Fix codegen for rvalue aggregate raw pointer to an adt with slice tail

kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs

@@ -6,6 +6,7 @@ use crate::codegen_cprover_gotoc::codegen::place::ProjectedPlace;
 use crate::codegen_cprover_gotoc::codegen::ty_stable::pointee_type_stable;
 use crate::codegen_cprover_gotoc::utils::{dynamic_fat_ptr, slice_fat_ptr};
 use crate::codegen_cprover_gotoc::{GotocCtx, VtableCtx};
+use crate::kani_middle::abi::LayoutOf;
 use crate::kani_middle::coercion::{
     CoerceUnsizedInfo, CoerceUnsizedIterator, CoercionBaseStable, extract_unsize_casting_stable,
 };
@@ -710,21 +711,32 @@ impl GotocCtx<'_> {
                         slice_fat_ptr(typ, data_cast, meta, &self.symbol_table)
                     }
                     TyKind::RigidTy(RigidTy::Adt(..)) => {
+                        let layout = LayoutOf::new(pointee_ty);
                         let pointee_goto_typ = self.codegen_ty_stable(pointee_ty);
                         let data_cast =
                             data.cast_to(Type::Pointer { typ: Box::new(pointee_goto_typ) });
-                        let meta = self.codegen_operand_stable(&operands[1]);
-                        if meta.typ().sizeof(&self.symbol_table) == 0 {
-                            data_cast
-                        } else {
-                            let vtable_expr = meta
-                                .member("_vtable_ptr", &self.symbol_table)
-                                .member("pointer", &self.symbol_table)
-                                .cast_to(
-                                    typ.lookup_field_type("vtable", &self.symbol_table).unwrap(),
-                                );
-                            dynamic_fat_ptr(typ, data_cast, vtable_expr, &self.symbol_table)
-                        }
+                        layout.unsized_tail().map_or(data_cast.clone(), |tail| {
+                            let meta = self.codegen_operand_stable(&operands[1]);
+                            match tail.kind().rigid().unwrap() {
+                                RigidTy::Foreign(..) => data_cast,
+                                RigidTy::Slice(..) | RigidTy::Str => {
+                                    slice_fat_ptr(typ, data_cast, meta, &self.symbol_table)
+                                }
+                                RigidTy::Dynamic(..) => {
+                                    let vtable_expr = meta
+                                        .member("_vtable_ptr", &self.symbol_table)
+                                        .member("pointer", &self.symbol_table)
+                                        .cast_to(
+                                            typ.lookup_field_type("vtable", &self.symbol_table)
+                                                .unwrap(),
+                                        );
+                                    dynamic_fat_ptr(typ, data_cast, vtable_expr, &self.symbol_table)
+                                }
+                                _ => {
+                                    unreachable!("Unexpected unsized tail: {tail:?}");
+                                }
+                            }
+                        })
                     }
                     TyKind::RigidTy(RigidTy::Dynamic(..)) => {
                         let pointee_goto_typ = self.codegen_ty_stable(pointee_ty);

kani-compiler/src/codegen_cprover_gotoc/codegen/typ.rs

@@ -1571,14 +1571,11 @@ impl<'tcx> GotocCtx<'tcx> {
             return None;
         }
 
-        let mut typ = struct_type;
-        while let ty::Adt(adt_def, adt_args) = typ.kind() {
-            assert_eq!(adt_def.variants().len(), 1, "Expected a single-variant ADT. Found {typ:?}");
-            let fields = &adt_def.variants().get(VariantIdx::from_u32(0)).unwrap().fields;
-            let last_field = fields.last_index().expect("Trait should be the last element.");
-            typ = fields[last_field].ty(self.tcx, adt_args);
-        }
-        if typ.is_trait() { Some(typ) } else { None }
+        let ty = rustc_internal::stable(struct_type);
+        rustc_internal::internal(
+            self.tcx,
+            crate::kani_middle::abi::LayoutOf::new(ty).unsized_tail(),
+        )
     }
 
     /// This function provides an iterator that traverses the data path of a receiver type. I.e.:

kani-compiler/src/kani_middle/abi.rs

@@ -0,0 +1,194 @@
+// Copyright Kani Contributors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+//! This module contains code for handling type abi information.
+
+use stable_mir::abi::{FieldsShape, LayoutShape};
+use stable_mir::ty::{RigidTy, Ty, TyKind, UintTy};
+use tracing::debug;
+
+/// A struct to encapsulate the layout information for a given type
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct LayoutOf {
+    ty: Ty,
+    layout: LayoutShape,
+}
+
+#[allow(dead_code)] // TODO: Remove this in https://github.com/model-checking/kani/pull/3687
+impl LayoutOf {
+    /// Create the layout structure for the given type
+    pub fn new(ty: Ty) -> LayoutOf {
+        LayoutOf { ty, layout: ty.layout().unwrap().shape() }
+    }
+
+    /// Return whether the type is sized.
+    pub fn is_sized(&self) -> bool {
+        self.layout.is_sized()
+    }
+
+    /// Return whether the type is unsized and its tail is a foreign item.
+    ///
+    /// This will also return `true` if the type is foreign.
+    pub fn has_foreign_tail(&self) -> bool {
+        self.unsized_tail()
+            .map_or(false, |t| matches!(t.kind(), TyKind::RigidTy(RigidTy::Foreign(_))))
+    }
+
+    /// Return whether the type is unsized and its tail is a trait object.
+    pub fn has_trait_tail(&self) -> bool {
+        self.unsized_tail().map_or(false, |t| t.kind().is_trait())
+    }
+
+    /// Return whether the type is unsized and its tail is a slice.
+    #[allow(dead_code)]
+    pub fn has_slice_tail(&self) -> bool {
+        self.unsized_tail().map_or(false, |tail| {
+            let kind = tail.kind();
+            kind.is_slice() | kind.is_str()
+        })
+    }
+
+    /// Return the unsized tail of the type if this is an unsized type.
+    ///
+    /// For foreign types, return None.
+    /// For unsized types, this should return either a slice, a string slice, a dynamic type.
+    /// For other types, this function will return `None`.
+    pub fn unsized_tail(&self) -> Option<Ty> {
+        if self.layout.is_unsized() {
+            match self.ty.kind().rigid().unwrap() {
+                RigidTy::Slice(..) | RigidTy::Dynamic(..) | RigidTy::Str => Some(self.ty),
+                RigidTy::Adt(..) | RigidTy::Tuple(..) => {
+                    // Recurse the tail field type until we find the unsized tail.
+                    self.last_field_layout().unsized_tail()
+                }
+                RigidTy::Foreign(_) => Some(self.ty),
+                _ => unreachable!("Expected unsized type but found `{}`", self.ty),
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Return the type of the elements of the array or slice at the unsized tail of this type.
+    ///
+    /// For sized types and trait unsized type, this function will return `None`.
+    pub fn unsized_tail_elem_ty(&self) -> Option<Ty> {
+        self.unsized_tail().and_then(|tail| match tail.kind().rigid().unwrap() {
+            RigidTy::Slice(elem_ty) => Some(*elem_ty),
+            // String slices have the same layout as slices of u8.
+            // https://doc.rust-lang.org/reference/type-layout.html#str-layout
+            RigidTy::Str => Some(Ty::unsigned_ty(UintTy::U8)),
+            _ => None,
+        })
+    }
+
+    /// Return the size of the sized portion of this type.
+    ///
+    /// For a sized type, this function will return the size of the type.
+    /// For an unsized type, this function will return the size of the sized portion including
+    /// any padding bytes that lead to the unsized field.
+    /// I.e.: the size of the type, excluding the trailing unsized portion.
+    ///
+    /// For example, this function will return 2 as the sized portion of `*const (u8,  [u16])`:
+    pub fn size_of_head(&self) -> usize {
+        if self.is_sized() {
+            self.layout.size.bytes()
+        } else {
+            match self.ty.kind().rigid().unwrap() {
+                RigidTy::Slice(_) | RigidTy::Str | RigidTy::Dynamic(..) | RigidTy::Foreign(..) => 0,
+                RigidTy::Adt(..) | RigidTy::Tuple(..) => {
+                    let fields_sorted = self.layout.fields.fields_by_offset_order();
+                    let last = *fields_sorted.last().unwrap();
+                    let FieldsShape::Arbitrary { ref offsets } = self.layout.fields else {
+                        unreachable!()
+                    };
+
+                    // We compute the size of the sized portion by taking the position of the
+                    // last element + the sized portion of that element.
+                    let unsized_offset_unadjusted = offsets[last].bytes();
+                    debug!(ty=?self.ty, ?unsized_offset_unadjusted, "size_of_sized_portion");
+                    unsized_offset_unadjusted + self.last_field_layout().size_of_head()
+                }
+                _ => {
+                    unreachable!("Expected sized type, but found: `{}`", self.ty)
+                }
+            }
+        }
+    }
+
+    /// Return the alignment of the fields that are sized from the head of the object.
+    ///
+    /// For a sized type, this function will return the alignment of the type.
+    ///
+    /// For an unsized type, this function will return the alignment of the sized portion.
+    /// The alignment of the type will be the maximum of the alignment of the sized portion
+    /// and the alignment of the unsized portion.
+    ///
+    /// If there's no sized portion, this function will return the minimum alignment (i.e.: 1).
+    pub fn align_of_head(&self) -> usize {
+        if self.is_sized() {
+            self.layout.abi_align.try_into().unwrap()
+        } else {
+            match self.ty.kind().rigid().unwrap() {
+                RigidTy::Slice(_) | RigidTy::Str | RigidTy::Dynamic(..) | RigidTy::Foreign(..) => 1,
+                RigidTy::Adt(..) | RigidTy::Tuple(..) => {
+                    // We have to recurse and get the maximum alignment of all sized portions.
+                    let field_layout = self.last_field_layout();
+                    field_layout.align_of_head().max(self.layout.abi_align.try_into().unwrap())
+                }
+                _ => {
+                    unreachable!("Expected sized type, but found: `{}`", self.ty);
+                }
+            }
+        }
+    }
+
+    /// Return the size of the type if it's known at compilation type.
+    pub fn size_of(&self) -> Option<usize> {
+        if self.is_sized() { Some(self.layout.size.bytes()) } else { None }
+    }
+
+    /// Return the alignment of the type if it's know at compilation time.
+    ///
+    /// The alignment is known at compilation type for sized types and types with slice tail.
+    ///
+    /// Note: We assume u64 and usize are the same since Kani is only supported in 64bits machines.
+    /// Add a configuration in case we ever decide to port this to a 32-bits machine.
+    #[cfg(target_pointer_width = "64")]
+    pub fn align_of(&self) -> Option<usize> {
+        if self.is_sized() || self.has_slice_tail() {
+            self.layout.abi_align.try_into().ok()
+        } else {
+            None
+        }
+    }
+
+    /// Return the layout of the last field of the type.
+    ///
+    /// This function is used to get the layout of the last field of an unsized type.
+    /// For example, if we have `*const (u8, [u16])`, the last field is `[u16]`.
+    /// This function will return the layout of `[u16]`.
+    ///
+    /// If the type is not a struct, an enum, or a tuple, with at least one field, this function
+    /// will panic.
+    fn last_field_layout(&self) -> LayoutOf {
+        match self.ty.kind().rigid().unwrap() {
+            RigidTy::Adt(adt_def, adt_args) => {
+                let fields = adt_def.variants_iter().next().unwrap().fields();
+                let fields_sorted = self.layout.fields.fields_by_offset_order();
+                let last_field_idx = *fields_sorted.last().unwrap();
+                LayoutOf::new(fields[last_field_idx].ty_with_args(adt_args))
+            }
+            RigidTy::Tuple(tys) => {
+                // For tuples, the unsized field is currently the last declared.
+                // To be on the safe side, we still get the sorted list by offset order.
+                let fields_sorted = self.layout.fields.fields_by_offset_order();
+                let last_field_idx = *fields_sorted.last().unwrap();
+                let last_ty = tys[last_field_idx];
+                LayoutOf::new(last_ty)
+            }
+            _ => {
+                unreachable!("Expected struct, enum or tuple. Found: `{}`", self.ty);
+            }
+        }
+    }
+}

kani-compiler/src/kani_middle/mod.rs

@@ -26,6 +26,7 @@ use std::ops::ControlFlow;
 
 use self::attributes::KaniAttributes;
 
+pub mod abi;
 pub mod analysis;
 pub mod attributes;
 pub mod codegen_units;

tests/kani/AggregateRvalue/slice_ptr.rs

@@ -0,0 +1,58 @@
+// Copyright Kani Contributors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+// Test codegen for a raw pointer to a struct whose last field is a slice
+
+#![feature(layout_for_ptr)]
+#![feature(ptr_metadata)]
+
+// https://github.com/model-checking/kani/issues/3615
+mod issue_3615 {
+    use std::ptr;
+
+    #[derive(Clone, Copy, kani::Arbitrary)]
+    struct Wrapper<T: ?Sized> {
+        _size: usize,
+        _value: T,
+    }
+
+    #[kani::proof]
+    pub fn from_raw_parts_for_slices() {
+        let var: Wrapper<[u64; 4]> = kani::any();
+        let fat_ptr: *const Wrapper<[u64]> = &var as *const _;
+        let (thin_ptr, _) = fat_ptr.to_raw_parts();
+        let new_size: usize = kani::any();
+        let _new_ptr: *const Wrapper<[u64]> = ptr::from_raw_parts(thin_ptr, new_size);
+    }
+
+    #[kani::proof]
+    pub fn from_raw_parts_for_slices_nested() {
+        let var: Wrapper<Wrapper<[u8; 4]>> = kani::any();
+        let fat_ptr: *const Wrapper<Wrapper<[u8]>> = &var as *const _;
+        let (thin_ptr, _) = fat_ptr.to_raw_parts();
+        let new_size: usize = kani::any();
+        let _new_ptr: *const Wrapper<Wrapper<[u8]>> = ptr::from_raw_parts(thin_ptr, new_size);
+    }
+}
+
+// https://github.com/model-checking/kani/issues/3638
+mod issue_3638 {
+    use std::ptr::NonNull;
+
+    #[derive(kani::Arbitrary)]
+    struct Wrapper<T: ?Sized>(usize, T);
+
+    #[cfg(kani)]
+    #[kani::proof]
+    fn slice_from_raw() {
+        // Create a SampleSlice object from SampleStruct
+        let original: Wrapper<[u8; 10]> = kani::any();
+        let slice: &Wrapper<[u8]> = &original;
+
+        // Get the raw data pointer and metadata for the slice object
+        let slice_ptr = NonNull::new(slice as *const _ as *mut ()).unwrap();
+        let metadata = std::ptr::metadata(slice);
+
+        // Create NonNull<[u8]> from the data pointer and metadata
+        let _: NonNull<Wrapper<[u8]>> = NonNull::from_raw_parts(slice_ptr, metadata);
+    }
+}