It is possible for argv[0] to be a null pointer, but the __progname
variable is used to implement functions in src/legacy/err.c that do not
expect it to be null. It is also available to the user via the
program_invocation_name alias as a GNU extension, and the implementation
in Glibc initializes it to a pointer to empty string rather than NULL.

Since argv[0] is usually non-null and it's preferable to keep those
variables in BSS, implement the fallbacks in __init_libc, which also
allows to have an intermediate fallback to AT_EXECFN.

it is defined in linux asm/sockios.h since commit
ae40eb1ef30ab4120bd3c8b7e3da99ee53d27a23 (linux v2.6.22)
but was missing from musl by accident.

in musl the sockios macros are exposed in sys/ioctl.h together
with other ioctl requests instead of in sys/socket.h because of
namespace rules. (glibc has them in sys/socket.h under _GNU_SOURCE.)

commit c002668e inadvertently moved
the check for unflushed write buffer outside of the scope of the
existing lock.

Due to a missing ":" in an asm() statement, the "memory" clobber is
considered by gcc as an input operand and not a clobber, which causes a
build failure.

passing to pthread_join the id of a thread which is not joinable
results in undefined behavior.

in principle the check to trap does not necessarily work if
pthread_detach was called after thread creation, since no effort is
made here to synchronize access to t->detached, but the check is
well-defined and harmless for callers which did not invoke UB, and
likely to help catch erroneous code that would otherwise mysteriously
hang.

patch by William Pitcock.

The TOC pointer is constant within a single dso, but needs to be saved
and restored around cross-dso calls.  The PLT stub saves it to the
caller's stack frame, and the linker adds code to the caller to restore
it.

With a local call, as within a single dso or with static linking, this
doesn't happen and the TOC pointer is always in r2.  Therefore,
setjmp/longjmp need to save/restore the TOC pointer from/to different
locations depending on whether the call to setjmp was a local or non-local
call.

It is always safe for longjmp to restore to both r2 and the caller's stack.
If the call to setjmp was local, and only r2 matters and the stack location
will be ignored, but is required by the ABI to be reserved for the TOC
pointer.  If the call was non-local, then only the stack location matters,
and whatever is restored into r2 will be clobbered anyway when the caller
reloads r2 from the stack.

A little extra care is required for sigsetjmp, because it uses setjmp
internally.  After the second return from this setjmp call, r2 will contain
the caller's TOC pointer instead of libc's TOC pointer.  We need to save
and restore the correct libc pointer before we can tail call to
__sigsetjmp_tail.

neither current compilers nor linkers treat protected visibility the
way I expected, as having fixed source-level semantics rather than
being dependent on target-specific ABI details, and change seems
unlikely. while the use here does not actually depend on the specific
semantics, at least some versions of some linkers, especially lld,
refuse to allow linking to a libc.so where the symbols have protected
visibility. this cannot be detected at configure-time because linking
libc.so itself works fine, and because even if we could test linking
an application against libc.so successfully, we could not justifiably
assume that the same linker used to link libc.so would also be used
later to link applications.

disable the vis.h hack by default at the configure level, but add an
explicit "auto" option to request the old configure-time detection
rather than just removing it. this leaves it easy to evaluate whether
it actually resulted in significant size or performance benefits while
ensuring that out-of-the-box builds are not unlinkable for some users.

fortunately, preliminary evaluation suggests that at least x86_64,
arm, and aarch64 don't suffer at all from the change, and impact on
other archs is low. if low is not low enough, it should not be hard to
analyze where the significant PLT call ABI costs are present and
mitigate them without the hack.

since setlocale(cat, NULL) is required to return the setting for the
global locale, there is no standard mechanism to obtain the name of
the currently active thread-local locale set by uselocale. this makes
it impossible for application/library software to load appropriate
translations, etc. unless using the gettext implementation provided by
libc, which has privileged access to libc internals.

to fill this gap, glibc introduced the _NL_LOCALE_NAME macro which can
be used with nl_langinfo to obtain the name. GNU gettext/gnulib code
already use this functionality on glibc, and can easily be adapted to
make use of it on non-glibc systems if it's available; for other
systems they poke at locale implementation internals, which we want to
avoid. this patch provides a compatible interface to the one glibc
introduced.

The switch statement has no 'default:' case and the function ends
immediately following the switch, so the extra comparison did not
communicate any extra information to the compiler.

The flag 1<<7 is used in several places for different purposes that are
not always easy to distinguish. Mark those usages that correspond to the
flag that is used by the kernel for futexes.

commit 58e2396a missed that the same
code was duplicated in implementation of vfwprintf.

The two functions str{,n}casecmp_l are specified to be declared in
<strings.h> which is already included from <string.h> under _GNU_SOURCE.

previously, the pathname used to load the program was always used as
argv[0]. the default remains the same, but a new --argv0 option can be
used to provide a different value.

commit 4ff234f6 inadvertently removed
the logic to do this when changing the representation of global
status.

a null pointer for a library's deps list was ambiguous: it could
indicate either no dependencies or that the dependency list had not
yet been populated. inability to distinguish could lead to spurious
work when dlopen is called multiple times on a library with no deps,
and due to related bugs, could actually cause other libraries to
falsely appear as dependencies, translating into false positives for
dlsym.

avoid the problem by always initializing the deps pointer, pointing to
an empty list if there are no deps. rather than wasting memory and
introducing another failure path by allocating an empty list per
library, simply share a global dummy list.

further fixes will be needed for related bugs, and much of this code
may end up being replaced.

while the official elfv2 abi for "powerpc64le" sets power8 as the
baseline isa, we use it for both little and big endian powerpc64
targets and need to maintain compatibility with pre-power8 models. the
instructions for sqrt, fabs, and fma are in the baseline isa; support
for the rest is conditional via predefined isa-level macros.

patch by David Edelsohn.

these were introduced in z196 and not available in the baseline (z900)
ISA level. use __HTM__ as an alternate indicator for ISA level, since
gcc did not define __ARCH__ until 7.x.

patch by David Edelsohn.

in arm rtabi these __aeabi_* functions have special abi (they are
only allowed to clobber r0,r1,r2,r3,ip,lr,cpsr), so they cannot
be simple wrappers around normal string functions (which may
clobber other registers), the safest solution is to write them in
asm, a minimalistic implementation works because these are not
supposed to be emitted by compilers or used in general.

commit 2d7d05f0 wrongly changed ERANGE
to EINVAL, likely as the result of copy-and-paste error.

commit 97bd6b09 refactored the table
lookup into a function and introduced an error in index computation.
the error caused garbage to be read from the table if the given charmap
had a non-zero number of elided entries.

POSIX requires ctime_r return a null pointer on failure, which can
occur if the input time_t value is not representable in broken down
form.

based on patch by Alexander Monakov.

these functions return an error code, and are not explicitly
documented to set errno, but they are nonstandard and the historical
implementations do set errno as well, and some applications expect
this behavior. do likewise for compatibility.

patch by Rudolph Pereira.

ctime passes the result from localtime directly to asctime. But in case
of error, localtime returns 0. This causes an error (NULL pointer
dereference) in asctime.

based on patch by Omer Anson.

mremap seems to always fail on nommu, and on some non-Linux
implementations of the Linux syscall API, it at least fails to
increase allocation size, and may fail to move (i.e. defragment) the
existing mapping when shrinking it too. instead of failing realloc or
leaving an over-sized allocation that may waste a large amount of
memory, fallback to malloc-memcpy-free if mremap fails.

POSIX defines getdate error #5 as:
"An I/O error is encountered while reading the template file."

POSIX defines getdate error #7 as:
"There is no line in the template that matches the input."

This change correctly disambiguates between the two error conditions.

Per 1003.1-2008 (2016 ed.), catopen must set errno on failure.

We set errno to EOPNOTSUPP because musl does not currently support
message catalogues.

the check to prevent matching empty string wrongly blocked matching
of "/" due to checking emptiness after stripping leading slashes
rather than checking the full original argument string.

simplified from patch by Julien Ramseier.

when using the sh4a opcodes, the assembler tags the resulting object
file as requiring sh4a. the linker then refuses to (static) link it
with object files marked as requiring j2, since there is no isa level
that includes both sh4a and j2 instructions.

Make a fast path for ascii chars which is assumed to be the most common
case. This has significant performance benefit on xml json and similar

at one point, clang reportedly failed to support the asm register
constraints needed for inline syscalls. versions of clang that old
have much bigger problems that preclude using them to compile musl
libc.

mips64 requires 'struct stat' conversion due to incorrect 32-bit
fields where time_t should be in the kernel version of the structure.
syscall_arch.h already performed the correct translation for stat,
fstat, and lstat syscalls, but omitted special handling for fstatat.

The flags argument was missing, causing uninitalized data to be passed
to fchownat(2). The correct value of flags should match the fallback for
chown(3).