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>

39 files changed, 171 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 29d3d47b64..0427eb3269 100644
--- a/NEWS
+++ b/NEWS
@@ -16,6 +16,8 @@ Major new features:
 
   - Power and absolute-value functions: rsqrt.
 
+* On Linux, the pthread_gettid_np function has been added.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
   [Add deprecations, removals and changes affecting compatibility here]
diff --git a/manual/process.texi b/manual/process.texi
index 8254e5ee86..a8f37e55a3 100644
--- a/manual/process.texi
+++ b/manual/process.texi
@@ -239,6 +239,24 @@ 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 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>
diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
index 050b4ab8d1..b4d10a37c6 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
diff --git a/sysdeps/unix/sysv/linux/aarch64/libc.abilist b/sysdeps/unix/sysv/linux/aarch64/libc.abilist
index 38db77e4f7..0889725c79 100644
--- a/sysdeps/unix/sysv/linux/aarch64/libc.abilist
+++ b/sysdeps/unix/sysv/linux/aarch64/libc.abilist
@@ -2750,3 +2750,4 @@ GLIBC_2.39 stdc_trailing_zeros_ull F
 GLIBC_2.39 stdc_trailing_zeros_us F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
diff --git a/sysdeps/unix/sysv/linux/alpha/libc.abilist b/sysdeps/unix/sysv/linux/alpha/libc.abilist
index 637bfce9fb..b33a52db70 100644
--- a/sysdeps/unix/sysv/linux/alpha/libc.abilist
+++ b/sysdeps/unix/sysv/linux/alpha/libc.abilist
@@ -3097,6 +3097,7 @@ GLIBC_2.4 wprintf F
 GLIBC_2.4 wscanf F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/arc/libc.abilist b/sysdeps/unix/sysv/linux/arc/libc.abilist
index 4a305cf730..0c78cb6d9d 100644
--- a/sysdeps/unix/sysv/linux/arc/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arc/libc.abilist
@@ -2511,3 +2511,4 @@ GLIBC_2.39 stdc_trailing_zeros_ull F
 GLIBC_2.39 stdc_trailing_zeros_us F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
diff --git a/sysdeps/unix/sysv/linux/arm/be/libc.abilist b/sysdeps/unix/sysv/linux/arm/be/libc.abilist
index 1d54f71b14..a4571bfcb3 100644
--- a/sysdeps/unix/sysv/linux/arm/be/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arm/be/libc.abilist
@@ -2803,6 +2803,7 @@ GLIBC_2.4 xprt_register F
 GLIBC_2.4 xprt_unregister F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/arm/le/libc.abilist b/sysdeps/unix/sysv/linux/arm/le/libc.abilist
index ff7e8bc40b..060ab80000 100644
--- a/sysdeps/unix/sysv/linux/arm/le/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arm/le/libc.abilist
@@ -2800,6 +2800,7 @@ GLIBC_2.4 xprt_register F
 GLIBC_2.4 xprt_unregister F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/csky/libc.abilist b/sysdeps/unix/sysv/linux/csky/libc.abilist
index c3ed65467d..5c4f912dd8 100644
--- a/sysdeps/unix/sysv/linux/csky/libc.abilist
+++ b/sysdeps/unix/sysv/linux/csky/libc.abilist
@@ -2787,3 +2787,4 @@ GLIBC_2.39 stdc_trailing_zeros_ull F
 GLIBC_2.39 stdc_trailing_zeros_us F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
diff --git a/sysdeps/unix/sysv/linux/hppa/libc.abilist b/sysdeps/unix/sysv/linux/hppa/libc.abilist
index 991475380c..f837bf9dd1 100644
--- a/sysdeps/unix/sysv/linux/hppa/libc.abilist
+++ b/sysdeps/unix/sysv/linux/hppa/libc.abilist
@@ -2824,6 +2824,7 @@ GLIBC_2.4 unshare F
 GLIBC_2.41 cacheflush F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/i386/libc.abilist b/sysdeps/unix/sysv/linux/i386/libc.abilist
index 4fedf775d4..9ea9e656c1 100644
--- a/sysdeps/unix/sysv/linux/i386/libc.abilist
+++ b/sysdeps/unix/sysv/linux/i386/libc.abilist
@@ -3007,6 +3007,7 @@ GLIBC_2.4 unlinkat F
 GLIBC_2.4 unshare F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/loongarch/lp64/libc.abilist b/sysdeps/unix/sysv/linux/loongarch/lp64/libc.abilist
index 0024282289..243422f515 100644
--- a/sysdeps/unix/sysv/linux/loongarch/lp64/libc.abilist
+++ b/sysdeps/unix/sysv/linux/loongarch/lp64/libc.abilist
@@ -2271,3 +2271,4 @@ GLIBC_2.39 stdc_trailing_zeros_ull F
 GLIBC_2.39 stdc_trailing_zeros_us F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
diff --git a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
index 142595eb3e..88397ad130 100644
--- a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
+++ b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
@@ -2783,6 +2783,7 @@ GLIBC_2.4 xprt_register F
 GLIBC_2.4 xprt_unregister F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
index 85e7746c10..81d6333345 100644
--- a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
+++ b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
@@ -2950,6 +2950,7 @@ GLIBC_2.4 unlinkat F
 GLIBC_2.4 unshare F
 GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
+GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.5 __readlinkat_chk F
 GLIBC_2.5 inet6_opt_append F
 GLIBC_2.5 inet6_opt_find F
diff --git a/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist b/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist
index 91dc1b8378..9522c31329 100644
--- a/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist