src/operator.rs

   1 use std::convert::TryFrom;
   2
   3 use log::trace;
   4
   5 use rustc_middle::{mir, ty::Ty};
   6 use rustc_target::abi::{LayoutOf, Size};
   7
   8 use crate::*;
   9
  10 pub trait EvalContextExt<'tcx> {
  11     fn binary_ptr_op(
  12         &self,
  13         bin_op: mir::BinOp,
  14         left: ImmTy<'tcx, Tag>,
  15         right: ImmTy<'tcx, Tag>,
  16     ) -> InterpResult<'tcx, (Scalar<Tag>, bool, Ty<'tcx>)>;
  17
  18     fn ptr_eq(&self, left: Scalar<Tag>, right: Scalar<Tag>) -> InterpResult<'tcx, bool>;
  19
  20     fn pointer_offset_inbounds(
  21         &self,
  22         ptr: Scalar<Tag>,
  23         pointee_ty: Ty<'tcx>,
  24         offset: i64,
  25     ) -> InterpResult<'tcx, Scalar<Tag>>;
  26 }
  27
  28 impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
  29     fn binary_ptr_op(
  30         &self,
  31         bin_op: mir::BinOp,
  32         left: ImmTy<'tcx, Tag>,
  33         right: ImmTy<'tcx, Tag>,
  34     ) -> InterpResult<'tcx, (Scalar<Tag>, bool, Ty<'tcx>)> {
  35         use rustc_middle::mir::BinOp::*;
  36
  37         trace!("ptr_op: {:?} {:?} {:?}", *left, bin_op, *right);
  38
  39         Ok(match bin_op {
  40             Eq | Ne => {
  41                 // This supports fat pointers.
  42                 #[rustfmt::skip]
  43                 let eq = match (*left, *right) {
  44                     (Immediate::Scalar(left), Immediate::Scalar(right)) => {
  45                         self.ptr_eq(left.not_undef()?, right.not_undef()?)?
  46                     }
  47                     (Immediate::ScalarPair(left1, left2), Immediate::ScalarPair(right1, right2)) => {
  48                         self.ptr_eq(left1.not_undef()?, right1.not_undef()?)?
  49                             && self.ptr_eq(left2.not_undef()?, right2.not_undef()?)?
  50                     }
  51                     _ => bug!("Type system should not allow comparing Scalar with ScalarPair"),
  52                 };
  53                 (Scalar::from_bool(if bin_op == Eq { eq } else { !eq }), false, self.tcx.types.bool)
  54             }
  55
  56             Lt | Le | Gt | Ge => {
  57                 // Just compare the integers.
  58                 // TODO: Do we really want to *always* do that, even when comparing two live in-bounds pointers?
  59                 let left = self.force_bits(left.to_scalar()?, left.layout.size)?;
  60                 let right = self.force_bits(right.to_scalar()?, right.layout.size)?;
  61                 let res = match bin_op {
  62                     Lt => left < right,
  63                     Le => left <= right,
  64                     Gt => left > right,
  65                     Ge => left >= right,
  66                     _ => bug!("We already established it has to be one of these operators."),
  67                 };
  68                 (Scalar::from_bool(res), false, self.tcx.types.bool)
  69             }
  70
  71             Offset => {
  72                 let pointee_ty =
  73                     left.layout.ty.builtin_deref(true).expect("Offset called on non-ptr type").ty;
  74                 let ptr = self.pointer_offset_inbounds(
  75                     left.to_scalar()?,
  76                     pointee_ty,
  77                     right.to_scalar()?.to_machine_isize(self)?,
  78                 )?;
  79                 (ptr, false, left.layout.ty)
  80             }
  81
  82             _ => bug!("Invalid operator on pointers: {:?}", bin_op),
  83         })
  84     }
  85
  86     fn ptr_eq(&self, left: Scalar<Tag>, right: Scalar<Tag>) -> InterpResult<'tcx, bool> {
  87         let size = self.pointer_size();
  88         // Just compare the integers.
  89         // TODO: Do we really want to *always* do that, even when comparing two live in-bounds pointers?
  90         let left = self.force_bits(left, size)?;
  91         let right = self.force_bits(right, size)?;
  92         Ok(left == right)
  93     }
  94
  95     /// Raises an error if the offset moves the pointer outside of its allocation.
  96     /// For integers, we consider each of them their own tiny allocation of size 0,
  97     /// so offset-by-0 is okay for them -- except for NULL, which we rule out entirely.
  98     fn pointer_offset_inbounds(
  99         &self,
 100         ptr: Scalar<Tag>,
 101         pointee_ty: Ty<'tcx>,
 102         offset: i64,
 103     ) -> InterpResult<'tcx, Scalar<Tag>> {
 104         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 105         let offset = offset.checked_mul(pointee_size).ok_or_else(|| {
 106             err_ub_format!("overflow during offset comutation for inbounds pointer arithmetic")
 107         })?;
 108         // We do this first, to rule out overflows.
 109         let offset_ptr = ptr.ptr_signed_offset(offset, self)?;
 110         // What we need to check is that starting at `min(ptr, offset_ptr)`,
 111         // we could do an access of size `abs(offset)`. Alignment does not matter.
 112         let (min_ptr, abs_offset) = if offset >= 0 {
 113             (ptr, u64::try_from(offset).unwrap())
 114         } else {
 115             // Negative offset.
 116             // If the negation overflows, the result will be negative so the try_from will fail.
 117             (offset_ptr, u64::try_from(-offset).unwrap())
 118         };
 119         self.memory.check_ptr_access_align(
 120             min_ptr,
 121             Size::from_bytes(abs_offset),
 122             None,
 123             CheckInAllocMsg::InboundsTest,
 124         )?;
 125         // That's it!
 126         Ok(offset_ptr)
 127     }
 128 }