Auto merge of #77611 - oli-obk:atomic_miri_leakage, r=nagisa

Directly use raw pointers in `AtomicPtr` store/load

I was unable to find any reason for this limitation in the latest source of LLVM or in the documentation [here](http://llvm.org/docs/Atomics.html#libcalls-atomic).

fixes https://github.com/rust-lang/miri/issues/1574

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -146,12 +146,12 @@ macro atomic_minmax($fx:expr, $cc:expr, <$T:ident> ($ptr:ident, $src:ident) -> $
 
 macro validate_atomic_type($fx:ident, $intrinsic:ident, $span:ident, $ty:expr) {
     match $ty.kind() {
-        ty::Uint(_) | ty::Int(_) => {}
+        ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
         _ => {
             $fx.tcx.sess.span_err(
                 $span,
                 &format!(
-                    "`{}` intrinsic: expected basic integer type, found `{:?}`",
+                    "`{}` intrinsic: expected basic integer or raw pointer type, found `{:?}`",
                     $intrinsic, $ty
                 ),
             );

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -437,16 +437,20 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 match split[1] {
                     "cxchg" | "cxchgweak" => {
                         let ty = substs.type_at(0);
-                        if int_type_width_signed(ty, bx.tcx()).is_some() {
+                        if int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_unsafe_ptr() {
                             let weak = split[1] == "cxchgweak";
-                            let pair = bx.atomic_cmpxchg(
+                            let mut dst = args[0].immediate();
-                                args[0].immediate(),
+                            let mut cmp = args[1].immediate();
-                                args[1].immediate(),
+                            let mut src = args[2].immediate();
-                                args[2].immediate(),
+                            if ty.is_unsafe_ptr() {
-                                order,
+                                // Some platforms do not support atomic operations on pointers,
-                                failorder,
+                                // so we cast to integer first.
-                                weak,
+                                let ptr_llty = bx.type_ptr_to(bx.type_isize());
-                            );
+                                dst = bx.pointercast(dst, ptr_llty);
+                                cmp = bx.ptrtoint(cmp, bx.type_isize());
+                                src = bx.ptrtoint(src, bx.type_isize());
+                            }
+                            let pair = bx.atomic_cmpxchg(dst, cmp, src, order, failorder, weak);
                             let val = bx.extract_value(pair, 0);
                             let success = bx.extract_value(pair, 1);
                             let val = bx.from_immediate(val);
@@ -464,9 +468,23 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                     "load" => {
                         let ty = substs.type_at(0);
-                        if int_type_width_signed(ty, bx.tcx()).is_some() {
+                        if int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_unsafe_ptr() {
-                            let size = bx.layout_of(ty).size;
+                            let layout = bx.layout_of(ty);
-                            bx.atomic_load(args[0].immediate(), order, size)
+                            let size = layout.size;
+                            let mut source = args[0].immediate();
+                            if ty.is_unsafe_ptr() {
+                                // Some platforms do not support atomic operations on pointers,
+                                // so we cast to integer first...
+                                let ptr_llty = bx.type_ptr_to(bx.type_isize());
+                                source = bx.pointercast(source, ptr_llty);
+                            }
+                            let result = bx.atomic_load(source, order, size);
+                            if ty.is_unsafe_ptr() {
+                                // ... and then cast the result back to a pointer
+                                bx.inttoptr(result, bx.backend_type(layout))
+                            } else {
+                                result
+                            }
                         } else {
                             return invalid_monomorphization(ty);
                         }
@@ -474,9 +492,18 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                     "store" => {
                         let ty = substs.type_at(0);
-                        if int_type_width_signed(ty, bx.tcx()).is_some() {
+                        if int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_unsafe_ptr() {
                             let size = bx.layout_of(ty).size;
-                            bx.atomic_store(args[1].immediate(), args[0].immediate(), order, size);
+                            let mut val = args[1].immediate();
+                            let mut ptr = args[0].immediate();
+                            if ty.is_unsafe_ptr() {
+                                // Some platforms do not support atomic operations on pointers,
+                                // so we cast to integer first.
+                                let ptr_llty = bx.type_ptr_to(bx.type_isize());
+                                ptr = bx.pointercast(ptr, ptr_llty);
+                                val = bx.ptrtoint(val, bx.type_isize());
+                            }
+                            bx.atomic_store(val, ptr, order, size);
                             return;
                         } else {
                             return invalid_monomorphization(ty);

library/core/src/sync/atomic.rs

@@ -966,8 +966,16 @@ impl<T> AtomicPtr<T> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn load(&self, order: Ordering) -> *mut T {
+        #[cfg(not(bootstrap))]
         // SAFETY: data races are prevented by atomic intrinsics.
-        unsafe { atomic_load(self.p.get() as *mut usize, order) as *mut T }
+        unsafe {
+            atomic_load(self.p.get(), order)
+        }
+        #[cfg(bootstrap)]
+        // SAFETY: data races are prevented by atomic intrinsics.
+        unsafe {
+            atomic_load(self.p.get() as *mut usize, order) as *mut T
+        }
     }
 
     /// Stores a value into the pointer.
@@ -994,6 +1002,12 @@ impl<T> AtomicPtr<T> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn store(&self, ptr: *mut T, order: Ordering) {
+        #[cfg(not(bootstrap))]
+        // SAFETY: data races are prevented by atomic intrinsics.
+        unsafe {
+            atomic_store(self.p.get(), ptr, order);
+        }
+        #[cfg(bootstrap)]
         // SAFETY: data races are prevented by atomic intrinsics.
         unsafe {
             atomic_store(self.p.get() as *mut usize, ptr as usize, order);
@@ -1105,6 +1119,7 @@ impl<T> AtomicPtr<T> {
         success: Ordering,
         failure: Ordering,
     ) -> Result<*mut T, *mut T> {
+        #[cfg(bootstrap)]
         // SAFETY: data races are prevented by atomic intrinsics.
         unsafe {
             let res = atomic_compare_exchange(
@@ -1119,6 +1134,11 @@ impl<T> AtomicPtr<T> {
                 Err(x) => Err(x as *mut T),
             }
         }
+        #[cfg(not(bootstrap))]
+        // SAFETY: data races are prevented by atomic intrinsics.
+        unsafe {
+            atomic_compare_exchange(self.p.get(), current, new, success, failure)
+        }
     }
 
     /// Stores a value into the pointer if the current value is the same as the `current` value.
@@ -1165,6 +1185,7 @@ impl<T> AtomicPtr<T> {
         success: Ordering,
         failure: Ordering,
     ) -> Result<*mut T, *mut T> {
+        #[cfg(bootstrap)]
         // SAFETY: data races are prevented by atomic intrinsics.
         unsafe {
             let res = atomic_compare_exchange_weak(
@@ -1179,6 +1200,14 @@ impl<T> AtomicPtr<T> {
                 Err(x) => Err(x as *mut T),
             }
         }
+        #[cfg(not(bootstrap))]
+        // SAFETY: This intrinsic is unsafe because it operates on a raw pointer
+        // but we know for sure that the pointer is valid (we just got it from
+        // an `UnsafeCell` that we have by reference) and the atomic operation
+        // itself allows us to safely mutate the `UnsafeCell` contents.
+        unsafe {
+            atomic_compare_exchange_weak(self.p.get(), current, new, success, failure)
+        }
     }
 
     /// Fetches the value, and applies a function to it that returns an optional

library/std/src/sys/windows/thread_local_key.rs

@@ -110,16 +110,6 @@ struct Node {
     next: *mut Node,
 }
 
-#[cfg(miri)]
-extern "Rust" {
-    /// Miri-provided extern function to mark the block `ptr` points to as a "root"
-    /// for some static memory. This memory and everything reachable by it is not
-    /// considered leaking even if it still exists when the program terminates.
-    ///
-    /// `ptr` has to point to the beginning of an allocated block.
-    fn miri_static_root(ptr: *const u8);
-}
-
 unsafe fn register_dtor(key: Key, dtor: Dtor) {
     let mut node = Box::new(Node { key, dtor, next: ptr::null_mut() });
 
@@ -128,9 +118,6 @@ unsafe fn register_dtor(key: Key, dtor: Dtor) {
         node.next = head;
         match DTORS.compare_exchange(head, &mut *node, SeqCst, SeqCst) {
             Ok(_) => {
-                #[cfg(miri)]
-                miri_static_root(&*node as *const _ as *const u8);
-
                 mem::forget(node);
                 return;
             }