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From 24484e80b3e329c9edee1995e102f8612eedb79c Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date: Tue, 13 May 2014 23:32:27 +0200
Subject: [PATCH] Add AO_REQUIRE_CAS to fix build on ARM < v6
ARM earlier than ARMv6, such as ARMv4 and ARMv5 do not provide
optimize atomic operations in libatomic_ops. Since libunwind is using
such operations, it should define AO_REQUIRE_CAS before including
<atomic_ops.h> so that libatomic_ops knows it should use emulated
atomic operations instead (even though they are obviously a lot more
expensive).
Also, while real atomic operations are all inline functions and
therefore linking against libatomic_ops was not required, the emulated
atomic operations actually require linking against libatomic_ops, so
the commented AC_CHECK_LIB test in acinclude.m4 is uncommented to make
sure we link against libatomic_ops.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
acinclude.m4 | 8 +-------
include/libunwind_i.h | 1 +
2 files changed, 2 insertions(+), 7 deletions(-)
diff --git a/acinclude.m4 b/acinclude.m4
index 497f7c2..9c15af1 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -22,11 +22,5 @@ fi])
AC_DEFUN([CHECK_ATOMIC_OPS],
[dnl Check whether the system has the atomic_ops package installed.
AC_CHECK_HEADERS(atomic_ops.h)
-#
-# Don't link against libatomic_ops for now. We don't want libunwind
-# to depend on libatomic_ops.so. Fortunately, none of the platforms
-# we care about so far need libatomic_ops.a (everything is done via
-# inline macros).
-#
-# AC_CHECK_LIB(atomic_ops, main)
+ AC_CHECK_LIB(atomic_ops, main)
])
diff --git a/include/libunwind_i.h b/include/libunwind_i.h
index 23f615e..deabdfd 100644
--- a/include/libunwind_i.h
+++ b/include/libunwind_i.h
@@ -95,6 +95,7 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
(pthread_mutex_unlock != NULL ? pthread_mutex_unlock (l) : 0)
#ifdef HAVE_ATOMIC_OPS_H
+# define AO_REQUIRE_CAS
# include <atomic_ops.h>
static inline int
cmpxchg_ptr (void *addr, void *old, void *new)
--
1.9.2
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