Auto merge of rust-lang#3745 - joboet:os_unfair_lock, r=RalfJung

Implement the `os_unfair_lock` functions on macOS

These are needed for rust-lang#122408. See the documentation [here](https://developer.apple.com/documentation/os/synchronization?language=objc) and the implementation [here](https://github.com/apple-oss-distributions/libplatform/blob/a00a4cc36da2110578bcf3b8eeeeb93dcc7f4e11/src/os/lock.c#L645).

Author: bors

src/tools/miri/src/concurrency/sync.rs

@@ -269,7 +269,7 @@ pub(super) trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let this = self.eval_context_mut();
         if this.mutex_is_locked(mutex) {
             assert_ne!(this.mutex_get_owner(mutex), this.active_thread());
-            this.mutex_enqueue_and_block(mutex, retval, dest);
+            this.mutex_enqueue_and_block(mutex, Some((retval, dest)));
         } else {
             // We can have it right now!
             this.mutex_lock(mutex);
@@ -390,9 +390,15 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     }
 
     /// Put the thread into the queue waiting for the mutex.
-    /// Once the Mutex becomes available, `retval` will be written to `dest`.
+    ///
+    /// Once the Mutex becomes available and if it exists, `retval_dest.0` will
+    /// be written to `retval_dest.1`.
     #[inline]
-    fn mutex_enqueue_and_block(&mut self, id: MutexId, retval: Scalar, dest: MPlaceTy<'tcx>) {
+    fn mutex_enqueue_and_block(
+        &mut self,
+        id: MutexId,
+        retval_dest: Option<(Scalar, MPlaceTy<'tcx>)>,
+    ) {
         let this = self.eval_context_mut();
         assert!(this.mutex_is_locked(id), "queing on unlocked mutex");
         let thread = this.active_thread();
@@ -403,13 +409,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             callback!(
                 @capture<'tcx> {
                     id: MutexId,
-                    retval: Scalar,
-                    dest: MPlaceTy<'tcx>,
+                    retval_dest: Option<(Scalar, MPlaceTy<'tcx>)>,
                 }
                 @unblock = |this| {
                     assert!(!this.mutex_is_locked(id));
                     this.mutex_lock(id);
-                    this.write_scalar(retval, &dest)?;
+
+                    if let Some((retval, dest)) = retval_dest {
+                        this.write_scalar(retval, &dest)?;
+                    }
+
                     Ok(())
                 }
             ),

src/tools/miri/src/provenance_gc.rs

@@ -30,6 +30,17 @@ impl<T: VisitProvenance> VisitProvenance for Option<T> {
     }
 }
 
+impl<A, B> VisitProvenance for (A, B)
+where
+    A: VisitProvenance,
+    B: VisitProvenance,
+{
+    fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
+        self.0.visit_provenance(visit);
+        self.1.visit_provenance(visit);
+    }
+}
+
 impl<T: VisitProvenance> VisitProvenance for std::cell::RefCell<T> {
     fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
         self.borrow().visit_provenance(visit)

src/tools/miri/src/shims/unix/macos/foreign_items.rs

@@ -1,6 +1,7 @@
 use rustc_span::Symbol;
 use rustc_target::spec::abi::Abi;
 
+use super::sync::EvalContextExt as _;
 use crate::shims::unix::*;
 use crate::*;
 
@@ -174,6 +175,27 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_scalar(res, dest)?;
             }
 
+            "os_unfair_lock_lock" => {
+                let [lock_op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                this.os_unfair_lock_lock(lock_op)?;
+            }
+            "os_unfair_lock_trylock" => {
+                let [lock_op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                this.os_unfair_lock_trylock(lock_op, dest)?;
+            }
+            "os_unfair_lock_unlock" => {
+                let [lock_op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                this.os_unfair_lock_unlock(lock_op)?;
+            }
+            "os_unfair_lock_assert_owner" => {
+                let [lock_op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                this.os_unfair_lock_assert_owner(lock_op)?;
+            }
+            "os_unfair_lock_assert_not_owner" => {
+                let [lock_op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                this.os_unfair_lock_assert_not_owner(lock_op)?;
+            }
+
             _ => return Ok(EmulateItemResult::NotSupported),
         };
 

src/tools/miri/src/shims/unix/macos/mod.rs

@@ -1 +1,2 @@
 pub mod foreign_items;
+pub mod sync;

src/tools/miri/src/shims/unix/macos/sync.rs

@@ -0,0 +1,107 @@
+//! Contains macOS-specific synchronization functions.
+//!
+//! For `os_unfair_lock`, see the documentation
+//! <https://developer.apple.com/documentation/os/synchronization?language=objc>
+//! and in case of underspecification its implementation
+//! <https://github.com/apple-oss-distributions/libplatform/blob/a00a4cc36da2110578bcf3b8eeeeb93dcc7f4e11/src/os/lock.c#L645>.
+//!
+//! Note that we don't emulate every edge-case behaviour of the locks. Notably,
+//! we don't abort when locking a lock owned by a thread that has already exited
+//! and we do not detect copying of the lock, but macOS doesn't guarantee anything
+//! in that case either.
+
+use crate::*;
+
+impl<'tcx> EvalContextExtPriv<'tcx> for crate::MiriInterpCx<'tcx> {}
+trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
+    fn os_unfair_lock_getid(&mut self, lock_op: &OpTy<'tcx>) -> InterpResult<'tcx, MutexId> {
+        let this = self.eval_context_mut();
+        // os_unfair_lock holds a 32-bit value, is initialized with zero and
+        // must be assumed to be opaque. Therefore, we can just store our
+        // internal mutex ID in the structure without anyone noticing.
+        this.mutex_get_or_create_id(lock_op, this.libc_ty_layout("os_unfair_lock"), 0)
+    }
+}
+
+impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
+pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
+    fn os_unfair_lock_lock(&mut self, lock_op: &OpTy<'tcx>) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        let id = this.os_unfair_lock_getid(lock_op)?;
+        if this.mutex_is_locked(id) {
+            if this.mutex_get_owner(id) == this.active_thread() {
+                // Matching the current macOS implementation: abort on reentrant locking.
+                throw_machine_stop!(TerminationInfo::Abort(
+                    "attempted to lock an os_unfair_lock that is already locked by the current thread".to_owned()
+                ));
+            }
+
+            this.mutex_enqueue_and_block(id, None);
+        } else {
+            this.mutex_lock(id);
+        }
+
+        Ok(())
+    }
+
+    fn os_unfair_lock_trylock(
+        &mut self,
+        lock_op: &OpTy<'tcx>,
+        dest: &MPlaceTy<'tcx>,
+    ) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        let id = this.os_unfair_lock_getid(lock_op)?;
+        if this.mutex_is_locked(id) {
+            // Contrary to the blocking lock function, this does not check for
+            // reentrancy.
+            this.write_scalar(Scalar::from_bool(false), dest)?;
+        } else {
+            this.mutex_lock(id);
+            this.write_scalar(Scalar::from_bool(true), dest)?;
+        }
+
+        Ok(())
+    }
+
+    fn os_unfair_lock_unlock(&mut self, lock_op: &OpTy<'tcx>) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        let id = this.os_unfair_lock_getid(lock_op)?;
+        if this.mutex_unlock(id)?.is_none() {
+            // Matching the current macOS implementation: abort.
+            throw_machine_stop!(TerminationInfo::Abort(
+                "attempted to unlock an os_unfair_lock not owned by the current thread".to_owned()
+            ));
+        }
+
+        Ok(())
+    }
+
+    fn os_unfair_lock_assert_owner(&mut self, lock_op: &OpTy<'tcx>) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        let id = this.os_unfair_lock_getid(lock_op)?;
+        if !this.mutex_is_locked(id) || this.mutex_get_owner(id) != this.active_thread() {
+            throw_machine_stop!(TerminationInfo::Abort(
+                "called os_unfair_lock_assert_owner on an os_unfair_lock not owned by the current thread".to_owned()
+            ));
+        }
+
+        Ok(())
+    }
+
+    fn os_unfair_lock_assert_not_owner(&mut self, lock_op: &OpTy<'tcx>) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        let id = this.os_unfair_lock_getid(lock_op)?;
+        if this.mutex_is_locked(id) && this.mutex_get_owner(id) == this.active_thread() {
+            throw_machine_stop!(TerminationInfo::Abort(
+                "called os_unfair_lock_assert_not_owner on an os_unfair_lock owned by the current thread".to_owned()
+            ));
+        }
+
+        Ok(())
+    }
+}

src/tools/miri/src/shims/unix/sync.rs

@@ -473,7 +473,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let ret = if this.mutex_is_locked(id) {
             let owner_thread = this.mutex_get_owner(id);
             if owner_thread != this.active_thread() {
-                this.mutex_enqueue_and_block(id, Scalar::from_i32(0), dest.clone());
+                this.mutex_enqueue_and_block(id, Some((Scalar::from_i32(0), dest.clone())));
                 return Ok(());
             } else {
                 // Trying to acquire the same mutex again.

src/tools/miri/tests/fail-dep/concurrency/apple_os_unfair_lock_assert_not_owner.rs

@@ -0,0 +1,13 @@
+//@ only-target-darwin
+
+use std::cell::UnsafeCell;
+
+fn main() {
+    let lock = UnsafeCell::new(libc::OS_UNFAIR_LOCK_INIT);
+
+    unsafe {
+        libc::os_unfair_lock_lock(lock.get());
+        libc::os_unfair_lock_assert_not_owner(lock.get());
+        //~^ error: abnormal termination: called os_unfair_lock_assert_not_owner on an os_unfair_lock owned by the current thread
+    }
+}

src/tools/miri/tests/fail-dep/concurrency/apple_os_unfair_lock_assert_not_owner.stderr

@@ -0,0 +1,13 @@
+error: abnormal termination: called os_unfair_lock_assert_not_owner on an os_unfair_lock owned by the current thread
+  --> $DIR/apple_os_unfair_lock_assert_not_owner.rs:LL:CC
+   |
+LL |         libc::os_unfair_lock_assert_not_owner(lock.get());
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ called os_unfair_lock_assert_not_owner on an os_unfair_lock owned by the current thread
+   |
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/apple_os_unfair_lock_assert_not_owner.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+

src/tools/miri/tests/fail-dep/concurrency/apple_os_unfair_lock_assert_owner.rs

@@ -0,0 +1,12 @@
+//@ only-target-darwin
+
+use std::cell::UnsafeCell;
+
+fn main() {
+    let lock = UnsafeCell::new(libc::OS_UNFAIR_LOCK_INIT);
+
+    unsafe {
+        libc::os_unfair_lock_assert_owner(lock.get());
+        //~^ error: abnormal termination: called os_unfair_lock_assert_owner on an os_unfair_lock not owned by the current thread
+    }
+}

src/tools/miri/tests/fail-dep/concurrency/apple_os_unfair_lock_assert_owner.stderr

@@ -0,0 +1,13 @@
+error: abnormal termination: called os_unfair_lock_assert_owner on an os_unfair_lock not owned by the current thread
+  --> $DIR/apple_os_unfair_lock_assert_owner.rs:LL:CC
+   |
+LL |         libc::os_unfair_lock_assert_owner(lock.get());
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ called os_unfair_lock_assert_owner on an os_unfair_lock not owned by the current thread
+   |
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/apple_os_unfair_lock_assert_owner.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+