1 use std::convert::TryFrom;
3 use rustc_middle::mir::interpret::{InterpResult, Pointer, PointerArithmetic, Scalar};
4 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
5 use rustc_target::abi::{Align, HasDataLayout, LayoutOf, Size};
7 use super::{FnVal, InterpCx, Machine, MemoryKind};
9 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
10 /// Creates a dynamic vtable for the given type and vtable origin. This is used only for
13 /// The `trait_ref` encodes the erased self type. Hence, if we are
14 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
15 /// `trait_ref` would map `T: Trait`.
19 poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
20 ) -> InterpResult<'tcx, Pointer<M::PointerTag>> {
21 trace!("get_vtable(trait_ref={:?})", poly_trait_ref);
23 let (ty, poly_trait_ref) = self.tcx.erase_regions(&(ty, poly_trait_ref));
25 // All vtables must be monomorphic, bail out otherwise.
26 if ty.needs_subst() || poly_trait_ref.needs_subst() {
27 throw_inval!(TooGeneric);
30 if let Some(&vtable) = self.vtables.get(&(ty, poly_trait_ref)) {
31 // This means we guarantee that there are no duplicate vtables, we will
32 // always use the same vtable for the same (Type, Trait) combination.
33 // That's not what happens in rustc, but emulating per-crate deduplication
34 // does not sound like it actually makes anything any better.
38 let methods = if let Some(poly_trait_ref) = poly_trait_ref {
39 let trait_ref = poly_trait_ref.with_self_ty(*self.tcx, ty);
40 let trait_ref = self.tcx.erase_regions(&trait_ref);
42 self.tcx.vtable_methods(trait_ref)
47 let layout = self.layout_of(ty)?;
48 assert!(!layout.is_unsized(), "can't create a vtable for an unsized type");
49 let size = layout.size.bytes();
50 let align = layout.align.abi.bytes();
52 let ptr_size = self.pointer_size();
53 let ptr_align = self.tcx.data_layout.pointer_align.abi;
54 // /////////////////////////////////////////////////////////////////////////////////////////
55 // If you touch this code, be sure to also make the corresponding changes to
56 // `get_vtable` in `rust_codegen_llvm/meth.rs`.
57 // /////////////////////////////////////////////////////////////////////////////////////////
58 let vtable = self.memory.allocate(
59 ptr_size * u64::try_from(methods.len()).unwrap().checked_add(3).unwrap(),
65 let drop = Instance::resolve_drop_in_place(*tcx, ty);
66 let drop = self.memory.create_fn_alloc(FnVal::Instance(drop));
68 // No need to do any alignment checks on the memory accesses below, because we know the
69 // allocation is correctly aligned as we created it above. Also we're only offsetting by
70 // multiples of `ptr_align`, which means that it will stay aligned to `ptr_align`.
71 let vtable_alloc = self.memory.get_raw_mut(vtable.alloc_id)?;
72 vtable_alloc.write_ptr_sized(tcx, vtable, drop.into())?;
74 let size_ptr = vtable.offset(ptr_size, tcx)?;
75 vtable_alloc.write_ptr_sized(tcx, size_ptr, Scalar::from_uint(size, ptr_size).into())?;
76 let align_ptr = vtable.offset(ptr_size * 2, tcx)?;
77 vtable_alloc.write_ptr_sized(tcx, align_ptr, Scalar::from_uint(align, ptr_size).into())?;
79 for (i, method) in methods.iter().enumerate() {
80 if let Some((def_id, substs)) = *method {
81 // resolve for vtable: insert shims where needed
83 ty::Instance::resolve_for_vtable(*tcx, self.param_env, def_id, substs)
84 .ok_or_else(|| err_inval!(TooGeneric))?;
85 let fn_ptr = self.memory.create_fn_alloc(FnVal::Instance(instance));
86 // We cannot use `vtable_allic` as we are creating fn ptrs in this loop.
87 let method_ptr = vtable.offset(ptr_size * (3 + i as u64), tcx)?;
88 self.memory.get_raw_mut(vtable.alloc_id)?.write_ptr_sized(
96 self.memory.mark_immutable(vtable.alloc_id)?;
97 assert!(self.vtables.insert((ty, poly_trait_ref), vtable).is_none());
102 /// Resolves the function at the specified slot in the provided
103 /// vtable. An index of '0' corresponds to the first method
104 /// declared in the trait of the provided vtable.
105 pub fn get_vtable_slot(
107 vtable: Scalar<M::PointerTag>,
109 ) -> InterpResult<'tcx, FnVal<'tcx, M::ExtraFnVal>> {
110 let ptr_size = self.pointer_size();
111 // Skip over the 'drop_ptr', 'size', and 'align' fields.
112 let vtable_slot = vtable.ptr_offset(ptr_size * idx.checked_add(3).unwrap(), self)?;
113 let vtable_slot = self
115 .check_ptr_access(vtable_slot, ptr_size, self.tcx.data_layout.pointer_align.abi)?
116 .expect("cannot be a ZST");
119 .get_raw(vtable_slot.alloc_id)?
120 .read_ptr_sized(self, vtable_slot)?
122 Ok(self.memory.get_fn(fn_ptr)?)
125 /// Returns the drop fn instance as well as the actual dynamic type.
126 pub fn read_drop_type_from_vtable(
128 vtable: Scalar<M::PointerTag>,
129 ) -> InterpResult<'tcx, (ty::Instance<'tcx>, Ty<'tcx>)> {
130 // We don't care about the pointee type; we just want a pointer.
135 self.tcx.data_layout.pointer_size,
136 self.tcx.data_layout.pointer_align.abi,
138 .expect("cannot be a ZST");
140 self.memory.get_raw(vtable.alloc_id)?.read_ptr_sized(self, vtable)?.not_undef()?;
141 // We *need* an instance here, no other kind of function value, to be able
142 // to determine the type.
143 let drop_instance = self.memory.get_fn(drop_fn)?.as_instance()?;
144 trace!("Found drop fn: {:?}", drop_instance);
145 let fn_sig = drop_instance.ty_env(*self.tcx, self.param_env).fn_sig(*self.tcx);
146 let fn_sig = self.tcx.normalize_erasing_late_bound_regions(self.param_env, &fn_sig);
147 // The drop function takes `*mut T` where `T` is the type being dropped, so get that.
148 let args = fn_sig.inputs();
150 throw_ub!(InvalidDropFn(fn_sig));
152 let ty = args[0].builtin_deref(true).ok_or_else(|| err_ub!(InvalidDropFn(fn_sig)))?.ty;
153 Ok((drop_instance, ty))
156 pub fn read_size_and_align_from_vtable(
158 vtable: Scalar<M::PointerTag>,
159 ) -> InterpResult<'tcx, (Size, Align)> {
160 let pointer_size = self.pointer_size();
161 // We check for `size = 3 * ptr_size`, which covers the drop fn (unused here),
162 // the size, and the align (which we read below).
165 .check_ptr_access(vtable, 3 * pointer_size, self.tcx.data_layout.pointer_align.abi)?
166 .expect("cannot be a ZST");
167 let alloc = self.memory.get_raw(vtable.alloc_id)?;
168 let size = alloc.read_ptr_sized(self, vtable.offset(pointer_size, self)?)?.not_undef()?;
169 let size = u64::try_from(self.force_bits(size, pointer_size)?).unwrap();
171 alloc.read_ptr_sized(self, vtable.offset(pointer_size * 2, self)?)?.not_undef()?;
172 let align = u64::try_from(self.force_bits(align, pointer_size)?).unwrap();
174 if size >= self.tcx.data_layout().obj_size_bound() {
177 size is bigger than largest supported object"
180 Ok((Size::from_bytes(size), Align::from_bytes(align).unwrap()))