rust/src/helpers.rs

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use std::mem;
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use rustc::ty::{self, layout};
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use rustc::hir::def_id::{DefId, CRATE_DEF_INDEX};
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use crate::*;
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impl<'a, 'mir, 'tcx> EvalContextExt<'a, 'mir, 'tcx> for crate::MiriEvalContext<'a, 'mir, 'tcx> {}
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pub trait EvalContextExt<'a, 'mir, 'tcx: 'a + 'mir>: crate::MiriEvalContextExt<'a, 'mir, 'tcx> {
/// Gets an instance for a path.
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fn resolve_path(&self, path: &[&str]) -> EvalResult<'tcx, ty::Instance<'tcx>> {
let this = self.eval_context_ref();
this.tcx
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.crates()
.iter()
.find(|&&krate| this.tcx.original_crate_name(krate) == path[0])
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.and_then(|krate| {
let krate = DefId {
krate: *krate,
index: CRATE_DEF_INDEX,
};
let mut items = this.tcx.item_children(krate);
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let mut path_it = path.iter().skip(1).peekable();
while let Some(segment) = path_it.next() {
for item in mem::replace(&mut items, Default::default()).iter() {
if item.ident.name == *segment {
if path_it.peek().is_none() {
return Some(ty::Instance::mono(this.tcx.tcx, item.def.def_id()));
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}
items = this.tcx.item_children(item.def.def_id());
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break;
}
}
}
None
})
.ok_or_else(|| {
let path = path.iter().map(|&s| s.to_owned()).collect();
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InterpError::PathNotFound(path).into()
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})
}
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/// Visits the memory covered by `place`, sensitive to freezing: the 3rd parameter
/// will be true if this is frozen, false if this is in an `UnsafeCell`.
fn visit_freeze_sensitive(
&self,
place: MPlaceTy<'tcx, Borrow>,
size: Size,
mut action: impl FnMut(Pointer<Borrow>, Size, bool) -> EvalResult<'tcx>,
) -> EvalResult<'tcx> {
let this = self.eval_context_ref();
trace!("visit_frozen(place={:?}, size={:?})", *place, size);
debug_assert_eq!(size,
this.size_and_align_of_mplace(place)?
.map(|(size, _)| size)
.unwrap_or_else(|| place.layout.size)
);
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// Store how far we proceeded into the place so far. Everything to the left of
// this offset has already been handled, in the sense that the frozen parts
// have had `action` called on them.
let mut end_ptr = place.ptr;
// Called when we detected an `UnsafeCell` at the given offset and size.
// Calls `action` and advances `end_ptr`.
let mut unsafe_cell_action = |unsafe_cell_ptr: Scalar<Borrow>, unsafe_cell_size: Size| {
if unsafe_cell_size != Size::ZERO {
debug_assert_eq!(unsafe_cell_ptr.to_ptr().unwrap().alloc_id,
end_ptr.to_ptr().unwrap().alloc_id);
debug_assert_eq!(unsafe_cell_ptr.to_ptr().unwrap().tag,
end_ptr.to_ptr().unwrap().tag);
}
// We assume that we are given the fields in increasing offset order,
// and nothing else changes.
let unsafe_cell_offset = unsafe_cell_ptr.get_ptr_offset(this);
let end_offset = end_ptr.get_ptr_offset(this);
assert!(unsafe_cell_offset >= end_offset);
let frozen_size = unsafe_cell_offset - end_offset;
// Everything between the end_ptr and this `UnsafeCell` is frozen.
if frozen_size != Size::ZERO {
action(end_ptr.to_ptr()?, frozen_size, /*frozen*/true)?;
}
// This `UnsafeCell` is NOT frozen.
if unsafe_cell_size != Size::ZERO {
action(unsafe_cell_ptr.to_ptr()?, unsafe_cell_size, /*frozen*/false)?;
}
// Update end end_ptr.
end_ptr = unsafe_cell_ptr.ptr_wrapping_offset(unsafe_cell_size, this);
// Done
Ok(())
};
// Run a visitor
{
let mut visitor = UnsafeCellVisitor {
ecx: this,
unsafe_cell_action: |place| {
trace!("unsafe_cell_action on {:?}", place.ptr);
// We need a size to go on.
let unsafe_cell_size = this.size_and_align_of_mplace(place)?
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.map(|(size, _)| size)
// for extern types, just cover what we can
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.unwrap_or_else(|| place.layout.size);
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// Now handle this `UnsafeCell`, unless it is empty.
if unsafe_cell_size != Size::ZERO {
unsafe_cell_action(place.ptr, unsafe_cell_size)
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} else {
Ok(())
}
},
};
visitor.visit_value(place)?;
}
// The part between the end_ptr and the end of the place is also frozen.
// So pretend there is a 0-sized `UnsafeCell` at the end.
unsafe_cell_action(place.ptr.ptr_wrapping_offset(size, this), Size::ZERO)?;
// Done!
return Ok(());
/// Visiting the memory covered by a `MemPlace`, being aware of
/// whether we are inside an `UnsafeCell` or not.
struct UnsafeCellVisitor<'ecx, 'a, 'mir, 'tcx, F>
where F: FnMut(MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
{
ecx: &'ecx MiriEvalContext<'a, 'mir, 'tcx>,
unsafe_cell_action: F,
}
impl<'ecx, 'a, 'mir, 'tcx, F>
ValueVisitor<'a, 'mir, 'tcx, Evaluator<'tcx>>
for
UnsafeCellVisitor<'ecx, 'a, 'mir, 'tcx, F>
where
F: FnMut(MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
{
type V = MPlaceTy<'tcx, Borrow>;
#[inline(always)]
fn ecx(&self) -> &MiriEvalContext<'a, 'mir, 'tcx> {
&self.ecx
}
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// Hook to detect `UnsafeCell`.
fn visit_value(&mut self, v: MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
{
trace!("UnsafeCellVisitor: {:?} {:?}", *v, v.layout.ty);
let is_unsafe_cell = match v.layout.ty.sty {
ty::Adt(adt, _) => Some(adt.did) == self.ecx.tcx.lang_items().unsafe_cell_type(),
_ => false,
};
if is_unsafe_cell {
// We do not have to recurse further, this is an `UnsafeCell`.
(self.unsafe_cell_action)(v)
} else if self.ecx.type_is_freeze(v.layout.ty) {
// This is `Freeze`, there cannot be an `UnsafeCell`
Ok(())
} else {
// Proceed further
self.walk_value(v)
}
}
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// Make sure we visit aggregrates in increasing offset order.
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fn visit_aggregate(
&mut self,
place: MPlaceTy<'tcx, Borrow>,
fields: impl Iterator<Item=EvalResult<'tcx, MPlaceTy<'tcx, Borrow>>>,
) -> EvalResult<'tcx> {
match place.layout.fields {
layout::FieldPlacement::Array { .. } => {
// For the array layout, we know the iterator will yield sorted elements so
// we can avoid the allocation.
self.walk_aggregate(place, fields)
}
layout::FieldPlacement::Arbitrary { .. } => {
// Gather the subplaces and sort them before visiting.
let mut places = fields.collect::<EvalResult<'tcx, Vec<MPlaceTy<'tcx, Borrow>>>>()?;
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places.sort_by_key(|place| place.ptr.get_ptr_offset(self.ecx()));
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self.walk_aggregate(place, places.into_iter().map(Ok))
}
layout::FieldPlacement::Union { .. } => {
// Uh, what?
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bug!("a union is not an aggregate we should ever visit")
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}
}
}
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// We have to do *something* for unions.
fn visit_union(&mut self, v: MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
{
// With unions, we fall back to whatever the type says, to hopefully be consistent
// with LLVM IR.
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// FIXME: are we consistent, and is this really the behavior we want?
let frozen = self.ecx.type_is_freeze(v.layout.ty);
if frozen {
Ok(())
} else {
(self.unsafe_cell_action)(v)
}
}
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// We should never get to a primitive, but always short-circuit somewhere above.
fn visit_primitive(&mut self, _v: MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
{
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bug!("we should always short-circuit before coming to a primitive")
}
}
}
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}