Move the maxevents.try_into().unwrap() after value check

Author: tiif

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

@@ -403,18 +403,20 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         let epfd = this.read_scalar(epfd)?.to_i32()?;
         let maxevents = this.read_scalar(maxevents)?.to_i32()?;
-        let event = this.deref_pointer_as(
-            events_op,
-            this.libc_array_ty_layout("epoll_event", maxevents.try_into().unwrap()),
-        )?;
         let timeout = this.read_scalar(timeout)?.to_i32()?;
-
         if epfd <= 0 || maxevents <= 0 {
             let einval = this.eval_libc("EINVAL");
             this.set_last_error(einval)?;
             return Ok(Scalar::from_i32(-1));
         }
 
+        // This needs to come after the maxevents value check, or else maxevents.try_into().unwrap()
+        // will fail.
+        let event = this.deref_pointer_as(
+            events_op,
+            this.libc_array_ty_layout("epoll_event", maxevents.try_into().unwrap()),
+        )?;
+
         // FIXME: Implement blocking support
         if timeout != 0 {
             throw_unsup_format!("epoll_wait: timeout value can only be 0");

src/tools/miri/tests/pass-dep/libc/libc-epoll.rs

@@ -19,7 +19,7 @@ fn main() {
     test_epoll_ctl_del();
     test_pointer();
     test_two_same_fd_in_same_epoll_instance();
-    test_epoll_wait_less_maxevent_zero();
+    test_epoll_wait_maxevent_zero();
 }
 
 // Using `as` cast since `EPOLLET` wraps around
@@ -530,8 +530,7 @@ fn test_no_notification_for_unregister_flag() {
     check_epoll_wait::<8>(epfd, &[(expected_event, expected_value)]);
 }
 
-
-fn test_epoll_wait_less_maxevent_zero() {
+fn test_epoll_wait_maxevent_zero() {
     // Create an epoll instance.
     let epfd = unsafe { libc::epoll_create1(0) };
     assert_ne!(epfd, -1);