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Date: Wed, 16 Nov 2005 23:19:00 -0000
From: Jakub Jelinek <jakub@redhat.com>
To: Ulrich Drepper <drepper@redhat.com>
Cc: Glibc hackers <libc-hacker@sources.redhat.com>
Subject: [PATCH] Add write barrier into pthread_cancel_init
Message-ID: <20051116231843.GL16723@sunsite.mff.cuni.cz>
Reply-To: Jakub Jelinek <jakub@redhat.com>
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Hi!

If the compiler and/or processor reorders the writes to libgcc_s_*
variables in pthread_cancel_init, pthread_cancel_init might return early
if libgcc_s_getcfa has been already written, but some other libgcc_s_*
pointer the caller is actually interested in has not been written yet.

2005-11-17  Jakub Jelinek  <jakub@redhat.com>

	* sysdeps/pthread/unwind-forcedunwind.c (pthread_cancel_init): Put
	a write barrier before writing libgcc_s_getcfa.

--- libc/nptl/sysdeps/pthread/unwind-forcedunwind.c.jj	2003-09-04 07:41:57.000000000 +0200
+++ libc/nptl/sysdeps/pthread/unwind-forcedunwind.c	2005-11-17 00:13:37.000000000 +0100
@@ -1,4 +1,4 @@
-/* Copyright (C) 2003 Free Software Foundation, Inc.
+/* Copyright (C) 2003, 2005 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Jakub Jelinek <jakub@redhat.com>.
 
@@ -56,6 +56,10 @@ pthread_cancel_init (void)
   libgcc_s_resume = resume;
   libgcc_s_personality = personality;
   libgcc_s_forcedunwind = forcedunwind;
+  /* Make sure libgcc_s_getcfa is written last.  Otherwise,
+     pthread_cancel_init might return early even when the pointer the
+     caller is interested in is not initialized yet.  */
+  atomic_write_barrier ();
   libgcc_s_getcfa = getcfa;
 }
 

	Jakub