have been fixed, and performance may be
better than before, but it has not been tested.

apparently this was never noticed before because the linker normally
optimizes dynamic TLS models to non-dynamic ones when static linking,
thus eliminating the calls to __tls_get_addr which crash when the dtv
is missing. however, some libsupc++ code on ARM was calling
__tls_get_addr when static linked and crashing. the reason is unclear
to me, but with this issue fixed it should work now anyway.

patch by Timo Teräs

map_library was saving pointers to an automatic-storage buffer rather
than pointers into the mapping. this should be a fairly simple fix,
but the patch here is slightly complicated by two issues:

1. supporting gratuitously obfuscated ELF files where the program
headers are not right at the beginning of the file.

2. cleaning up the map_library function so that data isn't clobbered
by the time we need it.

there are still several more that are misleading, but SIGFPE (integer
division error misdescribed as floating point) and and SIGCHLD
(possibly non-exit status change events described as exiting) were the
worst offenders.

the name format RTnn/RTnnn was chosen to minimized bloat while
uniquely identifying the signal.

also clean up, optimize, and simplify the code, removing branches by
simply pre-setting the result string to an empty string, which will be
preserved if other operations fail.

the main use for this macro seems to be knowing the correct allocation
granularity for dynamic-sized fd_set objects. such usage is
non-conforming and results in undefined behavior, but it is widespread
in applications.

there are two motivations for this change. one is to avoid
gratuitously depending on a C11 symbol for implementing a POSIX
function. the other pertains to the documented semantics. C11 does not
define any behavior for aligned_alloc when the length argument is not
a multiple of the alignment argument. posix_memalign on the other hand
places no requirements on the length argument. using __memalign as the
implementation of both, rather than trying to implement one in terms
of the other when their documented contracts differ, eliminates this
confusion.

C11 has no requirement that the alignment be a multiple of
sizeof(void*), and in fact seems to require any "valid alignment
supported by the implementation" to work. since the alignment of char
is 1 and thus a valid alignment, an alignment argument of 1 should be
accepted.

a research in debian codesearch and grepping over the pkgsrc
directory tree have shown that these macros are all either unused,
or defined by programs in case they need them.

these would not be expensive to actually implement, but reading
/etc/ethers does not sound like a particularly useful feature, so for
now I'm leaving them as stubs.

previously, determination of the list of header files for installation
depended on the include/bits symlink (to the arch-specific files)
already having been created. in other words, running "make install"
immediately after configure without first running "make" caused the
bits headers not to be installed.

the solution I have applied is to pull the list of headers directly
from arch/$(ARCH)/bits rather than include/bits, and likewise to
install directly from arch/$(ARCH)/bits rather than via the symlink.

at this point, the only purpose served by keeping the symlink around
is that it enables use of the in-tree headers and libs directly via -I
and -L, which can be useful when testing against a new version of the
library before installing it. on the other hand, removing the bits
symlink would be beneficial if we ever want to support building
multiple archs in the same source tree.

in theory this should not be an issue, since major() should only be
applied to type dev_t, which is 64-bit. however, it appears some
applications are not using dev_t but a smaller integer type (which
works on Linux because the kernel's dev_t is really only 32-bit). to
avoid the undefined behavior, do it as two shifts.

this change is needed to correctly handle the case where a constructor
creates a new thread which calls dlopen. previously, the lock was not
held in this case. the reason for the complex logic to avoid locking
whenever possible is that, since the mutex is recursive, it will need
to inspect the thread pointer to get the current thread's tid, and
this requires initializing the thread pointer. we do not want
non-multi-threaded programs to attempt to access the thread pointer
unnecessarily; doing so could make them crash on ancient kernels that
don't support threads but which may otherwise be capable of running
the program.

rather than returning an error, we have to increase the size argument
so high that the kernel will have no choice but to fail. this is
because POSIX only permits the EINVAL error for size errors when a new
shared memory segment would be created; if it already exists, the size
argument must be ignored. unfortunately Linux is non-conforming in
this regard, but I want to keep the code correct in userspace anyway
so that if/when Linux is fixed, the behavior applications see will be
conforming.

rejecting invalid values for n is fine even in the case where a new
sem will not be created, since the kernel does its range checks on n
even in this case as well.

by default, the kernel will bound the limit well below USHRT_MAX
anyway, but it's presumably possible that an administrator could
override this limit and break things.

this type is not really intended to be used; it's just there to allow
implementations to choose the type for the shm_nattch member of
struct shmid_sh, presumably since historical implementations disagreed
on the type. in any case, it needs to be there, so now it is.

in the process, I refactored the week-number code so it can be used by
the week-based-year formats to determine year adjustments at the
boundary values. this also improves indention/code readability.

that's what I get for changing a hard-coded threshold to a proper
non-magic-number without testing.

output for plain week numbers (%U and %W) has been sanity-checked, and
output for the week-based-year week numbers (%V) has been checked
extensively against known-good data for the full non-negative range of
32-bit time_t.

year numbers for week-based years (%g and %G) are not yet implemented.

the pathnames prefixed with /dev/null/ are guaranteed never to be
valid. the previous use of /dev/null alone was mildly dangerous in
that bad software might attempt to unlink the name when it found a
non-regular file there and create a new file.

internally, other parts of the library assume sizes don't overflow
ssize_t and/or ptrdiff_t, and the way this assumption is made valid is
by preventing creating of such large objects. malloc already does so,
but the check was missing from mmap.

this is also a quality of implementation issue: even if the
implementation internally could handle such objects, applications
could inadvertently invoke undefined behavior by subtracting pointers
within an object. it is very difficult to guard against this in
applications, so a good implementation should simply ensure that it
does not happen.

the address of the pointer to the sched param, rather than the
pointer, was being passed to the kernel.

fstat should not fail under normal circumstances, so this fix is
mostly theoretical.