From 37ded328c4240f5a84c69b8cb803f0652fa68d20 Mon Sep 17 00:00:00 2001
From: Michael Jeanson <mjeanson@efficios.com>
Date: Wed, 20 Nov 2024 14:15:42 -0500
Subject: [PATCH] nptl: initialize cpu_id_start prior to rseq registration

When adding explicit initialization of rseq fields prior to
registration, I glossed over the fact that 'cpu_id_start' is also
documented as initialized by user-space.

While current kernels don't validate the content of this field on
registration, future ones could.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
(cherry picked from commit d9f40387d3305d97e30a8cf8724218c42a63680a)
---
 sysdeps/unix/sysv/linux/rseq-internal.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
index 8fd26f335e..0ad79174bd 100644
--- a/sysdeps/unix/sysv/linux/rseq-internal.h
+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
@@ -56,6 +56,7 @@ rseq_register_current_thread (struct pthread *self, bool do_rseq)
          registration, there is no guarantee that struct pthread is
          cleared on all architectures.  */
       THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_UNINITIALIZED);
+      THREAD_SETMEM (self, rseq_area.cpu_id_start, 0);
       THREAD_SETMEM (self, rseq_area.rseq_cs, 0);
       THREAD_SETMEM (self, rseq_area.flags, 0);
 
-- 
2.27.0

