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sanity check field offsets in unsizeable structs

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This commit is contained in:
Lukas Markeffsky 2023-07-02 14:07:08 +02:00
parent 478071ba9d
commit e3de14e463
1 changed files with 49 additions and 0 deletions
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49
compiler/rustc_ty_utils/src/layout.rs
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@ -499,6 +499,55 @@ fn layout_of_uncached<'tcx>(
return Err(error(cx, LayoutError::SizeOverflow(ty)));
};
// If the struct tail is sized and can be unsized, check that unsizing doesn't move the fields around.
if cfg!(debug_assertions)
&& maybe_unsized
&& def
.non_enum_variant()
.fields
.raw
.last()
.unwrap()
.ty(tcx, substs)
.is_sized(tcx, cx.param_env)
{
let mut variants = variants;
let tail_replacement = cx.layout_of(Ty::new_slice(tcx, tcx.types.u8)).unwrap();
*variants[FIRST_VARIANT].raw.last_mut().unwrap() = tail_replacement.layout;
let Some(unsized_layout) = cx.layout_of_struct_or_enum(
&def.repr(),
&variants,
def.is_enum(),
def.is_unsafe_cell(),
tcx.layout_scalar_valid_range(def.did()),
get_discriminant_type,
discriminants_iter(),
dont_niche_optimize_enum,
!maybe_unsized,
) else {
bug!("failed to compute unsized layout of {ty:?}");
};
let FieldsShape::Arbitrary { offsets: sized_offsets, .. } = &layout.fields else {
bug!("unexpected FieldsShape for sized layout of {ty:?}: {:?}", layout.fields);
};
let FieldsShape::Arbitrary { offsets: unsized_offsets, .. } = &unsized_layout.fields else {
bug!("unexpected FieldsShape for unsized layout of {ty:?}: {:?}", unsized_layout.fields);
};
let (sized_tail, sized_fields) = sized_offsets.raw.split_last().unwrap();
let (unsized_tail, unsized_fields) = unsized_offsets.raw.split_last().unwrap();
if sized_fields != unsized_fields {
bug!("unsizing {ty:?} changed field order!\n{layout:?}\n{unsized_layout:?}");
}
if sized_tail < unsized_tail {
bug!("unsizing {ty:?} moved tail backwards!\n{layout:?}\n{unsized_layout:?}");
}
}
tcx.mk_layout(layout)
}