src/operator.rs

   1 use std::convert::TryFrom;
   2
   3 use rustc::mir;
   4 use rustc::ty::{
   5     layout::{LayoutOf, Size},
   6     Ty,
   7 };
   8
   9 use crate::*;
  10
  11 pub trait EvalContextExt<'tcx> {
  12     fn binary_ptr_op(
  13         &self,
  14         bin_op: mir::BinOp,
  15         left: ImmTy<'tcx, Tag>,
  16         right: ImmTy<'tcx, Tag>,
  17     ) -> InterpResult<'tcx, (Scalar<Tag>, bool, Ty<'tcx>)>;
  18
  19     fn ptr_eq(&self, left: Scalar<Tag>, right: Scalar<Tag>) -> InterpResult<'tcx, bool>;
  20
  21     fn pointer_offset_inbounds(
  22         &self,
  23         ptr: Scalar<Tag>,
  24         pointee_ty: Ty<'tcx>,
  25         offset: i64,
  26     ) -> InterpResult<'tcx, Scalar<Tag>>;
  27 }
  28
  29 impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
  30     fn binary_ptr_op(
  31         &self,
  32         bin_op: mir::BinOp,
  33         left: ImmTy<'tcx, Tag>,
  34         right: ImmTy<'tcx, Tag>,
  35     ) -> InterpResult<'tcx, (Scalar<Tag>, bool, Ty<'tcx>)> {
  36         use rustc::mir::BinOp::*;
  37
  38         trace!("ptr_op: {:?} {:?} {:?}", *left, bin_op, *right);
  39
  40         Ok(match bin_op {
  41             Eq | Ne => {
  42                 // This supports fat pointers.
  43                 #[rustfmt::skip]
  44                 let eq = match (*left, *right) {
  45                     (Immediate::Scalar(left), Immediate::Scalar(right)) => {
  46                         self.ptr_eq(left.not_undef()?, right.not_undef()?)?
  47                     }
  48                     (Immediate::ScalarPair(left1, left2), Immediate::ScalarPair(right1, right2)) => {
  49                         self.ptr_eq(left1.not_undef()?, right1.not_undef()?)?
  50                             && self.ptr_eq(left2.not_undef()?, right2.not_undef()?)?
  51                     }
  52                     _ => bug!("Type system should not allow comparing Scalar with ScalarPair"),
  53                 };
  54                 (Scalar::from_bool(if bin_op == Eq { eq } else { !eq }), false, self.tcx.types.bool)
  55             }
  56
  57             Lt | Le | Gt | Ge => {
  58                 // Just compare the integers.
  59                 // TODO: Do we really want to *always* do that, even when comparing two live in-bounds pointers?
  60                 let left = self.force_bits(left.to_scalar()?, left.layout.size)?;
  61                 let right = self.force_bits(right.to_scalar()?, right.layout.size)?;
  62                 let res = match bin_op {
  63                     Lt => left < right,
  64                     Le => left <= right,
  65                     Gt => left > right,
  66                     Ge => left >= right,
  67                     _ => bug!("We already established it has to be one of these operators."),
  68                 };
  69                 (Scalar::from_bool(res), false, self.tcx.types.bool)
  70             }
  71
  72             Offset => {
  73                 let pointee_ty =
  74                     left.layout.ty.builtin_deref(true).expect("Offset called on non-ptr type").ty;
  75                 let ptr = self.pointer_offset_inbounds(
  76                     left.to_scalar()?,
  77                     pointee_ty,
  78                     right.to_scalar()?.to_machine_isize(self)?,
  79                 )?;
  80                 (ptr, false, left.layout.ty)
  81             }
  82
  83             _ => bug!("Invalid operator on pointers: {:?}", bin_op),
  84         })
  85     }
  86
  87     fn ptr_eq(&self, left: Scalar<Tag>, right: Scalar<Tag>) -> InterpResult<'tcx, bool> {
  88         let size = self.pointer_size();
  89         // Just compare the integers.
  90         // TODO: Do we really want to *always* do that, even when comparing two live in-bounds pointers?
  91         let left = self.force_bits(left, size)?;
  92         let right = self.force_bits(right, size)?;
  93         Ok(left == right)
  94     }
  95
  96     /// Raises an error if the offset moves the pointer outside of its allocation.
  97     /// For integers, we consider each of them their own tiny allocation of size 0,
  98     /// so offset-by-0 is okay for them -- except for NULL, which we rule out entirely.
  99     fn pointer_offset_inbounds(
 100         &self,
 101         ptr: Scalar<Tag>,
 102         pointee_ty: Ty<'tcx>,
 103         offset: i64,
 104     ) -> InterpResult<'tcx, Scalar<Tag>> {
 105         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 106         let offset = offset
 107             .checked_mul(pointee_size)
 108             .ok_or_else(|| err_ub_format!("overflow during offset comutation for inbounds pointer arithmetic"))?;
 109         // We do this first, to rule out overflows.
 110         let offset_ptr = ptr.ptr_signed_offset(offset, self)?;
 111         // What we need to check is that starting at `min(ptr, offset_ptr)`,
 112         // we could do an access of size `abs(offset)`. Alignment does not matter.
 113         let (min_ptr, abs_offset) = if offset >= 0 {
 114             (ptr, u64::try_from(offset).unwrap())
 115         } else {
 116             // Negative offset.
 117             // If the negation overflows, the result will be negative so the try_from will fail.
 118             (offset_ptr, u64::try_from(-offset).unwrap())
 119         };
 120         self.memory.check_ptr_access_align(
 121             min_ptr,
 122             Size::from_bytes(abs_offset),
 123             None,
 124             CheckInAllocMsg::InboundsTest,
 125         )?;
 126         // That's it!
 127         Ok(offset_ptr)
 128     }
 129 }