misc: Set generic pselect as ENOSYS

The generic pselect implementation has the very specific race condition
that motived the creation of the pselect syscall (no atomicity in
signal mask set/reset).  Using it as generic implementation is
counterproductive  Also currently only microblaze uses it as fallback
when used on kernel prior 3.15.

This patch moves the generic implementation to a microblaze specific
one, sets the generic internal as a ENOSYS, and cleanups the Linux
generic implementation.

The microblaze implementation mimics the previous Linux generic one,
where it either uses pselect6 directly if __ASSUME_PSELECT or a
first try pselect6 then the fallback otherwise.

Checked on x86_64-linux-gnu and microblaze-linux-gnu.

2 files changed, 77 insertions, 33 deletions

diff --git a/sysdeps/unix/sysv/linux/microblaze/pselect.c b/sysdeps/unix/sysv/linux/microblaze/pselect.c
new file mode 100644
index 0000000000..19efce86d8
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/microblaze/pselect.c
@@ -0,0 +1,73 @@
+/* Synchronous I/O multiplexing.  Linux/microblaze version.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <signal.h>
+#include <time.h>
+#include <sys/poll.h>
+#include <sysdep-cancel.h>
+
+#ifndef __ASSUME_PSELECT
+# define __pselect __pselect_syscall
+#endif
+
+/* If pselect is supported, just use the Linux generic implementation.  */
+#include <sysdeps/unix/sysv/linux/pselect.c>
+
+#ifndef __ASSUME_PSELECT
+# undef __pselect
+int
+__pselect (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
+	   const struct timespec *timeout, const sigset_t *sigmask)
+{
+  int ret = __pselect_syscall (nfds, readfds, writefds, exceptfds, timeout,
+			       sigmask);
+  if (ret >= 0 || errno != ENOSYS)
+    return ret;
+
+  /* The fallback uses 'select' which shows the race condition regarding
+     signal mask set/restore, requires two additional syscalls, and has
+     a worse timeout precision (microseconds instead of nanoseconds).  */
+
+  struct timeval tval, *ptval = NULL;
+  if (timeout != NULL)
+    {
+      if (! valid_nanoseconds (timeout->tv_nsec))
+	{
+	  __set_errno (EINVAL);
+	  return -1;
+	}
+
+      TIMESPEC_TO_TIMEVAL (&tval, timeout);
+      ptval = &tval;
+    }
+
+  sigset_t savemask;
+  if (sigmask != NULL)
+    __sigprocmask (SIG_SETMASK, sigmask, &savemask);
+
+  /* select itself is a cancellation entrypoint.  */
+  ret = __select (nfds, readfds, writefds, exceptfds, ptval);
+
+  if (sigmask != NULL)
+    __sigprocmask (SIG_SETMASK, &savemask, NULL);
+
+  return ret;
+}
+weak_alias (__pselect, pselect)
+#endif
diff --git a/sysdeps/unix/sysv/linux/pselect.c b/sysdeps/unix/sysv/linux/pselect.c
index acda3e0cdd..7a3dc8c4ed 100644
--- a/sysdeps/unix/sysv/linux/pselect.c
+++ b/sysdeps/unix/sysv/linux/pselect.c
@@ -16,23 +16,9 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <signal.h>
-#include <time.h>
-#include <sys/poll.h>
-#include <kernel-features.h>
+#include <sys/select.h>
 #include <sysdep-cancel.h>
 
-
-#ifdef __NR_pselect6
-# ifndef __ASSUME_PSELECT
-static int __generic_pselect (int nfds, fd_set *readfds, fd_set *writefds,
-			      fd_set *exceptfds,
-			      const struct timespec *timeout,
-			      const sigset_t *sigmask);
-# endif
-
-
 int
 __pselect (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 	   const struct timespec *timeout, const sigset_t *sigmask)
@@ -59,24 +45,9 @@ __pselect (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
   data.ss = (__syscall_ulong_t) (uintptr_t) sigmask;
   data.ss_len = _NSIG / 8;
 
-  int result = SYSCALL_CANCEL (pselect6, nfds, readfds, writefds, exceptfds,
-                               timeout, &data);
-
-# ifndef __ASSUME_PSELECT
-  if (result == -1 && errno == ENOSYS)
-    result = __generic_pselect (nfds, readfds, writefds, exceptfds, timeout,
-				sigmask);
-# endif
-
-  return result;
+  return SYSCALL_CANCEL (pselect6, nfds, readfds, writefds, exceptfds,
+                         timeout, &data);
 }
+#ifndef __pselect
 weak_alias (__pselect, pselect)
-
-# ifndef __ASSUME_PSELECT
-#  define __pselect static __generic_pselect
-# endif
-#endif
-
-#ifndef __ASSUME_PSELECT
-# include <misc/pselect.c>
 #endif