mlock2 syscall was added in linux v4.4 and glibc has api for it.
It falls back to mlock in case of flags==0, so that case works
even on older kernels.

MLOCK_ONFAULT is moved under _GNU_SOURCE following glibc.

unlike the x86 variant, the m68k ld80 format allows (biased) exponent
zero with mantissa msb set, thereby extending the normal range.

the mode member of struct ipc_perm is specified by POSIX to have type
mode_t, which is uniformly defined as unsigned int. however, Linux
defines it with type __kernel_mode_t, and defines __kernel_mode_t as
unsigned short on some archs. since there is a subsequent padding
field, treating it as a 32-bit unsigned int works on little endian
archs, but the order is backwards on big endian archs with the
erroneous definition.

since multiple archs are affected, remedy the situation with fixup
code in the affected functions (shmctl, semctl, and msgctl) rather
than repeating the same shims in syscall_arch.h for every affected
arch.

new in linux commit 71406883fd35794d573b3085433c41d0a3bf6c21

new in linux commit 256211f2b0b251e532d1899b115e374feb16fa7a

hwcaps for armv8.4, new in linux commit
7206dc93a58fb76421c4411eefa3c003337bcb2d

PR_{SET,GET}_SPECULATION_CTRL controls speculation related vulnerability
mitigations, new in commits
b617cfc858161140d69cc0b5cc211996b557a1c7
356e4bfff2c5489e016fdb925adbf12a1e3950ee

added in linux commit 4fe0de5b143762d327bfaf1d7be7c5b58041a18c

new and missing netlink attributes types for SCM_TIMESTAMPING_OPT_STATS,
new ones were added in commits
7156d194a0772f733865267e7207e0b08f81b02b
be631892948060f44b1ceee3132be1266932071e
87ecc95d81d951b0984f2eb9c5c118cb68d0dce8

introduced to stat ipc objects without permission checks since the
info is available in /proc/sysvipc anyway, new in linux commits
23c8cec8cf679b10997a512abb1e86f0cedc42ba
a280d6dc77eb6002f269d58cd47c7c7e69b617b6
c21a6970ae727839a2f300cd8dd957de0d0238c3

to map at a fixed address without unmapping underlying mappings
(fails with EEXIST unlike MAP_FIXED), new in linux commits
4ed28639519c7bad5f518e70b3284c6e0763e650 and
a4ff8e8620d3f4f50ac4b41e8067b7d395056843.

add pkey_mprotect, pkey_alloc, pkey_free syscall numbers,
new in linux commits 3350eb2ea127978319ced883523d828046af4045
and 9499ec1b5e82321829e1c1510bcc37edc20b6f38

armv8.4 fp mul instructions.
added in commit 3b3b681097fae73b7f5dcdd42db6cfdf32943d4c

to get seccomp state for checkpoint restore.
added in linux commit 26500475ac1b499d8636ff281311d633909f5d20

struct tag follows the glibc api and ptrace_peeksiginfo_args
got changed too accordingly.

octets in ethernet type field
added in linux commit 4bbb3e0e8239f9079bf1fe20b3c0cb598714ae61

protocol number for erspan v2 support
added in linux commit f551c91de262ba36b20c3ac19538afb4f4507441

added to uapi in commit 65aaf87b3aa2d049c6b9fd85221858a895df3393
used since commit a9a08845e9acbd224e4ee466f5c1275ed50054e8,
which renamed POLL* to EPOLL* in the kernel.

three ABIs are supported: the default with 68881 80-bit fpu format and
results returned in floating point registers, softfloat-only with the
same format, and coldfire fpu with IEEE single/double only. only the
first is tested at all, and only under qemu which has fpu emulation
bugs.

basic functionality smoke tests have been performed for the most
common arch-specific breakage via libc-test and qemu user-level
emulation. some sysvipc failures remain, but are shared with other big
endian archs and will be fixed separately.

since x86 and m68k are the only archs with 80-bit long double and each
has mandatory endianness, select the variant via endianness.
differences are minor: apparently just byte order and representation
of infinities. the m68k format is not well-documented anywhere I could
find, so if other differences are found they may require additional
changes later.

In TLS variant I the TLS is above TP (or above a fixed offset from TP)
but on some targets there is a reserved gap above TP before TLS starts.

This matters for the local-exec tls access model when the offsets of
TLS variables from the TP are hard coded by the linker into the
executable, so the libc must compute these offsets the same way as the
linker.  The tls offset of the main module has to be

	alignup(GAP_ABOVE_TP, main_tls_align).

If there is no TLS in the main module then the gap can be ignored
since musl does not use it and the tls access models of shared
libraries are not affected.

The previous setup only worked if (tls_align & -GAP_ABOVE_TP) == 0
(i.e. TLS did not require large alignment) because the gap was
treated as a fixed offset from TP.  Now the TP points at the end
of the pthread struct (which is aligned) and there is a gap above
it (which may also need alignment).

The fix required changing TP_ADJ and __pthread_self on affected
targets (aarch64, arm and sh) and in the tlsdesc asm the offset to
access the dtv changed too.

since this iconv implementation's output is stateless, it's necessary
to know before writing anything to the output buffer whether the
conversion of the current input character will fit.

previously we used a hard-coded table of the output size needed for
each supported output encoding, but failed to update the table when
adding support for conversion to jis-based encodings and again when
adding separate encoding identifiers for implicit-endianness utf-16/32
and ucs-2/4 variants, resulting in out-of-bound table reads and
incorrect size checks. no buffer overflow was possible, but the
affected characters could be converted incorrectly, and iconv could
potentially produce an incorrect return value as a result.

remove the hard-coded table, and instead perform the recursive iconv
conversion to a temporary buffer, measuring the output size and
transferring it to the actual output buffer only if the whole
converted result fits.

this case is handled with a recursive call to iconv using a
specially-constructed conversion descriptor. the constant 0 was used
as the offset for utf-8, since utf-8 appears first in the charmaps
table, but the offset used needs to point into the charmap entry, past
the name/aliases at the beginning, to the byte identifying the
encoding. as a result of this error, junk was produced.

instead, call find_charmap so we don't have to hard-code a nontrivial
offset. with this change, the code has been tested and found to work
in the case of converting the affected hkscs characters to utf-8.

maintainer's notes:

commit 95c6044e split UTF-32 and
UTF-32BE but neglected to add a case for the former as a destination
encoding, resulting in it wrongly being handled by the default case.
the intent was that the value of the macro be chosen to encode "big
endian" in the low bits, so that no code would be needed, but this was
botched; instead, handle it the way UCS2 is handled.

maintainer's notes:

commit a223dbd2 added the reverse
conversions to JIS-based encodings, but omitted the check for remining
buffer space in the case where the next character to be written was
single-byte, allowing conversion to continue past the end of the
destination buffer.

the wrapper start function that performs scheduling operations is
unreachable if pthread_attr_setinheritsched is never called, so move
it there rather than the pthread_create source file, saving some code
size for static-linked programs.

eliminate the awkward startlock mechanism and corresponding fields of
the pthread structure that were only used at startup.

instead of having pthread_create perform the scheduling operations and
having the new thread wait for them to be completed, start the new
thread with a wrapper start function that performs its own scheduling,
sending the result code back via a futex. this way the new thread can
use storage from the calling thread's stack rather than permanent
fields in the pthread structure.

over time the pthread structure has accumulated a lot of cruft taking
up size. this commit removes unused fields and packs booleans and
other small data more efficiently. changes which would also require
changing code are not included at this time.

non-volatile booleans are packed as unsigned char bitfield members.

the canceldisable and cancelasync fields need volatile qualification
due to how they're accessed from the cancellation signal handler and
cancellable syscalls called from signal handlers. since volatile
bitfield semantics are not clearly defined, discrete char objects are
used instead.

the pid field is completely removed; it has been unused since commit
83dc6eb0.

the tid field's type is changed to int because its use is as a value
in futexes, which are defined as plain int. it has no conceptual
relationship to pid_t. also, its position is not ABI.

startlock is reduced to a length-1 array. the second element was
presumably intended as a waiter count, but it was never used and made
no sense, since there is at most one waiter.

previously, some accesses to the detached state (from pthread_join and
pthread_getattr_np) were unsynchronized; they were harmless in
programs with well-defined behavior, but ugly. other accesses (in
pthread_exit and pthread_detach) were synchronized by a poorly named
"exitlock", with an ad-hoc trylock operation on it open-coded in
pthread_detach, whose only purpose was establishing protocol for which
thread is responsible for deallocation of detached-thread resources.

instead, use an atomic detach_state and unify it with the futex used
to wait for thread exit. this eliminates 2 members from the pthread
structure, gets rid of the hackish lock usage, and makes rigorous the
trap added in commit 80bf5952 for
catching attempts to join detached threads. it should also make
attempt to detach an already-detached thread reliably trap.

if the last thread exited via pthread_exit, the logic that marked it
dead did not account for the possibility of it targeting itself via
atexit handlers. for example, an atexit handler calling
pthread_kill(pthread_self(), SIGKILL) would return success
(previously, ESRCH) rather than causing termination via the signal.

move the release of killlock after the determination is made whether
the exiting thread is the last thread. in the case where it's not,
move the release all the way to the end of the function. this way we
can clear the tid rather than spending storage on a dedicated
dead-flag. clearing the tid is also preferable in that it hardens
against inadvertent use of the value after the thread has terminated
but before it is joined.

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.

in thumb mode, r7 is the ABI frame pointer register, and unless frame
pointer is disabled, gcc insists on treating it as a fixed register,
refusing to spill it to satisfy constraints. unfortunately, r7 is also
used in the syscall ABI for passing the syscall number.

up til now we just treated this as a requirement to disable frame
pointer when generating code as thumb, but it turns out gcc forcibly
enables frame pointer, and the fixed register constraint that goes
with it, for functions which contain VLAs. this produces an
unacceptable arch-specific constraint that (non-arm-specific) source
files making syscalls cannot use VLAs.

as a workaround, avoid r7 register constraints when producing thumb
code and instead save/restore r7 in a temp register as part of the asm
block. at some point we may want/need to support armv6-m/thumb1, so
the asm has been tweaked to be thumb1-compatible while also
near-optimal for thumb2: it allows the temp and/or syscall number to
be in high registers (necessary since r0-r5 may all be used for
syscalll args) and in thumb2 mode allows the syscall number to be an
8-bit immediate.

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.