aarch64: Fix _dl_tlsdesc_dynamic unwind for pac-ret (BZ 32612)

When libgcc is built with pac-ret, it requires to autenticate the
unwinding frame based on CFI information.  The _dl_tlsdesc_dynamic
uses a custom calling convention, where it is responsible to save
and restore all registers it might use (even volatile).

The pac-ret support added by 1be3d6eb823d8b952fa54b7bbc90cbecb8981380
was added only on the slow-path, but the fast path also adds DWARF
Register Rule Instruction (cfi_adjust_cfa_offset) since it requires
to save/restore some auxiliary register.  It seems that this is not
fully supported neither by libgcc nor AArch64 ABI [1].

Instead, move paciasp/autiasp to function prologue/epilogue to be
used on both fast and slow paths.

I also corrected the _dl_tlsdesc_dynamic comment description, it was
copied from i386 implementation without any adjustment.

Checked on aarch64-linux-gnu with a toolchain built with
--enable-standard-branch-protection on a system with pac-ret
support.

[1]  https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst#id1

Reviewed-by: Yury Khrustalev <yury.khrustalev@arm.com>

3 files changed, 88 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/aarch64/Makefile b/sysdeps/unix/sysv/linux/aarch64/Makefile
index 0839f0b..15a2b44 100644
--- a/sysdeps/unix/sysv/linux/aarch64/Makefile
+++ b/sysdeps/unix/sysv/linux/aarch64/Makefile
@@ -1,3 +1,16 @@
+ifeq ($(subdir),elf)
+tests += \
+  tst-tlsdesc-pac \
+  # tests
+modules-names += \
+  tst-tlsdesc-pac-mod \
+  # modules-names
+
+LDFLAGS-tst-tlsdesc-pac = -rdynamic
+
+$(objpfx)tst-tlsdesc-pac.out: $(objpfx)tst-tlsdesc-pac-mod.so
+endif
+
 ifeq ($(subdir),misc)
 sysdep_headers += sys/elf.h
 tests += \
diff --git a/sysdeps/unix/sysv/linux/aarch64/tst-tlsdesc-pac-mod.c b/sysdeps/unix/sysv/linux/aarch64/tst-tlsdesc-pac-mod.c
new file mode 100644
index 0000000..d34c8be
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/aarch64/tst-tlsdesc-pac-mod.c
@@ -0,0 +1,27 @@
+/* AArch64 tests for unwinding TLSDESC (BZ 32612)
+   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/>.  */
+
+_Thread_local int foo;
+/* Make the TLS segment large enough to trigger _dl_tlsdesc_dynamic.  */
+_Thread_local int foobar[1000];
+
+void
+bar (void)
+{
+  foo = 1;
+}
diff --git a/sysdeps/unix/sysv/linux/aarch64/tst-tlsdesc-pac.c b/sysdeps/unix/sysv/linux/aarch64/tst-tlsdesc-pac.c
new file mode 100644
index 0000000..24d656a
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/aarch64/tst-tlsdesc-pac.c
@@ -0,0 +1,48 @@
+/* AArch64 tests for unwinding TLSDESC (BZ 32612)
+   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 <stdlib.h>
+#include <unwind.h>
+#include <support/xdlfcn.h>
+
+static _Unwind_Reason_Code
+unwind_callback (struct _Unwind_Context* context, void* closure)
+{
+  return _URC_NO_REASON;
+}
+
+/* Assume that TLS variable from tst-tlsdesc-pac-mod.so will trigger
+   the slow-path that allocates the required memory with malloc.  */
+void *
+malloc (size_t s)
+{
+  _Unwind_Backtrace (unwind_callback, NULL);
+  return calloc (1, s);
+}
+
+static int
+do_test (void)
+{
+  void *h = xdlopen ("tst-tlsdesc-pac-mod.so", RTLD_LAZY);
+  void (*func)(void) = xdlsym (h, "bar");
+  func ();
+
+  return 0;
+}
+
+#include <support/test-driver.c>