rust-lang · bors · May 14, 2022 · May 13, 2022
diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -18,7 +18,7 @@ use rustc_target::spec::abi::Abi;
 
 use crate::interpret::{
     self, compile_time_machine, AllocId, ConstAllocation, Frame, ImmTy, InterpCx, InterpResult,
-    OpTy, PlaceTy, Scalar, StackPopUnwind,
+    OpTy, PlaceTy, Pointer, Scalar, StackPopUnwind,
 };
 
 use super::error::*;
@@ -443,6 +443,14 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         Ok(())
     }
 
+    #[inline(always)]
+    fn expose_ptr(
+        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        _ptr: Pointer<AllocId>,
+    ) -> InterpResult<'tcx> {
+        Err(ConstEvalErrKind::NeedsRfc("exposing pointers".to_string()).into())
+    }
+
     #[inline(always)]
     fn init_frame_extra(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,

diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -98,7 +98,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     pub fn misc_cast(
-        &self,
+        &mut self,
         src: &ImmTy<'tcx, M::PointerTag>,
         cast_ty: Ty<'tcx>,
     ) -> InterpResult<'tcx, Immediate<M::PointerTag>> {
@@ -139,7 +139,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 if let Some(discr) = src.layout.ty.discriminant_for_variant(*self.tcx, index) {
                     assert!(src.layout.is_zst());
                     let discr_layout = self.layout_of(discr.ty)?;
-                    return Ok(self.cast_from_int_like(discr.val, discr_layout, cast_ty).into());
+
+                    let scalar = Scalar::from_uint(discr.val, discr_layout.layout.size());
+                    return Ok(self.cast_from_int_like(scalar, discr_layout, cast_ty)?.into());
                 }
             }
             Variants::Multiple { .. } => {}
@@ -170,38 +172,65 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         }
 
         // # The remaining source values are scalar and "int-like".
+        let scalar = src.to_scalar()?;
+
+        // If we are casting from a pointer to something
+        // that is not a pointer, mark the pointer as exposed
+        if src.layout.ty.is_any_ptr() && !cast_ty.is_any_ptr() {
+            let ptr = self.scalar_to_ptr(scalar)?;
+
+            match ptr.into_pointer_or_addr() {
+                Ok(ptr) => {
+                    M::expose_ptr(self, ptr)?;
+                }
+                Err(_) => {
+                    // do nothing, exposing an invalid pointer
+                    // has no meaning
+                }
+            };
+        }
 
-        // For all remaining casts, we either
-        // (a) cast a raw ptr to usize, or
-        // (b) cast from an integer-like (including bool, char, enums).
-        // In both cases we want the bits.
-        let bits = src.to_scalar()?.to_bits(src.layout.size)?;
-        Ok(self.cast_from_int_like(bits, src.layout, cast_ty).into())
+        Ok(self.cast_from_int_like(scalar, src.layout, cast_ty)?.into())
     }
 
-    fn cast_from_int_like(
+    pub fn cast_from_int_like(
         &self,
-        v: u128, // raw bits (there is no ScalarTy so we separate data+layout)
+        scalar: Scalar<M::PointerTag>, // input value (there is no ScalarTy so we separate data+layout)
         src_layout: TyAndLayout<'tcx>,
         cast_ty: Ty<'tcx>,
-    ) -> Scalar<M::PointerTag> {
+    ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
         // Let's make sure v is sign-extended *if* it has a signed type.
         let signed = src_layout.abi.is_signed(); // Also asserts that abi is `Scalar`.
+
+        let v = scalar.to_bits(src_layout.size)?;
         let v = if signed { self.sign_extend(v, src_layout) } else { v };
         trace!("cast_from_scalar: {}, {} -> {}", v, src_layout.ty, cast_ty);
         use rustc_middle::ty::TyKind::*;
-        match *cast_ty.kind() {
-            Int(_) | Uint(_) | RawPtr(_) => {
+
+        Ok(match *cast_ty.kind() {
+            Int(_) | Uint(_) => {
                 let size = match *cast_ty.kind() {
                     Int(t) => Integer::from_int_ty(self, t).size(),
                     Uint(t) => Integer::from_uint_ty(self, t).size(),
-                    RawPtr(_) => self.pointer_size(),
                     _ => bug!(),
                 };
                 let v = size.truncate(v);
                 Scalar::from_uint(v, size)
             }
 
+            RawPtr(_) => {
+                assert!(src_layout.ty.is_integral());
+
+                let size = self.pointer_size();
+                let addr = u64::try_from(size.truncate(v)).unwrap();
+
+                let ptr = M::ptr_from_addr_cast(&self, addr);
+                if addr == 0 {
+                    assert!(ptr.provenance.is_none(), "null pointer can never have an AllocId");
+                }
+                Scalar::from_maybe_pointer(ptr, self)
+            }
+
             Float(FloatTy::F32) if signed => Scalar::from_f32(Single::from_i128(v as i128).value),
             Float(FloatTy::F64) if signed => Scalar::from_f64(Double::from_i128(v as i128).value),
             Float(FloatTy::F32) => Scalar::from_f32(Single::from_u128(v).value),
@@ -214,7 +243,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
             // Casts to bool are not permitted by rustc, no need to handle them here.
             _ => span_bug!(self.cur_span(), "invalid int to {:?} cast", cast_ty),
-        }
+        })
     }
 
     fn cast_from_float<F>(&self, f: F, dest_ty: Ty<'tcx>) -> Scalar<M::PointerTag>

diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -905,7 +905,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             trace!(
                 "deallocating local {:?}: {:?}",
                 local,
-                self.dump_alloc(ptr.provenance.unwrap().get_alloc_id())
+                // Locals always have a `alloc_id` (they are never the result of a int2ptr).
+                self.dump_alloc(ptr.provenance.unwrap().get_alloc_id().unwrap())
             );
             self.deallocate_ptr(ptr, None, MemoryKind::Stack)?;
         };
@@ -1013,9 +1014,13 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> std::fmt::Debug
                     }
                 }
 
-                write!(fmt, ": {:?}", self.ecx.dump_allocs(allocs))
+                write!(
+                    fmt,
+                    ": {:?}",
+                    self.ecx.dump_allocs(allocs.into_iter().filter_map(|x| x).collect())
+                )
             }
-            Place::Ptr(mplace) => match mplace.ptr.provenance.map(Provenance::get_alloc_id) {
+            Place::Ptr(mplace) => match mplace.ptr.provenance.and_then(Provenance::get_alloc_id) {
                 Some(alloc_id) => write!(
                     fmt,
                     "by align({}) ref {:?}: {:?}",

diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -286,19 +286,36 @@ pub trait Machine<'mir, 'tcx>: Sized {
     ) -> Pointer<Self::PointerTag>;
 
     /// "Int-to-pointer cast"
-    fn ptr_from_addr(
+    fn ptr_from_addr_cast(
         ecx: &InterpCx<'mir, 'tcx, Self>,
         addr: u64,
     ) -> Pointer<Option<Self::PointerTag>>;
 
+    // FIXME: Transmuting an integer to a pointer should just always return a `None`
+    // provenance, but that causes problems with function pointers in Miri.
+    /// Hook for returning a pointer from a transmute-like operation on an addr.
+    fn ptr_from_addr_transmute(
+        ecx: &InterpCx<'mir, 'tcx, Self>,
+        addr: u64,
+    ) -> Pointer<Option<Self::PointerTag>>;
+
+    /// Marks a pointer as exposed, allowing it's provenance
+    /// to be recovered. "Pointer-to-int cast"
+    fn expose_ptr(
+        ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        ptr: Pointer<Self::PointerTag>,
+    ) -> InterpResult<'tcx>;
+
     /// Convert a pointer with provenance into an allocation-offset pair
     /// and extra provenance info.
     ///
     /// The returned `AllocId` must be the same as `ptr.provenance.get_alloc_id()`.
+    ///
+    /// When this fails, that means the pointer does not point to a live allocation.
     fn ptr_get_alloc(
         ecx: &InterpCx<'mir, 'tcx, Self>,
         ptr: Pointer<Self::PointerTag>,
-    ) -> (AllocId, Size, Self::TagExtra);
+    ) -> Option<(AllocId, Size, Self::TagExtra)>;
 
     /// Called to initialize the "extra" state of an allocation and make the pointers
     /// it contains (in relocations) tagged.  The way we construct allocations is
@@ -480,17 +497,28 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     }
 
     #[inline(always)]
-    fn ptr_from_addr(_ecx: &InterpCx<$mir, $tcx, Self>, addr: u64) -> Pointer<Option<AllocId>> {
+    fn ptr_from_addr_transmute(
+        _ecx: &InterpCx<$mir, $tcx, Self>,
+        addr: u64,
+    ) -> Pointer<Option<AllocId>> {
+        Pointer::new(None, Size::from_bytes(addr))
+    }
+
+    #[inline(always)]
+    fn ptr_from_addr_cast(
+        _ecx: &InterpCx<$mir, $tcx, Self>,
+        addr: u64,
+    ) -> Pointer<Option<AllocId>> {
         Pointer::new(None, Size::from_bytes(addr))
     }
 
     #[inline(always)]
     fn ptr_get_alloc(
         _ecx: &InterpCx<$mir, $tcx, Self>,
         ptr: Pointer<AllocId>,
-    ) -> (AllocId, Size, Self::TagExtra) {
+    ) -> Option<(AllocId, Size, Self::TagExtra)> {
         // We know `offset` is relative to the allocation, so we can use `into_parts`.
         let (alloc_id, offset) = ptr.into_parts();
-        (alloc_id, offset, ())
+        Some((alloc_id, offset, ()))
     }
 }
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -770,7 +770,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 if reachable.insert(id) {
                     // This is a new allocation, add its relocations to `todo`.
                     if let Some((_, alloc)) = self.memory.alloc_map.get(id) {
-                        todo.extend(alloc.relocations().values().map(|tag| tag.get_alloc_id()));
+                        todo.extend(
+                            alloc.relocations().values().filter_map(|tag| tag.get_alloc_id()),
+                        );
                     }
                 }
             }
@@ -805,7 +807,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> std::fmt::Debug for DumpAllocs<'a,
             allocs_to_print: &mut VecDeque<AllocId>,
             alloc: &Allocation<Tag, Extra>,
         ) -> std::fmt::Result {
-            for alloc_id in alloc.relocations().values().map(|tag| tag.get_alloc_id()) {
+            for alloc_id in alloc.relocations().values().filter_map(|tag| tag.get_alloc_id()) {
                 allocs_to_print.push_back(alloc_id);
             }
             write!(fmt, "{}", display_allocation(tcx, alloc))
@@ -1125,7 +1127,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 Err(ptr) => ptr.into(),
                 Ok(bits) => {
                     let addr = u64::try_from(bits).unwrap();
-                    let ptr = M::ptr_from_addr(&self, addr);
+                    let ptr = M::ptr_from_addr_transmute(&self, addr);
                     if addr == 0 {
                         assert!(ptr.provenance.is_none(), "null pointer can never have an AllocId");
                     }
@@ -1165,10 +1167,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         ptr: Pointer<Option<M::PointerTag>>,
     ) -> Result<(AllocId, Size, M::TagExtra), u64> {
         match ptr.into_pointer_or_addr() {
-            Ok(ptr) => {
-                let (alloc_id, offset, extra) = M::ptr_get_alloc(self, ptr);
-                Ok((alloc_id, offset, extra))
-            }
+            Ok(ptr) => match M::ptr_get_alloc(self, ptr) {
+                Some((alloc_id, offset, extra)) => Ok((alloc_id, offset, extra)),
+                None => {
+                    assert!(M::PointerTag::OFFSET_IS_ADDR);
+                    let (_, addr) = ptr.into_parts();
+                    Err(addr.bytes())
+                }
+            },
             Err(addr) => Err(addr.bytes()),
         }
     }

diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -695,17 +695,18 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Figure out which discriminant and variant this corresponds to.
         Ok(match *tag_encoding {
             TagEncoding::Direct => {
+                let scalar = tag_val.to_scalar()?;
                 // Generate a specific error if `tag_val` is not an integer.
                 // (`tag_bits` itself is only used for error messages below.)
-                let tag_bits = tag_val
-                    .to_scalar()?
+                let tag_bits = scalar
                     .try_to_int()
                     .map_err(|dbg_val| err_ub!(InvalidTag(dbg_val)))?
                     .assert_bits(tag_layout.size);
                 // Cast bits from tag layout to discriminant layout.
-                // After the checks we did above, this cannot fail.
+                // After the checks we did above, this cannot fail, as
+                // discriminants are int-like.
                 let discr_val =
-                    self.misc_cast(&tag_val, discr_layout.ty).unwrap().to_scalar().unwrap();
+                    self.cast_from_int_like(scalar, tag_val.layout, discr_layout.ty).unwrap();
                 let discr_bits = discr_val.assert_bits(discr_layout.size);
                 // Convert discriminant to variant index, and catch invalid discriminants.
                 let index = match *op.layout.ty.kind() {

diff --git a/compiler/rustc_middle/src/mir/interpret/pointer.rs b/compiler/rustc_middle/src/mir/interpret/pointer.rs
@@ -120,9 +120,11 @@ pub trait Provenance: Copy + fmt::Debug {
     where
         Self: Sized;
 
-    /// Provenance must always be able to identify the allocation this ptr points to.
+    /// If `OFFSET_IS_ADDR == false`, provenance must always be able to
+    /// identify the allocation this ptr points to (i.e., this must return `Some`).
+    /// Otherwise this function is best-effort (but must agree with `Machine::ptr_get_alloc`).
     /// (Identifying the offset in that allocation, however, is harder -- use `Memory::ptr_get_alloc` for that.)
-    fn get_alloc_id(self) -> AllocId;
+    fn get_alloc_id(self) -> Option<AllocId>;
 }
 
 impl Provenance for AllocId {
@@ -147,8 +149,8 @@ impl Provenance for AllocId {
         Ok(())
     }
 
-    fn get_alloc_id(self) -> AllocId {
-        self
+    fn get_alloc_id(self) -> Option<AllocId> {
+        Some(self)
     }
 }
 

diff --git a/compiler/rustc_middle/src/mir/interpret/value.rs b/compiler/rustc_middle/src/mir/interpret/value.rs
@@ -344,7 +344,8 @@ impl<'tcx, Tag: Provenance> Scalar<Tag> {
                 } else {
                     // We know `offset` is relative, since `OFFSET_IS_ADDR == false`.
                     let (tag, offset) = ptr.into_parts();
-                    Err(Scalar::Ptr(Pointer::new(tag.get_alloc_id(), offset), sz))
+                    // Because `OFFSET_IS_ADDR == false`, this unwrap can never fail.
+                    Err(Scalar::Ptr(Pointer::new(tag.get_alloc_id().unwrap(), offset), sz))
                 }
             }
         }

diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -28,7 +28,8 @@ use crate::MirPass;
 use rustc_const_eval::interpret::{
     self, compile_time_machine, AllocId, ConstAllocation, ConstValue, CtfeValidationMode, Frame,
     ImmTy, Immediate, InterpCx, InterpResult, LocalState, LocalValue, MemPlace, MemoryKind, OpTy,
-    Operand as InterpOperand, PlaceTy, Scalar, ScalarMaybeUninit, StackPopCleanup, StackPopUnwind,
+    Operand as InterpOperand, PlaceTy, Pointer, Scalar, ScalarMaybeUninit, StackPopCleanup,
+    StackPopUnwind,
 };
 
 /// The maximum number of bytes that we'll allocate space for a local or the return value.
@@ -285,6 +286,14 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
         Ok(())
     }
 
+    #[inline(always)]
+    fn expose_ptr(
+        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        _ptr: Pointer<AllocId>,
+    ) -> InterpResult<'tcx> {
+        throw_machine_stop_str!("exposing pointers isn't supported in ConstProp")
+    }
+
     #[inline(always)]
     fn init_frame_extra(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,

diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs
@@ -30,8 +30,8 @@ use crate::MirLint;
 use rustc_const_eval::const_eval::ConstEvalErr;
 use rustc_const_eval::interpret::{
     self, compile_time_machine, AllocId, ConstAllocation, Frame, ImmTy, InterpCx, InterpResult,
-    LocalState, LocalValue, MemPlace, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy, Scalar,
-    ScalarMaybeUninit, StackPopCleanup, StackPopUnwind,
+    LocalState, LocalValue, MemPlace, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy, Pointer,
+    Scalar, ScalarMaybeUninit, StackPopCleanup, StackPopUnwind,
 };
 
 /// The maximum number of bytes that we'll allocate space for a local or the return value.
@@ -280,6 +280,14 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
         Ok(())
     }
 
+    #[inline(always)]
+    fn expose_ptr(
+        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        _ptr: Pointer<AllocId>,
+    ) -> InterpResult<'tcx> {
+        throw_machine_stop_str!("exposing pointers isn't supported in ConstProp")
+    }
+
     #[inline(always)]
     fn init_frame_extra(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,

diff --git a/src/test/ui/consts/miri_unleashed/ptr_arith.rs b/src/test/ui/consts/miri_unleashed/ptr_arith.rs
@@ -14,7 +14,7 @@ static CMP: () = {
 static PTR_INT_CAST: () = {
     let x = &0 as *const _ as usize;
     //~^ ERROR could not evaluate static initializer
-    //~| unable to turn pointer into raw bytes
+    //~| "exposing pointers" needs an rfc before being allowed inside constants
     let _v = x == x;
 };