1 //! Intrinsics and other functions that the miri engine executes without
2 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
5 use std::convert::TryFrom;
7 use rustc_hir::def_id::DefId;
8 use rustc_middle::mir::{
10 interpret::{ConstValue, GlobalId, InterpResult, Scalar},
14 use rustc_middle::ty::layout::LayoutOf as _;
15 use rustc_middle::ty::subst::SubstsRef;
16 use rustc_middle::ty::{Ty, TyCtxt};
17 use rustc_span::symbol::{sym, Symbol};
18 use rustc_target::abi::{Abi, Align, Primitive, Size};
21 util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
28 fn numeric_intrinsic<Tag>(name: Symbol, bits: u128, kind: Primitive) -> Scalar<Tag> {
29 let size = match kind {
30 Primitive::Int(integer, _) => integer.size(),
31 _ => bug!("invalid `{}` argument: {:?}", name, bits),
33 let extra = 128 - u128::from(size.bits());
34 let bits_out = match name {
35 sym::ctpop => u128::from(bits.count_ones()),
36 sym::ctlz => u128::from(bits.leading_zeros()) - extra,
37 sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
38 sym::bswap => (bits << extra).swap_bytes(),
39 sym::bitreverse => (bits << extra).reverse_bits(),
40 _ => bug!("not a numeric intrinsic: {}", name),
42 Scalar::from_uint(bits_out, size)
45 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
46 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
47 pub(crate) fn eval_nullary_intrinsic<'tcx>(
49 param_env: ty::ParamEnv<'tcx>,
51 substs: SubstsRef<'tcx>,
52 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
53 let tp_ty = substs.type_at(0);
54 let name = tcx.item_name(def_id);
57 ensure_monomorphic_enough(tcx, tp_ty)?;
58 let alloc = type_name::alloc_type_name(tcx, tp_ty);
59 ConstValue::Slice { data: alloc, start: 0, end: alloc.inner().len() }
62 ensure_monomorphic_enough(tcx, tp_ty)?;
63 ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env))
65 sym::pref_align_of => {
66 // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
67 let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
68 ConstValue::from_machine_usize(layout.align.pref.bytes(), &tcx)
71 ensure_monomorphic_enough(tcx, tp_ty)?;
72 ConstValue::from_u64(tcx.type_id_hash(tp_ty))
74 sym::variant_count => match tp_ty.kind() {
75 // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
76 ty::Adt(ref adt, _) => {
77 ConstValue::from_machine_usize(adt.variants().len() as u64, &tcx)
84 | ty::Infer(_) => throw_inval!(TooGeneric),
100 | ty::Generator(_, _, _)
101 | ty::GeneratorWitness(_)
104 | ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
106 other => bug!("`{}` is not a zero arg intrinsic", other),
110 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
111 /// Returns `true` if emulation happened.
112 /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
113 /// intrinsic handling.
114 pub fn emulate_intrinsic(
116 instance: ty::Instance<'tcx>,
117 args: &[OpTy<'tcx, M::PointerTag>],
118 dest: &PlaceTy<'tcx, M::PointerTag>,
119 ret: Option<mir::BasicBlock>,
120 ) -> InterpResult<'tcx, bool> {
121 let substs = instance.substs;
122 let intrinsic_name = self.tcx.item_name(instance.def_id());
124 // First handle intrinsics without return place.
125 let ret = match ret {
126 None => match intrinsic_name {
127 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
128 sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
129 // Unsupported diverging intrinsic.
130 _ => return Ok(false),
135 match intrinsic_name {
136 sym::caller_location => {
137 let span = self.find_closest_untracked_caller_location();
138 let location = self.alloc_caller_location_for_span(span);
139 self.write_immediate(location.to_ref(self), dest)?;
142 sym::min_align_of_val | sym::size_of_val => {
143 // Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
145 let place = self.ref_to_mplace(&self.read_immediate(&args[0])?)?;
146 let (size, align) = self
147 .size_and_align_of_mplace(&place)?
148 .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
150 let result = match intrinsic_name {
151 sym::min_align_of_val => align.bytes(),
152 sym::size_of_val => size.bytes(),
156 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
163 | sym::variant_count => {
164 let gid = GlobalId { instance, promoted: None };
165 let ty = match intrinsic_name {
166 sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
167 sym::needs_drop => self.tcx.types.bool,
168 sym::type_id => self.tcx.types.u64,
169 sym::type_name => self.tcx.mk_static_str(),
173 self.tcx.const_eval_global_id(self.param_env, gid, Some(self.tcx.span))?;
174 let val = self.const_val_to_op(val, ty, Some(dest.layout))?;
175 self.copy_op(&val, dest, /*allow_transmute*/ false)?;
184 | sym::bitreverse => {
185 let ty = substs.type_at(0);
186 let layout_of = self.layout_of(ty)?;
187 let val = self.read_scalar(&args[0])?.check_init()?;
188 let bits = val.to_bits(layout_of.size)?;
189 let kind = match layout_of.abi {
190 Abi::Scalar(scalar) => scalar.primitive(),
193 "{} called on invalid type {:?}",
198 let (nonzero, intrinsic_name) = match intrinsic_name {
199 sym::cttz_nonzero => (true, sym::cttz),
200 sym::ctlz_nonzero => (true, sym::ctlz),
201 other => (false, other),
203 if nonzero && bits == 0 {
204 throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
206 let out_val = numeric_intrinsic(intrinsic_name, bits, kind);
207 self.write_scalar(out_val, dest)?;
209 sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
210 let lhs = self.read_immediate(&args[0])?;
211 let rhs = self.read_immediate(&args[1])?;
212 let bin_op = match intrinsic_name {
213 sym::add_with_overflow => BinOp::Add,
214 sym::sub_with_overflow => BinOp::Sub,
215 sym::mul_with_overflow => BinOp::Mul,
218 self.binop_with_overflow(
219 bin_op, /*force_overflow_checks*/ true, &lhs, &rhs, dest,
222 sym::saturating_add | sym::saturating_sub => {
223 let l = self.read_immediate(&args[0])?;
224 let r = self.read_immediate(&args[1])?;
225 let val = self.saturating_arith(
226 if intrinsic_name == sym::saturating_add { BinOp::Add } else { BinOp::Sub },
230 self.write_scalar(val, dest)?;
232 sym::discriminant_value => {
233 let place = self.deref_operand(&args[0])?;
234 let discr_val = self.read_discriminant(&place.into())?.0;
235 self.write_scalar(discr_val, dest)?;
243 | sym::unchecked_rem => {
244 let l = self.read_immediate(&args[0])?;
245 let r = self.read_immediate(&args[1])?;
246 let bin_op = match intrinsic_name {
247 sym::unchecked_shl => BinOp::Shl,
248 sym::unchecked_shr => BinOp::Shr,
249 sym::unchecked_add => BinOp::Add,
250 sym::unchecked_sub => BinOp::Sub,
251 sym::unchecked_mul => BinOp::Mul,
252 sym::unchecked_div => BinOp::Div,
253 sym::unchecked_rem => BinOp::Rem,
256 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
258 let layout = self.layout_of(substs.type_at(0))?;
259 let r_val = r.to_scalar()?.to_bits(layout.size)?;
260 if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
261 throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
263 throw_ub_format!("overflow executing `{}`", intrinsic_name);
266 self.write_scalar(val, dest)?;
268 sym::rotate_left | sym::rotate_right => {
269 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
270 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
271 let layout = self.layout_of(substs.type_at(0))?;
272 let val = self.read_scalar(&args[0])?.check_init()?;
273 let val_bits = val.to_bits(layout.size)?;
274 let raw_shift = self.read_scalar(&args[1])?.check_init()?;
275 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
276 let width_bits = u128::from(layout.size.bits());
277 let shift_bits = raw_shift_bits % width_bits;
278 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
279 let result_bits = if intrinsic_name == sym::rotate_left {
280 (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
282 (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
284 let truncated_bits = self.truncate(result_bits, layout);
285 let result = Scalar::from_uint(truncated_bits, layout.size);
286 self.write_scalar(result, dest)?;
289 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
291 sym::write_bytes => {
292 self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
295 let ptr = self.read_pointer(&args[0])?;
296 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
297 let pointee_ty = substs.type_at(0);
299 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
300 self.write_pointer(offset_ptr, dest)?;
302 sym::arith_offset => {
303 let ptr = self.read_pointer(&args[0])?;
304 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
305 let pointee_ty = substs.type_at(0);
307 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
308 let offset_bytes = offset_count.wrapping_mul(pointee_size);
309 let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
310 self.write_pointer(offset_ptr, dest)?;
312 sym::ptr_offset_from | sym::ptr_offset_from_unsigned => {
313 let a = self.read_pointer(&args[0])?;
314 let b = self.read_pointer(&args[1])?;
316 let usize_layout = self.layout_of(self.tcx.types.usize)?;
317 let isize_layout = self.layout_of(self.tcx.types.isize)?;
319 // Get offsets for both that are at least relative to the same base.
320 let (a_offset, b_offset) =
321 match (self.ptr_try_get_alloc_id(a), self.ptr_try_get_alloc_id(b)) {
322 (Err(a), Err(b)) => {
323 // Neither poiner points to an allocation.
324 // If these are inequal or null, this *will* fail the deref check below.
327 (Err(_), _) | (_, Err(_)) => {
328 // We managed to find a valid allocation for one pointer, but not the other.
329 // That means they are definitely not pointing to the same allocation.
331 "{} called on pointers into different allocations",
335 (Ok((a_alloc_id, a_offset, _)), Ok((b_alloc_id, b_offset, _))) => {
336 // Found allocation for both. They must be into the same allocation.
337 if a_alloc_id != b_alloc_id {
339 "{} called on pointers into different allocations",
343 // Use these offsets for distance calculation.
344 (a_offset.bytes(), b_offset.bytes())
350 // The subtraction is always done in `isize` to enforce
351 // the "no more than `isize::MAX` apart" requirement.
352 let a_offset = ImmTy::from_uint(a_offset, isize_layout);
353 let b_offset = ImmTy::from_uint(b_offset, isize_layout);
354 let (val, overflowed, _ty) =
355 self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?;
357 throw_ub_format!("pointers were too far apart for {}", intrinsic_name);
359 val.to_machine_isize(self)?
362 // Check that the range between them is dereferenceable ("in-bounds or one past the
363 // end of the same allocation"). This is like the check in ptr_offset_inbounds.
364 let min_ptr = if distance >= 0 { b } else { a };
365 self.check_ptr_access_align(
367 Size::from_bytes(distance.unsigned_abs()),
369 CheckInAllocMsg::OffsetFromTest,
372 if intrinsic_name == sym::ptr_offset_from_unsigned && distance < 0 {
374 "{} called when first pointer has smaller offset than second: {} < {}",
381 // Perform division by size to compute return value.
382 let ret_layout = if intrinsic_name == sym::ptr_offset_from_unsigned {
387 let pointee_layout = self.layout_of(substs.type_at(0))?;
388 // If ret_layout is unsigned, we checked that so is the distance, so we are good.
389 let val = ImmTy::from_int(distance, ret_layout);
390 let size = ImmTy::from_int(pointee_layout.size.bytes(), ret_layout);
391 self.exact_div(&val, &size, dest)?;
395 self.copy_op(&args[0], dest, /*allow_transmute*/ true)?;
397 sym::assert_inhabited | sym::assert_zero_valid | sym::assert_uninit_valid => {
398 let ty = instance.substs.type_at(0);
399 let layout = self.layout_of(ty)?;
401 // For *all* intrinsics we first check `is_uninhabited` to give a more specific
403 if layout.abi.is_uninhabited() {
404 // The run-time intrinsic panics just to get a good backtrace; here we abort
405 // since there is no problem showing a backtrace even for aborts.
409 "aborted execution: attempted to instantiate uninhabited type `{}`",
415 if intrinsic_name == sym::assert_zero_valid {
416 let should_panic = !self.tcx.permits_zero_init(layout);
422 "aborted execution: attempted to zero-initialize type `{}`, which is invalid",
429 if intrinsic_name == sym::assert_uninit_valid {
430 let should_panic = !self.tcx.permits_uninit_init(layout);
436 "aborted execution: attempted to leave type `{}` uninitialized, which is invalid",
443 sym::simd_insert => {
444 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
446 let (input, input_len) = self.operand_to_simd(&args[0])?;
447 let (dest, dest_len) = self.place_to_simd(dest)?;
448 assert_eq!(input_len, dest_len, "Return vector length must match input length");
451 "Index `{}` must be in bounds of vector with length {}`",
456 for i in 0..dest_len {
457 let place = self.mplace_index(&dest, i)?;
458 let value = if i == index {
461 self.mplace_index(&input, i)?.into()
463 self.copy_op(&value, &place.into(), /*allow_transmute*/ false)?;
466 sym::simd_extract => {
467 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
468 let (input, input_len) = self.operand_to_simd(&args[0])?;
471 "index `{}` must be in bounds of vector with length `{}`",
476 &self.mplace_index(&input, index)?.into(),
478 /*allow_transmute*/ false,
481 sym::likely | sym::unlikely | sym::black_box => {
482 // These just return their argument
483 self.copy_op(&args[0], dest, /*allow_transmute*/ false)?;
486 let cond = self.read_scalar(&args[0])?.check_init()?.to_bool()?;
488 throw_ub_format!("`assume` intrinsic called with `false`");
492 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
493 self.write_scalar(result, dest)?;
495 _ => return Ok(false),
498 trace!("{:?}", self.dump_place(**dest));
499 self.go_to_block(ret);
505 a: &ImmTy<'tcx, M::PointerTag>,
506 b: &ImmTy<'tcx, M::PointerTag>,
507 dest: &PlaceTy<'tcx, M::PointerTag>,
508 ) -> InterpResult<'tcx> {
509 // Performs an exact division, resulting in undefined behavior where
510 // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
511 // First, check x % y != 0 (or if that computation overflows).
512 let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
513 assert!(!overflow); // All overflow is UB, so this should never return on overflow.
514 if res.assert_bits(a.layout.size) != 0 {
515 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b)
517 // `Rem` says this is all right, so we can let `Div` do its job.
518 self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
521 pub fn saturating_arith(
524 l: &ImmTy<'tcx, M::PointerTag>,
525 r: &ImmTy<'tcx, M::PointerTag>,
526 ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
527 assert!(matches!(mir_op, BinOp::Add | BinOp::Sub));
528 let (val, overflowed, _ty) = self.overflowing_binary_op(mir_op, l, r)?;
530 let size = l.layout.size;
531 let num_bits = size.bits();
532 if l.layout.abi.is_signed() {
533 // For signed ints the saturated value depends on the sign of the first
534 // term since the sign of the second term can be inferred from this and
535 // the fact that the operation has overflowed (if either is 0 no
536 // overflow can occur)
537 let first_term: u128 = l.to_scalar()?.to_bits(l.layout.size)?;
538 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
539 if first_term_positive {
540 // Negative overflow not possible since the positive first term
541 // can only increase an (in range) negative term for addition
542 // or corresponding negated positive term for subtraction
543 Scalar::from_int(size.signed_int_max(), size)
545 // Positive overflow not possible for similar reason
547 Scalar::from_int(size.signed_int_min(), size)
551 if matches!(mir_op, BinOp::Add) {
553 Scalar::from_uint(size.unsigned_int_max(), size)
556 Scalar::from_uint(0u128, size)
564 /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
565 /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
566 /// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
567 pub fn ptr_offset_inbounds(
569 ptr: Pointer<Option<M::PointerTag>>,
570 pointee_ty: Ty<'tcx>,
572 ) -> InterpResult<'tcx, Pointer<Option<M::PointerTag>>> {
573 // We cannot overflow i64 as a type's size must be <= isize::MAX.
574 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
575 // The computed offset, in bytes, must not overflow an isize.
576 // `checked_mul` enforces a too small bound, but no actual allocation can be big enough for
577 // the difference to be noticeable.
579 offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
580 // The offset being in bounds cannot rely on "wrapping around" the address space.
581 // So, first rule out overflows in the pointer arithmetic.
582 let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
583 // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
584 // memory between these pointers must be accessible. Note that we do not require the
585 // pointers to be properly aligned (unlike a read/write operation).
586 let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
587 // This call handles checking for integer/null pointers.
588 self.check_ptr_access_align(
590 Size::from_bytes(offset_bytes.unsigned_abs()),
592 CheckInAllocMsg::PointerArithmeticTest,
597 /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
598 pub(crate) fn copy_intrinsic(
600 src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
601 dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
602 count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
603 nonoverlapping: bool,
604 ) -> InterpResult<'tcx> {
605 let count = self.read_scalar(&count)?.to_machine_usize(self)?;
606 let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
607 let (size, align) = (layout.size, layout.align.abi);
608 // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
609 // but no actual allocation can be big enough for the difference to be noticeable.
610 let size = size.checked_mul(count, self).ok_or_else(|| {
612 "overflow computing total size of `{}`",
613 if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
617 let src = self.read_pointer(&src)?;
618 let dst = self.read_pointer(&dst)?;
620 self.mem_copy(src, align, dst, align, size, nonoverlapping)
623 pub(crate) fn write_bytes_intrinsic(
625 dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
626 byte: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
627 count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
628 ) -> InterpResult<'tcx> {
629 let layout = self.layout_of(dst.layout.ty.builtin_deref(true).unwrap().ty)?;
631 let dst = self.read_pointer(&dst)?;
632 let byte = self.read_scalar(&byte)?.to_u8()?;
633 let count = self.read_scalar(&count)?.to_machine_usize(self)?;
635 // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
636 // but no actual allocation can be big enough for the difference to be noticeable.
639 .checked_mul(count, self)
640 .ok_or_else(|| err_ub_format!("overflow computing total size of `write_bytes`"))?;
642 let bytes = std::iter::repeat(byte).take(len.bytes_usize());
643 self.write_bytes_ptr(dst, bytes)
646 pub(crate) fn raw_eq_intrinsic(
648 lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
649 rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
650 ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
651 let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
652 assert!(!layout.is_unsized());
654 let lhs = self.read_pointer(lhs)?;
655 let rhs = self.read_pointer(rhs)?;
656 let lhs_bytes = self.read_bytes_ptr(lhs, layout.size)?;
657 let rhs_bytes = self.read_bytes_ptr(rhs, layout.size)?;
658 Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))