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//! Implement thread-local storage.
use std::collections::btree_map::Entry as BTreeEntry;
use std::collections::hash_map::Entry as HashMapEntry;
use std::collections::BTreeMap;
use log::trace;
use rustc_data_structures::fx::FxHashMap;
use rustc_middle::ty;
use rustc_target::abi::{HasDataLayout, Size};
use rustc_target::spec::abi::Abi;
use crate::*;
pub type TlsKey = u128;
#[derive(Clone, Debug)]
pub struct TlsEntry<'tcx> {
/// The data for this key. None is used to represent NULL.
/// (We normalize this early to avoid having to do a NULL-ptr-test each time we access the data.)
data: BTreeMap<ThreadId, Scalar<Provenance>>,
dtor: Option<ty::Instance<'tcx>>,
}
#[derive(Clone, Debug)]
struct RunningDtorsState {
/// The last TlsKey used to retrieve a TLS destructor. `None` means that we
/// have not tried to retrieve a TLS destructor yet or that we already tried
/// all keys.
last_dtor_key: Option<TlsKey>,
}
#[derive(Debug)]
pub struct TlsData<'tcx> {
/// The Key to use for the next thread-local allocation.
next_key: TlsKey,
/// pthreads-style thread-local storage.
keys: BTreeMap<TlsKey, TlsEntry<'tcx>>,
/// A single per thread destructor of the thread local storage (that's how
/// things work on macOS) with a data argument.
macos_thread_dtors: BTreeMap<ThreadId, (ty::Instance<'tcx>, Scalar<Provenance>)>,
/// State for currently running TLS dtors. If this map contains a key for a
/// specific thread, it means that we are in the "destruct" phase, during
/// which some operations are UB.
dtors_running: FxHashMap<ThreadId, RunningDtorsState>,
}
impl<'tcx> Default for TlsData<'tcx> {
fn default() -> Self {
TlsData {
next_key: 1, // start with 1 as we must not use 0 on Windows
keys: Default::default(),
macos_thread_dtors: Default::default(),
dtors_running: Default::default(),
}
}
}
impl<'tcx> TlsData<'tcx> {
/// Generate a new TLS key with the given destructor.
/// `max_size` determines the integer size the key has to fit in.
#[allow(clippy::integer_arithmetic)]
pub fn create_tls_key(
&mut self,
dtor: Option<ty::Instance<'tcx>>,
max_size: Size,
) -> InterpResult<'tcx, TlsKey> {
let new_key = self.next_key;
self.next_key += 1;
self.keys.try_insert(new_key, TlsEntry { data: Default::default(), dtor }).unwrap();
trace!("New TLS key allocated: {} with dtor {:?}", new_key, dtor);
if max_size.bits() < 128 && new_key >= (1u128 << max_size.bits()) {
throw_unsup_format!("we ran out of TLS key space");
}
Ok(new_key)
}
pub fn delete_tls_key(&mut self, key: TlsKey) -> InterpResult<'tcx> {
match self.keys.remove(&key) {
Some(_) => {
trace!("TLS key {} removed", key);
Ok(())
}
None => throw_ub_format!("removing a non-existig TLS key: {}", key),
}
}
pub fn load_tls(
&self,
key: TlsKey,
thread_id: ThreadId,
cx: &impl HasDataLayout,
) -> InterpResult<'tcx, Scalar<Provenance>> {
match self.keys.get(&key) {
Some(TlsEntry { data, .. }) => {
let value = data.get(&thread_id).copied();
trace!("TLS key {} for thread {:?} loaded: {:?}", key, thread_id, value);
Ok(value.unwrap_or_else(|| Scalar::null_ptr(cx)))
}
None => throw_ub_format!("loading from a non-existing TLS key: {}", key),
}
}
pub fn store_tls(
&mut self,
key: TlsKey,
thread_id: ThreadId,
new_data: Scalar<Provenance>,
cx: &impl HasDataLayout,
) -> InterpResult<'tcx> {
match self.keys.get_mut(&key) {
Some(TlsEntry { data, .. }) => {
if new_data.to_machine_usize(cx)? != 0 {
trace!("TLS key {} for thread {:?} stored: {:?}", key, thread_id, new_data);
data.insert(thread_id, new_data);
} else {
trace!("TLS key {} for thread {:?} removed", key, thread_id);
data.remove(&thread_id);
}
Ok(())
}
None => throw_ub_format!("storing to a non-existing TLS key: {}", key),
}
}
/// Set the thread wide destructor of the thread local storage for the given
/// thread. This function is used to implement `_tlv_atexit` shim on MacOS.
///
/// Thread wide dtors are available only on MacOS. There is one destructor
/// per thread as can be guessed from the following comment in the
/// [`_tlv_atexit`
/// implementation](https://github.com/opensource-apple/dyld/blob/195030646877261f0c8c7ad8b001f52d6a26f514/src/threadLocalVariables.c#L389):
///
/// NOTE: this does not need locks because it only operates on current thread data
pub fn set_macos_thread_dtor(
&mut self,
thread: ThreadId,
dtor: ty::Instance<'tcx>,
data: Scalar<Provenance>,
) -> InterpResult<'tcx> {
if self.dtors_running.contains_key(&thread) {
// UB, according to libstd docs.
throw_ub_format!(
"setting thread's local storage destructor while destructors are already running"
);
}
if self.macos_thread_dtors.insert(thread, (dtor, data)).is_some() {
throw_unsup_format!(
"setting more than one thread local storage destructor for the same thread is not supported"
);
}
Ok(())
}
/// Returns a dtor, its argument and its index, if one is supposed to run.
/// `key` is the last dtors that was run; we return the *next* one after that.
///
/// An optional destructor function may be associated with each key value.
/// At thread exit, if a key value has a non-NULL destructor pointer,
/// and the thread has a non-NULL value associated with that key,
/// the value of the key is set to NULL, and then the function pointed
/// to is called with the previously associated value as its sole argument.
/// **The order of destructor calls is unspecified if more than one destructor
/// exists for a thread when it exits.**
///
/// If, after all the destructors have been called for all non-NULL values
/// with associated destructors, there are still some non-NULL values with
/// associated destructors, then the process is repeated.
/// If, after at least {PTHREAD_DESTRUCTOR_ITERATIONS} iterations of destructor
/// calls for outstanding non-NULL values, there are still some non-NULL values
/// with associated destructors, implementations may stop calling destructors,
/// or they may continue calling destructors until no non-NULL values with
/// associated destructors exist, even though this might result in an infinite loop.
fn fetch_tls_dtor(
&mut self,
key: Option<TlsKey>,
thread_id: ThreadId,
) -> Option<(ty::Instance<'tcx>, Scalar<Provenance>, TlsKey)> {
use std::ops::Bound::*;
let thread_local = &mut self.keys;
let start = match key {
Some(key) => Excluded(key),
None => Unbounded,
};
// We interpret the documentaion above (taken from POSIX) as saying that we need to iterate
// over all keys and run each destructor at least once before running any destructor a 2nd
// time. That's why we have `key` to indicate how far we got in the current iteration. If we
// return `None`, `schedule_next_pthread_tls_dtor` will re-try with `ket` set to `None` to
// start the next round.
// TODO: In the future, we might consider randomizing destructor order, but we still have to
// uphold this requirement.
for (&key, TlsEntry { data, dtor }) in thread_local.range_mut((start, Unbounded)) {
match data.entry(thread_id) {
BTreeEntry::Occupied(entry) => {
if let Some(dtor) = dtor {
// Set TLS data to NULL, and call dtor with old value.
let data_scalar = entry.remove();
let ret = Some((*dtor, data_scalar, key));
return ret;
}
}
BTreeEntry::Vacant(_) => {}
}
}
None
}
/// Set that dtors are running for `thread`. It is guaranteed not to change
/// the existing values stored in `dtors_running` for this thread. Returns
/// `true` if dtors for `thread` are already running.
fn set_dtors_running_for_thread(&mut self, thread: ThreadId) -> bool {
match self.dtors_running.entry(thread) {
HashMapEntry::Occupied(_) => true,
HashMapEntry::Vacant(entry) => {
// We cannot just do `self.dtors_running.insert` because that
// would overwrite `last_dtor_key` with `None`.
entry.insert(RunningDtorsState { last_dtor_key: None });
false
}
}
}
/// Delete all TLS entries for the given thread. This function should be
/// called after all TLS destructors have already finished.
fn delete_all_thread_tls(&mut self, thread_id: ThreadId) {
for TlsEntry { data, .. } in self.keys.values_mut() {
data.remove(&thread_id);
}
}
}
impl<'mir, 'tcx: 'mir> EvalContextPrivExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
trait EvalContextPrivExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
/// Schedule TLS destructors for Windows.
/// On windows, TLS destructors are managed by std.
fn schedule_windows_tls_dtors(&mut self) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
let active_thread = this.get_active_thread();
// Windows has a special magic linker section that is run on certain events.
// Instead of searching for that section and supporting arbitrary hooks in there
// (that would be basically https://github.com/rust-lang/miri/issues/450),
// we specifically look up the static in libstd that we know is placed
// in that section.
let thread_callback =
this.eval_windows("thread_local_key", "p_thread_callback")?.to_pointer(this)?;
let thread_callback = this.get_ptr_fn(thread_callback)?.as_instance()?;
// FIXME: Technically, the reason should be `DLL_PROCESS_DETACH` when the main thread exits
// but std treats both the same.
let reason = this.eval_windows("c", "DLL_THREAD_DETACH")?;
// The signature of this function is `unsafe extern "system" fn(h: c::LPVOID, dwReason: c::DWORD, pv: c::LPVOID)`.
// FIXME: `h` should be a handle to the current module and what `pv` should be is unknown
// but both are ignored by std
this.call_function(
thread_callback,
Abi::System { unwind: false },
&[Scalar::null_ptr(this).into(), reason.into(), Scalar::null_ptr(this).into()],
None,
StackPopCleanup::Root { cleanup: true },
)?;
this.enable_thread(active_thread);
Ok(())
}
/// Schedule the MacOS thread destructor of the thread local storage to be
/// executed. Returns `true` if scheduled.
///
/// Note: It is safe to call this function also on other Unixes.
fn schedule_macos_tls_dtor(&mut self) -> InterpResult<'tcx, bool> {
let this = self.eval_context_mut();
let thread_id = this.get_active_thread();
if let Some((instance, data)) = this.machine.tls.macos_thread_dtors.remove(&thread_id) {
trace!("Running macos dtor {:?} on {:?} at {:?}", instance, data, thread_id);
this.call_function(
instance,
Abi::C { unwind: false },
&[data.into()],
None,
StackPopCleanup::Root { cleanup: true },
)?;
// Enable the thread so that it steps through the destructor which
// we just scheduled. Since we deleted the destructor, it is
// guaranteed that we will schedule it again. The `dtors_running`
// flag will prevent the code from adding the destructor again.
this.enable_thread(thread_id);
Ok(true)
} else {
Ok(false)
}
}
/// Schedule a pthread TLS destructor. Returns `true` if found
/// a destructor to schedule, and `false` otherwise.
fn schedule_next_pthread_tls_dtor(&mut self) -> InterpResult<'tcx, bool> {
let this = self.eval_context_mut();
let active_thread = this.get_active_thread();
assert!(this.has_terminated(active_thread), "running TLS dtors for non-terminated thread");
// Fetch next dtor after `key`.
let last_key = this.machine.tls.dtors_running[&active_thread].last_dtor_key;
let dtor = match this.machine.tls.fetch_tls_dtor(last_key, active_thread) {
dtor @ Some(_) => dtor,
// We ran each dtor once, start over from the beginning.
None => this.machine.tls.fetch_tls_dtor(None, active_thread),
};
if let Some((instance, ptr, key)) = dtor {
this.machine.tls.dtors_running.get_mut(&active_thread).unwrap().last_dtor_key =
Some(key);
trace!("Running TLS dtor {:?} on {:?} at {:?}", instance, ptr, active_thread);
assert!(
!ptr.to_machine_usize(this).unwrap() != 0,
"data can't be NULL when dtor is called!"
);
this.call_function(
instance,
Abi::C { unwind: false },
&[ptr.into()],
None,
StackPopCleanup::Root { cleanup: true },
)?;
this.enable_thread(active_thread);
return Ok(true);
}
this.machine.tls.dtors_running.get_mut(&active_thread).unwrap().last_dtor_key = None;
Ok(false)
}
}
impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
/// Schedule an active thread's TLS destructor to run on the active thread.
/// Note that this function does not run the destructors itself, it just
/// schedules them one by one each time it is called and reenables the
/// thread so that it can be executed normally by the main execution loop.
///
/// Note: we consistently run TLS destructors for all threads, including the
/// main thread. However, it is not clear that we should run the TLS
/// destructors for the main thread. See issue:
/// <https://github.com/rust-lang/rust/issues/28129>.
fn schedule_next_tls_dtor_for_active_thread(&mut self) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
let active_thread = this.get_active_thread();
trace!("schedule_next_tls_dtor_for_active_thread on thread {:?}", active_thread);
if !this.machine.tls.set_dtors_running_for_thread(active_thread) {
// This is the first time we got asked to schedule a destructor. The
// Windows schedule destructor function must be called exactly once,
// this is why it is in this block.
if this.tcx.sess.target.os == "windows" {
// On Windows, we signal that the thread quit by starting the
// relevant function, reenabling the thread, and going back to
// the scheduler.
this.schedule_windows_tls_dtors()?;
return Ok(());
}
}
// The remaining dtors make some progress each time around the scheduler loop,
// until they return `false` to indicate that they are done.
// The macOS thread wide destructor runs "before any TLS slots get
// freed", so do that first.
if this.schedule_macos_tls_dtor()? {
// We have scheduled a MacOS dtor to run on the thread. Execute it
// to completion and come back here. Scheduling a destructor
// destroys it, so we will not enter this branch again.
return Ok(());
}
if this.schedule_next_pthread_tls_dtor()? {
// We have scheduled a pthread destructor and removed it from the
// destructors list. Run it to completion and come back here.
return Ok(());
}
// All dtors done!
this.machine.tls.delete_all_thread_tls(active_thread);
this.thread_terminated()?;
Ok(())
}
}