based on patch by Vadim Ushakov. in general overriding LC_ALL rather
than specific categories (here, LC_MESSAGES) is undesirable, but
LC_ALL is easier and in this case there is nothing else that depends
on the locale in this invocation of the compiler.

when using /etc/shadow (rather than tcb) as its backend, getspnam_r
matched any username starting with the caller-provided string rather
than requiring an exact match. in practice this seems to have affected
only systems where one valid username is a prefix for another valid
username, and where the longer username appears first in the shadow
file.

as a result of commit e8e4e56a,
the later code path for setting optarg to a null pointer is no longer
necessary, and removing it eliminates an indention level and arguably
makes the code more readable.

the standard getopt does not touch optarg unless processing an option
with an argument. however, programs using the GNU getopt API, which we
attempt to provide in getopt_long, expect optarg to be a null pointer
after processing an option without an argument.

before argument permutation support was added, such programs typically
detected its absence and used their own replacement getopt_long,
masking the discrepency in behavior.

multi-threaded set*id and setrlimit use the internal __synccall
function to work around the kernel's wrongful treatment of these
process properties as thread-local. the old implementation of
__synccall failed to be AS-safe, despite POSIX requiring setuid and
setgid to be AS-safe, and was not rigorous in assuring that all
threads were caught. in a worst case, threads late in the process of
exiting could retain permissions after setuid reported success, in
which case attacks to regain dropped permissions may have been
possible under the right conditions.

the new implementation of __synccall depends on the presence of
/proc/self/task and will fail if it can't be opened, but is able to
determine that it has caught all threads, and does not use any locks
except its own. it thereby achieves AS-safety simply by blocking
signals to preclude re-entry in the same thread.

with this commit, all known conformance and safety issues in set*id
functions should be fixed.

per POSIX, the EINTR condition is an optional error for these
functions, not a mandatory one. since old kernels (pre-2.6.22) failed
to honor SA_RESTART for the futex syscall, it's dangerous to trust
EINTR from the kernel. thankfully POSIX offers an easy way out.

in the current version of __synccall, the callback is always run, so
failure to handle this case did not matter. however, the upcoming
overhaul of __synccall will have failure cases, in which case the
callback does not run and errno is already set. the changes being
committed now are in preparation for that.

this addresses alpine linux issue #3692 and brings the syslog message
length limit in alignment with uclibc's implementation.

the code being removed was introduced to work around "partial failure"
of multi-threaded set*id() operations, where some threads would
succeed in changing their ids but an RLIMIT_NPROC setting would
prevent the rest from succeeding, leaving the process in an
inconsistent and dangerous state. however, the workaround code did not
handle important usage cases like swapping real and effective uids
then restoring their original values, and the wrongful kernel
enforcement of RLIMIT_NPROC at setuid time was removed in Linux 3.1,
making the workaround obsolete.

since the partial failure still is dangerous on old kernels, and could
in principle happen on post-fix kernels as well if set*id() syscalls
fail for another spurious reason such as resource-related failures,
new code is added to detect and forcibly kill the process if/when such
a situation arises. future documentation releases should be updated to
reflect that setting RLIMIT_NPROC to RLIM_INFINITY is necessary to
avoid this forced-kill on old kernels. ideally, at some point the
kernel will get proper multi-threaded set*id() syscalls capable of
performing their actions atomically, and all of the userspace code to
emulate them can be treated as a fallback for outdated kernels.

opening /dev/tty then using ttyname_r on it does not produce a
canonical terminal name; it simply yields "/dev/tty".

it would be possible to make ctermid determine the actual controlling
terminal device via field 7 of /proc/self/stat, but doing so would
introduce a buffer overflow into applications built with L_ctermid==9,
which glibc defines, adversely affecting the quality of ABI compat.

commit b72cd07f added support for a
this feature in getopt, but it was later broken in the case where
getopt_long is used as a side effect of the changes made in commit
91184c4f, which prevented the
underlying getopt call from seeing the leading '-' or '+' character in
optstring.

this commit changes the logic in the getopt_long core to check for a
leading colon, possibly after the leading '-' or '+', without
depending on the latter having been skipped by the caller. a minor
incorrectness in the return value for one error condition in
getopt_long is also fixed when opterr has been set to zero but
optstring has no leading ':'.

based on patch by Dima Krasner, with minor improvements for code size.
connect can fail if there is no listening syslogd, in which case a
useless socket was kept open, preventing subsequent syslog call from
attempting to connect again.

PR_SET_MM_MAP was introduced as a subcommand for PR_SET_MM in
linux v3.18 commit f606b77f1a9e362451aca8f81d8f36a3a112139e

the associated struct type is replicated in sys/prctl.h using
libc types.

example usage:

 struct prctl_mm_map *p;
 ...
 prctl(PR_SET_MM, PR_SET_MM_MAP, p, sizeof *p);

the kernel side supported struct size may be queried with
the PR_SET_MM_MAP_SIZE subcommand.

these syscalls are new in linux v3.18, bpf is present on all
supported archs except sh, kexec_file_load is only allocted for
x86_64 and x32 yet.

bpf was added in linux commit 99c55f7d47c0dc6fc64729f37bf435abf43f4c60

kexec_file_load syscall number was allocated in commit
f0895685c7fd8c938c91a9d8a6f7c11f22df58d2

per the rules for hexadecimal integer constants, the previous
definitions were correctly treated as having unsigned type except
possibly when used in preprocessor conditionals, where all artithmetic
takes place as intmax_t or uintmax_t. the explicit 'u' suffix ensures
that they are treated as unsigned in all contexts.

based on discussion with and patches by Felix Janda. these changes
started as an effort to factor forkpty in terms of login_tty, which
returns an error and skips fd reassignment and closing if setting the
controlling terminal failed. the previous forkpty code was unable to
handle errors in the child, and did not attempt to; it just silently
ignored them. but this would have been unacceptable when switching to
using login_tty, since the child would start with the wrong stdin,
stdout, and stderr and thereby clobber the parent's files.

the new code uses the same technique as the posix_spawn implementation
to convey any possible error in the child to the parent so that the
parent can report failure to the caller. it is also safe against
thread cancellation and against signal delivery in the child prior to
the determination of success.

being a nonstandard function, this isn't strictly necessary, but it's
inexpensive and avoids unpleasant surprises. eventually I would like
all functions in libc to be safe against cancellation, either ignoring
it or acting on it cleanly.

not only is this semantically more correct; it also reduces code size
slightly by eliminating the need for the compiler to assume the
possibility of aliasing.

this is undocumented but possibly expected behavior of GNU
getopt_long, and useful when error message printing has been
suppressed.

some related changes are also made to getopt, and the return value of
getopt_long in the case of missing arguments is fixed.

if writing the error message fails, POSIX requires that ferror(stderr)
be set. and as a function that operates on a stdio stream, getopt is
required to lock the stream it uses, stderr.

fwrite calls are used instead of fprintf since there is a demand from
some users not to pull in heavy stdio machinery via getopt. this
mimics the original code using write.

this shaves off a useless syscall for getting the caller's pid and
brings raise into alignment with other functions which were adapted to
use tkill rather than tgkill.

commit 83dc6eb0 documents the
rationale for this change, and in particular why the tgkill syscall is
useless for its designed purpose of avoiding races.

formally, it seems a sign is only required when the '+' modifier
appears in the format specifier, in which case either '+' or '-' must
be present in the output. but the specification is written such that
an optional negative sign is part of the output format anyway, and the
simplest approach to fixing the problem is removing the code that was
suppressing the sign.

the affected code was wrongly counting characters instead of bytes.

since wint_t is unsigned, WINT_MIN needs to expand to an unsigned zero.

it's unclear whether compilers which provide pure imaginary types
might produce a pure imaginary expression for 1.0fi. using 0.0f+1.0fi
ensures that the result is explicitly complex and makes this obvious
to human readers too.

this change is not necessary but helps diagnose invalid code. based on
patch by Jens Gustedt.

based on patches by Jens Gustedt. these macros need to be usable in
static initializers, and the old definitions were not.

there is no portable way to provide correct definitions for these
macros unless the compiler supports pure imaginary types. a portable
definition is provided for this case even though there are presently
no compilers that can use it. gcc and compatible compilers provide a
builtin function that can be used, but clang fails to support this and
instead requires a construct which is a constraint violation and which
is only a constant expression as a clang-specific extension.

since these macros are a namespace violation in pre-C11 profiles, and
since no known pre-C11 compilers provide any way to define them
correctly anyway, the definitions have been made conditional on C11.

this avoids assuming the presence of C11 macro definitions in the
public complex.h, which need changes potentially incompatible with the
way these macros are being used internally.

based on patch by Timo Teräs, with some corrections to bounds checking
code and other minor changes.

while they are borderline scope creep, the functions added are fairly
small and are roughly the minimum code needed to use the results of
the res_query API without re-implementing error-prone DNS packet
parsing, and they are used in practice by some kerberos related
software and possibly other things. at this time there is no intent to
implement further nameser.h API functions.

previously, write errors neither stopped further output attempts nor
caused the function to return an error to the caller. this could
result in silent loss of output, possibly in the middle of output in
the event of a non-permanent error.

the simplest solution is temporarily clearing the error flag for the
target stream, then suppressing further output when the error flag is
set and checking/restoring it at the end of the operation to determine
the correct return value.

since the wide version of the code internally calls the narrow fprintf
to perform some of its underlying operations, initial clearing of the
error flag is suppressed when performing a narrow vfprintf on a
wide-oriented stream. this is not a problem since the behavior of
narrow operations on wide-oriented streams is undefined.

if argv permutation is used, the option terminator "--" should be
moved before any skipped non-option arguments rather than being left
in the argv tail where the caller will see and interpret it.

this is an undocumented feature of GNU getopt_long that the BSD
version also mimics, and is reportedly needed by some programs.