previously we detected this bug in configure and issued advice for a
workaround, but this turned out not to work. since then gcc 4.9.0 has
appeared in several distributions, and now 4.9.1 has been released
without a fix despite this being a wrong code generation bug which is
supposed to be a release-blocker, per gcc policy.

since the scope of the bug seems to affect only data objects (rather
than functions) whose definitions are overridable, and there are only
a very small number of these in musl, I am just changing them from
const to volatile for the time being. simply removing the const would
be sufficient to make gcc 4.9.1 work (the non-const case was
inadvertently fixed as part of another change in gcc), and this would
also be sufficient with 4.9.0 if we forced -O0 on the affected files
or on the whole build. however it's cleaner to just remove all the
broken compiler detection and use volatile, which will ensure that
they are never constant-folded. the quality of a non-broken compiler's
output should not be affected except for the fact that these objects
are no longer const and thus possibly add a few bytes to data/bss.

this change can be reconsidered and possibly reverted at some point in
the future when the broken gcc versions are no longer relevant.

the purpose of this logic is to avoid linking __stdio_exit unless any
stdio reads (which might require repositioning the file offset at exit
time) or writes (which might require flushing at exit time) could have
been performed.

previously, exit called two wrapper functions for __stdio_exit named
__flush_on_exit and __seek_on_exit. both of these functions actually
performed both tasks (seek and flushing) by calling the underlying
__stdio_exit. in order to avoid doing this twice, an overridable data
object __towrite_used was used to cause __seek_on_exit to act as a nop
when __towrite was linked.

now, exit only makes one call, directly to __stdio_exit. this is
satisfiable by a weak dummy definition in exit.c, but the real
definition is pulled in by either __toread.c or __towrite.c through
their referencing a symbol which is defined only in __stdio_exit.c.

this was previously a no-op, somewhat intentionally, because I failed
to understand that it only has an effect when sending to the logging
facility fails and thus is not the nuisance that it would be if always
sent output to the console.

this behavior is no longer valid in general, and was never necessary.
if the LOG_PERROR option is set, output to stderr could still succeed.
also, when the LOG_CONS option is added, it will need syslog to
proceed even if opening the log socket fails.

this is a nonstandard feature, but easy and inexpensive to add. since
the corresponding macro has always been defined in our syslog.h, it
makes sense to actually support it. applications may reasonably be
using the presence of the macro to assume that the feature is
supported.

the behavior of omitting the 'header' part of the log message does not
seem to be well-documented, but matches other implementations (at
least glibc) which have this option.

based on a patch by Clément Vasseur, but simplified using %n.

errno must be saved upon vsyslog entry, otherwise its value could be
changed by some libc function before reaching the %m handler in
vsnprintf.

previously passing an empty string for name resulted in failure, as
expected, but only after spurious syscalls, and it produced confusing
errno values (and thus dlerror strings).

in addition to dlopen calls, this issue affected use of LD_PRELOAD
with trailing whitespace or colon characters.

r24 was wrongly being saved at a misaligned offset of 30 rather than
the correct offset of 40 in the jmp_buf. the exact effects of this
error have not been studied, but it's clear that the value of r24 was
lost across setjmp/longjmp and the saved values of r21 and/or r22 may
also have been corrupted.

if the order of object files in the static archive libc.a was not
respected by the linker, the old logic could wrongly cause POSIX
symbols outside of the ISO C namespace to be pulled into pure C
programs. this should not happen with well-behaved linkers, but
relying on the link order was a bad idea anyway.

files are renamed to better reflect their contents now that they don't
need names to control their order as members in the archive file.

1. failure to output a newline after the password is read
2. fd leaks via missing FD_CLOEXEC
3. fd leaks via failure-to-close when any of the standard streams are
   closed at the time of the call
4. wrongful fallback to use of stdin when opening /dev/tty fails
5. wrongful use of stderr rather than /dev/tty for prompt
6. failure to report error reading password

the main motivation for this change is to remove the assumption that
the tid of the main thread is also the pid of the process. (the value
returned by the set_tid_address syscall was used to fill both fields
despite it semantically being the tid.) this is historically and
presently true on linux and unlikely to change, but it conceivably
could be false on other systems that otherwise reproduce the linux
syscall api/abi.

only a few parts of the code were actually still using the cached pid.
in a couple places (aio and synccall) it was a minor optimization to
avoid a syscall. caching could be reintroduced, but lazily as part of
the public getpid function rather than at program startup, if it's
deemed important for performance later. in other places (cancellation
and pthread_kill) the pid was completely unnecessary; the tkill
syscall can be used instead of tgkill. this is actually a rather
subtle issue, since tgkill is supposedly a solution to race conditions
that can affect use of tkill. however, as documented in the commit
message for commit 7779dbd2, tgkill
does not actually solve this race; it just limits it to happening
within one process rather than between processes. we use a lock that
avoids the race in pthread_kill, and the use in the cancellation
signal handler is self-targeted and thus not subject to tid reuse
races, so both are safe regardless of which syscall (tgkill or tkill)
is used.

this change is presently non-functional since the callees do not yet
use their locale argument for anything.

this is mainly done for consistency with the ctype functions and to
declutter the src/locale directory.

the main practical purposes of this commit are to remove a huge amount
of clutter from the src/locale directory, to cut down on the length of
the $(AR) and $(LD) command lines, and to reduce the amount of space
wasted by object file headers in the static libc.a. build time may
also be reduced, though this has not been measured.

as an additional justification, if there ever were a need for the
behavior of these functions to vary by locale, it would be necessary
for the non-_l versions to call the _l versions, so that linking the
former without the latter would not be possible anyway.

this commit adds non-stub implementations of setlocale, duplocale,
newlocale, and uselocale, along with the data structures and minimal
code needed for representing the active locale on a per-thread basis
and optimizing the common case where thread-local locale settings are
not in use.

at this point, the data structures only contain what is necessary to
represent LC_CTYPE (a single flag) and LC_MESSAGES (a name for use in
finding message translation files). representation for the other
categories will be added later; the expectation is that a single
pointer will suffice for each.

for LC_CTYPE, the strings "C" and "POSIX" are treated as special; any
other string is accepted and treated as "C.UTF-8". for other
categories, any string is accepted after being truncated to a maximum
supported length (currently 15 bytes). for LC_MESSAGES, the name is
kept regardless of whether libc itself can use such a message
translation locale, since applications using catgets or gettext should
be able to use message locales libc is not aware of. for other
categories, names which are not successfully loaded as locales (which,
at present, means all names) are treated as aliases for "C". setlocale
never fails.

locale settings are not yet used anywhere, so this commit should have
no visible effects except for the contents of the string returned by
setlocale.

in some cases, these functions internally call a byte-based input or
output function before calling getwc/putwc, so they cannot rely on the
latter to set the orientation.

when the orientation of the stream was already set, fwide was
incorrectly returning its argument (the requested orientation) rather
than the actual orientation of the stream.

these functions were setting wc to point to wchar_t aliasing itself as
a "cheap" way to support null wc arguments. doing so was anything but
cheap, since even without the aliasing violation, it would limit the
compiler's ability to optimize.

making wc point to a dummy object is equally easy and does not suffer
from the above problems.

this issue caused the address of functions in shared libraries to
resolve to their PLT thunks in the main program rather than their
correct addresses. it was observed causing crashes, though the
mechanism of the crash was not thoroughly investigated. since the
issue is very subtle, it calls for some explanation:

on all well-behaved archs, GOT entries that belong to the PLT use a
special relocation type, typically called JMP_SLOT, so that the
dynamic linker can avoid having the jump destinations for the PLT
resolve to PLT thunks themselves (they also provide a definition for
the symbol, which must be used whenever the address of the function is
taken so that all DSOs see the same address).

however, the traditional mips PIC ABI lacked such a JMP_SLOT
relocation type, presumably because, due to the way PIC works, the
address of the PLT thunk was never needed and could always be ignored.

prior to commit adf94c19, the mips
version of reloc.h contained a hack that caused all symbol lookups to
be treated like JMP_SLOT, inhibiting undefined symbols from ever being
used to resolve symbolic relocations. this hack goes all the way back
to commit babf8201, when the mips
dynamic linker was first made usable.

during the recent refactoring to eliminate arch-specific relocation
processing (commit adf94c19), this
hack was overlooked and no equivalent functionality was provided in
the new code.

fixing the problem is not as simple as adding back an equivalent hack,
since there is now also a "non-PIC ABI" that can be used for the main
executable, which actually does use a PLT. the closest thing to
official documentation I could find for this ABI is nonpic.txt,
attached to Message-ID: 20080701202236.GA1534@caradoc.them.org, which
can be found in the gcc mailing list archives and elsewhere. per this
document, undefined symbols corresponding to PLT thunks have the
STO_MIPS_PLT bit set in the symbol's st_other field. thus, I have
added an arch-specific rule for mips, applied at the find_sym level
rather than the relocation level, to reject undefined symbols with the
STO_MIPS_PLT bit clear.

the previous hack of treating all mips relocations as JMP_SLOT-like,
rather than rejecting the unwanted symbols in find_sym, probably also
caused dlsym to wrongly return PLT thunks in place of the correct
address of a function under at least some conditions. this should now
be fixed, at least for global-scope symbol lookups.

due to a mistake when refactoring the error printing for the dynamic
linker (commit 7c73cacd), all messages
were suppressed and replaced by blank lines.

my old, out-of-tree release script that performed a clone rather than
using git archive checked the VERSION file to make sure that it
matched before doing a release. I believe there should be a way to do
the same with git commands (without resorting to checking out the
desired tag) but I have not yet found a way, so care should be taken
when using these targets that the correctness of the VERSION file is
not overlooked.

iptables and quagga need them to work.

the renaming was previously applied to all real versions of the
function in commit 3fa2eb2a.

it should be noted that the "real" __sysv_signal, which we do not
implement, is semantically different from signal. references to
__sysv_signal arise in code built against glibc under certain
combinations of feature test macros, and are almost surely
unintentional since the legacy sysv signal behavior has fundamental
race conditions that cannot be worked around and which make it
impossible to use safely.

these are put alongside the similar functions for __xstat, etc. in
__xstat.c to avoid bloating the number of source files.

these are mostly intended for use with dynamic linking (although they
can also be used statically with object files compiled against glibc
headers), so having them broken down into separate source files to
optimize for static linking is unlikely to be worth the cost having
more files in the source tree (which contributes to libc.a overhead,
compile time, link time, ar/linker command line size exhaustion, and
so on).

contributed by Isaac Dunham. this seems to be the last interface that
was missing for complete POSIX 2008 base + XSI coverage.

this issue affected the prioritynames and facilitynames arrays which
are only provided when requested (usually by syslogd implementations)
and which are presently defined as compound literals. the aliasing
violation seems to have been introduced as a workaround for bad
behavior by gcc's -Wwrite-strings option, but it caused compilers to
completely optimize out the contents of prioritynames and
facilitynames since, under many usage cases, the aliasing rules prove
that the contents are never accessed.

this behavior turned out to be counter-intuitive to users and in any
case it's unnecessary. optimization can be disabled explicitly using
the --disable-optimize option, or both can be achieved without any
enable/disable options by passing CFLAGS="-O0 -g".

according to the documentation in the man pages, the GNU extension
functions gethostbyaddr_r, gethostbyname_r and gethostbyname2_r are
guaranteed to set the result pointer to NULL in case of error or no
result.

this case is not even documented, but the kernel returns 0 here and it
makes sense to be consistent.

the main motivation for this change is to aid in debugging. since the
main program's entry point is also named _start, it was difficult to
set breakpoints or quickly identify which _start execution stopped in.