1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use rustc::ty::{self, Ty};
12 use rustc::ty::layout::{Size, Align, LayoutOf};
13 use rustc::mir::interpret::{Scalar, Pointer, EvalResult, PointerArithmetic};
15 use super::{EvalContext, Machine, MemoryKind};
17 impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
18 /// Creates a dynamic vtable for the given type and vtable origin. This is used only for
21 /// The `trait_ref` encodes the erased self type. Hence if we are
22 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
23 /// `trait_ref` would map `T:Trait`.
27 poly_trait_ref: ty::PolyExistentialTraitRef<'tcx>,
28 ) -> EvalResult<'tcx, Pointer<M::PointerTag>> {
29 trace!("get_vtable(trait_ref={:?})", poly_trait_ref);
31 let (ty, poly_trait_ref) = self.tcx.erase_regions(&(ty, poly_trait_ref));
33 if let Some(&vtable) = self.vtables.get(&(ty, poly_trait_ref)) {
34 return Ok(Pointer::from(vtable).with_default_tag());
37 let trait_ref = poly_trait_ref.with_self_ty(*self.tcx, ty);
38 let trait_ref = self.tcx.erase_regions(&trait_ref);
40 let methods = self.tcx.vtable_methods(trait_ref);
42 let layout = self.layout_of(ty)?;
43 assert!(!layout.is_unsized(), "can't create a vtable for an unsized type");
44 let size = layout.size.bytes();
45 let align = layout.align.abi.bytes();
47 let ptr_size = self.pointer_size();
48 let ptr_align = self.tcx.data_layout.pointer_align.abi;
49 // /////////////////////////////////////////////////////////////////////////////////////////
50 // If you touch this code, be sure to also make the corresponding changes to
51 // `get_vtable` in rust_codegen_llvm/meth.rs
52 // /////////////////////////////////////////////////////////////////////////////////////////
53 let vtable = self.memory.allocate(
54 ptr_size * (3 + methods.len() as u64),
57 )?.with_default_tag();
60 let drop = ::monomorphize::resolve_drop_in_place(*tcx, ty);
61 let drop = self.memory.create_fn_alloc(drop).with_default_tag();
62 // no need to do any alignment checks on the memory accesses below, because we know the
63 // allocation is correctly aligned as we created it above. Also we're only offsetting by
64 // multiples of `ptr_align`, which means that it will stay aligned to `ptr_align`.
66 .get_mut(vtable.alloc_id)?
67 .write_ptr_sized(tcx, vtable, Scalar::Ptr(drop).into())?;
69 let size_ptr = vtable.offset(ptr_size, self)?;
71 .get_mut(size_ptr.alloc_id)?
72 .write_ptr_sized(tcx, size_ptr, Scalar::from_uint(size, ptr_size).into())?;
73 let align_ptr = vtable.offset(ptr_size * 2, self)?;
75 .get_mut(align_ptr.alloc_id)?
76 .write_ptr_sized(tcx, align_ptr, Scalar::from_uint(align, ptr_size).into())?;
78 for (i, method) in methods.iter().enumerate() {
79 if let Some((def_id, substs)) = *method {
80 let instance = self.resolve(def_id, substs)?;
81 let fn_ptr = self.memory.create_fn_alloc(instance).with_default_tag();
82 let method_ptr = vtable.offset(ptr_size * (3 + i as u64), self)?;
84 .get_mut(method_ptr.alloc_id)?
85 .write_ptr_sized(tcx, method_ptr, Scalar::Ptr(fn_ptr).into())?;
89 self.memory.mark_immutable(vtable.alloc_id)?;
90 assert!(self.vtables.insert((ty, poly_trait_ref), vtable.alloc_id).is_none());
95 /// Return the drop fn instance as well as the actual dynamic type
96 pub fn read_drop_type_from_vtable(
98 vtable: Pointer<M::PointerTag>,
99 ) -> EvalResult<'tcx, (ty::Instance<'tcx>, ty::Ty<'tcx>)> {
100 // we don't care about the pointee type, we just want a pointer
101 self.memory.check_align(vtable.into(), self.tcx.data_layout.pointer_align.abi)?;
102 let drop_fn = self.memory
103 .get(vtable.alloc_id)?
104 .read_ptr_sized(self, vtable)?
106 let drop_instance = self.memory.get_fn(drop_fn)?;
107 trace!("Found drop fn: {:?}", drop_instance);
108 let fn_sig = drop_instance.ty(*self.tcx).fn_sig(*self.tcx);
109 let fn_sig = self.tcx.normalize_erasing_late_bound_regions(self.param_env, &fn_sig);
110 // the drop function takes *mut T where T is the type being dropped, so get that
111 let ty = fn_sig.inputs()[0].builtin_deref(true).unwrap().ty;
112 Ok((drop_instance, ty))
115 pub fn read_size_and_align_from_vtable(
117 vtable: Pointer<M::PointerTag>,
118 ) -> EvalResult<'tcx, (Size, Align)> {
119 let pointer_size = self.pointer_size();
120 self.memory.check_align(vtable.into(), self.tcx.data_layout.pointer_align.abi)?;
121 let alloc = self.memory.get(vtable.alloc_id)?;
122 let size = alloc.read_ptr_sized(self, vtable.offset(pointer_size, self)?)?
123 .to_bits(pointer_size)? as u64;
124 let align = alloc.read_ptr_sized(
126 vtable.offset(pointer_size * 2, self)?,
127 )?.to_bits(pointer_size)? as u64;
128 Ok((Size::from_bytes(size), Align::from_bytes(align).unwrap()))