Identical to riscv64 except for stack offsets in clone.
According to LoongArch ABI Specs, stack need to be 16 align to improve performance and compiler layout of stack frames.
Author: Xiaojuan Zhai <zhaixiaojuan@loongson.cn> Author: Meidan Li <limeidan@loongson.cn> Author: Guoqi Chen <chenguoqi@loongson.cn> Author: Xiaolin Zhao <zhaoxiaolin@loongson.cn> Author: Fan peng <fanpeng@loongson.cn> Author: Jiantao Shan <shanjiantao@loongson.cn> Author: Xuhui Qiang <qiangxuhui@loongson.cn> Author: Jingyun Hua <huajingyun@loongson.cn> Author: Liu xue <liuxue@loongson.cn> Author: Hongliang Wang <wanghongliang@loongson.cn>
The code intends for the sem_post() in line 97 (now 98) to only unblock target threads waiting on line 29. But after the first thread is released, the next sem_post() might also unblock a thread waiting on line 36. That would cause the thread to return to the execution of user code before all threads are done, leading to user code being executed in a mixed-credentials environment. What's more, if this happens more than once, then the mass release on line 110 (now line 111) will cause multiple threads to execute the callback at the same time, and the callbacks are currently not written to cope with that situation. Adding another semaphore allows the caller to say explicitly which threads it wants to release.
disabling cancellation around the pthread_join call seems to be the safest and logically simplest fix. i believe it would also be possible to just perform the unmap directly here after __tl_sync, removing the dependency on pthread_join, but such an approach duplicately encodes a lot more implementation assumptions.
while no lock is held here making it a lock-order issue, replacement malloc is likely to want to use pthread_atfork, possibly making the call to malloc infinitely recursive. even if not, there is no reason to prefer an application-provided malloc here.
because the has-waiters state in the semaphore value futex word is only representable when the value is zero (the special value -1 represents "0 with potential new waiters"), it's lost if intervening operations make the semaphore value positive again. this creates an ABA issue in sem_post, whereby the post uses a stale waiters count rather than re-evaluating it, skipping the futex wake if the stale count was zero. the fix here is based on a proposal by Alexey Izbyshev, with minor changes to eliminate costly new spurious wake syscalls. the basic idea is to replace the special value -1 with a sticky waiters bit (repurposing the sign bit) preserved under both wait and post. any post that takes place with the waiters bit set will perform a futex wake. to be useful, the waiters bit needs to be removable, and to remove it safely, we perform a broadcast wake instead of a normal single-task wake whenever removing the bit. this lets any un-accounted-for waiters wake and re-add the waiters bit if they still need it. there are multiple possible choices for when to perform this broadcast, but the optimal choice seems to be doing it whenever the observed waiters count is less than two (semantically, this means exactly one, but we might see a stale count of zero). in this case, the expected number of threads to be woken is one, with exactly the same cost as a non-broadcast wake.
POSIX requires pthread_atfork to report errors via its return value, not via errno. The only specified error is ENOMEM.
if async cancellation is enabled and acted upon, the stack pointer is not necessarily pointing to a __syscall_cp_asm stack frame. the contents of the stack being wrong don't really matter, but if the stack pointer is not suitably aligned, the procedure call ABI is violated when calling back into C code via __cancel, and pthread_exit, cancellation cleanup handlers, TSD destructors, etc. may malfunction or crash. for the async cancel case, just call __cancel directly like we did prior to commit 102f6a01e249ce4495f1119ae6d963a2a4a53ce5. restore the signal mask prior to doing this since the cancellation handler runs with all signals blocked.
commit 167390f05564e0a4d3fcb4329377fd7743267560 seems to have overlooked the presence of a lock here, probably because it was one of the exceptions not using LOCK() but a rwlock. as such, it can't be added to the generic table of locks to take, so add an explicit atfork function for the pthread keys table. the order it is called does not particularly matter since nothing else in libc but pthread_exit interacts with keys.