make sure we only guess field alignment at offset 0

This commit is contained in:
Ralf Jung 2018-11-06 08:41:56 +01:00
parent a6622c265c
commit ba0bab39e0
2 changed files with 14 additions and 11 deletions

View File

@ -374,13 +374,12 @@ pub(super) fn size_and_align_of(
let (unsized_size, unsized_align) = match self.size_and_align_of(metadata, field)? {
Some(size_and_align) => size_and_align,
None => {
// A field with extern type. If this field is at offset 0 and the sized
// part makes no alignment constraints, we behave like the underlying
// extern type.
// A field with extern type. If this field is at offset 0, we behave
// like the underlying extern type.
// FIXME: Once we have made decisions for how to handle size and alignment
// of `extern type`, this should be adapted. It is just a temporary hack
// to get some code to work that probably ought to work.
if sized_size == Size::ZERO && sized_align.abi() == 1 {
if sized_size == Size::ZERO {
return Ok(None)
} else {
bug!("Fields cannot be extern types, unless they are at offset 0")

View File

@ -353,13 +353,17 @@ pub fn mplace_field(
// Offset may need adjustment for unsized fields
let (meta, offset) = if field_layout.is_unsized() {
// re-use parent metadata to determine dynamic field layout
let align = self.size_and_align_of(base.meta, field_layout)?
.map(|(_, align)| align)
// If this is an extern type, we fall back to its static alignment.
// FIXME: Once we have made decisions for how to handle size and alignment
// of `extern type`, this should be adapted. It is just a temporary hack
// to get some code to work that probably ought to work.
.unwrap_or_else(|| base.layout.align);
let align = match self.size_and_align_of(base.meta, field_layout)? {
Some((_, align)) => align,
None if offset == Size::ZERO =>
// An extern type at offset 0, we fall back to its static alignment.
// FIXME: Once we have made decisions for how to handle size and alignment
// of `extern type`, this should be adapted. It is just a temporary hack
// to get some code to work that probably ought to work.
field_layout.align,
None =>
bug!("Cannot compute offset for extern type field at non-0 offset"),
};
(base.meta, offset.abi_align(align))
} else {
// base.meta could be present; we might be accessing a sized field of an unsized