rustup; ptr atomics

Author: RalfJung

rust-version

@@ -1 +1 @@
-049308cf8b48e9d67e54d6d0b01c10c79d1efc3a
+7665c3543079ebc3710b676d0fd6951bedfd4b29

src/helpers.rs

@@ -195,9 +195,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
     /// Test if this pointer equals 0.
     fn ptr_is_null(&self, ptr: Pointer<Option<Tag>>) -> InterpResult<'tcx, bool> {
-        let this = self.eval_context_ref();
-        let null = Scalar::null_ptr(this);
-        this.ptr_eq(Scalar::from_maybe_pointer(ptr, this), null)
+        Ok(ptr.addr().bytes() == 0)
     }
 
     /// Get the `Place` for a local

src/operator.rs

@@ -1,6 +1,7 @@
 use log::trace;
 
 use rustc_middle::{mir, ty::Ty};
+use rustc_target::abi::Size;
 
 use crate::*;
 
@@ -11,8 +12,6 @@ pub trait EvalContextExt<'tcx> {
         left: &ImmTy<'tcx, Tag>,
         right: &ImmTy<'tcx, Tag>,
     ) -> InterpResult<'tcx, (Scalar<Tag>, bool, Ty<'tcx>)>;
-
-    fn ptr_eq(&self, left: Scalar<Tag>, right: Scalar<Tag>) -> InterpResult<'tcx, bool>;
 }
 
 impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
@@ -27,23 +26,8 @@ impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
         trace!("ptr_op: {:?} {:?} {:?}", *left, bin_op, *right);
 
         Ok(match bin_op {
-            Eq | Ne => {
-                // This supports fat pointers.
-                #[rustfmt::skip]
-                let eq = match (**left, **right) {
-                    (Immediate::Scalar(left), Immediate::Scalar(right)) => {
-                        self.ptr_eq(left.check_init()?, right.check_init()?)?
-                    }
-                    (Immediate::ScalarPair(left1, left2), Immediate::ScalarPair(right1, right2)) => {
-                        self.ptr_eq(left1.check_init()?, right1.check_init()?)?
-                            && self.ptr_eq(left2.check_init()?, right2.check_init()?)?
-                    }
-                    _ => bug!("Type system should not allow comparing Scalar with ScalarPair"),
-                };
-                (Scalar::from_bool(if bin_op == Eq { eq } else { !eq }), false, self.tcx.types.bool)
-            }
-
-            Lt | Le | Gt | Ge => {
+            Eq | Ne | Lt | Le | Gt | Ge => {
+                assert_eq!(left.layout.abi, right.layout.abi); // types an differ, e.g. fn ptrs with different `for`
                 let size = self.pointer_size();
                 // Just compare the bits. ScalarPairs are compared lexicographically.
                 // We thus always compare pairs and simply fill scalars up with 0.
@@ -58,35 +42,49 @@ impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
                         (r1.check_init()?.to_bits(size)?, r2.check_init()?.to_bits(size)?),
                 };
                 let res = match bin_op {
+                    Eq => left == right,
+                    Ne => left != right,
                     Lt => left < right,
                     Le => left <= right,
                     Gt => left > right,
                     Ge => left >= right,
-                    _ => bug!("We already established it has to be one of these operators."),
+                    _ => bug!(),
                 };
                 (Scalar::from_bool(res), false, self.tcx.types.bool)
             }
 
             Offset => {
+                assert!(left.layout.ty.is_unsafe_ptr());
+                let ptr = self.scalar_to_ptr(left.to_scalar()?)?;
+                let offset = right.to_scalar()?.to_machine_isize(self)?;
+
                 let pointee_ty =
                     left.layout.ty.builtin_deref(true).expect("Offset called on non-ptr type").ty;
-                let ptr = self.ptr_offset_inbounds(
-                    self.scalar_to_ptr(left.to_scalar()?)?,
-                    pointee_ty,
-                    right.to_scalar()?.to_machine_isize(self)?,
-                )?;
+                let ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset)?;
                 (Scalar::from_maybe_pointer(ptr, self), false, left.layout.ty)
             }
 
-            _ => bug!("Invalid operator on pointers: {:?}", bin_op),
-        })
-    }
+            // Some more operations are possible with atomics.
+            // The return value always has the provenance of the *left* operand.
+            Add | Sub | BitOr | BitAnd | BitXor => {
+                assert!(left.layout.ty.is_unsafe_ptr());
+                assert!(right.layout.ty.is_unsafe_ptr());
+                let ptr = self.scalar_to_ptr(left.to_scalar()?)?;
+                // We do the actual operation with usize-typed scalars.
+                let left = ImmTy::from_uint(ptr.addr().bytes(), self.machine.layouts.usize);
+                let right = ImmTy::from_uint(
+                    right.to_scalar()?.to_machine_usize(self)?,
+                    self.machine.layouts.usize,
+                );
+                let (result, overflowing, _ty) =
+                    self.overflowing_binary_op(bin_op, &left, &right)?;
+                // Construct a new pointer with the provenance of `ptr` (the LHS).
+                let result_ptr =
+                    Pointer::new(ptr.provenance, Size::from_bytes(result.to_machine_usize(self)?));
+                (Scalar::from_maybe_pointer(result_ptr, self), overflowing, left.layout.ty)
+            }
 
-    fn ptr_eq(&self, left: Scalar<Tag>, right: Scalar<Tag>) -> InterpResult<'tcx, bool> {
-        let size = self.pointer_size();
-        // Just compare the integers.
-        let left = left.to_bits(size)?;
-        let right = right.to_bits(size)?;
-        Ok(left == right)
+            _ => span_bug!(self.cur_span(), "Invalid operator on pointers: {:?}", bin_op),
+        })
     }
 }

src/shims/intrinsics.rs

@@ -314,7 +314,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                     ty::Float(FloatTy::F64) =>
                         this.float_to_int_unchecked(val.to_scalar()?.to_f64()?, dest.layout.ty)?,
                     _ =>
-                        bug!(
+                        span_bug!(
+                            this.cur_span(),
                             "`float_to_int_unchecked` called with non-float input type {:?}",
                             val.layout.ty
                         ),
@@ -371,7 +372,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                         Op::Abs => {
                             // Works for f32 and f64.
                             let ty::Float(float_ty) = op.layout.ty.kind() else {
-                                bug!("{} operand is not a float", intrinsic_name)
+                                span_bug!(this.cur_span(), "{} operand is not a float", intrinsic_name)
                             };
                             let op = op.to_scalar()?;
                             match float_ty {
@@ -381,7 +382,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                         }
                         Op::HostOp(host_op) => {
                             let ty::Float(float_ty) = op.layout.ty.kind() else {
-                                bug!("{} operand is not a float", intrinsic_name)
+                                span_bug!(this.cur_span(), "{} operand is not a float", intrinsic_name)
                             };
                             // FIXME using host floats
                             match float_ty {
@@ -546,7 +547,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
                     // Works for f32 and f64.
                     let ty::Float(float_ty) = dest.layout.ty.kind() else {
-                        bug!("{} operand is not a float", intrinsic_name)
+                        span_bug!(this.cur_span(), "{} operand is not a float", intrinsic_name)
                     };
                     let val = match float_ty {
                         FloatTy::F32 =>
@@ -763,7 +764,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
                 // `index` is an array, not a SIMD type
                 let ty::Array(_, index_len) = index.layout.ty.kind() else {
-                    bug!("simd_shuffle index argument has non-array type {}", index.layout.ty)
+                    span_bug!(this.cur_span(), "simd_shuffle index argument has non-array type {}", index.layout.ty)
                 };
                 let index_len = index_len.eval_usize(*this.tcx, this.param_env());
 
@@ -785,10 +786,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                             &this.mplace_index(&right, src_index - left_len)?.into(),
                         )?
                     } else {
-                        bug!(
-                            "simd_shuffle index {} is out of bounds for 2 vectors of size {}",
-                            src_index,
-                            left_len
+                        span_bug!(
+                            this.cur_span(),
+                            "simd_shuffle index {src_index} is out of bounds for 2 vectors of size {left_len}",
                         );
                     };
                     this.write_immediate(*val, &dest.into())?;
@@ -1187,8 +1187,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let [place, rhs] = check_arg_count(args)?;
         let place = this.deref_operand(place)?;
 
-        if !place.layout.ty.is_integral() {
-            bug!("Atomic arithmetic operations only work on integer types");
+        if !place.layout.ty.is_integral() && !place.layout.ty.is_unsafe_ptr() {
+            span_bug!(
+                this.cur_span(),
+                "atomic arithmetic operations only work on integer and raw pointer types",
+            );
         }
         let rhs = this.read_immediate(rhs)?;
 
@@ -1355,7 +1358,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 }
             }
             // Nothing else
-            _ => bug!("`float_to_int_unchecked` called with non-int output type {dest_ty:?}"),
+            _ =>
+                span_bug!(
+                    this.cur_span(),
+                    "`float_to_int_unchecked` called with non-int output type {dest_ty:?}"
+                ),
         })
     }
 }

tests/pass/atomic.rs

@@ -1,10 +1,15 @@
-use std::sync::atomic::{compiler_fence, fence, AtomicBool, AtomicIsize, AtomicU64, Ordering::*};
+// compile-flags: -Zmiri-strict-provenance
+#![feature(strict_provenance, strict_provenance_atomic_ptr)]
+use std::sync::atomic::{
+    compiler_fence, fence, AtomicBool, AtomicIsize, AtomicPtr, AtomicU64, Ordering::*,
+};
 
 fn main() {
     atomic_bool();
     atomic_all_ops();
     atomic_u64();
     atomic_fences();
+    atomic_ptr();
     weak_sometimes_fails();
 }
 
@@ -130,6 +135,54 @@ fn atomic_fences() {
     compiler_fence(AcqRel);
 }
 
+fn atomic_ptr() {
+    use std::ptr;
+    let array: Vec<i32> = (0..100).into_iter().collect(); // a target to point to, to test provenance things
+    let x = array.as_ptr() as *mut i32;
+
+    let ptr = AtomicPtr::<i32>::new(ptr::null_mut());
+    assert!(ptr.load(Relaxed).addr() == 0);
+    ptr.store(ptr::invalid_mut(13), SeqCst);
+    assert!(ptr.swap(x, Relaxed).addr() == 13);
+    unsafe { assert!(*ptr.load(Acquire) == 0) };
+
+    // comparison ignores provenance
+    assert_eq!(
+        ptr.compare_exchange(
+            (&mut 0 as *mut i32).with_addr(x.addr()),
+            ptr::invalid_mut(0),
+            SeqCst,
+            SeqCst
+        )
+        .unwrap()
+        .addr(),
+        x.addr(),
+    );
+    assert_eq!(
+        ptr.compare_exchange(
+            (&mut 0 as *mut i32).with_addr(x.addr()),
+            ptr::invalid_mut(0),
+            SeqCst,
+            SeqCst
+        )
+        .unwrap_err()
+        .addr(),
+        0,
+    );
+    ptr.store(x, Relaxed);
+
+    assert_eq!(ptr.fetch_ptr_add(13, AcqRel).addr(), x.addr());
+    unsafe { assert_eq!(*ptr.load(SeqCst), 13) }; // points to index 13 now
+    assert_eq!(ptr.fetch_ptr_sub(4, AcqRel).addr(), x.addr() + 13 * 4);
+    unsafe { assert_eq!(*ptr.load(SeqCst), 9) };
+    assert_eq!(ptr.fetch_or(3, AcqRel).addr(), x.addr() + 9 * 4); // ptr is 4-aligned, so set the last 2 bits
+    assert_eq!(ptr.fetch_and(!3, AcqRel).addr(), (x.addr() + 9 * 4) | 3); // and unset them again
+    unsafe { assert_eq!(*ptr.load(SeqCst), 9) };
+    assert_eq!(ptr.fetch_xor(0xdeadbeef, AcqRel).addr(), x.addr() + 9 * 4);
+    assert_eq!(ptr.fetch_xor(0xdeadbeef, AcqRel).addr(), (x.addr() + 9 * 4) ^ 0xdeadbeef);
+    unsafe { assert_eq!(*ptr.load(SeqCst), 9) }; // after XORing twice with the same thing, we get our ptr back
+}
+
 fn weak_sometimes_fails() {
     let atomic = AtomicBool::new(false);
     let tries = 100;