glibc/glibc-RHEL-56627-5.patch

Partial backport (without ABI changes, using libc_nonshared.a instead)
of:

commit 74d463c50bb1096efef47022405c7db33f83fb5a
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed Mar 12 10:16:31 2025 +0100

    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>

Conflicts:
	sysdeps/unix/sysv/linux/*/libc.abilist
	  (not backported)
	nptl/Versions
	  (not backported)

The alternate libc_nonshared.a implementation relies on the UAPI
encoding of pthread_getcpuclockid, and avoids a TCB layout
dependency.

diff --git a/manual/process.texi b/manual/process.texi
index 9307379194c6f666..8535363546520d62 100644
--- a/manual/process.texi
+++ b/manual/process.texi
@@ -238,6 +238,24 @@ especially regarding reuse of the IDs of threads which have exited.
 This function is specific to Linux.
 @end deftypefun
 
+@deftypefun pid_t pthread_gettid_np (pthread_t @var{thread})
+@standards{Linux, pthread.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function returns the same value that @code{gettid} would return if
+executed on the running thread @var{thread}.
+
+If @var{thread} is no longer running but it is joinable, it is
+unspecified whether this function returns @minus{}1, or if it returns
+the thread ID of the thread while it was running.  If @var{thread} is
+not running and is not joinable, the behavior is undefined.
+
+@strong{Portability Note:} Linux thread IDs can be reused rather quickly,
+so this function differs from the @code{pthread_getunique_np} function
+found on other systems.
+
+This function is specific to Linux.
+@end deftypefun
+
 @node Creating a Process
 @section Creating a Process
 
diff --git a/nptl/Makefile b/nptl/Makefile
index d03846c2e04afa2f..cac75eb8f5b68320 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -118,6 +118,7 @@ routines = \
   pthread_getname \
   pthread_getschedparam \
   pthread_getspecific \
+  pthread_gettid_np \
   pthread_join \
   pthread_join_common \
   pthread_key_create \
@@ -203,6 +204,10 @@ routines = \
   vars \
   # routines
 
+static-only-routines += \
+  pthread_gettid_np \
+  # static-only-routines
+
 libpthread-routines = libpthread-compat
 libpthread-shared-only-routines = libpthread-compat
 
@@ -314,6 +319,7 @@ 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/pthread_gettid_np.c b/nptl/pthread_gettid_np.c
new file mode 100644
index 0000000000000000..b602eb7a30bf42a5
--- /dev/null
+++ b/nptl/pthread_gettid_np.c
@@ -0,0 +1,32 @@
+/* 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
+attribute_hidden
+pthread_gettid_np (pthread_t threadid)
+{
+  clockid_t clock;
+  if (pthread_getcpuclockid (threadid, &clock) != 0)
+    return -1;
+  /* Reverse the clock ID encoding to obtain the TID.  This is part of
+     the kernel/userspace interface, so it is stable ABI.  */
+  return ~(clock >> 3);
+}
diff --git a/nptl/tst-pthread_gettid_np.c b/nptl/tst-pthread_gettid_np.c
new file mode 100644
index 0000000000000000..6a98d864e222b9f5
--- /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>
diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
index 43146e91c9d9579b..b8bd9213da5c9bc0 100644
--- a/sysdeps/nptl/pthread.h
+++ b/sysdeps/nptl/pthread.h
@@ -1317,6 +1317,11 @@ extern int pthread_getcpuclockid (pthread_t __thread_id,
      __THROW __nonnull ((2));
 #endif
 
+#ifdef __USE_GNU
+/* Return the Linux TID for THREAD_ID.  Returns -1 on failure.  */
+extern pid_t pthread_gettid_np (pthread_t __thread_id);
+#endif
+
 
 /* Install handlers to be called when a new process is created with FORK.
    The PREPARE handler is called in the parent process just before performing