Both sqrt and sqrtf shifted the signed exponent as signed int to adjust
the bit representation of the result. There are signed right shifts too
in the code but those are implementation defined and are expected to
compile to arithmetic shift on supported compilers and targets.

mbsrtowcs contains "vectorized" loops to quickly step over bytes
without the high bit set; these have undefined behavior by virtue of
aliasing uint32_t over top of char data for the accesses.

commit 4d0a8217 fixed the
corresponding usage in string functions by using the may_alias
attribute conditional on __GNUC__ and disabled the vectorized code in
its absence. do the same for mbsrtowcs.

Several math functions are now from the ARM optimized-routines repo
licensed under standard MIT terms and copyrighted by Arm Limited,
so mention this in the COPYRIGHT too.

commit ab3eb89a removed it as part of
correcting the mcontext_t definition, but there is still code using
struct sigcontext and expecting the member names present in it, most
notably libgcc_eh. almost all such usage is incorrect, but bring back
struct sigcontext at least for now so as not to introduce regressions.

in order for sys/procfs.h (provided by sys/user.h) to be useful, it
needs to match the API its consumers (gdb, etc.) expect, including the
member names established by glibc.

this partly reverts commit 29e8737f,
which partly reverted d493206d,
eliminating struct user_fpregs_struct which seems to have had no
precedent and using union __riscv_mc_fp_state for elf_fpregset_t. this
requires indirect inclusion of signal.h to make union
__riscv_mc_fp_state visible, but being that these are nonstandard
"junk" headers with no official restrictions on what they can pull in,
that's no big deal.

split off and expanded from patch by Khem Raj.

the top-level mcontext_t member names were namespace-violating in
standards profiles before, and nested-level member names (some of them
single-letter) were egregiously bad namespace impositions even in
non-strict profiles. moreover, they mismatched those used in the
public API first defined in glibc, breaking any code making use of
them.

unlike most archs, the public API used in glibc for riscv mcontext_t
members was designed to be namespace-safe, so we can and should expose
the members regardless of feature test macros. only the typedefs for
greg_t, gregset_t, and fpregset_t need to be protected behind FTMs.

the struct tags for mcontext_t and ucontext_t are also changed. for
mcontext_t this is necessary to make the common definition across
profiles namespace-safe. for ucontext_t, it's just a matter of
matching the tag from the glibc-defined API.

these changes are split off and expanded from a patch by Khem Raj.

Some declarations of __tls_get_new were left in the code, even
though the definition got removed in

  commit 9d44b646
  install dynamic tls synchronously at dlopen, streamline access

this can make the build fail with

  ld: lib/libc.so: hidden symbol `__tls_get_new' isn't defined

when libc.so is linked without --gc-sections, because a .hidden
declaration in asm code creates a reference even if the symbol
is not actually used.

lrint in (LONG_MAX, 1/DBL_EPSILON) and in (-1/DBL_EPSILON, LONG_MIN)
is not trivial: rounding to int may be inexact, but the conversion to
int may overflow and then the inexact flag must not be raised. (the
overflow threshold is rounding mode dependent).

this matters on 32bit targets (without single instruction lrint or
rint), so the common case (when there is no overflow) is optimized by
inlining the lrint logic, otherwise the old code is kept as a fallback.

on my laptop an i486 lrint call is asm:10ns, old c:30ns, new c:21ns
on a smaller arm core: old c:71ns, new c:34ns
on a bigger arm core: old c:27ns, new c:19ns

analogous to commit ddc7c4f9 for
mips64 and n32, remove the hack to load the syscall number into $2 via
asm, and use a constraint to let the compiler load it instead.

now, only $4, $5, and $6 are potential input-only registers. $2 is
always input and output, and $7 is both when it's an argument,
otherwise output-only. previously, $7 was treated as an input (with a
"1" constraint matching its output position) even when it was not an
input, which was arguably undefined behavior (asm input from
indeterminate value). this is corrected.

as before, $8, $9, and $10 are conditionally input-output registers
for 5-, 6-, and 7-argument syscalls. their role in input is carrying
in the values that will be stored on the stack for arguments 5-7.
their role in output is carrying back whatever the kernel has
clobbered them with, so that the compiler cannot assume they still
contain the input values.

mips32 has two fpu register file variants: FR=0 with 32 32-bit
registers, where pairs of neighboring even/odd registers are used to
represent doubles, and FR=1 with 32 64-bit registers, each of which
can store a single or double.

up through r5 (our "mips" arch), the supported ABI uses FR=0, but
modern compilers generate "fpxx" model code that can safely operate
with either model. r6, which is an incompatible but similar ISA, drops
FR=0 and only provides the FR=1 model. as such, setjmp and longjmp,
which depended on being able to save and restore call-saved doubles by
storing and loading their 32-bit halves, were completely broken in the
presence of floating point code on mips r6.

to fix this, use the s.d and l.d mnemonics to store and load fpu
registers. these expand to the existing swc1 and lwc1 instructions for
pairs of 32-bit fpu registers on mips1, but on mips2 and later they
translate directly to the 64-bit sdc1 and ldc1.

with FR=0, sdc1 and ldc1 behave just like the pairs of swc1 and lwc1
instructions they replace, storing or loading the even/odd pair of fpu
registers that can be treated as separate single-precision floats or
as a unit representing a double. but with FR=1, they store/load
individual 64-bit registers. this yields the ABI-correct behavior on
mips r6, and should make linking of pre-r6 (plain "mips") code with
"fp64" model code workable, although this is and will likely remain
unsupported usage.

in addition to the mips r6 problem this change fixes, reportedly
clang's internal assembler refuses to assemble swc1 and lwc1
instructions for odd register indices when building for "fpxx" model
(the default). this caused setjmp and longjmp not to build. by using
the s.d and l.d forms, this problem is avoided too.

as a bonus, code size is reduced everywhere but mips1.

mips r6 (an incompatible isa from traditional mips) removes the hi and
lo registers used for mul/div results. older gcc versions accepted
them in the clobber list for asm, but their presence is incorrect and
breaks on later versions.

in the process of fixing this, the clobber list for 32-bit mips
syscalls has been deduplicated via a macro like on mips64 and n32.

armv8 removed the coprocessor instructions other than cp14, so
on an armv8 system the related hwcaps should never be set.

new llvm complains about the use of coprocessor instructions in
armv8-a mode (even though they are never executed at runtime),
so ifdef them out when musl is built for armv8.

in the timer thread start function, self->timer_id was accessed
without synchronization; the timer thread could fail to see the store
from the calling thread, resulting in timer_delete failing to delete
the correct kernel-level timer.

this fix is based on a patch by changdiankang, but with the load moved
to after receiving the timer_delete signal rather than just after the
start barrier, so as not to retain the possibility of data race with
timer_delete.

The operand sepcifiers in a_cas and a_cas_p for riscv64 were incorrect:
there's a backwards branch in the routine, so despite tmp being written
at the end of the assembly fragment it cannot be allocated in one of the
input registers because the input values may be needed for another trip
around the loop.

For code that follows the guaranteed forward progress requirements, the
backwards branch is rarely taken: SiFive's hardware only fails a store
conditional on execptional cases (ie, instruction cache misses inside
the loop), and until recently a bug in QEMU allowed back-to-back
store conditionals to succeed.  The bug has been fixed in the latest
QEMU release, but it turns out that the fix caused this latent bug in
musl to manifest.

commit 8a544ee3 introduced a
dependency of the failure path for explicit scheduling at thread
creation on __clone's handling of the start function returning, which
should result in SYS_exit.

as noted in commit 05870abe, the arm
version of __clone was broken in this case. in the past, the mips
version was also broken; it was fixed in commit
8b2b61e0.

since this code path is pretty much entirely untested (previously only
reachable in applications that call the public clone() and return from
the start function) and consists of fragile per-arch asm, don't assume
it works, at least not until it's been thoroughly tested. instead make
the SYS_exit syscall from the start function's failure path.

commit cc3a4466 fixed this for printf
but neglected to fix wprintf.

Previously, %lf caused a failure to output.

we don't actually support building asm source files as thumb1, but
it's possible that the condition __ARM_ARCH>=5 would be false on old
compilers that did not define __ARM_ARCH at all. avoiding that would
require enumerating all of the possible __ARM_ARCH_*__ macros for
testing.

as noted in commit 05870abe, mov lr,pc
is not valid for saving a return address when in thumb mode. since
this code is a hot path (dynamic TLS access), don't do the out-of-line
bl->bx chaining to save the return value; instead, use the fact that
this file is preprocessed asm to add the missing thumb bit with an add
in place of the mov.

the change here does not affect builds for ISA levels new enough to
have a thread pointer read instruction, or for armv5 and later as long
as the compiler properly defines __ARM_ARCH, or for any build as arm
(not thumb) code. it's likely that it makes no difference whatsoever
to any present-day practical build environments, but nonetheless now
it's safe.

as an alternative, we could just assume __thumb__ implies availability
of blx since we don't support building asm source files as thumb1. I
didn't do that in order to avoid having a wrong assumption here if
that ever changes.

as noted in commit 05870abe, mov lr,pc
is not a valid method for saving the return address in code that might
be built as thumb.

this one is unlikely to matter, since any ISA level that has thumb2
should also have native implementations of atomics that don't involve
kuser_helper, and the affected code is only used on very old kernels
to begin with.

mov lr,pc is not a valid way to save the return address in thumb mode
since it omits the thumb bit. use a chain of bl and bx to emulate blx.
this could be avoided by converting to a .S file with preprocessor
conditions to use blx if available, but the time cost here is
dominated by the syscall anyway.

while making this change, also remove the remnants of support for
pre-bx ISA levels. commit 9f290a49
removed the hack from the parent code paths, but left the unnecessary
code in the child. keeping it would require rewriting two code paths
rather than one, and is useless for reasons described in that commit.

AT_HWCAP2 flags, see

  linux commit 671db581815faf17cbedd7fcbc48823a247d90b1
  arm64: Expose DC CVADP to userspace

  linux commit 06a916feca2b262ab0c1a2aeb68882f4b1108a07
  arm64: Expose SVE2 features for userspace

new mount api syscalls were added, same numers on all targets, see

  linux commit a07b20004793d8926f78d63eb5980559f7813404
  vfs: syscall: Add open_tree(2) to reference or clone a mount

  linux commit 2db154b3ea8e14b04fee23e3fdfd5e9d17fbc6ae
  vfs: syscall: Add move_mount(2) to move mounts around

  linux commit 24dcb3d90a1f67fe08c68a004af37df059d74005
  vfs: syscall: Add fsopen() to prepare for superblock creation

  linux commit ecdab150fddb42fe6a739335257949220033b782
  vfs: syscall: Add fsconfig() for configuring and managing a context

  linux commit 93766fbd2696c2c4453dd8e1070977e9cd4e6b6d
  vfs: syscall: Add fsmount() to create a mount for a superblock

  linux commit cf3cba4a429be43e5527a3f78859b1bfd9ebc5fb
  vfs: syscall: Add fspick() to select a superblock for reconfiguration

  linux commit 9c8ad7a2ff0bfe58f019ec0abc1fb965114dde7d
  uapi, x86: Fix the syscall numbering of the mount API syscalls [ver #2]

  linux commit d8076bdb56af5e5918376cd1573a6b0007fc1a89
  uapi: Wire up the mount API syscalls on non-x86 arches [ver #2]

apply open_tree with OPEN_TREE_CLONE call to the entire subtree, see

  linux commit a07b20004793d8926f78d63eb5980559f7813404
  vfs: syscall: Add open_tree(2) to reference or clone a mount

see

  linux commit a528d35e8bfcc521d7cb70aaf03e1bd296c8493f
  statx: Add a system call to make enhanced file info available

these are linux specific and not reserved names for fcntl.h so they
are under _BSD_SOURCE|_GNU_SOURCE.

when set a pidfd is stored in parent_tidptr, see

  linux commit b3e5838252665ee4cfa76b82bdf1198dca81e5be
  clone: add CLONE_PIDFD

ethertype for fake VLAN header for DSA, see

  linux commit bf5bc3ce8a8f32a0d45b6820ede8f9fc3e9c23df
  ether: Add dedicated Ethertype for pseudo-802.1Q DSA tagging

historically, a number of 32-bit archs used long rather than int for
wchar_t, for no good reason. GCC still uses the historical types, but
clang replaced them all with int, and it seems PCC uses int too.
mismatching the compiler's type for wchar_t is not an option due to
wide string literals.

note that the mismatch does not affect C++ ABI since wchar_t is its
own builtin type/keyword in C++, distinct from both int and long, not
a typedef.

i386 already worked around this by honoring __WCHAR_TYPE__ if defined
by the compiler, and only using the official legacy ABI type if not.
add the same to the other affected archs.

it might make sense at some point to switch to using int as the
default if __WCHAR_TYPE__ is not defined, if the expectations is that
new compilers will treat int as the correct choice, but it's unlikely
that the case where __WCHAR_TYPE__ is undefined will ever be used
anyway. I actually wanted to move the definition of wchar_t to the
top-level shared alltypes.h.in, using __WCHAR_TYPE__ and falling back
to int if not defined, but that can't be done without assuming all
compilers define __WCHAR_TYPE__ thanks to some pathological archs
where the ABI has wchar_t as an unsigned type.

previously, when pthread_create failed due to inability to set
explicit scheduling according to the requested attributes, the nascent
thread was detached and made responsible for its own cleanup via the
standard pthread_exit code path. this left it consuming resources
potentially well after pthread_create returned, in a way that the
application could not see or mitigate, and unnecessarily exposed its
existence to the rest of the implementation via the global thread
list.

instead, attempt explicit scheduling early and reuse the failure path
for __clone failure if it fails. the nascent thread's exit futex is
not needed for unlocking the thread list, since the thread calling
pthread_create holds the thread list lock the whole time, so it can be
repurposed to ensure the thread has finished exiting. no pthread_exit
is needed, and freeing the stack, if needed, can happen just as it
would if __clone failed.

if setting scheduling properties succeeds, the new thread may end up
with lower priority than the caller, and may be unable to continue
running due to another intermediate-priority thread. this produces a
priority inversion situation for the thread calling pthread_create,
since it cannot return until the new thread reports success.

originally, the parent was responsible for setting the new thread's
priority; commits b8742f32 and
40bae2d3 changed it as part of
trimming down the pthread structure. since then, commit
04335d92 partly reversed the changes,
but did not switch responsibilities back. do that now.

commit 8f11e612 wrongly documented
that all changes to libc.threads_minus_1 were guarded by the thread
list lock, but the decrement for failed SYS_clone took place after the
thread list lock was released.

commit 030e5263 added optreset, a BSD
extension to getopt duplicating the functionality (also an extension)
of setting optind to 0, but failed to provide a public declaration for
it. according to the BSD documentation and headers, the application is
not supposed to need to provide its own declaration.

these are presently extensions, thus named with _np to match glibc and
other implementations that provide them; however they are likely to be
standardized in the future without the _np suffix as a result of
Austin Group issue 1208. if so, both names will be kept as aliases.

due to historical accident/sloppiness in glibc, the powerpc,
powerpc64, and sh versions of struct user, defined by sys/user.h, used
struct pt_regs from the kernel asm/ptrace.h for their regs member.
this made it impossible to define the type in an API-compatible manner
without either including asm/ptrace.h like glibc does (contrary to our
policy of not depending on kernel headers), or clashing with
asm/ptrace.h's definition of struct pt_regs if both headers are
included (which is almost always the case in software using
sys/user.h).

for a long time I viewed this problem as having no reasonable fix. I
even explored the possibility of having the powerpc[64] and sh
versions of user.h just include the kernel header (breaking with
policy), but that looked like it might introduce new clashes with
sys/ptrace.h. and it would also bring in a lot of additional cruft
that makes no sense for sys/user.h to expose. glibc goes out of its
way to suppress some of that with #undef, possibly leading to
different problems. this is a rabbit-hole that should be explored no
further.

as it turns out, however, nothing actually uses struct user
sufficiently to care about the type of the regs member; most software
including sys/user.h does not even use struct user at all. so, the
problem can be fixed just by doing away with the insistence on strict
glibc API compatibility for the struct tag of the regs member.

rather than renaming the tag, which might lead to the new name
entering use as API, simply use an untagged structure inside struct
user with the same members/layout as struct pt_regs.

for sh, struct pt_dspregs is just removed entirely since it was not
used.

commit 9b14ad54 introduced this
namespace violation.

these members are associated with an unsupported option group. with
time_t changing size on 32-bit archs, all interfaces taking struct
sched_param arguments would need redirection and compat shims in order
to be able to continue offering these members, for no benefit. just
convert them to reserved space instead.

d493206d deleted all the content of
user.h, but sys/procfs.h expects this from sys/user.h
threfore we retain the non conflicting parts

commit ffab4360 broke this by moving
relocations after not only the allocation of storage for the main
thread's static TLS, but after the copying of the TLS image. thus,
relocation results were not reflected in the main thread's copy. this
could be fixed by calling __reset_tls after relocations, but instead
split the allocation and installation before/after relocations so that
there's not a redundant copy.

due to commit 71af5309, updating of
static_tls_cnt needs to be kept with allocation of static TLS, before
relocations, rather than after installation.

commit 7590203c omitted static here.