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2019-04-01fix harmless-by-chance typo in priority inheritance mutex codeRich Felker-1/+1
commit 54ca677983d47529bab8752315ac1a2b49888870 inadvertently introduced bitwise and where logical and was intended. since the right-hand operand is always 0 or -1 whenever the left-hand operand is nonzero, the behavior happened to be equivalent.
2019-03-31implement priority inheritance mutexesRich Felker-8/+93
priority inheritance is a feature to mitigate priority inversion situations, where a execution of a medium-priority thread can unboundedly block forward progress of a high-priority thread when a lock it needs is held by a low-priority thread. the natural way to do priority inheritance would be with a simple futex flag to donate the calling thread's priority to a target thread while it waits on the futex. unfortunately, linux does not offer such an interface, but instead insists on implementing the whole locking protocol in kernelspace with special futex commands that exist solely for the purpose of doing PI mutexes. this would require the entire "trylock" logic to be duplicated in the timedlock code path for PI mutexes, since, once the previous lock holder releases the lock and the futex call returns, the lock is already held by the caller. obviously such code duplication is undesirable. instead, I've made the PI timedlock success path set the mutex lock count to -1, which can be thought of as "not yet complete", since a lock count of 0 is "locked, with no recursive references". a simple branch in a non-hot path of pthread_mutex_trylock can then see and act on this state, skipping past the code that would check and take the lock to the same code path that runs after the lock is obtained for a non-PI mutex. because we're forced to let the kernel perform the actual lock and unlock operations whenever the mutex is contended, we have to patch things up when it does the wrong thing: 1. the lock operation is not aware of whether the mutex is error-checking, so it will always fail with EDEADLK rather than deadlocking. 2. the lock operation is not aware of whether the mutex is robust, so it will successfully obtain mutexes in the owner-died state even if they're non-robust, whereas this operation should deadlock. 3. the unlock operation always sets the lock value to zero, whereas for robust mutexes, we want to set it to a special value indicating that the mutex obtained after its owner died was unlocked without marking it consistent, so that future operations all fail with ENOTRECOVERABLE. the first of these is easy to solve, just by performing a futex wait on a dummy futex address to simulate deadlock or ETIMEDOUT as appropriate. but problems 2 and 3 interact in a nasty way. to solve problem 2, we need to back out the spurious success. but if waiters are present -- which we can't just ignore, because even if we don't want to wake them, the calling thread is incorrectly inheriting their priorities -- this requires using the kernel's unlock operation, which will zero the lock value, thereby losing the "owner died with lock held" state. to solve these problems, we overload the mutex's waiters field, which is unused for PI mutexes since they don't call the normal futex wait functions, as an indicator that the PI mutex is permanently non-lockable. originally I wanted to use the count field, but there is one code path that needs to access this flag without synchronization: trylock's CAS failure path needs to be able to decide whether to fail with EBUSY or ENOTRECOVERABLE, the waiters field is already treated as a relaxed-order atomic in our memory model, so this works out nicely.
2019-03-29clean up access to mutex type in pthread_mutex_trylockRich Felker-2/+2
there was no point in masking off the pshared bit when first loading the type, since every subsequent access involves a mask anyway. not masking it may avoid a subsequent load to check the pshared flag, and it's just simpler.
2019-03-21fix data race choosing next key slot in pthread_key_createRich Felker-1/+1
commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58 wrongly moved the access to the global next_key outside of the scope of the lock. the error manifested as spurious failure to find an available key slot under concurrent calls to pthread_key_create, since the stopping condition could be met after only a small number of slots were examined.
2019-03-13fix namespace violation in dependencies of mtx_lockRich Felker-1/+1
commit 2de29bc994029b903a366b8a4a9f8c3c3ee2be90 left behind one reference to pthread_mutex_trylock. fixing this also improves code generation due to the namespace-safe version being hidde.
2019-02-22add membarrier syscall wrapper, refactor dynamic tls install to use itRich Felker-2/+2
the motivation for this change is twofold. first, it gets the fallback logic out of the dynamic linker, improving code readability and organization. second, it provides application code that wants to use the membarrier syscall, which depends on preregistration of intent before the process becomes multithreaded unless unbounded latency is acceptable, with a symbol that, when linked, ensures that this registration happens.
2019-02-22make thread list lock a recursive lockRich Felker-11/+21
this is a prerequisite for factoring the membarrier fallback code into a function that can be called from a context with the thread list already locked or independently.
2019-02-18install dynamic tls synchronously at dlopen, streamline accessRich Felker-14/+3
previously, dynamic loading of new libraries with thread-local storage allocated the storage needed for all existing threads at load-time, precluding late failure that can't be handled, but left installation in existing threads to take place lazily on first access. this imposed an additional memory access and branch on every dynamic tls access, and imposed a requirement, which was not actually met, that the dynamic tlsdesc asm functions preserve all call-clobbered registers before calling C code to to install new dynamic tls on first access. the x86[_64] versions of this code wrongly omitted saving and restoring of fpu/vector registers, assuming the compiler would not generate anything using them in the called C code. the arm and aarch64 versions saved known existing registers, but failed to be future-proof against expansion of the register file. now that we track live threads in a list, it's possible to install the new dynamic tls for each thread at dlopen time. for the most part, synchronization is not needed, because if a thread has not synchronized with completion of the dlopen, there is no way it can meaningfully request access to a slot past the end of the old dtv, which remains valid for accessing slots which already existed. however, it is necessary to ensure that, if a thread sees its new dtv pointer, it sees correct pointers in each of the slots that existed prior to the dlopen. my understanding is that, on most real-world coherency architectures including all the ones we presently support, a built-in consume order guarantees this; however, don't rely on that. instead, the SYS_membarrier syscall is used to ensure that all threads see the stores to the slots of their new dtv prior to the installation of the new dtv. if it is not supported, the same is implemented in userspace via signals, using the same mechanism as __synccall. the __tls_get_addr function, variants, and dynamic tlsdesc asm functions are all updated to remove the fallback paths for claiming new dynamic tls, and are now all branch-free.
2019-02-17fix data race between new pthread_key_delete and dtor executionRich Felker-2/+4
access to clear the entry in each thread's tsd array for the key being deleted was not synchronized with __pthread_tsd_run_dtors. I probably made this mistake from a mistaken belief that the thread list lock was held during the latter, which of course is not possible since it executes application code in a still-live-thread context. while we're at it, expand the interval during which signals are blocked to cover taking the write lock on key_lock, so that a signal at an inopportune time doesn't block forward progress of readers.
2019-02-16introduce namespace-safe rwlock aliases; use in pthread_key_createRich Felker-20/+34
commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58 inadvertently introduced namespace violations by using the pthread-namespace rwlock functions in pthread_key_create, which is in turn used for C11 tss. fix that and possible future uses of rwlocks elsewhere.
2019-02-16rewrite pthread_key_delete to use global thread listRich Felker-75/+19
with the availability of the thread list, there is no need to mark tsd key slots dirty and clean them up only when a free slot can't be found. instead, directly iterate threads and clear any value associated with the key being deleted. no synchronization is necessary for the clearing, since there is no way the slot can be accessed without having synchronized with the creation of a new key occupying the same slot, which is already sequenced after and synchronized with the deletion of the old key.
2019-02-16rewrite __synccall in terms of global thread listRich Felker-123/+59
the __synccall mechanism provides stop-the-world synchronous execution of a callback in all threads of the process. it is used to implement multi-threaded setuid/setgid operations, since Linux lacks them at the kernel level, and for some other less-critical purposes. this change eliminates dependency on /proc/self/task to determine the set of live threads, which in addition to being an unwanted dependency and a potential point of resource-exhaustion failure, turned out to be inaccurate. test cases provided by Alexey Izbyshev showed that it could fail to reflect newly created threads. due to how the presignaling phase worked, this usually yielded a deadlock if hit, but in the worst case it could also result in threads being silently missed (allowed to continue running without executing the callback).
2019-02-15track all live threads in an AS-safe, fully-consistent linked listRich Felker-38/+81
the hard problem here is unlinking threads from a list when they exit without creating a window of inconsistency where the kernel task for a thread still exists and is still executing instructions in userspace, but is not reflected in the list. the magic solution here is getting rid of per-thread exit futex addresses (set_tid_address), and instead using the exit futex to unlock the global thread list. since pthread_join can no longer see the thread enter a detach_state of EXITED (which depended on the exit futex address pointing to the detach_state), it must now observe the unlocking of the thread list lock before it can unmap the joined thread and return. it doesn't actually have to take the lock. for this, a __tl_sync primitive is offered, with a signature that will allow it to be enhanced for quick return even under contention on the lock, if needed. for now, the exiting thread always performs a futex wake on its detach_state. a future change could optimize this out except when there is already a joiner waiting. initial/dynamic variants of detached state no longer need to be tracked separately, since the futex address is always set to the global list lock, not a thread-local address that could become invalid on detached thread exit. all detached threads, however, must perform a second sigprocmask syscall to block implementation-internal signals, since locking the thread list with them already blocked is not permissible. the arch-independent C version of __unmapself no longer needs to take a lock or setup its own futex address to release the lock, since it must necessarily be called with the thread list lock already held, guaranteeing exclusive access to the temporary stack. changes to libc.threads_minus_1 no longer need to be atomic, since they are guarded by the thread list lock. it is largely vestigial at this point, and can be replaced with a cheaper boolean indicating whether the process is multithreaded at some point in the future.
2019-02-15always block signals for starting new threads, refactor start argsRich Felker-56/+56
whether signals need to be blocked at thread start, and whether unblocking is necessary in the entry point function, has historically depended on intricacies of the cancellation design and on whether there are scheduling operations to perform on the new thread before its successful creation can be committed. future changes to track an AS-safe list of live threads will require signals to be blocked whenever changes are made to the list, so ... prior to commits b8742f32602add243ee2ce74d804015463726899 and 40bae2d32fd6f3ffea437fa745ad38a1fe77b27e, a signal mask for the entry function to restore was part of the pthread structure. it was removed to trim down the size of the structure, which both saved a small amount of stack space and improved code generation on archs where small immediate displacements are less costly than arbitrary ones, by limiting the range of offsets between the base of the thread structure, its members, and the thread pointer. these commits moved the saved mask to a special structure used only when special scheduling was needed, in which case the pthread_create caller and new thread had to synchronize with each other and could use this memory to pass a mask. this commit partially reverts the above two commits, but instead of putting the mask back in the pthread structure, it moves all "start argument" members out of the pthread structure, trimming it down further, and puts them in a separate structure passed on the new thread's stack. the code path for explicit scheduling of the new thread is also changed to synchronize with the calling thread in such a way to avoid spurious futex wakes.
2019-02-12redesign robust mutex states to eliminate data races on type fieldRich Felker-12/+23
in order to implement ENOTRECOVERABLE, the implementation has traditionally used a bit of the mutex type field to indicate that it's recovered after EOWNERDEAD and will go into ENOTRECOVERABLE state if pthread_mutex_consistent is not called before unlocking. while it's only the thread that holds the lock that needs access to this information (except possibly for the sake of pthread_mutex_consistent choosing between EINVAL and EPERM for erroneous calls), the change to the type field is formally a data race with all other threads that perform any operation on the mutex. no individual bits race, and no write races are possible, so things are "okay" in some sense, but it's still not good. this patch moves the recovery/consistency state to the mutex owner/lock field which is rightfully mutable. bit 30, the same bit the kernel uses with a zero owner to indicate that the previous owner died holding the lock, is now used with a nonzero owner to indicate that the mutex is held but has not yet been marked consistent. note that the kernel ABI also reserves bit 29 not to appear in any tid, so the sentinel value we use for ENOTRECOVERABLE, 0x7fffffff, does not clash with any tid plus bit 30.
2019-01-16fix unintended linking dependency of pthread_key_create on __synccallRich Felker-0/+6
commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58 attempted to do this already, but omitted from pthread_key_create.c the weak definition of __pthread_key_delete_synccall, so that the definition provided by pthread_key_delete.c was always pulled in. based on patch by Markus Wichmann, but with a weak alias rather than weak reference for consistency/policy about dependence on tooling features.
2018-12-19make sem_wait and sem_timedwait interruptible by signalsRich Felker-1/+1
this reverts commit c0ed5a201b2bdb6d1896064bec0020c9973db0a1, which was based on a mistaken reading of POSIX due to inconsistency between the description (which requires return upon interruption by a signal) and the errors list (which wrongly lists EINTR as "may fail"). since the previously-introduced behavior was a workaround for an old kernel bug to ensure safety of correct programs that were not hardened against the bug, an effort has been made to preserve it for programs which do not use interrupting signal handlers. the stage for this was set in commit a63c0104e496f7ba78b64be3cd299b41e8cd427f, which makes the futex __timedwait backend suppress EINTR if it's seen when no interrupting signal handlers have been installed. based loosely on a patch submitted by Orivej Desh, but with unnecessary additional changes removed.
2018-12-18don't fail pthread_sigmask/sigprocmask on invalid how when set is nullRich Felker-1/+1
the resolution of Austin Group issue #1132 changes the requirement to fail so that it only applies when the set argument (new mask) is non-null. this change was made for consistency with the description, which specified "if set is a null pointer, the value of the argument how is not significant".
2018-12-18add __timedwait backend workaround for old kernels where futex EINTRsRich Felker-0/+8
prior to linux 2.6.22, futex wait could fail with EINTR even for non-interrupting (SA_RESTART) signals. this was no problem provided the caller simply restarted the wait, but sem_[timed]wait is required by POSIX to return when interrupted by a signal. commit a113434cd68ce30642c4995b1caadcd084be6f09 introduced this behavior, and commit c0ed5a201b2bdb6d1896064bec0020c9973db0a1 reverted it based on a mistaken belief that it was not required. this belief stems from a bug in the specification: the description requires the function to return when interrupted, but the errors section marks EINTR as a "may fail" condition rather than a "shall fail" one. since there does seem to be significant value in the change made in commit c0ed5a201b2bdb6d1896064bec0020c9973db0a1, making it so that programs that call sem_wait without checking for EINTR don't silently make forward progress without obtaining the semaphore or treat it as a fatal error and abort, add a behind-the-scenes mechanism in the __timedwait backend to suppress EINTR in programs that have never installed interrupting signal handlers, and have sigaction track and report this state. this way the semaphore code is not cluttered by workarounds and can be updated (to be done in next commit) to reflect the high-level logic for conforming behavior. these changes are based loosely on a patch by Markus Wichmann, with the main changes being atomic update to flag object and moving the workaround from sem_timedwait to the __timedwait futex backend.
2018-10-12combine arch ABI's DTP_OFFSET into DTV pointersRich Felker-2/+2
as explained in commit 6ba5517a460c6c438f64d69464fdfc3269a4c91a, some archs use an offset (typicaly -0x8000) with their DTPOFF relocations, which __tls_get_addr needs to invert. on affected archs, which lack direct support for large immediates, this can cost multiple extra instructions in the hot path. instead, incorporate the DTP_OFFSET into the DTV entries. this means they are no longer valid pointers, so store them as an array of uintptr_t rather than void *; this also makes it easier to access slot 0 as a valid slot count. commit e75b16cf93ebbc1ce758d3ea6b2923e8b2457c68 left behind cruft in two places, __reset_tls and __tls_get_new, from back when it was possible to have uninitialized gap slots indicated by a null pointer in the DTV. since the concept of null pointer is no longer meaningful with an offset applied, remove this cruft. presently there are no archs with both TLSDESC and nonzero DTP_OFFSET, but the dynamic TLSDESC relocation code is also updated to apply an inverted offset to its offset field, so that the offset DTV would not impose a runtime cost in TLSDESC resolver functions.
2018-09-18limit the configurable default stack/guard size for threadsRich Felker-6/+10
limit to 8MB/1MB, repectively. since the defaults cannot be reduced once increased, excessively large settings would lead to an unrecoverably broken state. this change is in preparation to allow defaults to be increased via program headers at the linker level. creation of threads that really need larger sizes needs to be done with an explicit attribute.
2018-09-18remove redundant declarations of __default_stacksize, __default_guardsizeRich Felker-8/+0
these are now declared in pthread_impl.h.
2018-09-18fix benign data race in pthread_attr_initRich Felker-0/+2
access to defaults should be protected against concurrent changes.
2018-09-18fix deletion of pthread tsd keys that still have non-null values storedRich Felker-18/+101
per POSIX, deletion of a key for which some threads still have values stored is permitted, and newly created keys must initially hold the null value in all threads. these properties were not met by our implementation; if a key was deleted with values left and a new key was created in the same slot, the old values were still visible. moreover, due to lack of any synchronization in pthread_key_delete, there was a TOCTOU race whereby a concurrent pthread_exit could attempt to call a null destructor pointer for the newly orphaned value. this commit introduces a solution based on __synccall, stopping the world to zero out the values for deleted keys, but only does so lazily when all key slots have been exhausted. pthread_key_delete is split off into a separate translation unit so that static-linked programs which only create keys but never delete them will not pull in the __synccall machinery. a global rwlock is added to synchronize creation and deletion of keys with dtor execution. since the dtor execution loop now has to release and retake the lock around its call to each dtor, checks are made not to call the nodtor dummy function for keys which lack a dtor.
2018-09-15check for kernel support before allowing robust mutex creationRich Felker-1/+17
on some archs, linux support for futex operations (including robust_list processing) that depend on kernelspace CAS is conditional on a runtime check. as of linux 4.18, this check fails unconditionally on nommu archs that perform it, and spurious failure on powerpc64 was observed but not explained. it's also possible that futex support is omitted entirely, or that the kernel is older than 2.6.17. for most futex ops, ENOSYS does not yield hard breakage; userspace will just spin at 100% cpu load. but for robust mutexes, correct behavior depends on the kernel functionality. use the get_robust_list syscall to probe for support at the first call to pthread_mutexattr_setrobust, and block creation of robust mutexes with a reportable error if they can't be supported.
2018-09-12split internal lock API out of libc.h, creating lock.hRich Felker-1/+8
this further reduces the number of source files which need to include libc.h and thereby be potentially exposed to libc global state and internals. this will also facilitate further improvements like adding an inline fast-path, if we want to do so later.
2018-09-12reduce spurious inclusion of libc.hRich Felker-8/+1
libc.h was intended to be a header for access to global libc state and related interfaces, but ended up included all over the place because it was the way to get the weak_alias macro. most of the inclusions removed here are places where weak_alias was needed. a few were recently introduced for hidden. some go all the way back to when libc.h defined CANCELPT_BEGIN and _END, and all (wrongly implemented) cancellation points had to include it. remaining spurious users are mostly callers of the LOCK/UNLOCK macros and files that use the LFS64 macro to define the awful *64 aliases. in a few places, new inclusion of libc.h is added because several internal headers no longer implicitly include libc.h. declarations for __lockfile and __unlockfile are moved from libc.h to stdio_impl.h so that the latter does not need libc.h. putting them in libc.h made no sense at all, since the macros in stdio_impl.h are needed to use them correctly anyway.
2018-09-12remove unused __futex function and source fileRich Felker-7/+0
the direct syscall or various thin and mostly-inline wrappers around it are used instead internally. at some point a public futex function should be added, but it's not yet clear what the signature should be, and in the mean time this file is not useful.
2018-09-12hide __pthread_once_full symbolRich Felker-1/+1
this is a special case that does not need a declaration, because it's not even a libc-internal interface between translation units. instead it's a poor hack around compilers' inability to shrink-wrap critical code paths. after vis.h was disabled, it became more of a pessimization on many archs due to the extra layer of machinery to support a call through the PLT, but now it should be efficient again.
2018-09-12overhaul internally-public declarations using wrapper headersRich Felker-53/+6
commits leading up to this one have moved the vast majority of libc-internal interface declarations to appropriate internal headers, allowing them to be type-checked and setting the stage to limit their visibility. the ones that have not yet been moved are mostly namespace-protected aliases for standard/public interfaces, which exist to facilitate implementing plain C functions in terms of POSIX functionality, or C or POSIX functionality in terms of extensions that are not standardized. some don't quite fit this description, but are "internally public" interfacs between subsystems of libc. rather than create a number of newly-named headers to declare these functions, and having to add explicit include directives for them to every source file where they're needed, I have introduced a method of wrapping the corresponding public headers. parallel to the public headers in $(srcdir)/include, we now have wrappers in $(srcdir)/src/include that come earlier in the include path order. they include the public header they're wrapping, then add declarations for namespace-protected versions of the same interfaces and any "internally public" interfaces for the subsystem they correspond to. along these lines, the wrapper for features.h is now responsible for the definition of the hidden, weak, and weak_alias macros. this means source files will no longer need to include any special headers to access these features. over time, it is my expectation that the scope of what is "internally public" will expand, reducing the number of source files which need to include *_impl.h and related headers down to those which are actually implementing the corresponding subsystems, not just using them.
2018-09-12use hidden visibility for sh __unmapself backendsRich Felker-2/+3
2018-09-12make arch __set_thread_area backends hiddenRich Felker-0/+9
this is not a public interface, and does not even necessarily match the syscall on all archs that have a syscall by that name. on archs where it's implemented in C, no action on the source file is needed; the hidden declaration in pthread_arch.h suffices.
2018-09-12make arch __clone backends hiddenRich Felker-0/+15
these are not a public interface and are not intended to be callable from anywhere but the public clone function or other places in libc.
2018-09-12move declarations of tls setup/access functions to pthread_impl.hRich Felker-4/+0
it's already included in all places where these are needed, and aside from __tls_get_addr, they're all implementation internals.
2018-09-12for c11 mtx and cnd functions, use externally consistent type namesRich Felker-12/+17
despite looking like undefined behavior, the affected code is correct both before and after this patch. the pairs mtx_t and pthread_mutex_t, and cnd_t and pthread_cond_t, are not mutually compatible within a single translation unit (because they are distinct untagged aggregate instances), but they are compatible with an object of either type from another translation unit (6.2.7 ΒΆ1), and therefore a given translation unit can choose which one it wants to use. in the interest of being able to move declarations out of source files to headers that facilitate checking, use the pthread type names in declaring the namespace-safe versions of the pthread functions and cast the argument pointer types when calling them.
2018-09-12make inadvertently exposed __pthread_{timed,try}join_np functions staticRich Felker-2/+2
these exist for the sake of defining the corresponding weak public aliases (for C11 and POSIX namespace conformance reasons). they are not referenced by anything else in libc, so make them static.
2018-09-12fix issues from public functions defined without declaration visibleRich Felker-0/+1
policy is that all public functions which have a public declaration should be defined in a context where that public declaration is visible, to avoid preventable type mismatches. an audit performed using GCC's -Wmissing-declarations turned up the violations corrected here. in some cases the public header had not been included; in others, a feature test macro needed to make the declaration visible had been omitted. in the case of gethostent and getnetent, the omission seems to have been intentional, as a hack to admit a single stub definition for both functions. this kind of hack is no longer acceptable; it's UB and would not fly with LTO or advanced toolchains. the hack is undone to make exposure of the declarations possible.
2018-09-05define and use internal macros for hidden visibility, weak refsRich Felker-26/+20
this cleans up what had become widespread direct inline use of "GNU C" style attributes directly in the source, and lowers the barrier to increased use of hidden visibility, which will be useful to recovering some of the efficiency lost when the protected visibility hack was dropped in commit dc2f368e565c37728b0d620380b849c3a1ddd78f, especially on archs where the PLT ABI is costly.
2018-09-04fix namespace violation for c11 mutex functionsRich Felker-1/+3
__pthread_mutex_timedlock is used to implement c11 mutex functions, and therefore cannot call pthread_mutex_trylock by name.
2018-09-04in pthread_mutex_timedlock, avoid repeatedly reading mutex type fieldRich Felker-3/+4
compiler cannot cache immutable fields of the mutex object across external calls it can't see, much less across atomics.
2018-09-04in pthread_mutex_trylock, EBUSY out more directly when possibleRich Felker-2/+2
avoid gratuitously setting up and tearing down the robust list pending slot.
2018-08-29fix async thread cancellation on sh-fdpicRich Felker-0/+3
if __cp_cancel was reached via __syscall_cp, r12 will necessarily still contain a GOT pointer (for or for the static-linked main program) valid for entering __cancel. however, in the case of async cancellation, r12 may contain any scratch value; it's not necessarily even a valid GOT pointer for the code that was interrupted. unlike in commit 0ec49dab6794166d67fae4764ce7fdea42ea6103 where the corresponding issue was fixed for powerpc64, there is fundamentally no way for fdpic code to recompute its GOT pointer. so a new mechanism is introduced for cancel_handler to write a GOT register value into the interrupted context on archs where it is needed.
2018-08-29fix async thread cancellation on powerpc64Rich Felker-0/+7
entering the local entry point for __cancel from __cp_cancel is valid if __cp_cancel was reached from __syscall_cp, since both are in libc and share the same TOC pointer, but it is not valid if __cp_cancel was reached when cancel_handler rewrote the program counter for asynchronous cancellation of code outside libc. to ensure __cancel is entered with a valid TOC pointer, recompute the correct value in a PC-relative manner before jumping.
2018-08-28reject invalid arguments to pthread_barrierattr_setpsharedRich Felker-0/+1
this is a POSIX requirement.
2018-08-28rewrite __aeabi_read_tp in asmSzabolcs Nagy-12/+6
__aeabi_read_tp used to call c code, but that was incorrect as the arm runtime abi specifies special pcs for this function: it is only allowed to clobber r0, ip, lr and cpsr. maintainer's note: the old code explicitly saved and restored all general-purpose registers which are call-clobbered in the normal calling convention, so it's unlikely that any real-world compilers produced code that could break. however theoretically they could have chosen to use floating point registers, in which case the caller's values of those registers would be clobbered.
2018-08-28fix deadlock in async thread self-cancellationRich Felker-1/+5
with async cancellation enabled, pthread_cancel(pthread_self()) deadlocked due to pthread_kill holding killlock which is needed by pthread_exit. this could be solved by making pthread_kill block signals around the critical section, at least when the target thread is itself, but the issue only arises for cancellation, and otherwise would just be imposing unnecessary cost. instead just have pthread_cancel explicitly check for async self-cancellation and call pthread_exit(PTHREAD_CANCELED) directly rather than going through the signal machinery.
2018-08-23fix tls access on arm targets before armv6kSzabolcs Nagy-1/+1
commit 610c5a8524c3d6cd3ac5a5f1231422e7648a3791 changed the thread pointer setup so tp points at the end of the pthread struct on arm, but failed to update __aeabi_read_tp so it was off by 8. this broke tls access in code that is compiled with -mtp=soft, which is the default when target arch is pre armv6k or thumb1. maintainer's note: no release versions are affected.
2018-08-18mips archs: fix runaway execution if start fn passed to clone returnsSegev Finer-3/+12
Call SYS_exit on return from fn in __clone. This is the expected behavior of this function. Without this the child task will crash on return from fn, since it will return to nowhere.
2018-08-16fix pthread_create return value with PTHREAD_EXPLICIT_SCHEDRich Felker-0/+1
due to moved code, commit b8742f32602add243ee2ce74d804015463726899 inadvertently used the return value of __clone, rather than the return value of SYS_sched_setscheduler in the new thread, to check whether it needed to report failure. since a successful __clone returns the tid of the new thread, which is never zero, this caused pthread_create always to return with an invalid error number in the code path for PTHREAD_EXPLICIT_SCHED. this regression was not present in any releases.
2018-07-27make pthread_attr_init honor defaults set by pthread_setattr_default_npRich Felker-4/+11
this fixes a major gap in the intended functionality of pthread_setattr_default_np. if application/library code creating a thread does not pass a null attribute pointer to pthread_create, but sets up an attribute object to change other properties while leaving the stack alone, the created thread will get a stack with size DEFAULT_STACK_SIZE. this makes pthread_setattr_default_np useless for working around stack overflow issues in such applications, and leaves a major risk of regression if previously-working code switches from using a null attribute pointer to an attribute object. this change aligns the behavior more closely with the glibc pthread_setattr_default_np functionality too, albeit via a different mechanism. glibc encodes "default" specially in the attribute object and reads the actual default at thread creation time. with this commit, we now copy the current default into the attribute object at pthread_attr_init time, so that applications that query the properties of the attribute object will see the right values.