this function is mainly (purely?) for obtaining stack address
information, but we also provide the detach state since it's easy to
do anyway.

the issue at hand is that many syscalls require as an argument the
kernel-ABI size of sigset_t, intended to allow the kernel to switch to
a larger sigset_t in the future. previously, each arch was defining
this size in syscall_arch.h, which was redundant with the definition
of _NSIG in bits/signal.h. as it's used in some not-quite-portable
application code as well, _NSIG is much more likely to be recognized
and understood immediately by someone reading the code, and it's also
shorter and less cluttered.

note that _NSIG is actually 65/129, not 64/128, but the division takes
care of throwing away the off-by-one part.

I'm not entirely happy with the amount of ugliness here, but since
F_DUPFD_CLOEXEC is used elsewhere in code that's expected to work on
old kernels (popen), it seems necessary. reportedly even some modern
kernels went back and broke F_DUPFD_CLOEXEC (making it behave like
plain F_DUPFD), so it might be necessary to add some additional fixup
code later to deal with that issue too.

SYS_pipe is not usable directly in general, since mips has a very
broken calling convention for the pipe syscall. instead, just call the
function, so that the mips-specific ugliness is isolated in
mips/pipe.s and not copied elsewhere.

reportedly some programs (e.g. showkeys in the kbd package) use it.

1. as reported by William Haddon, the value returned by snprintf was
wrongly used as a length passed to sendto, despite it possibly
exceeding the buffer length. this could lead to invalid reads and
leaking additional data to syslog.

2. openlog was storing a pointer to the ident string passed by the
caller, rather than copying it. this bug is shared with (and even
documented in) other implementations like glibc, but such behavior
does not seem to meet the requirements of the standard.

3. extremely long ident provided to openlog, or corrupt ident due to
the above issue, could possibly have resulted in buffer overflows.
despite having the potential for smashing the stack, i believe the
impact is low since ident points to a short string literal in typical
application usage (and per the above bug, other usages will break
horribly on other implementations).

4. when used with LOG_NDELAY, openlog was not connecting the
newly-opened socket; sendto was being used instead. this defeated the
main purpose of LOG_NDELAY: preparing for chroot.

5. the default facility was not being used at all, so all messages
without an explicit facility passed to syslog were getting logged at
the kernel facility.

6. setlogmask was not thread-safe; no synchronization was performed
updating the mask. the fix uses atomics rather than locking to avoid
introducing a lock in the fast path for messages whose priority is not
in the mask.

7. in some code paths, the syslog lock was being unlocked twice; this
could result in releasing a lock that was actually held by a different
thread.

some additional enhancements to syslog such as a default identifier
based on argv[0] or similar may still be desired; at this time, only
the above-listed bugs have been fixed.

it serves no purpose (binaries linked against musl as -lc/libc.so
automatically get the right DT_NEEDED value of libc.so) and causes
ldconfig to misbehave (making a symlink to ld-musl named libc.so in
/lib). ldconfig is not used on pure musl systems, but if ld-musl is
installed on a system where it's not the primary libc, this will
pollute the system /lib with a symlink to musl named libc.so, which
should NOT exist and could cause problems linking native apps. also,
the existence of the soname caused spurious warnings from ldconfig
when /lib and /usr/lib were the same physical directory.

this fix is far from ideal and breaks the rule of not using
arch-specific #ifdefs, but for now we just need a solution to the
existing breakage.

the underlying problem is that the kernel folks made a very stupid
decision to make misalignment of this struct part of the kernel
API/ABI for x86_64, in order to avoid writing a few extra lines of
code to handle both 32- and 64-bit userspace on 64-bit kernels. I had
just added the packed attribute unconditionally thinking it was
harmless on 32-bit archs, but non-x86 32-bit archs have 8-byte
alignment on 64-bit types.

wctype_t was incorrectly "int" rather than "long" on x86_64. not only
is this an ABI incompatibility; it's also a major design flaw if we
ever wanted wctype_t to be implemented as a pointer, which would be
necessary if locales support custom character classes, since int is
too small to store a converted pointer. this commit fixes wctype_t to
be unsigned long on all archs, matching the LSB ABI; this change does
not matter for C code, but for C++ it affects mangling.

the same issue applied to wctrans_t. glibc/LSB defines this type as
const __int32_t *, but since no such definition is visible, I've just
expanded the definition, int, everywhere.

it would be nice if these types (which don't vary by arch) could be in
wctype.h, but the OB XSI requirement in POSIX that wchar.h expose some
types and functions from wctype.h precludes doing so. glibc works
around this with some hideous hacks, but trying to duplicate that
would go against the intent of musl's headers.

x86_64 does not have excess precision, at all

patch by Chris Spiegel.

lenl-lenr is not a valid expression for a signed int return value from
strverscmp, since after implicit conversion from size_t to int this
difference could have the wrong sign or might even be zero. using the
difference for char values works since they're bounded well within the
range of differences representable by int, but it does not work for
size_t values.

patch by Isaac Dunham.

this macro is 100 on all archs, at least in userspace, according
to kernel headers.

1. wrong return value and missing errno for negative suffix len
2. failure to catch suffix len > strlen
3. remove unwanted clearing of input string in invalid case

based on patch contributed by Anthony G. Basile (blueness)

some issues remain with the filename generation algorithm and other
small bugs, but this patch has been sitting around long enough that I
feel it's best to get it committed and then work out any remaining
issues.

patch by Jens Gustedt.
previously, the intended policy was to use __environ in code that must
conform to the ISO C namespace requirements, and environ elsewhere.
this policy was not followed in practice anyway, making things
confusing. on top of that, Jens reported that certain combinations of
link-time optimization options were breaking with the inconsistent
references; this seems to be a compiler or linker bug, but having it
go away is a nice side effect of the changes made here.

based on patch by Isaac Dunham, moved to its own file to avoid
increasing bss on static linked programs not using this nonstandard
function but using the standard getgrent function, and vice versa.

this definitely has the potential to be a bikeshed topic, so some
justification is in order. most of the changes made fit into one of
the following categories:
1. alignment with text in posix, xsh 2.3
2. eliminating overly-specific text for shared error codes
3. making the message match more closely with the macro name
4. removing extraneous words

in particular, the EAGAIN/EWOULDBLOCK text is updated to match the
description of EAGAIN (which covers both uses) rather than saying the
operation would block, and ENOTSUP/EOPNOTSUPP is updated not to
mention sockets.

the distinction between ENFILE/EMFILE has also been clarified; ENFILE
is aligned with the posix text, and EMFILE, which lacks concise posix
text matching any historic message, is updated to emphasize that the
exhausted resource is not open files/open file descriptions, but
rather the integer 'address space' of file descriptors.

some messages may be further tweaked based on feedback.

arm eabi requires this symbol for static C++ dtors.
usually it is provided by libstdc++, but when a C++ program
doesn't use the std lib (free-standing), the libc has to provide
it.
this was encountered while building transmission, which
depends on such a C++ library (libutp).

this function is nearly identical to __cxa_atexit, but it has the
order of argumens swapped for "performance reasons".
see page 25 of

 http://infocenter.arm.com/help/topic/com.arm.doc.ihi0043d/IHI0043D_rtabi.pdf

there are other aeabi specific C++ support functions missing, but
it is not clear yet that GCC makes use of them so we omit them for
the moment.

this avoids duplicating the fragile logic for executing an external
program without fork.

read should never return anything but 0 or sizeof ec here, but if it
does, we want to treat any other return as "success". then the caller
will get back the pid and is responsible for waiting on it when it
immediately exits.

the proposed change was described in detail in detail previously on
the mailing list. in short, vfork is unsafe because:

1. the compiler could make optimizations that cause the child to
clobber the parent's local vars.

2. strace is buggy and allows the vforking parent to run before the
child execs when run under strace.

the new design uses a close-on-exec pipe instead of vfork semantics to
synchronize the parent and child so that the parent does not return
before the child has finished using its arguments (and now, also its
stack). this also allows reporting exec failures to the caller instead
of giving the caller a child that mysteriously exits with status 127
on exec error.

basic testing has been performed on both the success and failure code
paths. further testing should be done.

also, don't waste code/time on F_GETFL since pipes always have blank
flags initially (at least on old kernels, which are all this fallback
code matters for).

this change shaves ~1k off libc.so bss size, and also avoids hard
errors in the case where the static buffer was not large enough to
hold the result.

this whole framework is really ugly and might should be replaced or at
least heavily overhauled when some changes/factorizations are made to
getaddrinfo internals in the future.