Refactor: directly write to MPlaceTy inside fn epoll_wait

Author: tiif

src/shims/unix/linux/epoll.rs

@@ -378,7 +378,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         events_op: &OpTy<'tcx>,
         maxevents: &OpTy<'tcx>,
         timeout: &OpTy<'tcx>,
-    ) -> InterpResult<'tcx, Scalar> {
+        place: &MPlaceTy<'tcx>,
+    ) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
 
         let epfd = this.read_scalar(epfd)?.to_i32()?;
@@ -392,15 +393,18 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         if epfd <= 0 {
             let einval = this.eval_libc("EINVAL");
             this.set_last_error(einval)?;
-            return Ok(Scalar::from_i32(-1));
+            this.write_scalar(Scalar::from_i32(-1), place)?;
+            return Ok(());
         }
         // FIXME: Implement blocking support
         if timeout != 0 {
             throw_unsup_format!("epoll_wait: timeout value can only be 0");
         }
 
         let Some(epfd) = this.machine.fds.get_ref(epfd) else {
-            return Ok(Scalar::from_i32(this.fd_not_found()?));
+            let result_value = this.fd_not_found()?;
+            this.write_scalar(Scalar::from_i32(result_value), place)?;
+            return Ok(());
         };
         let mut binding = epfd.borrow_mut();
         let epoll_file_description = &mut binding
@@ -431,7 +435,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 }
             }
         }
-        Ok(Scalar::from_i32(num_of_events))
+        this.write_scalar(Scalar::from_i32(num_of_events), place)?;
+        Ok(())
     }
     /// For a specific unique file descriptor id, get its ready events and update
     /// the corresponding ready list. This function is called whenever a file description

src/shims/unix/linux/foreign_items.rs

@@ -62,8 +62,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             "epoll_wait" => {
                 let [epfd, events, maxevents, timeout] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let result = this.epoll_wait(epfd, events, maxevents, timeout)?;
-                this.write_scalar(result, dest)?;
+                this.epoll_wait(epfd, events, maxevents, timeout, dest)?;
             }
             "eventfd" => {
                 let [val, flag] =