posix documents in the rationale and future directions for
pthread_kill that, since the lifetime of the thread id for a joinable
thread lasts until it is joined, ESRCH is not a correct error for
pthread_kill to produce when the target thread has exited but not yet
been joined, and that conforming applications cannot attempt to detect
this state. future versions of the standard may explicitly require
that ESRCH not be returned for this case.

the tid field in the pthread structure is not volatile, and really
shouldn't be, so as not to limit the compiler's ability to reorder,
merge, or split loads in code paths that may be relevant to
performance (like controlling lock ownership).

however, use of objects which are not volatile or atomic with futex
wait is inherently broken, since the compiler is free to transform a
single load into multiple loads, thereby using a different value for
the controlling expression of the loop and the value passed to the
futex syscall, leading the syscall to block instead of returning.

reportedly glibc's pthread_join was actually affected by an equivalent
issue in glibc on s390.

add a separate, dedicated join_futex object for pthread_join to use.

the static const zero set ended up getting put in bss instead of
rodata, wasting writable memory, and the call to memcmp was
size-inefficient. generally for nonstandard extension functions we try
to avoid poking at any internals directly, but the way the zero set
was setup was arguably already doing so.

to support the GNU extension of allocating a buffer for getcwd's
result when a null pointer is passed without incurring a link
dependency on free, we use a PATH_MAX-sized buffer on the stack and
only duplicate it to allocated storage after the operation succeeds.
unfortunately this imposed excessive stack usage on all callers,
including those not making use of the GNU extension.

instead, use a VLA to make stack allocation conditional.

for getopt_long, partial (prefix) matches of long options always begin
with "--" and thus can never be ambiguous with a short option. for
getopt_long_only, though, a single-character option can match both a
short option and as a prefix for a long option. in this case, we
wrongly interpreted it as a prefix for the long option.

introduce a new pass, only in long-only mode, to check the prefix
match against short options before accepting it. the only reason
there's a slightly nontrivial loop being introduced rather than strchr
is that our getopt already supports multibyte short options, and
getopt_long_long should handle them consistently. a temp buffer and
strstr could have been used, but the code to set it up would be just
as large as what's introduced here and it would unnecessarily pull in
relatively large code for strstr.

commit 618b18c7 removed the previous
detection and hardening since it was incorrect. commit
72141795 already handled all that
remained for hardening the static-linked case. in the dynamic-linked
case, have the dynamic linker check whether malloc was replaced and
make that information available.

with these changes, the properties documented in commit
c9f415d7 are restored: if calloc is
not provided, it will behave as malloc+memset, and any of the
memalign-family functions not provided will fail with ENOMEM.

this change serves multiple purposes:

1. it ensures that static linking of memalign-family functions will
pull in the system malloc implementation, thereby causing link errors
if an attempt is made to link the system memalign functions with a
replacement malloc (incomplete allocator replacement).

2. it eliminates calls to free that are unpaired with allocations,
which are confusing when setting breakpoints or tracing execution.

as a bonus, making __bin_chunk external may discourage aggressive and
unnecessary inlining of it.

the generated code should be mostly unchanged, except for explicit use
of C_INUSE in place of copying the low bits from existing chunk
headers/footers.

these changes also remove mild UB due to dubious arithmetic on
pointers into imaginary size_t[] arrays.

commit c9f415d7 included checks to
make calloc fallback to memset if used with a replaced malloc that
didn't also replace calloc, and the memalign family fail if free has
been replaced. however, the checks gave false positives for
replacement whenever malloc or free resolved to a PLT entry in the
main program.

for now, disable the checks so as not to leave libc in a broken state.
this means that the properties documented in the above commit are no
longer satisfied; failure to replace calloc and the memalign family
along with malloc is unsafe if they are ever called.

the calloc checks were correct but useless for static linking. in both
cases (simple or full malloc), calloc and malloc are in a source file
together, so replacement of one but not the other would give linking
errors. the memalign-family check was useful for static linking, but
broken for dynamic as described above, and can be replaced with a
better link-time check.

Update atomic.h to provide a_ctz_l in all cases (atomic_arch.h should
now only provide a_ctz_32 and/or a_ctz_64).

The generic version of a_ctz_32 now takes advantage of a_clz_32 if
available and the generic a_ctz_64 now makes use of a_ctz_32.

bring these functions up to date with the current idioms we use/prefer
in fmemopen and fopencookie.

rather than manually performing pointer arithmetic to carve multiple
objects out of one allocation, use a containing struct that
encompasses them all.

assign entire struct rather than member-at-a-time. don't repeat buffer
sizes; always use sizeof to ensure consistency.

replacement is subject to conditions on the replacement functions.
they may only call functions which are async-signal-safe, as specified
either by POSIX or as an implementation-defined extension. if any
allocator functions are replaced, at least malloc, realloc, and free
must be provided. if calloc is not provided, it will behave as
malloc+memset. any of the memalign-family functions not provided will
fail with ENOMEM.

in order to implement the above properties, calloc and __memalign
check that they are using their own malloc or free, respectively.
choice to check malloc or free is based on considerations of
supporting __simple_malloc. in order to make this work, calloc is
split into separate versions for __simple_malloc and full malloc;
commit ba819787 already did most of
the split anyway, and completing it saves an extra call frame.

previously, use of -Bsymbolic-functions made dynamic interposition
impossible. now, we are using an explicit dynamic-list, so add
allocator functions to the list. most are not referenced anyway, but
all are added for completeness.

instead of using a waiters count, add a bit to the lock field
indicating that the lock may have waiters. threads which obtain the
lock after contending for it will perform a potentially-spurious wake
when they release the lock.

commit e3bc22f1 removed all references
to __brk.

Split 'free' into unmap_chunk and bin_chunk, use the latter to introduce
__malloc_donate and use it in reclaim_gaps instead of calling 'free'.

Fix an instance where realloc code would overallocate by OVERHEAD bytes
amount. Manually arrange for reuse of memcpy-free-return exit sequence.

the Linux SYS_nice syscall is unusable because it does not return the
newly set priority. always use SYS_setpriority. also avoid overflows
in addition of inc by handling large inc values directly without
examining the old nice value.

Implementation of __malloc0 in malloc.c takes care to preserve zero
pages by overwriting only non-zero data. However, malloc must have
already modified auxiliary heap data just before and beyond the
allocated region, so we know that edge pages need not be preserved.

For allocations smaller than one page, pass them immediately to memset.
Otherwise, use memset to handle partial pages at the head and tail of
the allocation, and scan complete pages in the interior. Optimize the
scanning loop by processing 16 bytes per iteration and handling rest of
page via memset as soon as a non-zero byte is found.

the catan implementation from OpenBSD includes a FIXME-annotated
"overflow" branch that produces a meaningless and incorrect
large-magnitude result. it was reachable via three paths,
corresponding to gotos removed by this commit, in order:

1. pure imaginary argument with imaginary component greater than 1 in
   magnitude. this case does not seem at all exceptional and is
   handled (at least with the quality currently expected from our
   complex math functions) by the existing non-exceptional code path.

2. arguments on the unit circle, including the pure-real argument 1.0.
   these are not exceptional except for ±i, which should produce
   results with infinite imaginary component and which lead to
   computation of atan2(±0,0) in the existing non-exceptional code
   path. such calls to atan2() however are well-defined by POSIX.

3. the specific argument +i. this route should be unreachable due to
   the above (2), but subtle rounding effects might have made it
   possible in rare cases. continuing on the non-exceptional code path
   in this case would lead to computing the (real) log of an infinite
   argument, then producing a NAN when multiplying it by I.

for now, remove the exceptional code paths entirely. replace the
multiplication by I with construction of a complex number using the
CMPLX macro so that the NAN issue (3) prevented cannot arise.

with these changes, catan should give reasonably correct results for
real arguments, and should no longer give completely-wrong results for
pure-imaginary arguments outside the interval (-i,+i).

the factor of -i noted in the comment at the top of casin.c was
omitted from the actual code, yielding a result rotated 90 degrees and
propagating into errors in other functions defined in terms of casin.

implement multiplication by -i as a rotation of the real and imaginary
parts of the result, rather than by actual multiplication, since the
latter cannot be optimized without knowledge that the operand is
finite. here, the rotation is the actual intent, anyway.

Commit 8a6bd730 added support for
padding specifier extensions to strftime, but did not modify wcsftime.
In the process, it added a parameter to __strftime_fmt_1 in strftime.c,
but failed to update the prototype in wcsftime.c. This was found by
compiling musl with LTO:

    src/time/wcsftime.c:7:13: warning: type of '__strftime_fmt_1' does \
        not match original declaration [-Wlto-type-mismatch]

Fix the prototype of __strftime_fmt_1 in wcsftime.c, and generate the
'pad' argument the same way as it is done in strftime.

it was reported by Erik Bosman that poll fails without setting revents
when the nfds argument exceeds the current value for RLIMIT_NOFILE,
causing the subsequent open calls to be bypassed. if the rlimit is
either 1 or 2, this leaves fd 0 and 1 potentially closed but openable
when the application code is reached.

based on a brief reading of the poll syscall documentation and code,
it may be possible for poll to fail under other attacker-controlled
conditions as well. if it turns out these are reasonable conditions
that may happen in the real world, we may have to go back and
implement fallbacks to probe each fd individually if poll fails, but
for now, keep things simple and treat all poll failures as fatal.

if double precision r=x*y+z is not a half way case between two single
precision floats or it is an exact result then fmaf returns (float)r.

however the exactness check was wrong when |x*y| < |z| and could cause
incorrectly rounded result in nearest rounding mode when r is a half
way case.

fmaf(-0x1.26524ep-54, -0x1.cb7868p+11, 0x1.d10f5ep-29)
was incorrectly rounded up to 0x1.d117ap-29 instead of 0x1.d1179ep-29.
(exact result is 0x1.d1179efffffffecp-29, r is 0x1.d1179fp-29)

use of MB_CUR_MAX encoded a hidden dependency on the currently active
locale for the calling thread, whereas nl_langinfo_l is supposed to
report for the locale passed as an argument.

general policy is that all source files defining a public API or an
ABI mechanism referenced by a public header should include the public
header that declares the interface, so that the compiler or analysis
tools can check the consistency of the declarations. Alexander Monakov
pointed out a number of violations of this principle a few years back.
fix them now.

add a member of appropriate type to the fpos_t union so that accesses
are well-defined. use long long instead of off_t since off_t is not
always exposed in stdio.h and there's no namespace-clean alias for it.

access is still performed using pointer casts rather than by naming
the union member as a matter of style; to the extent possible, the
naming of fields in opaque types defined in the public headers is not
treated as an API contract with the implementation. access via the
pointer cast is valid as long as the union has a member of matching
type.

previously this macro used an odd if/else form instead of the more
idiomatic do/while(0), making it unsafe against omission of trailing
semicolon. the omission would make the following statement conditional
instead of producing an error.

this is the idiom that's used elsewhere and should be more efficient
or at least no worse.

they seem to be relics of e3cd6c5c
where this code was refactored from a check that previously masked
against (F_ERR|F_NOWR) instead of just F_NOWR.

formally, calling readv with a zero-length first iov component should
behave identically to calling read on just the second component, but
presence of a zero-length iov component has triggered bugs in some
kernels and performs significantly worse than a simple read on some
file types.