There are two main abi variants for thread local storage layout:
(1) TLS is above the thread pointer at a fixed offset and the pthread
struct is below that. So the end of the struct is at known offset.
(2) the thread pointer points to the pthread struct and TLS starts
below it. So the start of the struct is at known (zero) offset.
Assembly code for the dynamic TLSDESC callback needs to access the
dynamic thread vector (dtv) pointer which is currently at the front
of the pthread struct. So in case of (1) the asm code needs to hard
code the offset from the end of the struct which can easily break if
the struct changes.
This commit adds a copy of the dtv at the end of the struct. New members
must not be added after dtv_copy, only before it. The size of the struct
is increased a bit, but there is opportunity for size optimizations.
the memory model we use internally for atomics permits plain loads of
values which may be subject to concurrent modification without
requiring that a special load function be used. since a compiler is
free to make transformations that alter the number of loads or the way
in which loads are performed, the compiler is theoretically free to
break this usage. the most obvious concern is with atomic cas
constructs: something of the form tmp=*p;a_cas(p,tmp,f(tmp)); could be
transformed to a_cas(p,*p,f(*p)); where the latter is intended to show
multiple loads of *p whose resulting values might fail to be equal;
this would break the atomicity of the whole operation. but even more
fundamental breakage is possible.
with the changes being made now, objects that may be modified by
atomics are modeled as volatile, and the atomic operations performed
on them by other threads are modeled as asynchronous stores by
hardware which happens to be acting on the request of another thread.
such modeling of course does not itself address memory synchronization
between cores/cpus, but that aspect was already handled. this all
seems less than ideal, but it's the best we can do without mandating a
C11 compiler and using the C11 model for atomics.
in the case of pthread_once_t, the ABI type of the underlying object
is not volatile-qualified. so we are assuming that accessing the
object through a volatile-qualified lvalue via casts yields volatile
access semantics. the language of the C standard is somewhat unclear
on this matter, but this is an assumption the linux kernel also makes,
and seems to be the correct interpretation of the standard.
previously, the __timedwait function was optionally a cancellation
point depending on whether it was passed a pointer to a cleaup
function and context to register. as of now, only one caller actually
used such a cleanup function (and it may face removal soon); most
callers either passed a null pointer to disable cancellation or a
dummy cleanup function.
now, __timedwait is never a cancellation point, and __timedwait_cp is
the cancellable version. this makes the intent of the calling code
more obvious and avoids ugly dummy functions and long argument lists.
just defining the necessary constants:
LD_B1B_MAX is 2^113 - 1 in base 10^9
KMAX is 2048 so the x array can hold up to 18432 decimal digits
(the worst case is converting 2^-16495 = 5^16495 * 10^-16495 to
binary, it requires the processing of int(log10(5)*16495)+1 = 11530
decimal digits after discarding the leading zeros, the conversion
requires some headroom in x, but KMAX is more than enough for that)
However this code is not optimal on archs with IEEE binary128
long double because the arithmetics is software emulated (on
all such platforms as far as i know) which means big and slow
strtod.
x86_64 syscall.h defined some musl internal syscall names and made
them public. These defines were already moved to src/internal/syscall.h
(except for SYS_fadvise which is added now) so the cruft in x86_64
syscall.h is not needed.
this avoids assuming the presence of C11 macro definitions in the
public complex.h, which need changes potentially incompatible with the
way these macros are being used internally.
except powerpc, which still lacks inline syscalls simply because
nobody has written the code, these are all fallbacks used to work
around a clang bug that probably does not exist in versions of clang
that can compile musl. however, it's useful to have the generic
non-inline code anyway, as it eases the task of porting to new archs:
writing inline syscall code is now optional. this approach could also
help support compilers which don't understand inline asm or lack
support for the needed register constraints.
mips could not be unified because it has special fixup code for broken
layout of the kernel's struct stat.
incorrect behavior occurred only in cases where the input overflows
unsigned long long, not just the (possibly lower) range limit for the
result type. in this case, processing of the '-' sign character was
not suppressed, and the function returned a value of 1 despite setting
errno to ERANGE.
based on patch by Jens Gustedt.
the main difficulty here is handling the difference between start
function signatures and thread return types for C11 threads versus
POSIX threads. pointers to void are assumed to be able to represent
faithfully all values of int. the function pointer for the thread
start function is cast to an incorrect type for passing through
pthread_create, but is cast back to its correct type before calling so
that the behavior of the call is well-defined.
changes to the existing threads implementation were kept minimal to
reduce the risk of regressions, and duplication of code that carries
implementation-specific assumptions was avoided for ease and safety of
future maintenance.
this is analogous commit fffc5cda10
which fixed the corresponding issue for mutexes.
the robust list can't be used here because the locks do not share a
common layout with mutexes. at some point it may make sense to simply
incorporate a mutex object into the FILE structure and use it, but
that would be a much more invasive change, and it doesn't mesh well
with the current design that uses a simpler code path for internal
locking and pulls in the recursive-mutex-like code when the flockfile
API is used explicitly.
the immediate issue that was reported by Jens Gustedt and needed to be
fixed was corruption of the cv/mutex waiter states when switching to
using a new mutex with the cv after all waiters were unblocked but
before they finished returning from the wait function.
self-synchronized destruction was also handled poorly and may have had
race conditions. and the use of sequence numbers for waking waiters
admitted a theoretical missed-wakeup if the sequence number wrapped
through the full 32-bit space.
the new implementation is largely documented in the comments in the
source. the basic principle is to use linked lists initially attached
to the cv object, but detachable on signal/broadcast, made up of nodes
residing in automatic storage (stack) on the threads that are waiting.
this eliminates the need for waiters to access the cv object after
they are signaled, and allows us to limit wakeup to one waiter at a
time during broadcasts even when futex requeue cannot be used.
performance is also greatly improved, roughly double some tests.
basically nothing is changed in the process-shared cond var case,
where this implementation does not work, since processes do not have
access to one another's local storage.
when manipulating the robust list, the order of stores matters,
because the code may be asynchronously interrupted by a fatal signal
and the kernel will then access the robust list in what is essentially
an async-signal context.
previously, aliasing considerations made it seem unlikely that a
compiler could reorder the stores, but proving that they could not be
reordered incorrectly would have been extremely difficult. instead
I've opted to make all the pointers used as part of the robust list,
including those in the robust list head and in the individual mutexes,
volatile.
in addition, the format of the robust list has been changed to point
back to the head at the end, rather than ending with a null pointer.
this is to match the documented kernel robust list ABI. the null
pointer, which was previously used, only worked because faults during
access terminate the robust list processing.
private-futex uses the virtual address of the futex int directly as
the hash key rather than requiring the kernel to resolve the address
to an underlying backing for the mapping in which it lies. for certain
usage patterns it improves performance significantly.
in many places, the code using futex __wake and __wait operations was
already passing a correct fixed zero or nonzero flag for the priv
argument, so no change was needed at the site of the call, only in the
__wake and __wait functions themselves. in other places, especially
where the process-shared attribute for a synchronization object was
not previously tracked, additional new code is needed. for mutexes,
the only place to store the flag is in the type field, so additional
bit masking logic is needed for accessing the type.
for non-process-shared condition variable broadcasts, the futex
requeue operation is unable to requeue from a private futex to a
process-shared one in the mutex structure, so requeue is simply
disabled in this case by waking all waiters.
for robust mutexes, the kernel always performs a non-private wake when
the owner dies. in order not to introduce a behavioral regression in
non-process-shared robust mutexes (when the owning thread dies), they
are simply forced to be treated as process-shared for now, giving
correct behavior at the expense of performance. this can be fixed by
adding explicit code to pthread_exit to do the right thing for
non-shared robust mutexes in userspace rather than relying on the
kernel to do it, and will be fixed in this way later.
since not all supported kernels have private futex support, the new
code detects EINVAL from the futex syscall and falls back to making
the call without the private flag. no attempt to cache the result is
made; caching it and using the cached value efficiently is somewhat
difficult, and not worth the complexity when the benefits would be
seen only on ancient kernels which have numerous other limitations and
bugs anyway.
the core is based on a binary search; hash table is not used. both
native and reverse-endian mo files are supported. all offsets read
from the mapped mo file are checked against the mapping size to
prevent the possibility of reads outside the mapping.
this commit has no observable effects since there are not yet any
callers to the message translation code.
there is still no code which actually uses the loaded locale files, so
the main observable effect of this commit is that calls to setlocale
store and give back the names of the selected locales for the
remaining categories (LC_TIME, LC_COLLATE, LC_MONETARY) if a locale
file by the requested name could be loaded.
With the exception of a fenv implementation, the port is fully featured.
The port has been tested in or1ksim, the golden reference functional
simulator for OpenRISC 1000.
It passes all libc-test tests (except the math tests that
requires a fenv implementation).
The port assumes an or1k implementation that has support for
atomic instructions (l.lwa/l.swa).
Although it passes all the libc-test tests, the port is still
in an experimental state, and has yet experienced very little
'real-world' use.
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.
the motivation for the errno_ptr field in the thread structure, which
this commit removes, was to allow the main thread's errno to keep its
address when lazy thread pointer initialization was used. &errno was
evaluated prior to setting up the thread pointer and stored in
errno_ptr for the main thread; subsequently created threads would have
errno_ptr pointing to their own errno_val in the thread structure.
since lazy initialization was removed, there is no need for this extra
level of indirection; __errno_location can simply return the address
of the thread's errno_val directly. this does cause &errno to change,
but the change happens before entry to application code, and thus is
not observable.
On 32 bit mips the kernel uses -1UL/2 to mark RLIM_INFINITY (and
this is the definition in the userspace api), but since it is in
the middle of the valid range of limits and limits are often
compared with relational operators, various kernel side logic is
broken if larger than -1UL/2 limits are used. So we truncate the
limits to -1UL/2 in get/setrlimit and prlimit.
Even if the kernel side logic consistently treated -1UL/2 as greater
than any other limit value, there wouldn't be any clean workaround
that allowed using large limits:
* using -1UL/2 as RLIM_INFINITY in userspace would mean different
infinity value for get/setrlimt and prlimit (where infinity is always
-1ULL) and userspace logic could break easily (just like the kernel
is broken now) and more special case code would be needed for mips.
* translating -1UL/2 kernel side value to -1ULL in userspace would
mean that -1UL/2 limit cannot be set (eg. -1UL/2+1 had to be passed
to the kernel instead).
using the existence of SYS_stat64 as the condition for remapping other
related syscalls is no longer valid, since new archs that omit the old
syscalls will not have SYS_stat or SYS_stat64, but still potentially
need SYS_fstat and others remapped. it would probably be possible to
get by with just one or two extra conditionals, but just breaking them
all down into separate conditions is robust and not significantly
heavier for the preprocessor.
somehow the remapping of this syscall to the 64-bit version was
overlooked. the issue was found, and patch provided, by Stefan
Kristiansson. presumably the reason this bug was not caught earlier is
that the syscall takes a pointer to off_t rather than a value, so on
little-endian systems, everything appears to work as long as the
offset value fits in the low 31 bits. on big-endian systems, though,
sendfile was presumably completely non-functional.
this was messed up during a recent commit when the socketcall macros
were moved to the common internal/syscall.h, and the following commit
expanded the problem by adding more new content outside the guard.
open is handled specially because it is used from so many places, in
so many variants (2 or 3 arguments, setting errno or not, and
cancellable or not). trying to do it as a function would not only
increase bloat, but would also risk subtle breakage.
this is the first step towards supporting "new" archs where linux
lacks "old" syscalls.
the vdso symbol lookup code is based on the original 2011 patch by
Nicholas J. Kain, with some streamlining, pointer arithmetic fixes,
and one symbol version matching fix.
on the consumer side (clock_gettime), per-arch macros for the
particular symbol name and version to lookup are added in
syscall_arch.h, and no vdso code is pulled in on archs which do not
define these macros. at this time, vdso is enabled only on x86_64.
the vdso support at the dynamic linker level is no longer useful to
libc, but is left in place for the sake of debuggers (which may need
the vdso in the link map to find its functions) and possibly use with
dlsym.
the use of visibility at all is purely an optimization to avoid the
need for the caller to load the GOT register or similar to prepare for
a call via the PLT. there is no reason for these symbols to be
externally visible, so hidden works just as well as protected, and
using protected visibility is undesirable due to toolchain bugs and
the lack of testing it receives.
in particular, GCC's microblaze target is known to generate symbolic
relocations in the GOT for functions with protected visibility. this
in turn results in a dynamic linker which crashes under any nontrivial
usage that requires making a syscall before symbolic relocations are
processed.
this is the first step in an overhaul aimed at greatly simplifying and
optimizing everything dealing with thread-local state.
previously, the thread pointer was initialized lazily on first access,
or at program startup if stack protector was in use, or at certain
random places where inconsistent state could be reached if it were not
initialized early. while believed to be fully correct, the logic was
fragile and non-obvious.
in the first phase of the thread pointer overhaul, support is retained
(and in some cases improved) for systems/situation where loading the
thread pointer fails, e.g. old kernels.
some notes on specific changes:
- the confusing use of libc.main_thread as an indicator that the
thread pointer is initialized is eliminated in favor of an explicit
has_thread_pointer predicate.
- sigaction no longer needs to ensure that the thread pointer is
initialized before installing a signal handler (this was needed to
prevent a situation where the signal handler caused the thread
pointer to be initialized and the subsequent sigreturn cleared it
again) but it still needs to ensure that implementation-internal
thread-related signals are not blocked.
- pthread tsd initialization for the main thread is deferred in a new
manner to minimize bloat in the static-linked __init_tp code.
- pthread_setcancelstate no longer needs special handling for the
situation before the thread pointer is initialized. it simply fails
on systems that cannot support a thread pointer, which are
non-conforming anyway.
- pthread_cleanup_push/pop now check for missing thread pointer and
nop themselves out in this case, so stdio no longer needs to avoid
the cancellable path when the thread pointer is not available.
a number of cases remain where certain interfaces may crash if the
system does not support a thread pointer. at this point, these should
be limited to pthread interfaces, and the number of such cases should
be fewer than before.
in general, we aim to always include the header that's declaring a
function before defining it so that the compiler can check that
prototypes match.
additionally, the internal syscall.h declares __syscall_ret with a
visibility attribute to improve code generation for shared libc (to
prevent gratuitous GOT-register loads). this declaration should be
visible at the point where __syscall_ret is defined, too, or the
inconsistency could theoretically lead to problems at link-time.
linux, gcc, etc. all use "sh" as the name for the superh arch. there
was already some inconsistency internally in musl: the dynamic linker
was searching for "ld-musl-sh.path" as its path file despite its own
name being "ld-musl-superh.so.1". there was some sentiment in both
directions as to how to resolve the inconsistency, but overall "sh"
was favored.
some 32-on-64 archs require that the actual syscall args be long long.
in that case syscall_arch.h can define syscall_arg_t to whatever it needs
and syscall.h picks it up.
all other archs just use long as usual.
this allows syscall_arch.h to define the macro __scc if special
casting is needed, as is the case for x32, where the actual syscall
arguments are 64bit, but, in case of pointers, would get sign-extended
and thus become invalid.
when there is unflushed output, ftello (and ftell) compute the logical
stream position as the underlying file descriptor's offset plus an
adjustment for the amount of buffered data. however, this can give the
wrong result for append-mode streams where the unflushed writes should
adjust the logical position to be at the end of the file, as if a seek
to end-of-file takes place before the write.
the solution turns out to be a simple trick: when ftello (indirectly)
calls lseek to determine the current file offset, use SEEK_END instead
of SEEK_CUR if the stream is append-mode and there's unwritten
buffered data.
the ISO C rules regarding switching between reading and writing for a
stream opened in an update mode, along with the POSIX rules regarding
switching "active handles", conveniently leave undefined the
hypothetical usage cases where this fix might lead to observably
incorrect offsets.
the bug being fixed was discovered via the test case for glibc issue
this is still experimental and subject to change. for git checkouts,
an attempt is made to record the exact revision to aid in bug reports
and debugging. no version information is recorded in the static libc.a
or binaries it's linked into.
if a multithreaded program became non-multithreaded (i.e. all other
threads exited) while one thread held an internal lock, the remaining
thread would fail to release the lock. the the program then became
multithreaded again at a later time, any further attempts to obtain
the lock would deadlock permanently.
the underlying cause is that the value of libc.threads_minus_1 at
unlock time might not match the value at lock time. one solution would
be returning a flag to the caller indicating whether the lock was
taken and needs to be unlocked, but there is a simpler solution: using
the lock itself as such a flag.
note that this flag is not needed anyway for correctness; if the lock
is not held, the unlock code is harmless. however, the memory
synchronization properties associated with a_store are costly on some
archs, so it's best to avoid executing the unlock code when it is
unnecessary.
PAGE_SIZE was hardcoded to 4096, which is historically what most
systems use, but on several archs it is a kernel config parameter,
user space can only know it at execution time from the aux vector.
PAGE_SIZE and PAGESIZE are not defined on archs where page size is
a runtime parameter, applications should use sysconf(_SC_PAGE_SIZE)
to query it. Internally libc code defines PAGE_SIZE to libc.page_size,
which is set to aux[AT_PAGESZ] in __init_libc and early in __dynlink
as well. (Note that libc.page_size can be accessed without GOT, ie.
before relocations are done)
Some fpathconf settings are hardcoded to 4096, these should be actually
queried from the filesystem using statfs.
gcc did not always drop excess precision according to c99 at assignments
before version 4.5 even if -std=c99 was requested which caused badly
broken mathematical functions on i386 when FLT_EVAL_METHOD!=0
but STRICT_ASSIGN was not used consistently and it is worked around for
old compilers with -ffloat-store so it is no longer needed
the new convention is to get the compiler respect c99 semantics and when
excess precision is not harmful use float_t or double_t or to specialize
code using FLT_EVAL_METHOD
new ldshape union, ld128 support is kept, code that used the old
ldshape union was rewritten (IEEEl2bits union of freebsd libm is
not touched yet)
ld80 __fpclassifyl no longer tries to handle invalid representation
1. the thread result field was reused for storing a kernel timer id,
but would be overwritten if the application code exited or cancelled
the thread.
2. low pointer values were used as the indicator that the timer id is
a kernel timer id rather than a thread id. this is not portable, as
mmap may return low pointers on some conditions. instead, use the fact
that pointers must be aligned and kernel timer ids must be
non-negative to map pointers into the negative integer space.
3. signals were not blocked until after the timer thread started, so a
race condition could allow a signal handler to run in the timer thread
when it's not supposed to exist. this is mainly problematic if the
calling thread was the only thread where the signal was unblocked and
the signal handler assumes it runs in that thread.
Szabolcs Nagy
Rich Felker
Stefan Kristiansson
Timo Teräs
Bobby Bingham
rofl0r