Linux: Add gettid system call wrapper [BZ #6399]

This commit adds gettid to <unistd.h> on Linux, and not to the
kernel-independent GNU API.

gettid is now supportable on Linux because too many things assume a
1:1 mapping between libpthread threads and kernel threads.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/tst-gettid.c b/sysdeps/unix/sysv/linux/tst-gettid.c
new file mode 100644
index 0000000000..26b579e1a1
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-gettid.c
@@ -0,0 +1,79 @@
+/* Smoke test for the gettid system call.
+   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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+
+/* TID of the initial (main) thread.  */
+static pid_t initial_tid;
+
+/* Check that PID and TID are the same in a subprocess.  */
+static void
+subprocess (void *closure)
+{
+  TEST_COMPARE (getpid (), gettid ());
+  TEST_VERIFY (gettid () != initial_tid);
+}
+
+/* Check that the TID changes in a new thread.  */
+static void *
+threadfunc (void *closure)
+{
+  TEST_VERIFY (getpid () != gettid ());
+  TEST_VERIFY (gettid () != initial_tid);
+  return NULL;
+}
+
+/* Check for interactions with vfork.  */
+static void
+test_vfork (void)
+{
+  pid_t proc = vfork ();
+  if (proc == 0)
+    {
+      if (getpid () != gettid ())
+        _exit (1);
+      if (gettid () == initial_tid)
+        _exit (2);
+      _exit (0);
+    }
+  int status;
+  xwaitpid (proc, &status, 0);
+  TEST_COMPARE (status, 0);
+}
+
+static int
+do_test (void)
+{
+  initial_tid = gettid ();
+
+  /* The main thread has the same TID as the PID.  */
+  TEST_COMPARE (getpid (), gettid ());
+
+  test_vfork ();
+
+  support_isolate_in_subprocess (subprocess, NULL);
+
+  xpthread_join (xpthread_create (NULL, threadfunc, NULL));
+
+  return 0;
+}
+
+#include <support/test-driver.c>