diff --git a/library/std/src/sys/xous/mod.rs b/library/std/src/sys/xous/mod.rs index e3f527912db..79d9c00f64a 100644 --- a/library/std/src/sys/xous/mod.rs +++ b/library/std/src/sys/xous/mod.rs @@ -28,7 +28,6 @@ pub mod pipe; pub mod process; pub mod stdio; pub mod thread; -#[path = "../unsupported/thread_local_key.rs"] pub mod thread_local_key; #[path = "../unsupported/thread_parking.rs"] pub mod thread_parking; diff --git a/library/std/src/sys/xous/thread_local_key.rs b/library/std/src/sys/xous/thread_local_key.rs new file mode 100644 index 00000000000..3771ea65700 --- /dev/null +++ b/library/std/src/sys/xous/thread_local_key.rs @@ -0,0 +1,190 @@ +use crate::mem::ManuallyDrop; +use crate::ptr; +use crate::sync::atomic::AtomicPtr; +use crate::sync::atomic::AtomicUsize; +use crate::sync::atomic::Ordering::SeqCst; +use core::arch::asm; + +use crate::os::xous::ffi::{map_memory, unmap_memory, MemoryFlags}; + +/// Thread Local Storage +/// +/// Currently, we are limited to 1023 TLS entries. The entries +/// live in a page of memory that's unique per-process, and is +/// stored in the `$tp` register. If this register is 0, then +/// TLS has not been initialized and thread cleanup can be skipped. +/// +/// The index into this register is the `key`. This key is identical +/// between all threads, but indexes a different offset within this +/// pointer. +pub type Key = usize; + +pub type Dtor = unsafe extern "C" fn(*mut u8); + +const TLS_MEMORY_SIZE: usize = 4096; + +/// TLS keys start at `1` to mimic POSIX. +static TLS_KEY_INDEX: AtomicUsize = AtomicUsize::new(1); + +fn tls_ptr_addr() -> *mut usize { + let mut tp: usize; + unsafe { + asm!( + "mv {}, tp", + out(reg) tp, + ); + } + core::ptr::from_exposed_addr_mut::(tp) +} + +/// Create an area of memory that's unique per thread. This area will +/// contain all thread local pointers. +fn tls_ptr() -> *mut usize { + let mut tp = tls_ptr_addr(); + + // If the TP register is `0`, then this thread hasn't initialized + // its TLS yet. Allocate a new page to store this memory. + if tp.is_null() { + tp = unsafe { + map_memory( + None, + None, + TLS_MEMORY_SIZE / core::mem::size_of::(), + MemoryFlags::R | MemoryFlags::W, + ) + } + .expect("Unable to allocate memory for thread local storage") + .as_mut_ptr(); + + unsafe { + // Key #0 is currently unused. + (tp).write_volatile(0); + + // Set the thread's `$tp` register + asm!( + "mv tp, {}", + in(reg) tp as usize, + ); + } + } + tp +} + +/// Allocate a new TLS key. These keys are shared among all threads. +fn tls_alloc() -> usize { + TLS_KEY_INDEX.fetch_add(1, SeqCst) +} + +#[inline] +pub unsafe fn create(dtor: Option) -> Key { + let key = tls_alloc(); + if let Some(f) = dtor { + unsafe { register_dtor(key, f) }; + } + key +} + +#[inline] +pub unsafe fn set(key: Key, value: *mut u8) { + assert!((key < 1022) && (key >= 1)); + unsafe { tls_ptr().add(key).write_volatile(value as usize) }; +} + +#[inline] +pub unsafe fn get(key: Key) -> *mut u8 { + assert!((key < 1022) && (key >= 1)); + core::ptr::from_exposed_addr_mut::(unsafe { tls_ptr().add(key).read_volatile() }) +} + +#[inline] +pub unsafe fn destroy(_key: Key) { + panic!("can't destroy keys on Xous"); +} + +// ------------------------------------------------------------------------- +// Dtor registration (stolen from Windows) +// +// Xous has no native support for running destructors so we manage our own +// list of destructors to keep track of how to destroy keys. We then install a +// callback later to get invoked whenever a thread exits, running all +// appropriate destructors. +// +// Currently unregistration from this list is not supported. A destructor can be +// registered but cannot be unregistered. There's various simplifying reasons +// for doing this, the big ones being: +// +// 1. Currently we don't even support deallocating TLS keys, so normal operation +// doesn't need to deallocate a destructor. +// 2. There is no point in time where we know we can unregister a destructor +// because it could always be getting run by some remote thread. +// +// Typically processes have a statically known set of TLS keys which is pretty +// small, and we'd want to keep this memory alive for the whole process anyway +// really. +// +// Perhaps one day we can fold the `Box` here into a static allocation, +// expanding the `StaticKey` structure to contain not only a slot for the TLS +// key but also a slot for the destructor queue on windows. An optimization for +// another day! + +static DTORS: AtomicPtr = AtomicPtr::new(ptr::null_mut()); + +struct Node { + dtor: Dtor, + key: Key, + next: *mut Node, +} + +unsafe fn register_dtor(key: Key, dtor: Dtor) { + let mut node = ManuallyDrop::new(Box::new(Node { key, dtor, next: ptr::null_mut() })); + + let mut head = DTORS.load(SeqCst); + loop { + node.next = head; + match DTORS.compare_exchange(head, &mut **node, SeqCst, SeqCst) { + Ok(_) => return, // nothing to drop, we successfully added the node to the list + Err(cur) => head = cur, + } + } +} + +pub unsafe fn destroy_tls() { + let tp = tls_ptr_addr(); + + // If the pointer address is 0, then this thread has no TLS. + if tp.is_null() { + return; + } + unsafe { run_dtors() }; + + // Finally, free the TLS array + unsafe { + unmap_memory(core::slice::from_raw_parts_mut( + tp, + TLS_MEMORY_SIZE / core::mem::size_of::(), + )) + .unwrap() + }; +} + +unsafe fn run_dtors() { + let mut any_run = true; + for _ in 0..5 { + if !any_run { + break; + } + any_run = false; + let mut cur = DTORS.load(SeqCst); + while !cur.is_null() { + let ptr = unsafe { get((*cur).key) }; + + if !ptr.is_null() { + unsafe { set((*cur).key, ptr::null_mut()) }; + unsafe { ((*cur).dtor)(ptr as *mut _) }; + any_run = true; + } + + unsafe { cur = (*cur).next }; + } + } +}