posix: New Linux posix_spawn{p} implementation

This patch implements a new posix_spawn{p} implementation for Linux.  The main
difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK
flags and a direct allocated stack.  The new stack and start function solves
most the vfork limitation (possible parent clobber due stack spilling).  The
remaning issue are related to signal handling:

  1. That no signal handlers must run in child context, to avoid corrupt
     parent's state.
  2. Child must synchronize with parent to enforce stack deallocation and
     to possible return execv issues.

The first one is solved by blocking all signals in child, even NPTL-internal
ones (SIGCANCEL and SIGSETXID).  The second issue is done by a stack allocation
in parent and a synchronization with using a pipe or waitpid (in case or error).
The pipe has the advantage of allowing the child signal an exec error (checked
with new tst-spawn2 test).

There is an inherent race condition in pipe2 usage for architectures that do not
support the syscall directly.  In such cases the a pipe plus fctnl is used
instead and it may lead to file descriptor leak in parent (as decribed by fcntl
documentation).

The child process stack is allocate with a mmap with MAP_STACK flag using
default architecture stack size.  Although it is slower than use a stack buffer
from parent, it allows some slack for the compatibility code to run scripts
with no shebang (which may use a buffer with size depending of argument list
count).

Performance should be similar to the vfork default posix implementation and
way faster than fork path (vfork on mostly linux ports are basically
clone with CLONE_VM plus CLONE_VFORK).  The only difference is the syscalls
required for the stack allocation/deallocation.

It fixes BZ#10354, BZ#14750, and BZ#18433.

Tested on i386, x86_64, powerpc64le, and aarch64.

	[BZ #14750]
	[BZ #10354]
	[BZ #18433]
	* include/sched.h (__clone): Add hidden prototype.
	(__clone2): Likewise.
	* include/unistd.h (__dup): Likewise.
	* posix/Makefile (tests): Add tst-spawn2.
	* posix/tst-spawn2.c: New file.
	* sysdeps/posix/dup.c (__dup): Add hidden definition.
	* sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/alpha/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/arm/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/hppa/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/i386/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/ia64/clone2.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/m68k/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/microblaze/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/mips/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/nios2/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S (__clone):
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S (__clone):
	Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/sh/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/tile/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/x86_64/clone.S (__clone): Likewise.
	* sysdeps/unix/sysv/linux/nptl-signals.h
	(____nptl_is_internal_signal): New function.
	* sysdeps/unix/sysv/linux/spawni.c: New file.

1 files changed, 72 insertions, 0 deletions

diff --git a/posix/tst-spawn2.c b/posix/tst-spawn2.c
new file mode 100644
index 0000000000..149f3d5cfa
--- /dev/null
+++ b/posix/tst-spawn2.c
@@ -0,0 +1,72 @@
+/* Further tests for spawn in case of invalid binary paths.
+   Copyright (C) 2016 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <spawn.h>
+#include <error.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+#include <stdio.h>
+
+int
+posix_spawn_test (void)
+{
+  /* Check if posix_spawn correctly returns an error and an invalid pid
+     by trying to spawn an invalid binary.  */
+
+  const char *program = "/path/to/invalid/binary";
+  char * const args[] = { 0 };
+  pid_t pid = -1;
+
+  int ret = posix_spawn (&pid, program, 0, 0, args, environ);
+  if (ret != ENOENT)
+    error (EXIT_FAILURE, errno, "posix_spawn");
+
+  /* POSIX states the value returned on pid variable in case of an error
+     is not specified.  GLIBC will update the value iff the child
+     execution is successful.  */
+  if (pid != -1)
+    error (EXIT_FAILURE, errno, "posix_spawn returned pid != -1");
+
+  /* Check if no child is actually created.  */
+  ret = waitpid (-1, NULL, 0);
+  if (ret != -1 || errno != ECHILD)
+    error (EXIT_FAILURE, errno, "waitpid");
+
+  /* Same as before, but with posix_spawnp.  */
+  char *args2[] = { (char*) program, 0 };
+
+  ret = posix_spawnp (&pid, args2[0], 0, 0, args2, environ);
+  if (ret != ENOENT)
+    error (EXIT_FAILURE, errno, "posix_spawnp");
+
+  if (pid != -1)
+    error (EXIT_FAILURE, errno, "posix_spawnp returned pid != -1");
+
+  ret = waitpid (-1, NULL, 0);
+  if (ret != -1 || errno != ECHILD)
+    error (EXIT_FAILURE, errno, "waitpid");
+
+  return 0;
+}
+
+#define TEST_FUNCTION  posix_spawn_test ()
+#include "../test-skeleton.c"