avoid integer overflow in ptr-to-int cast

Author: RalfJung

src/intptrcast.rs

@@ -4,7 +4,8 @@ use std::cmp::max;
 
 use rand::Rng;
 
-use rustc_mir::interpret::{AllocId, Pointer, InterpResult, Memory, AllocCheck};
+use rustc::ty::layout::HasDataLayout;
+use rustc_mir::interpret::{AllocId, Pointer, InterpResult, Memory, AllocCheck, PointerArithmetic};
 use rustc_target::abi::Size;
 
 use crate::{Evaluator, Tag, STACK_ADDR};
@@ -109,7 +110,9 @@ impl<'mir, 'tcx> GlobalState {
         };
 
         debug_assert_eq!(base_addr % align.bytes(), 0); // sanity check
-        Ok(base_addr + ptr.offset.bytes())
+        // Add offset with the right kind of pointer-overflowing arithmetic.
+        let dl = memory.data_layout();
+        Ok(dl.overflowing_offset(base_addr, ptr.offset.bytes()).0)
     }
 
     /// Shifts `addr` to make it aligned with `align` by rounding `addr` to the smallest multiple