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fix computing the dynamic alignment of packed structs with dyn trait tails

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This commit is contained in:
Ralf Jung 2023-12-02 13:40:24 +01:00
parent 7176b8babd
commit 7e4c4271f4
4 changed files with 98 additions and 47 deletions
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43
compiler/rustc_const_eval/src/interpret/eval_context.rs
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@ -686,14 +686,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
assert!(layout.fields.count() > 0);
trace!("DST layout: {:?}", layout);
let sized_size = layout.fields.offset(layout.fields.count() - 1);
let unsized_offset_unadjusted = layout.fields.offset(layout.fields.count() - 1);
let sized_align = layout.align.abi;
trace!(
"DST {} statically sized prefix size: {:?} align: {:?}",
layout.ty,
sized_size,
sized_align
);
// Recurse to get the size of the dynamically sized field (must be
// the last field). Can't have foreign types here, how would we
@ -707,36 +701,35 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
return Ok(None);
};
// FIXME (#26403, #27023): We should be adding padding
// to `sized_size` (to accommodate the `unsized_align`
// required of the unsized field that follows) before
// summing it with `sized_size`. (Note that since #26403
// is unfixed, we do not yet add the necessary padding
// here. But this is where the add would go.)
// # First compute the dynamic alignment
// Return the sum of sizes and max of aligns.
let size = sized_size + unsized_size; // `Size` addition
// Packed types ignore the alignment of their fields.
// Packed type alignment needs to be capped.
if let ty::Adt(def, _) = layout.ty.kind() {
if def.repr().packed() {
unsized_align = sized_align;
if let Some(packed) = def.repr().pack {
unsized_align = unsized_align.min(packed);
}
}
// Choose max of two known alignments (combined value must
// be aligned according to more restrictive of the two).
let align = sized_align.max(unsized_align);
let full_align = sized_align.max(unsized_align);
// Issue #27023: must add any necessary padding to `size`
// (to make it a multiple of `align`) before returning it.
let size = size.align_to(align);
// # Then compute the dynamic size
let unsized_offset_adjusted = unsized_offset_unadjusted.align_to(unsized_align);
let full_size = (unsized_offset_adjusted + unsized_size).align_to(full_align);
// Just for our sanitiy's sake, assert that this is equal to what codegen would compute.
assert_eq!(
full_size,
(unsized_offset_unadjusted + unsized_size).align_to(full_align)
);
// Check if this brought us over the size limit.
if size > self.max_size_of_val() {
if full_size > self.max_size_of_val() {
throw_ub!(InvalidMeta(InvalidMetaKind::TooBig));
}
Ok(Some((size, align)))
Ok(Some((full_size, full_align)))
}
ty::Dynamic(_, _, ty::Dyn) => {
let vtable = metadata.unwrap_meta().to_pointer(self)?;