add deref_pointer_as

Author: beepster4096

src/tools/miri/src/helpers.rs

@@ -746,6 +746,20 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         Ok(mplace)
     }
 
+    fn deref_pointer_as(
+        &self,
+        val: &ImmTy<'tcx, Provenance>,
+        layout: TyAndLayout<'tcx>,
+    ) -> InterpResult<'tcx, MPlaceTy<'tcx, Provenance>> {
+        let this = self.eval_context_ref();
+        let mut mplace = this.ref_to_mplace(val)?;
+
+        mplace.layout = layout;
+        mplace.align = layout.align.abi;
+
+        Ok(mplace)
+    }
+
     /// Calculates the MPlaceTy given the offset and layout of an access on an operand
     fn deref_operand_and_offset(
         &self,

src/tools/miri/src/shims/unix/linux/sync.rs

@@ -85,8 +85,11 @@ pub fn futex<'tcx>(
                 return Ok(());
             }
 
-            let timeout_op = &args[3];
-            let timeout_time = if this.ptr_is_null(this.read_pointer(timeout_op)?)? {
+            let timeout = this.deref_pointer_as(
+                &this.read_immediate(&args[3])?,
+                this.libc_ty_layout("timespec"),
+            )?;
+            let timeout_time = if this.ptr_is_null(timeout.ptr)? {
                 None
             } else {
                 let realtime = op & futex_realtime == futex_realtime;
@@ -95,7 +98,6 @@ pub fn futex<'tcx>(
                         "`futex` syscall with `op=FUTEX_WAIT` and non-null timeout with `FUTEX_CLOCK_REALTIME`",
                     )?;
                 }
-                let timeout = this.deref_operand_as(timeout_op, this.libc_ty_layout("timespec"))?;
                 let duration = match this.read_timespec(&timeout)? {
                     Some(duration) => duration,
                     None => {