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Rollup merge of #71101 - RalfJung:miri-alignment-check, r=ecstatic-morse
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Miri: let machine hook dynamically decide about alignment checks

This is needed for rust-lang/miri#1332.
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Dylan-DPC authored Apr 13, 2020
2 parents eb49f7f + 28e6b1a commit 73e56de
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Showing 4 changed files with 13 additions and 7 deletions.
9 changes: 6 additions & 3 deletions src/librustc_mir/const_eval/machine.rs
Original file line number Diff line number Diff line change
Expand Up @@ -179,9 +179,12 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter {

const GLOBAL_KIND: Option<!> = None; // no copying of globals from `tcx` to machine memory

// We do not check for alignment to avoid having to carry an `Align`
// in `ConstValue::ByRef`.
const CHECK_ALIGN: bool = false;
#[inline(always)]
fn enforce_alignment(_memory_extra: &Self::MemoryExtra) -> bool {
// We do not check for alignment to avoid having to carry an `Align`
// in `ConstValue::ByRef`.
false
}

#[inline(always)]
fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
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2 changes: 1 addition & 1 deletion src/librustc_mir/interpret/machine.rs
Original file line number Diff line number Diff line change
Expand Up @@ -118,7 +118,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
const GLOBAL_KIND: Option<Self::MemoryKind>;

/// Whether memory accesses should be alignment-checked.
const CHECK_ALIGN: bool;
fn enforce_alignment(memory_extra: &Self::MemoryExtra) -> bool;

/// Whether to enforce the validity invariant
fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
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4 changes: 2 additions & 2 deletions src/librustc_mir/interpret/memory.rs
Original file line number Diff line number Diff line change
Expand Up @@ -323,12 +323,12 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
size: Size,
align: Align,
) -> InterpResult<'tcx, Option<Pointer<M::PointerTag>>> {
let align = M::CHECK_ALIGN.then_some(align);
let align = M::enforce_alignment(&self.extra).then_some(align);
self.check_ptr_access_align(sptr, size, align, CheckInAllocMsg::MemoryAccessTest)
}

/// Like `check_ptr_access`, but *definitely* checks alignment when `align`
/// is `Some` (overriding `M::CHECK_ALIGN`). Also lets the caller control
/// is `Some` (overriding `M::enforce_alignment`). Also lets the caller control
/// the error message for the out-of-bounds case.
pub fn check_ptr_access_align(
&self,
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5 changes: 4 additions & 1 deletion src/librustc_mir/transform/const_prop.rs
Original file line number Diff line number Diff line change
Expand Up @@ -173,7 +173,10 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine {

const GLOBAL_KIND: Option<!> = None; // no copying of globals from `tcx` to machine memory

const CHECK_ALIGN: bool = false;
#[inline(always)]
fn enforce_alignment(_memory_extra: &Self::MemoryExtra) -> bool {
false
}

#[inline(always)]
fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
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