fix(redox-rt): close O_CLOEXEC fds individually in fexec_impl

The kernel proc scheme returns EBADF for writes to Filetable/NewFiletable
handles, so the bulk FileTableVerb::Close call was silently failing. Close
each O_CLOEXEC fd with SYS_CLOSE instead, which updates both the kernel file
table and the userspace FILETABLE. This unblocks Command::spawn() parents
waiting on the CLOEXEC sync pipe.

redox-rt/src/proc.rs

@@ -493,11 +493,24 @@ pub fn fexec_impl(
         let _siglock = crate::signal::tmp_disable_signals();
         let fds_to_close = {
             let guard = crate::current_filetable();
+            let old_filetable_fd = guard.fd().as_ref().map(|f| f.as_raw_fd());
             let mut fds = alloc::vec::Vec::new();
             for (fd, flags) in guard.iter() {
                 if fd == addrspace_selection_fd.as_raw_fd() {
                     continue; // Will be closed below
                 }
+                if Some(fd) == old_filetable_fd {
+                    continue;
+                }
+                if fd == thread_fd.as_raw_fd() {
+                    continue;
+                }
+                if fd == proc_fd.as_raw_fd() {
+                    continue;
+                }
+                if fd == grants_fd.as_raw_fd() {
+                    continue;
+                }
 
                 if flags & O_CLOEXEC == O_CLOEXEC || fd == image_file.as_raw_fd() {
                     fds.push(fd);
@@ -507,26 +520,8 @@ pub fn fexec_impl(
             fds
         };
 
-        let fds_to_close_bytes: &[u8] = unsafe {
-            core::slice::from_raw_parts(
-                fds_to_close.as_ptr() as *mut u8,
-                fds_to_close.len() * core::mem::size_of::<usize>(),
-            )
-        };
-
-    {
-            let filetable_fd = thread_fd.dup_into_upper(b"filetable-binary")?;
-            let _ = filetable_fd.call_wo(
-                fds_to_close_bytes,
-                CallFlags::empty(),
-                &[syscall::FileTableVerb::Close as u64],
-            );
-        }
-        {
-            let mut guard = crate::current_filetable();
-            for fd in fds_to_close {
-                let _ = guard.remove(fd);
-            }
+        for &fd in &fds_to_close {
+            let _ = crate::sys::close_raw(fd);
         }
 
         unsafe {