1 use std::convert::TryFrom;
3 use rustc_middle::mir::interpret::{InterpResult, Pointer, PointerArithmetic, Scalar};
4 use rustc_middle::ty::{self, Instance, Ty};
5 use rustc_target::abi::{Align, LayoutOf, Size};
7 use super::util::ensure_monomorphic_enough;
8 use super::{FnVal, InterpCx, Machine, MemoryKind};
10 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
11 /// Creates a dynamic vtable for the given type and vtable origin. This is used only for
14 /// The `trait_ref` encodes the erased self type. Hence, if we are
15 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
16 /// `trait_ref` would map `T: Trait`.
20 poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
21 ) -> InterpResult<'tcx, Pointer<M::PointerTag>> {
22 trace!("get_vtable(trait_ref={:?})", poly_trait_ref);
24 let (ty, poly_trait_ref) = self.tcx.erase_regions((ty, poly_trait_ref));
26 // All vtables must be monomorphic, bail out otherwise.
27 ensure_monomorphic_enough(*self.tcx, ty)?;
28 ensure_monomorphic_enough(*self.tcx, poly_trait_ref)?;
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();
53 let ptr_size = self.pointer_size();
54 let ptr_align = tcx.data_layout.pointer_align.abi;
55 // /////////////////////////////////////////////////////////////////////////////////////////
56 // If you touch this code, be sure to also make the corresponding changes to
57 // `get_vtable` in `rust_codegen_llvm/meth.rs`.
58 // /////////////////////////////////////////////////////////////////////////////////////////
59 let vtable_size = ptr_size * u64::try_from(methods.len()).unwrap().checked_add(3).unwrap();
60 let vtable = self.memory.allocate(vtable_size, ptr_align, MemoryKind::Vtable);
62 let drop = Instance::resolve_drop_in_place(tcx, ty);
63 let drop = self.memory.create_fn_alloc(FnVal::Instance(drop));
65 // No need to do any alignment checks on the memory accesses below, because we know the
66 // allocation is correctly aligned as we created it above. Also we're only offsetting by
67 // multiples of `ptr_align`, which means that it will stay aligned to `ptr_align`.
68 let vtable_alloc = self.memory.get_raw_mut(vtable.alloc_id)?;
69 vtable_alloc.write_ptr_sized(&tcx, vtable, drop.into())?;
71 let size_ptr = vtable.offset(ptr_size, &tcx)?;
72 vtable_alloc.write_ptr_sized(&tcx, size_ptr, Scalar::from_uint(size, ptr_size).into())?;
73 let align_ptr = vtable.offset(ptr_size * 2, &tcx)?;
74 vtable_alloc.write_ptr_sized(&tcx, align_ptr, Scalar::from_uint(align, ptr_size).into())?;
76 for (i, method) in methods.iter().enumerate() {
77 if let Some((def_id, substs)) = *method {
78 // resolve for vtable: insert shims where needed
80 ty::Instance::resolve_for_vtable(tcx, self.param_env, def_id, substs)
81 .ok_or_else(|| err_inval!(TooGeneric))?;
82 let fn_ptr = self.memory.create_fn_alloc(FnVal::Instance(instance));
83 // We cannot use `vtable_allic` as we are creating fn ptrs in this loop.
84 let method_ptr = vtable.offset(ptr_size * (3 + i as u64), &tcx)?;
85 self.memory.get_raw_mut(vtable.alloc_id)?.write_ptr_sized(
93 M::after_static_mem_initialized(self, vtable, vtable_size)?;
95 self.memory.mark_immutable(vtable.alloc_id)?;
96 assert!(self.vtables.insert((ty, poly_trait_ref), vtable).is_none());
101 /// Resolves the function at the specified slot in the provided
102 /// vtable. An index of '0' corresponds to the first method
103 /// declared in the trait of the provided vtable.
104 pub fn get_vtable_slot(
106 vtable: Scalar<M::PointerTag>,
108 ) -> InterpResult<'tcx, FnVal<'tcx, M::ExtraFnVal>> {
109 let ptr_size = self.pointer_size();
110 // Skip over the 'drop_ptr', 'size', and 'align' fields.
111 let vtable_slot = vtable.ptr_offset(ptr_size * idx.checked_add(3).unwrap(), self)?;
112 let vtable_slot = self
114 .check_ptr_access(vtable_slot, ptr_size, self.tcx.data_layout.pointer_align.abi)?
115 .expect("cannot be a ZST");
118 .get_raw(vtable_slot.alloc_id)?
119 .read_ptr_sized(self, vtable_slot)?
121 Ok(self.memory.get_fn(fn_ptr)?)
124 /// Returns the drop fn instance as well as the actual dynamic type.
125 pub fn read_drop_type_from_vtable(
127 vtable: Scalar<M::PointerTag>,
128 ) -> InterpResult<'tcx, (ty::Instance<'tcx>, Ty<'tcx>)> {
129 // We don't care about the pointee type; we just want a pointer.
134 self.tcx.data_layout.pointer_size,
135 self.tcx.data_layout.pointer_align.abi,
137 .expect("cannot be a ZST");
139 self.memory.get_raw(vtable.alloc_id)?.read_ptr_sized(self, vtable)?.check_init()?;
140 // We *need* an instance here, no other kind of function value, to be able
141 // to determine the type.
142 let drop_instance = self.memory.get_fn(drop_fn)?.as_instance()?;
143 trace!("Found drop fn: {:?}", drop_instance);
144 let fn_sig = drop_instance.ty(*self.tcx, self.param_env).fn_sig(*self.tcx);
145 let fn_sig = self.tcx.normalize_erasing_late_bound_regions(self.param_env, fn_sig);
146 // The drop function takes `*mut T` where `T` is the type being dropped, so get that.
147 let args = fn_sig.inputs();
149 throw_ub!(InvalidDropFn(fn_sig));
151 let ty = args[0].builtin_deref(true).ok_or_else(|| err_ub!(InvalidDropFn(fn_sig)))?.ty;
152 Ok((drop_instance, ty))
155 pub fn read_size_and_align_from_vtable(
157 vtable: Scalar<M::PointerTag>,
158 ) -> InterpResult<'tcx, (Size, Align)> {
159 let pointer_size = self.pointer_size();
160 // We check for `size = 3 * ptr_size`, which covers the drop fn (unused here),
161 // the size, and the align (which we read below).
164 .check_ptr_access(vtable, 3 * pointer_size, self.tcx.data_layout.pointer_align.abi)?
165 .expect("cannot be a ZST");
166 let alloc = self.memory.get_raw(vtable.alloc_id)?;
167 let size = alloc.read_ptr_sized(self, vtable.offset(pointer_size, self)?)?.check_init()?;
168 let size = u64::try_from(self.force_bits(size, pointer_size)?).unwrap();
170 alloc.read_ptr_sized(self, vtable.offset(pointer_size * 2, self)?)?.check_init()?;
171 let align = u64::try_from(self.force_bits(align, pointer_size)?).unwrap();
173 if size >= self.tcx.data_layout.obj_size_bound() {
176 size is bigger than largest supported object"
179 Ok((Size::from_bytes(size), Align::from_bytes(align).unwrap()))