linux: Add clone3 CLONE_CLEAR_SIGHAND optimization to posix_spawn

The clone3 flag resets all signal handlers of the child not set to
SIG_IGN to SIG_DFL.  It allows to skip most of the sigaction calls
to setup child signal handling, where previously a posix_spawn
had to issue 2 times NSIG sigaction calls (one to obtain the current
disposition and another to set either SIG_DFL or SIG_IGN).

With POSIX_SPAWN_SETSIGDEF the child will setup the signal for the case
where the disposition is SIG_IGN.

The code must handle the fallback where clone3 is not available. This is
done by splitting __clone_internal_fallback from __clone_internal.

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

include/clone_internal.h

@@ -24,6 +24,11 @@ extern int __clone3 (struct clone_args *__cl_args, size_t __size,
    fall back to clone or clone2.  */
 extern int __clone_internal (struct clone_args *__cl_args,
 			     int (*__func) (void *__arg), void *__arg);
+/* The fallback code which calls clone/clone2 based on clone3 arguments.  */
+extern int __clone_internal_fallback (struct clone_args *__cl_args,
+				      int (*__func) (void *__arg),
+				      void *__arg)
+     attribute_hidden;
 
 #ifndef _ISOMAC
 libc_hidden_proto (__clone3)

posix/Makefile

@@ -109,7 +109,7 @@ tests		:= test-errno tstgetopt testfnm runtests runptests \
 		   tst-glob-tilde test-ssize-max tst-spawn4 bug-regex37 \
 		   bug-regex38 tst-regcomp-truncated tst-spawn-chdir \
 		   tst-wordexp-nocmd tst-execveat tst-spawn5 \
-		   tst-sched_getaffinity tst-spawn6
+		   tst-sched_getaffinity tst-spawn6 tst-spawn7
 
 # Test for the glob symbol version that was replaced in glibc 2.27.
 ifeq ($(have-GLIBC_2.26)$(build-shared),yesyes)
@@ -291,6 +291,7 @@ tst-spawn-ARGS = -- $(host-test-program-cmd)
 tst-spawn-static-ARGS = $(tst-spawn-ARGS)
 tst-spawn5-ARGS = -- $(host-test-program-cmd)
 tst-spawn6-ARGS = -- $(host-test-program-cmd)
+tst-spawn7-ARGS = -- $(host-test-program-cmd)
 tst-dir-ARGS = `pwd` `cd $(common-objdir)/$(subdir); pwd` `cd $(common-objdir); pwd` $(objpfx)tst-dir
 tst-chmod-ARGS = $(objdir)
 tst-vfork3-ARGS = --test-dir=$(objpfx)

posix/tst-spawn7.c

@@ -0,0 +1,179 @@
+/* Tests for posix_spawn signal handling.
+   Copyright (C) 2023 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 <assert.h>
+#include <getopt.h>
+#include <spawn.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/xsignal.h>
+#include <support/xunistd.h>
+#include <unistd.h>
+
+/* Nonzero if the program gets called via `exec'.  */
+#define CMDLINE_OPTIONS \
+  { "restart", no_argument, &restart, 1 },
+static int restart;
+
+/* Hold the four initial argument used to respawn the process, plus the extra
+   '--direct', '--restart', the check type ('SIG_IGN' or 'SIG_DFL'), and a
+   final NULL.  */
+static char *spargs[8];
+static int check_type_argc;
+
+/* Called on process re-execution.  */
+_Noreturn static void
+handle_restart (int argc, char *argv[])
+{
+  assert (argc == 1);
+
+  if (strcmp (argv[0], "SIG_DFL") == 0)
+    {
+      for (int i = 1; i < NSIG; i++)
+	{
+	  struct sigaction sa;
+	  int r = sigaction (i, NULL, &sa);
+	  /* Skip internal signals (such as SIGCANCEL).  */
+	  if (r == -1)
+	    continue;
+	  TEST_VERIFY_EXIT (sa.sa_handler == SIG_DFL);
+	}
+      exit (EXIT_SUCCESS);
+    }
+  else if (strcmp (argv[0], "SIG_IGN") == 0)
+    {
+      for (int i = 1; i < NSIG; i++)
+	{
+	  struct sigaction sa;
+	  int r = sigaction (i, NULL, &sa);
+	  /* Skip internal signals (such as SIGCANCEL).  */
+	  if (r == -1)
+	    continue;
+	  if (i == SIGUSR1 || i == SIGUSR2)
+	    TEST_VERIFY_EXIT (sa.sa_handler == SIG_IGN);
+	  else
+	    TEST_VERIFY_EXIT (sa.sa_handler == SIG_DFL);
+	}
+      exit (EXIT_SUCCESS);
+    }
+
+  exit (EXIT_FAILURE);
+}
+
+static void
+spawn_signal_test (const char *type, const posix_spawnattr_t *attr)
+{
+  spargs[check_type_argc] = (char*) type;
+
+  pid_t pid;
+  int status;
+
+  TEST_COMPARE (posix_spawn (&pid, spargs[0], NULL, attr, spargs, environ), 0);
+  TEST_COMPARE (xwaitpid (pid, &status, 0), pid);
+  TEST_VERIFY (WIFEXITED (status));
+  TEST_VERIFY (!WIFSIGNALED (status));
+  TEST_COMPARE (WEXITSTATUS (status), 0);
+}
+
+static void
+dummy_sa_handler (int)
+{
+}
+
+static void
+do_test_signals (void)
+{
+  {
+    /* Check if all signals handler are set to SIG_DFL on spawned process.  */
+    spawn_signal_test ("SIG_DFL", NULL);
+  }
+
+  {
+    /* Same as before, but set SIGUSR1 and SIGUSR2 to a handler different than
+       SIG_IGN or SIG_DFL.  */
+    struct sigaction sa = { 0 };
+    sa.sa_handler = dummy_sa_handler;
+    xsigaction (SIGUSR1, &sa, NULL);
+    xsigaction (SIGUSR2, &sa, NULL);
+    spawn_signal_test ("SIG_DFL", NULL);
+  }
+
+  {
+    /* Check if SIG_IGN is keep as is.  */
+    struct sigaction sa = { 0 };
+    sa.sa_handler = SIG_IGN;
+    xsigaction (SIGUSR1, &sa, NULL);
+    xsigaction (SIGUSR2, &sa, NULL);
+    spawn_signal_test ("SIG_IGN", NULL);
+  }
+
+  {
+    /* Check if SIG_IGN handlers are set to SIG_DFL.  */
+    posix_spawnattr_t attr;
+    posix_spawnattr_init (&attr);
+    sigset_t mask;
+    sigemptyset (&mask);
+    sigaddset (&mask, SIGUSR1);
+    sigaddset (&mask, SIGUSR2);
+    posix_spawnattr_setsigdefault (&attr, &mask);
+    posix_spawnattr_setflags (&attr, POSIX_SPAWN_SETSIGDEF);
+    spawn_signal_test ("SIG_DFL", &attr);
+    posix_spawnattr_destroy (&attr);
+  }
+}
+
+static int
+do_test (int argc, char *argv[])
+{
+  /* We must have either:
+
+     - one or four parameters if called initially:
+       + argv[1]: path for ld.so        optional
+       + argv[2]: "--library-path"      optional
+       + argv[3]: the library path      optional
+       + argv[4]: the application name
+
+     - six parameters left if called through re-execution:
+       + argv[1]: the application name
+       + argv[2]: check SIG_IGN/SIG_DFL.
+
+     * When built with --enable-hardcoded-path-in-tests or issued without
+       using the loader directly.  */
+
+  if (restart)
+    handle_restart (argc - 1, &argv[1]);
+
+  TEST_VERIFY_EXIT (argc == 2 || argc == 5);
+
+  int i;
+  for (i = 0; i < argc - 1; i++)
+    spargs[i] = argv[i + 1];
+  spargs[i++] = (char *) "--direct";
+  spargs[i++] = (char *) "--restart";
+  check_type_argc = i++;
+  spargs[i] = NULL;
+
+
+  do_test_signals ();
+
+  return 0;
+}
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>

sysdeps/unix/sysv/linux/Makefile

@@ -269,8 +269,7 @@ tests-clone-internal = \
   tst-align-clone-internal \
   tst-clone2-internal \
   tst-clone3-internal \
-  tst-getpid1-internal \
-  tst-misalign-clone-internal
+  tst-getpid1-internal
 tests-internal += $(tests-clone-internal)
 tests-static += $(tests-clone-internal)
 

sysdeps/unix/sysv/linux/clone-internal.c

@@ -44,27 +44,15 @@ _Static_assert (sizeof (struct clone_args) == CLONE_ARGS_SIZE_VER2,
 		"sizeof (struct clone_args) != CLONE_ARGS_SIZE_VER2");
 
 int
-__clone_internal (struct clone_args *cl_args,
-		  int (*func) (void *arg), void *arg)
+__clone_internal_fallback (struct clone_args *cl_args,
+			   int (*func) (void *arg), void *arg)
 {
-  int ret;
-#ifdef HAVE_CLONE3_WRAPPER
-  /* Try clone3 first.  */
-  int saved_errno = errno;
-  ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
-  if (ret != -1 || errno != ENOSYS)
-    return ret;
-
-  /* NB: Restore errno since errno may be checked against non-zero
-     return value.  */
-  __set_errno (saved_errno);
-#endif
-
   /* Map clone3 arguments to clone arguments.  NB: No need to check
      invalid clone3 specific bits in flags nor exit_signal since this
      is an internal function.  */
   int flags = cl_args->flags | cl_args->exit_signal;
   void *stack = cast_to_pointer (cl_args->stack);
+  int ret;
 
 #ifdef __ia64__
   ret = __clone2 (func, stack, cl_args->stack_size,
@@ -88,4 +76,23 @@ __clone_internal (struct clone_args *cl_args,
   return ret;
 }
 
+
+int
+__clone_internal (struct clone_args *cl_args,
+		  int (*func) (void *arg), void *arg)
+{
+#ifdef HAVE_CLONE3_WRAPPER
+  int saved_errno = errno;
+  int ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
+  if (ret != -1 || errno != ENOSYS)
+    return ret;
+
+  /* NB: Restore errno since errno may be checked against non-zero
+     return value.  */
+  __set_errno (saved_errno);
+#endif
+
+  return __clone_internal_fallback (cl_args, func, arg);
+}
+
 libc_hidden_def (__clone_internal)

sysdeps/unix/sysv/linux/clone3.h

@@ -23,6 +23,13 @@
 #include <stddef.h>
 #include <bits/types.h>
 
+
+/* Flags for the clone3 syscall.  */
+#define CLONE_CLEAR_SIGHAND 0x100000000ULL /* Clear any signal handler and
+					      reset to SIG_DFL.  */
+#define CLONE_INTO_CGROUP 0x200000000ULL /* Clone into a specific cgroup given
+					    the right permissions.  */
+
 /* The unsigned 64-bit and 8-byte aligned integer type.  */
 typedef __U64_TYPE __aligned_uint64_t __attribute__ ((__aligned__ (8)));
 

sysdeps/unix/sysv/linux/spawni.c

@@ -66,6 +66,7 @@ struct posix_spawn_args
   ptrdiff_t argc;
   char *const *envp;
   int xflags;
+  bool use_clone3;
   int err;
 };
 
@@ -104,12 +105,11 @@ __spawni_child (void *arguments)
   const posix_spawnattr_t *restrict attr = args->attr;
   const posix_spawn_file_actions_t *file_actions = args->fa;
 
-  /* The child must ensure that no signal handler are enabled because it shared
-     memory with parent, so the signal disposition must be either SIG_DFL or
-     SIG_IGN.  It does by iterating over all signals and although it could
-     possibly be more optimized (by tracking which signal potentially have a
-     signal handler), it might requires system specific solutions (since the
-     sigset_t data type can be very different on different architectures).  */
+  /* The child must ensure that no signal handler is enabled because it
+     shares memory with parent, so all signal dispositions must be either
+     SIG_DFL or SIG_IGN.  If clone3/CLONE_CLEAR_SIGHAND is used, there is
+     only the need to set the defined signals POSIX_SPAWN_SETSIGDEF to
+     SIG_DFL; otherwise, the code iterates over all signals.  */
   struct sigaction sa;
   memset (&sa, '\0', sizeof (sa));
 
@@ -122,7 +122,7 @@ __spawni_child (void *arguments)
 	{
 	  sa.sa_handler = SIG_DFL;
 	}
-      else if (__sigismember (&hset, sig))
+      else if (!args->use_clone3 && __sigismember (&hset, sig))
 	{
 	  if (is_internal_signal (sig))
 	    sa.sa_handler = SIG_IGN;
@@ -382,12 +382,25 @@ __spawnix (pid_t * pid, const char *file,
      for instance).  */
   struct clone_args clone_args =
     {
-      .flags = CLONE_VM | CLONE_VFORK,
+      /* Unsupported flags like CLONE_CLEAR_SIGHAND will be cleared up by
+	 __clone_internal_fallback.  */
+      .flags = CLONE_CLEAR_SIGHAND | CLONE_VM | CLONE_VFORK,
       .exit_signal = SIGCHLD,
       .stack = (uintptr_t) stack,
       .stack_size = stack_size,
     };
-  new_pid = __clone_internal (&clone_args, __spawni_child, &args);
+#ifdef HAVE_CLONE3_WRAPPER
+  args.use_clone3 = true;
+  new_pid = __clone3 (&clone_args, sizeof (clone_args), __spawni_child,
+		      &args);
+  /* clone3 was added in 5.3 and CLONE_CLEAR_SIGHAND in 5.5.  */
+  if (new_pid == -1 && (errno == ENOSYS || errno == EINVAL))
+#endif
+    {
+      args.use_clone3 = false;
+      new_pid = __clone_internal_fallback (&clone_args, __spawni_child,
+					   &args);
+    }
 
   /* It needs to collect the case where the auxiliary process was created
      but failed to execute the file (due either any preparation step or