elf: Always define TLS_TP_OFFSET

This will be needed to compute __rseq_offset outside of the TLS
relocation machinery.

Reviewed-by: Michael Jeanson <mjeanson@efficios.com>

2 files changed, 58 insertions, 0 deletions

diff --git a/elf/Makefile b/elf/Makefile
index 048878d..4b1d0d8 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -322,6 +322,7 @@ tests := \
 tests-internal := \
   $(tests-static-internal) \
   tst-tls1 \
+  tst-tls_tp_offset \
   # tests-internal
 
 tests-static := $(tests-static-normal) $(tests-static-internal)
diff --git a/elf/tst-tls_tp_offset.c b/elf/tst-tls_tp_offset.c
new file mode 100644
index 0000000..e7c5066
--- /dev/null
+++ b/elf/tst-tls_tp_offset.c
@@ -0,0 +1,57 @@
+/* Check compile-time definition of TLS_TP_OFFSET against run-time value.
+   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; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <thread_pointer.h>
+
+#include <dl-tls.h>
+#include <link.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <support/check.h>
+
+static __thread char thread_var __attribute__ ((tls_model ("initial-exec")));
+
+static int
+do_test (void)
+{
+  printf ("thread variable address: %p\n", &thread_var);
+  printf ("thread pointer address: %p\n", __thread_pointer ());
+  printf ("pthread_self address: %p\n", (void *) pthread_self ());
+  ptrdiff_t block_offset = ((struct link_map *) _r_debug.r_map)->l_tls_offset;
+  printf ("main program TLS block offset: %td\n", block_offset);
+
+  if ((uintptr_t) &thread_var < (uintptr_t) pthread_self ())
+    {
+      puts("TLS variables are located before struct pthread.");
+      TEST_COMPARE (((intptr_t) __thread_pointer () - block_offset)
+                    - (intptr_t) &thread_var,
+                    TLS_TP_OFFSET);
+    }
+  else
+    {
+      puts("TLS variables are located after struct pthread.");
+      TEST_COMPARE (((intptr_t) __thread_pointer () + block_offset)
+                    - (intptr_t) &thread_var,
+                    TLS_TP_OFFSET);
+    }
+  return 0;
+}
+
+#include <support/test-driver.c>