1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
use std::convert::TryFrom;

use rustc_apfloat::ieee::{Double, Single};
use rustc_apfloat::{Float, FloatConvert};
use rustc_ast::ast::FloatTy;
use rustc_attr as attr;
use rustc_middle::mir::interpret::{InterpResult, PointerArithmetic, Scalar};
use rustc_middle::mir::CastKind;
use rustc_middle::ty::adjustment::PointerCast;
use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
use rustc_middle::ty::{self, Ty, TypeAndMut, TypeFoldable};
use rustc_span::symbol::sym;
use rustc_target::abi::{Integer, LayoutOf, Variants};

use super::{truncate, FnVal, ImmTy, Immediate, InterpCx, Machine, OpTy, PlaceTy};

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
    pub fn cast(
        &mut self,
        src: OpTy<'tcx, M::PointerTag>,
        cast_kind: CastKind,
        cast_ty: Ty<'tcx>,
        dest: PlaceTy<'tcx, M::PointerTag>,
    ) -> InterpResult<'tcx> {
        use rustc_middle::mir::CastKind::*;
        // FIXME: In which cases should we trigger UB when the source is uninit?
        match cast_kind {
            Pointer(PointerCast::Unsize) => {
                let cast_ty = self.layout_of(cast_ty)?;
                self.unsize_into(src, cast_ty, dest)?;
            }

            Misc => {
                let src = self.read_immediate(src)?;
                let res = self.misc_cast(src, cast_ty)?;
                self.write_immediate(res, dest)?;
            }

            Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer) => {
                // These are NOPs, but can be wide pointers.
                let v = self.read_immediate(src)?;
                self.write_immediate(*v, dest)?;
            }

            Pointer(PointerCast::ReifyFnPointer) => {
                // The src operand does not matter, just its type
                match src.layout.ty.kind {
                    ty::FnDef(def_id, substs) => {
                        // All reifications must be monomorphic, bail out otherwise.
                        if src.layout.ty.needs_subst() {
                            throw_inval!(TooGeneric);
                        }

                        if self.tcx.has_attr(def_id, sym::rustc_args_required_const) {
                            span_bug!(
                                self.cur_span(),
                                "reifying a fn ptr that requires const arguments"
                            );
                        }

                        let instance = ty::Instance::resolve_for_fn_ptr(
                            *self.tcx,
                            self.param_env,
                            def_id,
                            substs,
                        )
                        .ok_or_else(|| err_inval!(TooGeneric))?;

                        let fn_ptr = self.memory.create_fn_alloc(FnVal::Instance(instance));
                        self.write_scalar(fn_ptr, dest)?;
                    }
                    _ => span_bug!(self.cur_span(), "reify fn pointer on {:?}", src.layout.ty),
                }
            }

            Pointer(PointerCast::UnsafeFnPointer) => {
                let src = self.read_immediate(src)?;
                match cast_ty.kind {
                    ty::FnPtr(_) => {
                        // No change to value
                        self.write_immediate(*src, dest)?;
                    }
                    _ => span_bug!(self.cur_span(), "fn to unsafe fn cast on {:?}", cast_ty),
                }
            }

            Pointer(PointerCast::ClosureFnPointer(_)) => {
                // The src operand does not matter, just its type
                match src.layout.ty.kind {
                    ty::Closure(def_id, substs) => {
                        // All reifications must be monomorphic, bail out otherwise.
                        if src.layout.ty.needs_subst() {
                            throw_inval!(TooGeneric);
                        }

                        let instance = ty::Instance::resolve_closure(
                            *self.tcx,
                            def_id,
                            substs,
                            ty::ClosureKind::FnOnce,
                        );
                        let fn_ptr = self.memory.create_fn_alloc(FnVal::Instance(instance));
                        self.write_scalar(fn_ptr, dest)?;
                    }
                    _ => span_bug!(self.cur_span(), "closure fn pointer on {:?}", src.layout.ty),
                }
            }
        }
        Ok(())
    }

    fn misc_cast(
        &self,
        src: ImmTy<'tcx, M::PointerTag>,
        cast_ty: Ty<'tcx>,
    ) -> InterpResult<'tcx, Immediate<M::PointerTag>> {
        use rustc_middle::ty::TyKind::*;
        trace!("Casting {:?}: {:?} to {:?}", *src, src.layout.ty, cast_ty);

        match src.layout.ty.kind {
            // Floating point
            Float(FloatTy::F32) => {
                return Ok(self.cast_from_float(src.to_scalar()?.to_f32()?, cast_ty).into());
            }
            Float(FloatTy::F64) => {
                return Ok(self.cast_from_float(src.to_scalar()?.to_f64()?, cast_ty).into());
            }
            // The rest is integer/pointer-"like", including fn ptr casts and casts from enums that
            // are represented as integers.
            _ => assert!(
                src.layout.ty.is_bool()
                    || src.layout.ty.is_char()
                    || src.layout.ty.is_enum()
                    || src.layout.ty.is_integral()
                    || src.layout.ty.is_any_ptr(),
                "Unexpected cast from type {:?}",
                src.layout.ty
            ),
        }

        // # First handle non-scalar source values.

        // Handle cast from a univariant (ZST) enum.
        match src.layout.variants {
            Variants::Single { index } => {
                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_scalar(discr.val, discr_layout, cast_ty).into());
                }
            }
            Variants::Multiple { .. } => {}
        }

        // Handle casting any ptr to raw ptr (might be a fat ptr).
        if src.layout.ty.is_any_ptr() && cast_ty.is_unsafe_ptr() {
            let dest_layout = self.layout_of(cast_ty)?;
            if dest_layout.size == src.layout.size {
                // Thin or fat pointer that just hast the ptr kind of target type changed.
                return Ok(*src);
            } else {
                // Casting the metadata away from a fat ptr.
                assert_eq!(src.layout.size, 2 * self.memory.pointer_size());
                assert_eq!(dest_layout.size, self.memory.pointer_size());
                assert!(src.layout.ty.is_unsafe_ptr());
                return match *src {
                    Immediate::ScalarPair(data, _) => Ok(data.into()),
                    Immediate::Scalar(..) => span_bug!(
                        self.cur_span(),
                        "{:?} input to a fat-to-thin cast ({:?} -> {:?})",
                        *src,
                        src.layout.ty,
                        cast_ty
                    ),
                };
            }
        }

        // # The remaining source values are scalar.

        // 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 = self.force_bits(src.to_scalar()?, src.layout.size)?;
        Ok(self.cast_from_scalar(bits, src.layout, cast_ty).into())
    }

    pub(super) fn cast_from_scalar(
        &self,
        v: u128, // raw bits (there is no ScalarTy so we separate data+layout)
        src_layout: TyAndLayout<'tcx>,
        cast_ty: Ty<'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 = 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(_) => {
                let size = match cast_ty.kind {
                    Int(t) => Integer::from_attr(self, attr::IntType::SignedInt(t)).size(),
                    Uint(t) => Integer::from_attr(self, attr::IntType::UnsignedInt(t)).size(),
                    RawPtr(_) => self.pointer_size(),
                    _ => bug!(),
                };
                let v = truncate(v, size);
                Scalar::from_uint(v, size)
            }

            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),
            Float(FloatTy::F64) => Scalar::from_f64(Double::from_u128(v).value),

            Char => {
                // `u8` to `char` cast
                Scalar::from_u32(u8::try_from(v).unwrap().into())
            }

            // 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>
    where
        F: Float + Into<Scalar<M::PointerTag>> + FloatConvert<Single> + FloatConvert<Double>,
    {
        use rustc_middle::ty::TyKind::*;
        match dest_ty.kind {
            // float -> uint
            Uint(t) => {
                let size = Integer::from_attr(self, attr::IntType::UnsignedInt(t)).size();
                // `to_u128` is a saturating cast, which is what we need
                // (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
                let v = f.to_u128(size.bits_usize()).value;
                // This should already fit the bit width
                Scalar::from_uint(v, size)
            }
            // float -> int
            Int(t) => {
                let size = Integer::from_attr(self, attr::IntType::SignedInt(t)).size();
                // `to_i128` is a saturating cast, which is what we need
                // (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
                let v = f.to_i128(size.bits_usize()).value;
                Scalar::from_int(v, size)
            }
            // float -> f32
            Float(FloatTy::F32) => Scalar::from_f32(f.convert(&mut false).value),
            // float -> f64
            Float(FloatTy::F64) => Scalar::from_f64(f.convert(&mut false).value),
            // That's it.
            _ => span_bug!(self.cur_span(), "invalid float to {:?} cast", dest_ty),
        }
    }

    fn unsize_into_ptr(
        &mut self,
        src: OpTy<'tcx, M::PointerTag>,
        dest: PlaceTy<'tcx, M::PointerTag>,
        // The pointee types
        source_ty: Ty<'tcx>,
        cast_ty: Ty<'tcx>,
    ) -> InterpResult<'tcx> {
        // A<Struct> -> A<Trait> conversion
        let (src_pointee_ty, dest_pointee_ty) =
            self.tcx.struct_lockstep_tails_erasing_lifetimes(source_ty, cast_ty, self.param_env);

        match (&src_pointee_ty.kind, &dest_pointee_ty.kind) {
            (&ty::Array(_, length), &ty::Slice(_)) => {
                let ptr = self.read_immediate(src)?.to_scalar()?;
                // u64 cast is from usize to u64, which is always good
                let val =
                    Immediate::new_slice(ptr, length.eval_usize(*self.tcx, self.param_env), self);
                self.write_immediate(val, dest)
            }
            (&ty::Dynamic(..), &ty::Dynamic(..)) => {
                // For now, upcasts are limited to changes in marker
                // traits, and hence never actually require an actual
                // change to the vtable.
                let val = self.read_immediate(src)?;
                self.write_immediate(*val, dest)
            }
            (_, &ty::Dynamic(ref data, _)) => {
                // Initial cast from sized to dyn trait
                let vtable = self.get_vtable(src_pointee_ty, data.principal())?;
                let ptr = self.read_immediate(src)?.to_scalar()?;
                let val = Immediate::new_dyn_trait(ptr, vtable);
                self.write_immediate(val, dest)
            }

            _ => {
                span_bug!(self.cur_span(), "invalid unsizing {:?} -> {:?}", src.layout.ty, cast_ty)
            }
        }
    }

    fn unsize_into(
        &mut self,
        src: OpTy<'tcx, M::PointerTag>,
        cast_ty: TyAndLayout<'tcx>,
        dest: PlaceTy<'tcx, M::PointerTag>,
    ) -> InterpResult<'tcx> {
        trace!("Unsizing {:?} of type {} into {:?}", *src, src.layout.ty, cast_ty.ty);
        match (&src.layout.ty.kind, &cast_ty.ty.kind) {
            (&ty::Ref(_, s, _), &ty::Ref(_, c, _) | &ty::RawPtr(TypeAndMut { ty: c, .. }))
            | (&ty::RawPtr(TypeAndMut { ty: s, .. }), &ty::RawPtr(TypeAndMut { ty: c, .. })) => {
                self.unsize_into_ptr(src, dest, s, c)
            }
            (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
                assert_eq!(def_a, def_b);
                if def_a.is_box() || def_b.is_box() {
                    if !def_a.is_box() || !def_b.is_box() {
                        span_bug!(
                            self.cur_span(),
                            "invalid unsizing between {:?} -> {:?}",
                            src.layout.ty,
                            cast_ty.ty
                        );
                    }
                    return self.unsize_into_ptr(
                        src,
                        dest,
                        src.layout.ty.boxed_ty(),
                        cast_ty.ty.boxed_ty(),
                    );
                }

                // unsizing of generic struct with pointer fields
                // Example: `Arc<T>` -> `Arc<Trait>`
                // here we need to increase the size of every &T thin ptr field to a fat ptr
                for i in 0..src.layout.fields.count() {
                    let cast_ty_field = cast_ty.field(self, i)?;
                    if cast_ty_field.is_zst() {
                        continue;
                    }
                    let src_field = self.operand_field(src, i)?;
                    let dst_field = self.place_field(dest, i)?;
                    if src_field.layout.ty == cast_ty_field.ty {
                        self.copy_op(src_field, dst_field)?;
                    } else {
                        self.unsize_into(src_field, cast_ty_field, dst_field)?;
                    }
                }
                Ok(())
            }
            _ => span_bug!(
                self.cur_span(),
                "unsize_into: invalid conversion: {:?} -> {:?}",
                src.layout,
                dest.layout
            ),
        }
    }
}