libc: Implement call gate for I/O, FILE and stream flushing

nxtask_exit_cleanup performs the cleanup functions, but it needs
a call gate for BUILD_PROTECTED/BUILD_KERNEL.

include/nuttx/sched.h

@@ -1032,6 +1032,22 @@ void nxtask_starthook(FAR struct task_tcb_s *tcb, starthook_t starthook,
 void nxtask_startup(main_t entrypt, int argc, FAR char *argv[]);
 #endif
 
+/****************************************************************************
+ * Name: nxtask_exit_cleanup
+ *
+ * Description:
+ *   Perform cleanup before task is closed.
+ *
+ *   If SCHED_ATEXIT or SCHED_ONEXIT are defined, all functions registered
+ *   with atexit() and on_exit() are called, in the reverse order of their
+ *   registration.
+ *
+ *   All open streams are flushed and closed.
+ *
+ ****************************************************************************/
+
+void nxtask_exit_cleanup(int status);
+
 /****************************************************************************
  * Internal vfork support.  The overall sequence is:
  *

include/sys/syscall_lookup.h

@@ -271,6 +271,10 @@ SYSCALL_LOOKUP(futimens,                   2)
   SYSCALL_LOOKUP(nx_mkfifo,                3)
 #endif
 
+#ifndef CONFIG_BUILD_FLAT
+  SYSCALL_LOOKUP(nxtask_exit_cleanup,      1)
+#endif
+
 #ifdef CONFIG_FILE_STREAM
   SYSCALL_LOOKUP(fs_fdopen,                4)
   SYSCALL_LOOKUP(nxsched_get_streams,      0)

libs/libc/stdlib/lib_exit.c

@@ -24,17 +24,10 @@
 
 #include <nuttx/config.h>
 
-#include <stdlib.h>
-#include <unistd.h>
+#include "libc.h"
 
 #include "atexit.h"
 
-/****************************************************************************
- * Public Function Prototypes
- ****************************************************************************/
-
-void nxtask_exit_cleanup(int status);
-
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -43,8 +36,6 @@ void exit(int status)
 {
   __atexit_call_exitfuncs(status);
 
-  /* REVISIT: Need to flush files and streams */
-
   nxtask_exit_cleanup(status);
 
   _exit(status);

syscall/syscall.csv

@@ -77,6 +77,7 @@
 "nx_vsyslog","nuttx/syslog/syslog.h","","int","int","FAR const IPTR char *","FAR va_list *"
 "nxsched_get_stackinfo","nuttx/sched.h","","int","pid_t","FAR struct stackinfo_s *"
 "nxsched_get_streams","nuttx/sched.h","defined(CONFIG_FILE_STREAM)","FAR struct streamlist *"
+"nxtask_exit_cleanup","nuttx/sched.h","","void","int"
 "open","fcntl.h","","int","FAR const char *","int","...","mode_t"
 "opendir","dirent.h","","FAR DIR *","FAR const char *"
 "pgalloc", "nuttx/arch.h", "defined(CONFIG_BUILD_KERNEL)", "uintptr_t", "uintptr_t", "unsigned int"