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>

1 files changed, 179 insertions, 0 deletions

diff --git a/posix/tst-spawn7.c b/posix/tst-spawn7.c
new file mode 100644
index 0000000000..a1c0d9d942
--- /dev/null
+++ b/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>