it's possible that signaling a waiter races with cancellation of that
same waiter. previously, cancellation was acted upon, causing the
signal to be consumed with no waiter returning. by using the new
masked cancellation state, it's possible to refuse to act on the
cancellation request and instead leave it pending.

to ease review and understanding of the changes made, this commit
leaves the unwait function, which was previously the cancellation
cleanup handler, in place. additional simplifications could be made by
removing it.

this is a new extension which is presently intended only for
experimental and internal libc use. interface and behavior details may
change subject to feedback and experience from using it internally.

the basic concept for the new PTHREAD_CANCEL_MASKED state is that the
first cancellation point to observe the cancellation request fails
with an errno value of ECANCELED rather than acting on cancellation,
allowing the caller to process the status and choose whether/how to
act upon it.

commit 82dc1e2e addressed the
resolution of Austin Group issue 529, which requires close to leave
the fd open when failing with EINTR, by returning the newly defined
error code EINPROGRESS. this turns out to be a bad idea, though, since
legacy applications not aware of the new specification are likely to
interpret any error from close except EINTR as a hard failure.

this requirement is tucked away in XSH 2.9.5 Thread Cancellation under
the heading Thread Cancellation Cleanup Handlers.

a_store is only valid for int, but ssize_t may be defined as long or
another type. since there is no valid way for another thread to acess
the return value without first checking the error/completion status of
the aiocb anyway, an atomic store is not necessary.

this allows getgrnam and getgrgid to share code with the _r versions
in preparation for alternate backend support.

previously, aio operations were not tracked by file descriptor; each
operation was completely independent. this resulted in non-conforming
behavior for non-seekable/append-mode writes (which are required to be
ordered) and made it impossible to implement aio_cancel, which in turn
made closing file descriptors with outstanding aio operations unsafe.

the new implementation is significantly heavier (roughly twice the
size, and seems to be slightly slower) and presently aims mainly at
correctness, not performance.

most of the public interfaces have been moved into a single file,
aio.c, because there is little benefit to be had from splitting them.
whenever any aio functions are used, aio_cancel and the internal
queue lifetime management and fd-to-queue mapping code must be linked,
and these functions make up the bulk of the code size.

the close function's interaction with aio is implemented with weak
alias magic, to avoid pulling in heavy aio cancellation code in
programs that don't use aio, and the expensive cancellation path
(which includes signal blocking) is optimized out when there are no
active aio queues.

the character sequence '$((' was incorrectly interpreted as the
opening of arithmetic even within single-quoted contexts, thereby
suppressing the checks for bad characters after the closing quote.

presently bad character checking is only performed when the WRDE_NOCMD
is used; this patch only corrects checking in that case.

this allows getpwnam and getpwuid to share code with the _r versions
in preparation for alternate backend support.

The code does a potentially misaligned 8-byte store to fill the tail
of the buffer. Then it fills the initial part of the buffer
which is a multiple of 8 bytes.
Therefore, if size is divisible by 8, we were storing last word twice.

This patch decrements byte count before dividing it by 8,
making one less store in "size is divisible by 8" case,
and not changing anything in all other cases.
All at the cost of replacing one MOV insn with LEA insn.
Signed-off-by: NDenys Vlasenko <vda.linux@googlemail.com>

"and $0xff,%esi" is a six-byte insn (81 e6 ff 00 00 00), can use
4-byte "movzbl %sil,%esi" (40 0f b6 f6) instead.

64-bit imul is slow, move it as far up as possible so that the result
(rax) has more time to be ready by the time we start using it
in mem stores.

There is no need to shuffle registers in preparation to "rep movs"
if we are not going to take that code path. Thus, patch moves
"jump if len < 16" instructions up, and changes alternate code path
to use rdx and rdi instead of rcx and r8.
Signed-off-by: NDenys Vlasenko <vda.linux@googlemail.com>

this syscall allows fexecve to be implemented without /proc, it is new
in linux v3.19, added in commit 51f39a1f0cea1cacf8c787f652f26dfee9611874
(sh and microblaze do not have allocated syscall numbers yet)

added a x32 fix as well: the io_setup and io_submit syscalls are no
longer common with x86_64, so use the x32 specific numbers.

these socket options are new in linux v3.19, introduced in commit
2c8c56e15df3d4c2af3d656e44feb18789f75837 and commit
89aa075832b0da4402acebd698d0411dcc82d03e

with SO_INCOMING_CPU the cpu can be queried on which a socket is
managed inside the kernel and optimize polling of large number of
sockets accordingly.

SO_ATTACH_BPF lets eBPF programs (created by the bpf syscall) to
be attached to sockets.

the name was recently added for the setxid/synccall rework,
so use the name now that we have it.

just defining the necessary constants:

 LD_B1B_MAX is 2^113 - 1 in base 10^9
 KMAX is 2048 so the x array can hold up to 18432 decimal digits

(the worst case is converting 2^-16495 = 5^16495 * 10^-16495 to
binary, it requires the processing of int(log10(5)*16495)+1 = 11530
decimal digits after discarding the leading zeros, the conversion
requires some headroom in x, but KMAX is more than enough for that)

However this code is not optimal on archs with IEEE binary128
long double because the arithmetics is software emulated (on
all such platforms as far as i know) which means big and slow
strtod.

This trivial copy-paste bug went unnoticed due to lack of testing.
No currently supported target archs are affected.

armhf fesetenv implementation did a useless read of the fpscr.

mips fesetenv did not handle FE_DFL_ENV, now fcsr is cleared in that
case.

The sign bit was not cleared before checking for 0 so -0.0
was misclassified as FP_SUBNORMAL instead of FP_ZERO.

all socket types are accepted at this point, but that may be changed
at a later time if the behavior is not meaningful for other types. as
before, omitting type (a value of 0) gives both UDP and TCP results,
and SOCK_DGRAM or SOCK_STREAM restricts to UDP or TCP, respectively.
for other socket types, the service name argument is required to be a
null pointer, and the protocol number provided by the caller is used.

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.

in the case where a non-symlink file was replaced by a symlink during
the fchmodat operation with AT_SYMLINK_NOFOLLOW, mode change on the
new symlink target was successfully suppressed, but the error was not
reported. instead, fchmodat simply returned 0.

the specification for execvp itself is unclear as to whether
encountering a file that cannot be executed due to EACCES during the
PATH search is a mandatory error condition; however, XBD 8.3's
specification of the PATH environment variable clarifies that the
search continues until a file with "appropriate execution permissions"
is found.

since it seems undesirable/erroneous to report ENOENT rather than
EACCES when an early path element has a non-executable file and all
later path elements lack any file by the requested name, the new code
stores a flag indicating that EACCES was seen and sets errno back to
EACCES in this case.

in practice this was probably a non-issue, because the necessary
barrier almost certainly exists in kernel space -- implementing signal
delivery without such a barrier seems impossible -- but for the sake
of correctness, it should be done here too.

in principle, without a barrier, it is possible that the thread to be
cancelled does not see the store of its cancellation flag performed by
another thread. this affects both the case where the signal arrives
before entering the critical program counter range from __cp_begin to
__cp_end (in which case both the signal handler and the inline check
fail to see the value which was already stored) and the case where the
signal arrives during the critical range (in which case the signal
handler should be responsible for cancellation, but when it does not
see the cancellation flag, it assumes the signal is spurious and
refuses to act on it).

in the fix, the barrier is placed only in the signal handler, not in
the inline check at the beginning of the critical program counter
range. if the signal handler runs before the critical range is
entered, it will of course take no action, but its barrier will ensure
that the inline check subsequently sees the store. if on the other
hand the inline check runs first, it may miss seeing the store, but
the subsequent signal handler in the critical range will act upon the
cancellation request. this strategy avoids adding a memory barrier in
the common, non-cancellation code path.

mxcs_mask should be mxcr_mask

these are mandatory cancellation points per POSIX, so their omission
was a conformance bug.

the definitions are generic for all kernel archs. exposure of these
macros now only occurs on the same feature test as for the function
accepting them, which is believed to be more correct.

this typo did not result in an erroneous setjmp with at least binutils
2.22 but fix it for clarity and compatibility with potentially stricter
sh assemblers.

the errno values are unused by the kernel and the macro definitions were
never exposed by glibc.

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.