Linux: Add the pthread_gettid_np function (bug 27880)

Current Bionic has this function, with enhanced error checking
(the undefined case terminates the process).

Reviewed-by: Joseph Myers <josmyers@redhat.com>

4 files changed, 114 insertions, 0 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index f70d1e55bd..eca00936d7 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -124,6 +124,7 @@ routines = \
   pthread_getname \
   pthread_getschedparam \
   pthread_getspecific \
+  pthread_gettid_np \
   pthread_join \
   pthread_join_common \
   pthread_key_create \
@@ -326,6 +327,7 @@ tests = \
   tst-pthread-timedlock-lockloop \
   tst-pthread_exit-nothreads \
   tst-pthread_exit-nothreads-static \
+  tst-pthread_gettid_np \
   tst-robust-fork \
   tst-robustpi1 \
   tst-robustpi2 \
diff --git a/nptl/Versions b/nptl/Versions
index 3221de89d1..ef55376dd9 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -378,6 +378,9 @@ libc {
     tss_get;
     tss_set;
   }
+  GLIBC_2.42 {
+    pthread_gettid_np;
+  }
   GLIBC_PRIVATE {
     __libc_alloca_cutoff;
     __lll_lock_wake_private;
diff --git a/nptl/pthread_gettid_np.c b/nptl/pthread_gettid_np.c
new file mode 100644
index 0000000000..bf3a12cd52
--- /dev/null
+++ b/nptl/pthread_gettid_np.c
@@ -0,0 +1,30 @@
+/* Get the Linux TID from a pthread_t handle.
+   Copyright (C) 2025 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; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <pthreadP.h>
+
+pid_t
+pthread_gettid_np (pthread_t threadid)
+{
+  /* The kernel may concurrently set this field.  */
+  pid_t tid = atomic_load_relaxed (&((struct pthread *) threadid)->tid);
+  if (tid <= 0)
+    return -1;
+  return tid;
+}
diff --git a/nptl/tst-pthread_gettid_np.c b/nptl/tst-pthread_gettid_np.c
new file mode 100644
index 0000000000..6a98d864e2
--- /dev/null
+++ b/nptl/tst-pthread_gettid_np.c
@@ -0,0 +1,79 @@
+/* Test for pthread_gettid_np.
+   Copyright (C) 2025 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; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <pthread.h>
+#include <sched.h>
+#include <signal.h>
+#include <support/check.h>
+#include <support/xthread.h>
+#include <unistd.h>
+
+static pthread_barrier_t barrier;
+
+static pid_t thread_tid;
+
+static void *
+thread_func (void *ignored)
+{
+  thread_tid = gettid ();
+  TEST_VERIFY (thread_tid != getpid ());
+  TEST_COMPARE (thread_tid, pthread_gettid_np (pthread_self ()));
+  xpthread_barrier_wait (&barrier);
+  /* The main thread calls pthread_gettid_np here.  */
+  xpthread_barrier_wait (&barrier);
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  TEST_COMPARE (pthread_gettid_np (pthread_self ()), getpid ());
+  TEST_COMPARE (pthread_gettid_np (pthread_self ()), gettid ());
+
+  xpthread_barrier_init (&barrier, NULL, 2);
+
+  pthread_t thr = xpthread_create (NULL, thread_func, NULL);
+  xpthread_barrier_wait (&barrier);
+  TEST_COMPARE (thread_tid, pthread_gettid_np (thr));
+  xpthread_barrier_wait (&barrier);
+
+  while (true)
+    {
+      /* Check if the kernel thread is still running.  */
+      if (tgkill (getpid (), thread_tid, 0))
+        {
+          TEST_COMPARE (errno, ESRCH);
+          break;
+        }
+
+      pid_t tid = pthread_gettid_np (thr);
+      if (tid != thread_tid)
+        {
+          TEST_COMPARE (tid, -1);
+          break;
+        }
+      TEST_COMPARE (sched_yield (), 0);
+    }
+
+  TEST_VERIFY (xpthread_join (thr) == NULL);
+
+  return 0;
+}
+
+#include <support/test-driver.c>