From 10fee6d71a1f7d6e6319005196562b4a30b4e8ff Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date: Tue, 2 Feb 2016 14:58:52 +0100
Subject: [PATCH] Fix detection of C11 atomics

Currently, the CMakeLists.txt logic to detect the availability of C11
atomics is based on building a small program that uses the
atomic_load().

However, atomic_load() does not need to use any function from
libatomic (part of the gcc runtime). So even if libatomic is missing,
this test concludes that C11 atomic support is available. For example
on SPARC, the example program builds fine without linking to
libatomic, but calling other functions of the atomic_*() APIs fail
without linking to libatomic.

So, this patch adjusts the CMakeLists.txt test to use a function that
is known to require the libatomic run-time library (on architectures
where it is needed). This way, openal will only use the __atomic_*()
built-ins when they are actually functional.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
 CMakeLists.txt | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5784d35..a53f996 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -209,14 +209,17 @@ CHECK_C_SOURCE_COMPILES(
 HAVE_C11_ALIGNAS)
 
 # Check if we have C11 _Atomic
+set(OLD_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
+set(CMAKE_REQUIRED_LIBRARIES ${EXTRA_LIBS})
 CHECK_C_SOURCE_COMPILES(
 "#include <stdatomic.h>
- const int _Atomic foo = ATOMIC_VAR_INIT(~0);
+ int _Atomic foo = ATOMIC_VAR_INIT(~0);
  int main()
  {
-     return atomic_load(&foo);
+     return atomic_fetch_add(&foo, 2);
  }"
 HAVE_C11_ATOMIC)
+set(CMAKE_REQUIRED_LIBRARIES ${OLD_REQUIRED_LIBRARIES})
 
 # Add definitions, compiler switches, etc.
 INCLUDE_DIRECTORIES("${OpenAL_SOURCE_DIR}/include" "${OpenAL_BINARY_DIR}")
-- 
2.6.4