allows zeroing anonymous private pages inherited by a child process.
new in linux commit d2cd9ede6e193dd7d88b6d27399e96229a551b19

MSG_ZEROCOPY socket send flag avoids copy in the kernel
new in linux commit 52267790ef52d7513879238ca9fac22c1733e0e3
SO_ZEROCOPY socket option enables MSG_ZEROCOPY if availale
new in linux commit 76851d1212c11365362525e1e2c0a18c97478e6b

socket option for kernel TLS support
new in linux commit 3c4d7559159bfe1e3b94df3a657b2cda3a34e218

add AF_SMC and PF_SMC for the IBM shared memory communication protocol.
new in linux commit ac7138746e14137a451f8539614cdd349153e0c0
(linux socket.h is not in uapi so this update was missed earlier)

these additions were made by scanning git log since the last major
update in commit 790580b2. in addition
to git-level commit authorship, "patch by" text in the commit message
was also scanned. this idiom was used in the past for patches that
underwent substantial edits when merging or where the author did not
provide a commit message. going forward, my intent is to use commit
authorship consistently for attribution.

as before my aim was adding everyone with either substantial code
contributions or a pattern of ongoing simple patch submission; any
omissions are unintentional.

Maintainer's note: at one point, -lcompiler_rt apparently worked, and
may still work and be preferable if one has manually installed the
library in a public lib directory. but with current versions of clang,
the full pathname to the library file is needed. the original patch
removed the -lcompiler_rt check; I have left it in place in case there
are users depending on it, and since, when it does work, it's
preferable so as not to code a dependency on the specific compiler
version and paths in config.mak.

this is more extensible if we need to consider additional errors, and
more efficient as long as the compiler does not know it can cache the
result of __errno_location (a surprisingly complex issue detailed in
commit a603a75a).

It's better to make execvp continue PATH search on ENOTDIR rather than
issuing an error. Bogus entries should not render rest of PATH invalid.

Maintainer's note: POSIX seems to require the search to continue like
this as part of XBD 8.3 Other Environment Variables. Only errors that
conclusively determine non-existence are candidates for continuing;
otherwise for consistency we have to report the error.

when a null buffer pointer is passed to fmemopen, requesting it
allocate its own memory buffer, extremely large size arguments near
SIZE_MAX could overflow and result in underallocation. this results
from omission of the size of the cookie structure in the overflow
check but inclusion of it in the calloc call.

instead of accounting for individual small contributions to the total
allocation size needed, simply reject sizes larger than PTRDIFF_MAX,
which will necessarily fail anyway. then adding arbitrary fixed-size
structures is safe without matching up the expressions in the
comparison and the allocation.

Currently getcwd(3) can succeed without returning an absolute path
because the underlying getcwd syscall, starting with linux commit
v2.6.36-rc1~96^2~2, may succeed without returning an absolute path.

This is a conformance issue because "The getcwd() function shall
place an absolute pathname of the current working directory
in the array pointed to by buf, and return buf".

Fix this by checking the path returned by syscall and failing with
ENOENT if the path is not absolute.  The error code is chosen for
consistency with the case when the current directory is unlinked.

Similar issue was fixed in glibc recently, see
https://sourceware.org/bugzilla/show_bug.cgi?id=22679

in theory non-absolute origins can only arise when either the main
program is invoked by running ldso as a command (inherently non-suid)
or when dlopen was called with a relative pathname containing at least
one slash. such usage would be inherently insecure in an suid program
anyway, so the old behavior here does not seem to have been insecure.
harden against it anyway.

the rpath fixup code assumed any module's name field would contain at
least one slash, an invariant which is usually met but not in the case
of a main executable loaded from the current working directory by
running ldd or ldso as a command. it would be possible to make this
invariant always hold, but it has a higher runtime allocation cost and
does not seem useful elsewhere, so just patch things up in fixup_rpath
instead.

it's unclear from the specification whether the word "consumes" in
"consumes more than four bytes to represent a year" refers just to
significant places or includes leading zeros due to field width
padding. however the examples in the rationale indicate that the
latter was the intent. in particular, the year 270 is shown being
formatted by %+5Y as +0270 rather than 00270.

previously '+' prefixing was implemented just by comparing the year
against 10000. instead, count the number of significant digits and
padding bytes to be added, and use the total to determine whether to
apply the '+' prefix.

based on testing by Dennis Wölfing.

the code to strip initial sign and leading zeros inadvertently
stripped all the zeros and the subsequent '-' separating the month.
instead, only strip sign characters from the very first position, and
only strip zeros when they are followed by another digit.

based on testing by Dennis Wölfing.

in the original submission of the patch that became commit
7c709f2d, and in subsequent reading of
it by others, it was not clear that the new member had to be inserted
before canary_at_end, or that inserting it at that location was safe.
add comments to document.

Do not retry waitpid if the child was terminated by a signal. Do not
examine status: since we are not passing any flags, we will not receive
stop or continue notifications.

commit f9fb20b4 switched from using a
pipe for the result to conveying it via the child process exit status.
Alexander Monakov pointed out that the latter could fail if the
application is not expecting faccessat to produce a child and performs
a wait operation with __WCLONE or __WALL, and that it is not clear
whether it's guaranteed to work when SIGCHLD's disposition has been
set to SIG_IGN.

in addition, that commit introduced a bug that caused EACCES to be
produced instead of EBUSY due to an exit path that was overlooked when
the error channel was changed, and introduced a spurious retry loop
around the wait operation.

the Linux and FreeBSD man pages for dladdr document dli_fbase as the
"base address" of the library/module found. normally (e.g. AT_BASE)
the term "base" is used to denote the base address relative to which
p_vaddr addresses are interpreted; however in the case of dladdr's
Dl_info structure, existing implementations define it as the lowest
address of the mapping, which makes sense in the context of
determining which module's memory range the input address falls
within.

since this is a nonstandard interface provided to mimic one provided
by other implementations, adjust it to match their behavior.

Consider the first equals sign found in the option to be the delimiter
between it and its argument, even if it matches an equals sign in the
option name. This avoids consuming the equals sign, which would prevent
finding the argument. Instead, it forces a partial match of the part of
the option name before the equals sign.

Maintainer's note: GNU getopt_long does not explicitly document this
behavior, but it can be seen as a consequence of how partial matches
are specified, and at least GNU (bfd) ld is known to make use of it.

If we find a partial option name match, we need to keep looking for
ambiguous/conflicting options. However, we need to remember the position
in the candidate argument to find its option-argument later, if there is
one. This fixes e.g. option "foobar" being given as "--fooba=baz".

commit 78897b0d wrongly simplified
Dmitry Levin's original submitted patch fixing alt-form octal with the
zero flag and field width present, omitting the special case where the
value is zero. as a result, printf("%#o",0) wrongly prints "00" rather
than "0".

the logic prior to this commit was actually better, in that it was
aligned with how the alt-form flag (#) for printf is specified ("it
shall increase the precision"). at the time there was no good way to
avoid the zero flag issue with the old logic, but commit
167dfe96 added tracking of whether an
explicit precision was provided.

revert commit 78897b0d and switch to
using the explicit precision indicator for suppressing the zero flag.

In all cases this is just a change from two volatile int to one.

In some places there has been a direct usage of the functions. Use the
macros consistently everywhere, such that it might be easier later on to
capture the fast path directly inside the macro and only have the call
overhead on the slow path.

A variant of this new lock algorithm has been presented at SAC'16, see
https://hal.inria.fr/hal-01304108. A full version of that paper is
available at https://hal.inria.fr/hal-01236734.

The main motivation of this is to improve on the safety of the basic lock
implementation in musl. This is achieved by squeezing a lock flag and a
congestion count (= threads inside the critical section) into a single
int. Thereby an unlock operation does exactly one memory
transfer (a_fetch_add) and never touches the value again, but still
detects if a waiter has to be woken up.

This is a fix of a use-after-free bug in pthread_detach that had
temporarily been patched. Therefore this patch also reverts

         c1e27367

This is also the only place where internal knowledge of the lock
algorithm is used.

The main price for the improved safety is a little bit larger code.

Under high congestion, the scheduling behavior will be different
compared to the previous algorithm. In that case, a successful
put-to-sleep may appear out of order compared to the arrival in the
critical section.

With Linux kernel 4.16 it will be possible to guard more parts of the
Linux header files from a libc. Make use of this in musl to guard all
the structures and other definitions from the Linux header files which
are also defined by the header files provided by musl. This will make
it possible to compile source files which include both the libc
headers and the kernel userspace headers.

This extends the definitions done in commit 04983f22 ("make
netinet/in.h suppress clashing definitions from kernel headers")

in the unified code for handling utf-16 and ucs2 output, the check for
ucs2 wrongly looked at the source charset rather than the destination
charset.

previously, the charset names without endianness specified were always
interpreted as big endian. unicode specifies that UTF-16 and UTF-32
have BOM-determined endianness if BOM is present, and are otherwise
big endian. since commit 5b546faa
added support for stateful encodings, it is now possible to implement
BOM support via the conversion descriptor state.

for conversions to these charsets, the output is always big endian and
does not have a BOM.

the mapping tables and code are not automatically generated; they were
produced by comparing the output of towupper/towlower against the
mappings in the UCD, ignoring characters that were previously excluded
from case mappings or from alphabetic status (micro sign and circled
letters), and adding table entries or code for everything else
missing.

based very loosely on a patch by Reini Urban.

the new version of the code used to generate these tables forces a
newline every 256 entries, whereas at the time these files were
originally generated and committed, it only wrapped them at 80
columns. the new behavior ensures that localized changes to the
tables, if they are ever needed, will produce localized diffs.

commit d060edf6 made the corresponding
changes to the iconv tables.

notes by maintainer:

commit 2f853dd6 added these rules
because the new system for handling arch-provided replacement files
introduced for out-of-tree builds did not apply to the crt tree.

commit 63bcda4d later adapted the
makefile logic so that the crt and ldso trees go through the same
replacement logic as everything else, but failed to remove the
explicit rules that assumed the arch would always provide asm
replacements.

in addition to cleaning things up, removing these spurious rules
allows crti/crtn asm to be omitted by an arch (thereby using the empty
C files instead) if they are not needed.

notes by maintainer:

both C and POSIX use the term UTC to specify related functionality,
despite POSIX defining it as something more like UT1 or historical
(pre-UTC) GMT without leap seconds. neither specifies the associated
string for %Z. old choice of "GMT" violated principle of least
surprise for users and some applications/tests. use "UTC" instead.