[PATCH 1/2] misc: Set generic pselect as ENOSYS

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

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.

Also, the microblaze generic implementation first try to issue
pselect instead of use the fallback (since it is expect that if
the microblaze usage does rely on pselect, a sufficient updated
kernel will be used).  Microblaze defines __NR_pselect6 for Linux
v3.2, although it was only wire-up on v3.15 (and the syscall number
is the same as previous defined).

Checked with a build against i686-linux-gnu (smoke test) and
microblaze-linux-gnu.
---
 misc/pselect.c                               | 41 +-----------
 sysdeps/unix/sysv/linux/microblaze/pselect.c | 69 ++++++++++++++++++++
 sysdeps/unix/sysv/linux/pselect.c            | 31 +--------
 3 files changed, 75 insertions(+), 66 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/microblaze/pselect.c

diff --git a/misc/pselect.c b/misc/pselect.c
index 76ded850a5..7296b6ef61 100644
--- a/misc/pselect.c
+++ b/misc/pselect.c
@@ -34,43 +34,8 @@ int
 __pselect (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 	   const struct timespec *timeout, const sigset_t *sigmask)
 {
-  struct timeval tval;
-  int retval;
-  sigset_t savemask;
-
-  /* Change nanosecond number to microseconds.  This might mean losing
-     precision and therefore the `pselect` should be available.  But
-     for now it is hardly found.  */
-  if (timeout != NULL)
-    {
-      /* Catch bugs which would be hidden by the TIMESPEC_TO_TIMEVAL
-	 computations.  The division by 1000 truncates values.  */
-      if (__glibc_unlikely (timeout->tv_nsec < 0))
-	{
-	  __set_errno (EINVAL);
-	  return -1;
-	}
-
-      TIMESPEC_TO_TIMEVAL (&tval, timeout);
-    }
-
-  /* The setting and restoring of the signal mask and the select call
-     should be an atomic operation.  This can't be done without kernel
-     help.  */
-  if (sigmask != NULL)
-    __sigprocmask (SIG_SETMASK, sigmask, &savemask);
-
-  /* Note the pselect() is a cancellation point.  But since we call
-     select() which itself is a cancellation point we do not have
-     to do anything here.  */
-  retval = __select (nfds, readfds, writefds, exceptfds,
-		     timeout != NULL ? &tval : NULL);
-
-  if (sigmask != NULL)
-    __sigprocmask (SIG_SETMASK, &savemask, NULL);
-
-  return retval;
+  __set_errno (ENOSYS);
+  return -1;
 }
-#ifndef __pselect
 weak_alias (__pselect, pselect)
-#endif
+stub_warning (pselect)
diff --git a/sysdeps/unix/sysv/linux/microblaze/pselect.c b/sysdeps/unix/sysv/linux/microblaze/pselect.c
new file mode 100644
index 0000000000..62430ca69a
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/microblaze/pselect.c
@@ -0,0 +1,69 @@
+/* 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>
+
+/* Microblaze defines __NR_pselect6 for Linux v3.2, although it was wire-up
+   on v3.15.  */
+#define __pselect __pselect_syscall
+#include <sysdeps/unix/sysv/linux/pselect.c>
+#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 'selects' 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)
diff --git a/sysdeps/unix/sysv/linux/pselect.c b/sysdeps/unix/sysv/linux/pselect.c
index acda3e0cdd..77a5179925 100644
--- a/sysdeps/unix/sysv/linux/pselect.c
+++ b/sysdeps/unix/sysv/linux/pselect.c
@@ -23,16 +23,6 @@
 #include <kernel-features.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 +49,9 @@ __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
-- 
2.17.1