libunwind: add patch to fix behavior for ARM < v6

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

LIBUNWIND_INSTALL_STAGING = YES

LIBUNWIND_LICENSE_FILES = COPYING

LIBUNWIND_LICENSE = MIT

LIBUNWIND_AUTORECONF = YES

$(eval $(autotools-package))