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intrinsics.rs
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intrinsics.rs
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//! Intrinsics and other functions that the miri engine executes without
//! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
//! and miri.
use std::convert::TryFrom;
use rustc_hir::def_id::DefId;
use rustc_middle::mir::{
self,
interpret::{ConstValue, GlobalId, InterpResult, Scalar},
BinOp,
};
use rustc_middle::ty;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::{Ty, TyCtxt};
use rustc_span::symbol::{sym, Symbol};
use rustc_target::abi::{Abi, Align, LayoutOf as _, Primitive, Size};
use super::{
util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
Pointer,
};
mod caller_location;
mod type_name;
fn numeric_intrinsic<Tag>(name: Symbol, bits: u128, kind: Primitive) -> Scalar<Tag> {
let size = match kind {
Primitive::Int(integer, _) => integer.size(),
_ => bug!("invalid `{}` argument: {:?}", name, bits),
};
let extra = 128 - u128::from(size.bits());
let bits_out = match name {
sym::ctpop => u128::from(bits.count_ones()),
sym::ctlz => u128::from(bits.leading_zeros()) - extra,
sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
sym::bswap => (bits << extra).swap_bytes(),
sym::bitreverse => (bits << extra).reverse_bits(),
_ => bug!("not a numeric intrinsic: {}", name),
};
Scalar::from_uint(bits_out, size)
}
/// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
/// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
crate fn eval_nullary_intrinsic<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
def_id: DefId,
substs: SubstsRef<'tcx>,
) -> InterpResult<'tcx, ConstValue<'tcx>> {
let tp_ty = substs.type_at(0);
let name = tcx.item_name(def_id);
Ok(match name {
sym::type_name => {
ensure_monomorphic_enough(tcx, tp_ty)?;
let alloc = type_name::alloc_type_name(tcx, tp_ty);
ConstValue::Slice { data: alloc, start: 0, end: alloc.len() }
}
sym::needs_drop => {
ensure_monomorphic_enough(tcx, tp_ty)?;
ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env))
}
sym::min_align_of | sym::pref_align_of => {
// Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
let n = match name {
sym::pref_align_of => layout.align.pref.bytes(),
sym::min_align_of => layout.align.abi.bytes(),
_ => bug!(),
};
ConstValue::from_machine_usize(n, &tcx)
}
sym::type_id => {
ensure_monomorphic_enough(tcx, tp_ty)?;
ConstValue::from_u64(tcx.type_id_hash(tp_ty))
}
sym::variant_count => match tp_ty.kind() {
// Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
ty::Adt(ref adt, _) => ConstValue::from_machine_usize(adt.variants.len() as u64, &tcx),
ty::Projection(_)
| ty::Opaque(_, _)
| ty::Param(_)
| ty::Bound(_, _)
| ty::Placeholder(_)
| ty::Infer(_) => throw_inval!(TooGeneric),
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Slice(_)
| ty::RawPtr(_)
| ty::Ref(_, _, _)
| ty::FnDef(_, _)
| ty::FnPtr(_)
| ty::Dynamic(_, _)
| ty::Closure(_, _)
| ty::Generator(_, _, _)
| ty::GeneratorWitness(_)
| ty::Never
| ty::Tuple(_)
| ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
},
other => bug!("`{}` is not a zero arg intrinsic", other),
})
}
impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
/// Returns `true` if emulation happened.
/// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
/// intrinsic handling.
pub fn emulate_intrinsic(
&mut self,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx, M::PointerTag>],
ret: Option<(&PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
) -> InterpResult<'tcx, bool> {
let substs = instance.substs;
let intrinsic_name = self.tcx.item_name(instance.def_id());
// First handle intrinsics without return place.
let (dest, ret) = match ret {
None => match intrinsic_name {
sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
// Unsupported diverging intrinsic.
_ => return Ok(false),
},
Some(p) => p,
};
// Keep the patterns in this match ordered the same as the list in
// `src/librustc_middle/ty/constness.rs`
match intrinsic_name {
sym::caller_location => {
let span = self.find_closest_untracked_caller_location();
let location = self.alloc_caller_location_for_span(span);
self.write_immediate(location.to_ref(self), dest)?;
}
sym::min_align_of_val | sym::size_of_val => {
// Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
// dereferencable!
let place = self.ref_to_mplace(&self.read_immediate(&args[0])?)?;
let (size, align) = self
.size_and_align_of_mplace(&place)?
.ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
let result = match intrinsic_name {
sym::min_align_of_val => align.bytes(),
sym::size_of_val => size.bytes(),
_ => bug!(),
};
self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
}
sym::min_align_of
| sym::pref_align_of
| sym::needs_drop
| sym::type_id
| sym::type_name
| sym::variant_count => {
let gid = GlobalId { instance, promoted: None };
let ty = match intrinsic_name {
sym::min_align_of | sym::pref_align_of | sym::variant_count => {
self.tcx.types.usize
}
sym::needs_drop => self.tcx.types.bool,
sym::type_id => self.tcx.types.u64,
sym::type_name => self.tcx.mk_static_str(),
_ => bug!("already checked for nullary intrinsics"),
};
let val =
self.tcx.const_eval_global_id(self.param_env, gid, Some(self.tcx.span))?;
let val = self.const_val_to_op(val, ty, Some(dest.layout))?;
self.copy_op(&val, dest)?;
}
sym::ctpop
| sym::cttz
| sym::cttz_nonzero
| sym::ctlz
| sym::ctlz_nonzero
| sym::bswap
| sym::bitreverse => {
let ty = substs.type_at(0);
let layout_of = self.layout_of(ty)?;
let val = self.read_scalar(&args[0])?.check_init()?;
let bits = val.to_bits(layout_of.size)?;
let kind = match layout_of.abi {
Abi::Scalar(ref scalar) => scalar.value,
_ => span_bug!(
self.cur_span(),
"{} called on invalid type {:?}",
intrinsic_name,
ty
),
};
let (nonzero, intrinsic_name) = match intrinsic_name {
sym::cttz_nonzero => (true, sym::cttz),
sym::ctlz_nonzero => (true, sym::ctlz),
other => (false, other),
};
if nonzero && bits == 0 {
throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
}
let out_val = numeric_intrinsic(intrinsic_name, bits, kind);
self.write_scalar(out_val, dest)?;
}
sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
let lhs = self.read_immediate(&args[0])?;
let rhs = self.read_immediate(&args[1])?;
let bin_op = match intrinsic_name {
sym::add_with_overflow => BinOp::Add,
sym::sub_with_overflow => BinOp::Sub,
sym::mul_with_overflow => BinOp::Mul,
_ => bug!("Already checked for int ops"),
};
self.binop_with_overflow(bin_op, &lhs, &rhs, dest)?;
}
sym::saturating_add | sym::saturating_sub => {
let l = self.read_immediate(&args[0])?;
let r = self.read_immediate(&args[1])?;
let is_add = intrinsic_name == sym::saturating_add;
let (val, overflowed, _ty) = self.overflowing_binary_op(
if is_add { BinOp::Add } else { BinOp::Sub },
&l,
&r,
)?;
let val = if overflowed {
let num_bits = l.layout.size.bits();
if l.layout.abi.is_signed() {
// For signed ints the saturated value depends on the sign of the first
// term since the sign of the second term can be inferred from this and
// the fact that the operation has overflowed (if either is 0 no
// overflow can occur)
let first_term: u128 = l.to_scalar()?.to_bits(l.layout.size)?;
let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
if first_term_positive {
// Negative overflow not possible since the positive first term
// can only increase an (in range) negative term for addition
// or corresponding negated positive term for subtraction
Scalar::from_uint(
(1u128 << (num_bits - 1)) - 1, // max positive
Size::from_bits(num_bits),
)
} else {
// Positive overflow not possible for similar reason
// max negative
Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
}
} else {
// unsigned
if is_add {
// max unsigned
Scalar::from_uint(
u128::MAX >> (128 - num_bits),
Size::from_bits(num_bits),
)
} else {
// underflow to 0
Scalar::from_uint(0u128, Size::from_bits(num_bits))
}
}
} else {
val
};
self.write_scalar(val, dest)?;
}
sym::discriminant_value => {
let place = self.deref_operand(&args[0])?;
let discr_val = self.read_discriminant(&place.into())?.0;
self.write_scalar(discr_val, dest)?;
}
sym::unchecked_shl
| sym::unchecked_shr
| sym::unchecked_add
| sym::unchecked_sub
| sym::unchecked_mul
| sym::unchecked_div
| sym::unchecked_rem => {
let l = self.read_immediate(&args[0])?;
let r = self.read_immediate(&args[1])?;
let bin_op = match intrinsic_name {
sym::unchecked_shl => BinOp::Shl,
sym::unchecked_shr => BinOp::Shr,
sym::unchecked_add => BinOp::Add,
sym::unchecked_sub => BinOp::Sub,
sym::unchecked_mul => BinOp::Mul,
sym::unchecked_div => BinOp::Div,
sym::unchecked_rem => BinOp::Rem,
_ => bug!("Already checked for int ops"),
};
let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
if overflowed {
let layout = self.layout_of(substs.type_at(0))?;
let r_val = r.to_scalar()?.to_bits(layout.size)?;
if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
} else {
throw_ub_format!("overflow executing `{}`", intrinsic_name);
}
}
self.write_scalar(val, dest)?;
}
sym::rotate_left | sym::rotate_right => {
// rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
// rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
let layout = self.layout_of(substs.type_at(0))?;
let val = self.read_scalar(&args[0])?.check_init()?;
let val_bits = val.to_bits(layout.size)?;
let raw_shift = self.read_scalar(&args[1])?.check_init()?;
let raw_shift_bits = raw_shift.to_bits(layout.size)?;
let width_bits = u128::from(layout.size.bits());
let shift_bits = raw_shift_bits % width_bits;
let inv_shift_bits = (width_bits - shift_bits) % width_bits;
let result_bits = if intrinsic_name == sym::rotate_left {
(val_bits << shift_bits) | (val_bits >> inv_shift_bits)
} else {
(val_bits >> shift_bits) | (val_bits << inv_shift_bits)
};
let truncated_bits = self.truncate(result_bits, layout);
let result = Scalar::from_uint(truncated_bits, layout.size);
self.write_scalar(result, dest)?;
}
sym::copy => {
self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
}
sym::offset => {
let ptr = self.read_pointer(&args[0])?;
let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
let pointee_ty = substs.type_at(0);
let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
self.write_pointer(offset_ptr, dest)?;
}
sym::arith_offset => {
let ptr = self.read_pointer(&args[0])?;
let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
let pointee_ty = substs.type_at(0);
let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
let offset_bytes = offset_count.wrapping_mul(pointee_size);
let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
self.write_pointer(offset_ptr, dest)?;
}
sym::ptr_offset_from => {
let a = self.read_immediate(&args[0])?.to_scalar()?;
let b = self.read_immediate(&args[1])?.to_scalar()?;
// Special case: if both scalars are *equal integers*
// and not null, we pretend there is an allocation of size 0 right there,
// and their offset is 0. (There's never a valid object at null, making it an
// exception from the exception.)
// This is the dual to the special exception for offset-by-0
// in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
//
// Control flow is weird because we cannot early-return (to reach the
// `go_to_block` at the end).
let done = if let (Ok(a), Ok(b)) = (a.try_to_int(), b.try_to_int()) {
let a = a.try_to_machine_usize(*self.tcx).unwrap();
let b = b.try_to_machine_usize(*self.tcx).unwrap();
if a == b && a != 0 {
self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
true
} else {
false
}
} else {
false
};
if !done {
// General case: we need two pointers.
let a = self.scalar_to_ptr(a);
let b = self.scalar_to_ptr(b);
let (a_alloc_id, a_offset, _) = self.memory.ptr_get_alloc(a)?;
let (b_alloc_id, b_offset, _) = self.memory.ptr_get_alloc(b)?;
if a_alloc_id != b_alloc_id {
throw_ub_format!(
"ptr_offset_from cannot compute offset of pointers into different \
allocations.",
);
}
let usize_layout = self.layout_of(self.tcx.types.usize)?;
let isize_layout = self.layout_of(self.tcx.types.isize)?;
let a_offset = ImmTy::from_uint(a_offset.bytes(), usize_layout);
let b_offset = ImmTy::from_uint(b_offset.bytes(), usize_layout);
let (val, _overflowed, _ty) =
self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?;
let pointee_layout = self.layout_of(substs.type_at(0))?;
let val = ImmTy::from_scalar(val, isize_layout);
let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
self.exact_div(&val, &size, dest)?;
}
}
sym::transmute => {
self.copy_op_transmute(&args[0], dest)?;
}
sym::assert_inhabited => {
let ty = instance.substs.type_at(0);
let layout = self.layout_of(ty)?;
if layout.abi.is_uninhabited() {
// The run-time intrinsic panics just to get a good backtrace; here we abort
// since there is no problem showing a backtrace even for aborts.
M::abort(
self,
format!(
"aborted execution: attempted to instantiate uninhabited type `{}`",
ty
),
)?;
}
}
sym::simd_insert => {
let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
let elem = &args[2];
let input = &args[0];
let (len, e_ty) = input.layout.ty.simd_size_and_type(*self.tcx);
assert!(
index < len,
"Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
index,
e_ty,
len
);
assert_eq!(
input.layout, dest.layout,
"Return type `{}` must match vector type `{}`",
dest.layout.ty, input.layout.ty
);
assert_eq!(
elem.layout.ty, e_ty,
"Scalar element type `{}` must match vector element type `{}`",
elem.layout.ty, e_ty
);
for i in 0..len {
let place = self.place_index(dest, i)?;
let value = if i == index { *elem } else { self.operand_index(input, i)? };
self.copy_op(&value, &place)?;
}
}
sym::simd_extract => {
let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
let (len, e_ty) = args[0].layout.ty.simd_size_and_type(*self.tcx);
assert!(
index < len,
"index `{}` is out-of-bounds of vector type `{}` with length `{}`",
index,
e_ty,
len
);
assert_eq!(
e_ty, dest.layout.ty,
"Return type `{}` must match vector element type `{}`",
dest.layout.ty, e_ty
);
self.copy_op(&self.operand_index(&args[0], index)?, dest)?;
}
sym::likely | sym::unlikely => {
// These just return their argument
self.copy_op(&args[0], dest)?;
}
sym::assume => {
let cond = self.read_scalar(&args[0])?.check_init()?.to_bool()?;
if !cond {
throw_ub_format!("`assume` intrinsic called with `false`");
}
}
sym::raw_eq => {
let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
self.write_scalar(result, dest)?;
}
_ => return Ok(false),
}
trace!("{:?}", self.dump_place(**dest));
self.go_to_block(ret);
Ok(true)
}
pub fn exact_div(
&mut self,
a: &ImmTy<'tcx, M::PointerTag>,
b: &ImmTy<'tcx, M::PointerTag>,
dest: &PlaceTy<'tcx, M::PointerTag>,
) -> InterpResult<'tcx> {
// Performs an exact division, resulting in undefined behavior where
// `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
// First, check x % y != 0 (or if that computation overflows).
let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
if overflow || res.assert_bits(a.layout.size) != 0 {
// Then, check if `b` is -1, which is the "MIN / -1" case.
let minus1 = Scalar::from_int(-1, dest.layout.size);
let b_scalar = b.to_scalar().unwrap();
if b_scalar == minus1 {
throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
} else {
throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
}
}
// `Rem` says this is all right, so we can let `Div` do its job.
self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
}
/// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
/// allocation. For integer pointers, we consider each of them their own tiny allocation of size
/// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
pub fn ptr_offset_inbounds(
&self,
ptr: Pointer<Option<M::PointerTag>>,
pointee_ty: Ty<'tcx>,
offset_count: i64,
) -> InterpResult<'tcx, Pointer<Option<M::PointerTag>>> {
// We cannot overflow i64 as a type's size must be <= isize::MAX.
let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
// The computed offset, in bytes, cannot overflow an isize.
let offset_bytes =
offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
// The offset being in bounds cannot rely on "wrapping around" the address space.
// So, first rule out overflows in the pointer arithmetic.
let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
// ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
// memory between these pointers must be accessible. Note that we do not require the
// pointers to be properly aligned (unlike a read/write operation).
let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
let size = offset_bytes.unsigned_abs();
// This call handles checking for integer/null pointers.
self.memory.check_ptr_access_align(
min_ptr,
Size::from_bytes(size),
Align::ONE,
CheckInAllocMsg::PointerArithmeticTest,
)?;
Ok(offset_ptr)
}
/// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
pub(crate) fn copy_intrinsic(
&mut self,
src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
nonoverlapping: bool,
) -> InterpResult<'tcx> {
let count = self.read_scalar(&count)?.to_machine_usize(self)?;
let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
let (size, align) = (layout.size, layout.align.abi);
let size = size.checked_mul(count, self).ok_or_else(|| {
err_ub_format!(
"overflow computing total size of `{}`",
if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
)
})?;
let src = self.read_pointer(&src)?;
let dst = self.read_pointer(&dst)?;
self.memory.copy(src, align, dst, align, size, nonoverlapping)
}
pub(crate) fn raw_eq_intrinsic(
&mut self,
lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
assert!(!layout.is_unsized());
let lhs = self.read_pointer(lhs)?;
let rhs = self.read_pointer(rhs)?;
let lhs_bytes = self.memory.read_bytes(lhs, layout.size)?;
let rhs_bytes = self.memory.read_bytes(rhs, layout.size)?;
Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
}
}