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
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
#![warn(clippy::arithmetic_side_effects)]

mod atomic;
mod simd;

use std::iter;

use rand::Rng;
use rustc_apfloat::{Float, Round};
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::{
    mir,
    ty::{self, FloatTy},
};
use rustc_span::{sym, Symbol};
use rustc_target::abi::Size;

use crate::*;
use atomic::EvalContextExt as _;
use helpers::{check_arg_count, ToHost, ToSoft};
use simd::EvalContextExt as _;

impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
    fn call_intrinsic(
        &mut self,
        instance: ty::Instance<'tcx>,
        args: &[OpTy<'tcx>],
        dest: &MPlaceTy<'tcx>,
        ret: Option<mir::BasicBlock>,
        unwind: mir::UnwindAction,
    ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
        let this = self.eval_context_mut();

        // See if the core engine can handle this intrinsic.
        if this.eval_intrinsic(instance, args, dest, ret)? {
            return Ok(None);
        }
        let intrinsic_name = this.tcx.item_name(instance.def_id());
        let intrinsic_name = intrinsic_name.as_str();

        match this.emulate_intrinsic_by_name(intrinsic_name, instance.args, args, dest, ret)? {
            EmulateItemResult::NotSupported => {
                // We haven't handled the intrinsic, let's see if we can use a fallback body.
                if this.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {
                    throw_unsup_format!("unimplemented intrinsic: `{intrinsic_name}`")
                }
                let intrinsic_fallback_is_spec = Symbol::intern("intrinsic_fallback_is_spec");
                if this
                    .tcx
                    .get_attrs_by_path(instance.def_id(), &[sym::miri, intrinsic_fallback_is_spec])
                    .next()
                    .is_none()
                {
                    throw_unsup_format!(
                        "Miri can only use intrinsic fallback bodies that exactly reflect the specification: they fully check for UB and are as non-deterministic as possible. After verifying that `{intrinsic_name}` does so, add the `#[miri::intrinsic_fallback_is_spec]` attribute to it; also ping @rust-lang/miri when you do that"
                    );
                }
                Ok(Some(ty::Instance {
                    def: ty::InstanceKind::Item(instance.def_id()),
                    args: instance.args,
                }))
            }
            EmulateItemResult::NeedsReturn => {
                trace!("{:?}", this.dump_place(&dest.clone().into()));
                this.return_to_block(ret)?;
                Ok(None)
            }
            EmulateItemResult::NeedsUnwind => {
                // Jump to the unwind block to begin unwinding.
                this.unwind_to_block(unwind)?;
                Ok(None)
            }
            EmulateItemResult::AlreadyJumped => Ok(None),
        }
    }

    /// Emulates a Miri-supported intrinsic (not supported by the core engine).
    /// Returns `Ok(true)` if the intrinsic was handled.
    fn emulate_intrinsic_by_name(
        &mut self,
        intrinsic_name: &str,
        generic_args: ty::GenericArgsRef<'tcx>,
        args: &[OpTy<'tcx>],
        dest: &MPlaceTy<'tcx>,
        ret: Option<mir::BasicBlock>,
    ) -> InterpResult<'tcx, EmulateItemResult> {
        let this = self.eval_context_mut();

        if let Some(name) = intrinsic_name.strip_prefix("atomic_") {
            return this.emulate_atomic_intrinsic(name, args, dest);
        }
        if let Some(name) = intrinsic_name.strip_prefix("simd_") {
            return this.emulate_simd_intrinsic(name, generic_args, args, dest);
        }

        match intrinsic_name {
            // Basic control flow
            "abort" => {
                throw_machine_stop!(TerminationInfo::Abort(
                    "the program aborted execution".to_owned()
                ));
            }
            "catch_unwind" => {
                this.handle_catch_unwind(args, dest, ret)?;
                // This pushed a stack frame, don't jump to `ret`.
                return Ok(EmulateItemResult::AlreadyJumped);
            }

            // Raw memory accesses
            "volatile_load" => {
                let [place] = check_arg_count(args)?;
                let place = this.deref_pointer(place)?;
                this.copy_op(&place, dest)?;
            }
            "volatile_store" => {
                let [place, dest] = check_arg_count(args)?;
                let place = this.deref_pointer(place)?;
                this.copy_op(dest, &place)?;
            }

            "write_bytes" | "volatile_set_memory" => {
                let [ptr, val_byte, count] = check_arg_count(args)?;
                let ty = ptr.layout.ty.builtin_deref(true).unwrap();
                let ty_layout = this.layout_of(ty)?;
                let val_byte = this.read_scalar(val_byte)?.to_u8()?;
                let ptr = this.read_pointer(ptr)?;
                let count = this.read_target_usize(count)?;
                // `checked_mul` enforces a too small bound (the correct one would probably be target_isize_max),
                // but no actual allocation can be big enough for the difference to be noticeable.
                let byte_count = ty_layout.size.checked_mul(count, this).ok_or_else(|| {
                    err_ub_format!("overflow computing total size of `{intrinsic_name}`")
                })?;
                this.write_bytes_ptr(ptr, iter::repeat(val_byte).take(byte_count.bytes_usize()))?;
            }

            // Memory model / provenance manipulation
            "ptr_mask" => {
                let [ptr, mask] = check_arg_count(args)?;

                let ptr = this.read_pointer(ptr)?;
                let mask = this.read_target_usize(mask)?;

                let masked_addr = Size::from_bytes(ptr.addr().bytes() & mask);

                this.write_pointer(Pointer::new(ptr.provenance, masked_addr), dest)?;
            }

            // We want to return either `true` or `false` at random, or else something like
            // ```
            // if !is_val_statically_known(0) { unreachable_unchecked(); }
            // ```
            // Would not be considered UB, or the other way around (`is_val_statically_known(0)`).
            "is_val_statically_known" => {
                let [arg] = check_arg_count(args)?;
                this.validate_operand(arg, /*recursive*/ false)?;
                let branch: bool = this.machine.rng.get_mut().gen();
                this.write_scalar(Scalar::from_bool(branch), dest)?;
            }

            // Floating-point operations
            "fabsf32" => {
                let [f] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f32()?;
                // This is a "bitwise" operation, so there's no NaN non-determinism.
                this.write_scalar(Scalar::from_f32(f.abs()), dest)?;
            }
            "fabsf64" => {
                let [f] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f64()?;
                // This is a "bitwise" operation, so there's no NaN non-determinism.
                this.write_scalar(Scalar::from_f64(f.abs()), dest)?;
            }

            "floorf32" | "ceilf32" | "truncf32" | "roundf32" | "rintf32" => {
                let [f] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f32()?;
                let mode = match intrinsic_name {
                    "floorf32" => Round::TowardNegative,
                    "ceilf32" => Round::TowardPositive,
                    "truncf32" => Round::TowardZero,
                    "roundf32" => Round::NearestTiesToAway,
                    "rintf32" => Round::NearestTiesToEven,
                    _ => bug!(),
                };
                let res = f.round_to_integral(mode).value;
                let res = this.adjust_nan(res, &[f]);
                this.write_scalar(res, dest)?;
            }
            "floorf64" | "ceilf64" | "truncf64" | "roundf64" | "rintf64" => {
                let [f] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f64()?;
                let mode = match intrinsic_name {
                    "floorf64" => Round::TowardNegative,
                    "ceilf64" => Round::TowardPositive,
                    "truncf64" => Round::TowardZero,
                    "roundf64" => Round::NearestTiesToAway,
                    "rintf64" => Round::NearestTiesToEven,
                    _ => bug!(),
                };
                let res = f.round_to_integral(mode).value;
                let res = this.adjust_nan(res, &[f]);
                this.write_scalar(res, dest)?;
            }

            #[rustfmt::skip]
            | "sinf32"
            | "cosf32"
            | "sqrtf32"
            | "expf32"
            | "exp2f32"
            | "logf32"
            | "log10f32"
            | "log2f32"
            => {
                let [f] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f32()?;
                // Using host floats (but it's fine, these operations do not have guaranteed precision).
                let f_host = f.to_host();
                let res = match intrinsic_name {
                    "sinf32" => f_host.sin(),
                    "cosf32" => f_host.cos(),
                    "sqrtf32" => f_host.sqrt(), // FIXME Using host floats, this should use full-precision soft-floats
                    "expf32" => f_host.exp(),
                    "exp2f32" => f_host.exp2(),
                    "logf32" => f_host.ln(),
                    "log10f32" => f_host.log10(),
                    "log2f32" => f_host.log2(),
                    _ => bug!(),
                };
                let res = res.to_soft();
                let res = this.adjust_nan(res, &[f]);
                this.write_scalar(res, dest)?;
            }
            #[rustfmt::skip]
            | "sinf64"
            | "cosf64"
            | "sqrtf64"
            | "expf64"
            | "exp2f64"
            | "logf64"
            | "log10f64"
            | "log2f64"
            => {
                let [f] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f64()?;
                // Using host floats (but it's fine, these operations do not have guaranteed precision).
                let f_host = f.to_host();
                let res = match intrinsic_name {
                    "sinf64" => f_host.sin(),
                    "cosf64" => f_host.cos(),
                    "sqrtf64" => f_host.sqrt(), // FIXME Using host floats, this should use full-precision soft-floats
                    "expf64" => f_host.exp(),
                    "exp2f64" => f_host.exp2(),
                    "logf64" => f_host.ln(),
                    "log10f64" => f_host.log10(),
                    "log2f64" => f_host.log2(),
                    _ => bug!(),
                };
                let res = res.to_soft();
                let res = this.adjust_nan(res, &[f]);
                this.write_scalar(res, dest)?;
            }

            "minnumf32" | "maxnumf32" | "copysignf32" => {
                let [a, b] = check_arg_count(args)?;
                let a = this.read_scalar(a)?.to_f32()?;
                let b = this.read_scalar(b)?.to_f32()?;
                let res = match intrinsic_name {
                    "minnumf32" => this.adjust_nan(a.min(b), &[a, b]),
                    "maxnumf32" => this.adjust_nan(a.max(b), &[a, b]),
                    "copysignf32" => a.copy_sign(b), // bitwise, no NaN adjustments
                    _ => bug!(),
                };
                this.write_scalar(Scalar::from_f32(res), dest)?;
            }
            "minnumf64" | "maxnumf64" | "copysignf64" => {
                let [a, b] = check_arg_count(args)?;
                let a = this.read_scalar(a)?.to_f64()?;
                let b = this.read_scalar(b)?.to_f64()?;
                let res = match intrinsic_name {
                    "minnumf64" => this.adjust_nan(a.min(b), &[a, b]),
                    "maxnumf64" => this.adjust_nan(a.max(b), &[a, b]),
                    "copysignf64" => a.copy_sign(b), // bitwise, no NaN adjustments
                    _ => bug!(),
                };
                this.write_scalar(Scalar::from_f64(res), dest)?;
            }

            "fmaf32" => {
                let [a, b, c] = check_arg_count(args)?;
                let a = this.read_scalar(a)?.to_f32()?;
                let b = this.read_scalar(b)?.to_f32()?;
                let c = this.read_scalar(c)?.to_f32()?;
                // FIXME: Using host floats, to work around https://github.com/rust-lang/rustc_apfloat/issues/11
                let res = a.to_host().mul_add(b.to_host(), c.to_host()).to_soft();
                let res = this.adjust_nan(res, &[a, b, c]);
                this.write_scalar(res, dest)?;
            }
            "fmaf64" => {
                let [a, b, c] = check_arg_count(args)?;
                let a = this.read_scalar(a)?.to_f64()?;
                let b = this.read_scalar(b)?.to_f64()?;
                let c = this.read_scalar(c)?.to_f64()?;
                // FIXME: Using host floats, to work around https://github.com/rust-lang/rustc_apfloat/issues/11
                let res = a.to_host().mul_add(b.to_host(), c.to_host()).to_soft();
                let res = this.adjust_nan(res, &[a, b, c]);
                this.write_scalar(res, dest)?;
            }

            "powf32" => {
                let [f1, f2] = check_arg_count(args)?;
                let f1 = this.read_scalar(f1)?.to_f32()?;
                let f2 = this.read_scalar(f2)?.to_f32()?;
                // Using host floats (but it's fine, this operation does not have guaranteed precision).
                let res = f1.to_host().powf(f2.to_host()).to_soft();
                let res = this.adjust_nan(res, &[f1, f2]);
                this.write_scalar(res, dest)?;
            }
            "powf64" => {
                let [f1, f2] = check_arg_count(args)?;
                let f1 = this.read_scalar(f1)?.to_f64()?;
                let f2 = this.read_scalar(f2)?.to_f64()?;
                // Using host floats (but it's fine, this operation does not have guaranteed precision).
                let res = f1.to_host().powf(f2.to_host()).to_soft();
                let res = this.adjust_nan(res, &[f1, f2]);
                this.write_scalar(res, dest)?;
            }

            "powif32" => {
                let [f, i] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f32()?;
                let i = this.read_scalar(i)?.to_i32()?;
                // Using host floats (but it's fine, this operation does not have guaranteed precision).
                let res = f.to_host().powi(i).to_soft();
                let res = this.adjust_nan(res, &[f]);
                this.write_scalar(res, dest)?;
            }
            "powif64" => {
                let [f, i] = check_arg_count(args)?;
                let f = this.read_scalar(f)?.to_f64()?;
                let i = this.read_scalar(i)?.to_i32()?;
                // Using host floats (but it's fine, this operation does not have guaranteed precision).
                let res = f.to_host().powi(i).to_soft();
                let res = this.adjust_nan(res, &[f]);
                this.write_scalar(res, dest)?;
            }

            #[rustfmt::skip]
            | "fadd_algebraic"
            | "fsub_algebraic"
            | "fmul_algebraic"
            | "fdiv_algebraic"
            | "frem_algebraic"
            => {
                let [a, b] = check_arg_count(args)?;
                let a = this.read_immediate(a)?;
                let b = this.read_immediate(b)?;
                let op = match intrinsic_name {
                    "fadd_algebraic" => mir::BinOp::Add,
                    "fsub_algebraic" => mir::BinOp::Sub,
                    "fmul_algebraic" => mir::BinOp::Mul,
                    "fdiv_algebraic" => mir::BinOp::Div,
                    "frem_algebraic" => mir::BinOp::Rem,
                    _ => bug!(),
                };
                let res = this.binary_op(op, &a, &b)?;
                // `binary_op` already called `generate_nan` if necessary.
                this.write_immediate(*res, dest)?;
            }

            #[rustfmt::skip]
            | "fadd_fast"
            | "fsub_fast"
            | "fmul_fast"
            | "fdiv_fast"
            | "frem_fast"
            => {
                let [a, b] = check_arg_count(args)?;
                let a = this.read_immediate(a)?;
                let b = this.read_immediate(b)?;
                let op = match intrinsic_name {
                    "fadd_fast" => mir::BinOp::Add,
                    "fsub_fast" => mir::BinOp::Sub,
                    "fmul_fast" => mir::BinOp::Mul,
                    "fdiv_fast" => mir::BinOp::Div,
                    "frem_fast" => mir::BinOp::Rem,
                    _ => bug!(),
                };
                let float_finite = |x: &ImmTy<'tcx>| -> InterpResult<'tcx, bool> {
                    let ty::Float(fty) = x.layout.ty.kind() else {
                        bug!("float_finite: non-float input type {}", x.layout.ty)
                    };
                    Ok(match fty {
                        FloatTy::F16 => x.to_scalar().to_f16()?.is_finite(),
                        FloatTy::F32 => x.to_scalar().to_f32()?.is_finite(),
                        FloatTy::F64 => x.to_scalar().to_f64()?.is_finite(),
                        FloatTy::F128 => x.to_scalar().to_f128()?.is_finite(),
                    })
                };
                match (float_finite(&a)?, float_finite(&b)?) {
                    (false, false) => throw_ub_format!(
                        "`{intrinsic_name}` intrinsic called with non-finite value as both parameters",
                    ),
                    (false, _) => throw_ub_format!(
                        "`{intrinsic_name}` intrinsic called with non-finite value as first parameter",
                    ),
                    (_, false) => throw_ub_format!(
                        "`{intrinsic_name}` intrinsic called with non-finite value as second parameter",
                    ),
                    _ => {}
                }
                let res = this.binary_op(op, &a, &b)?;
                if !float_finite(&res)? {
                    throw_ub_format!("`{intrinsic_name}` intrinsic produced non-finite value as result");
                }
                // This cannot be a NaN so we also don't have to apply any non-determinism.
                // (Also, `binary_op` already called `generate_nan` if needed.)
                this.write_immediate(*res, dest)?;
            }

            "float_to_int_unchecked" => {
                let [val] = check_arg_count(args)?;
                let val = this.read_immediate(val)?;

                let res = this
                    .float_to_int_checked(&val, dest.layout, Round::TowardZero)?
                    .ok_or_else(|| {
                        err_ub_format!(
                            "`float_to_int_unchecked` intrinsic called on {val} which cannot be represented in target type `{:?}`",
                            dest.layout.ty
                        )
                    })?;

                this.write_immediate(*res, dest)?;
            }

            // Other
            "breakpoint" => {
                let [] = check_arg_count(args)?;
                // normally this would raise a SIGTRAP, which aborts if no debugger is connected
                throw_machine_stop!(TerminationInfo::Abort(format!("trace/breakpoint trap")))
            }

            _ => return Ok(EmulateItemResult::NotSupported),
        }

        Ok(EmulateItemResult::NeedsReturn)
    }
}