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Miri: mplace_access_checked: offer option to force different alignment on place #71280

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Merged
bors merged 2 commits into from
Apr 22, 2020
Merged

Miri: mplace_access_checked: offer option to force different alignment on place #71280

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Miri: mplace_access_checked: offer option to force different alignmen…
RalfJung Apr 18, 2020
5449e0f
comment explaining force_align usage
RalfJung Apr 22, 2020
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6 changes: 4 additions & 2 deletions src/librustc_mir/interpret/place.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -333,7 +333,7 @@ where
let val = self.read_immediate(src)?;
trace!("deref to {} on {:?}", val.layout.ty, *val);
let place = self.ref_to_mplace(val)?;
self.mplace_access_checked(place)
self.mplace_access_checked(place, None)
}

/// Check if the given place is good for memory access with the given
Expand Down Expand Up @@ -361,12 +361,14 @@ where
pub fn mplace_access_checked(
&self,
mut place: MPlaceTy<'tcx, M::PointerTag>,
force_align: Option<Align>,
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@oli-obk oli-obk Apr 22, 2020

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please leave a comment on this argument noting that is is only used to allow stacked borrows in miri to handle raw borrows.

) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
let (size, align) = self
.size_and_align_of_mplace(place)?
.unwrap_or((place.layout.size, place.layout.align.abi));
assert!(place.mplace.align <= align, "dynamic alignment less strict than static one?");
place.mplace.align = align; // maximally strict checking
// Check (stricter) dynamic alignment, unless forced otherwise.
place.mplace.align = force_align.unwrap_or(align);
// When dereferencing a pointer, it must be non-NULL, aligned, and live.
if let Some(ptr) = self.check_mplace_access(place, Some(size))? {
place.mplace.ptr = ptr.into();
Expand Down