[Libunwind-devel] [PATCH 03/57] Use GCC __BIGGEST_ALIGNMENT__ for sos-pool MAX_ALIGN

[Tommi Rantala]

Use the __BIGGEST_ALIGNMENT__ macro provided by GCC for sos_alloc()
allocation alignment. The macro gives ``the largest alignment ever used
for any data type on the target machine you are compiling for.''

__BIGGEST_ALIGNMENT__ also has some other nice properties, e.g. it is
power-of-two on all architectures (note that on i386, sizeof(long
double) = 12), and on some architectures (e.g. SuperH) the alignment
requirement can be lower than sizeof(long double).
---
 src/mi/mempool.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/mi/mempool.c b/src/mi/mempool.c
index 6fb5afe..b49202b 100644
--- a/src/mi/mempool.c
+++ b/src/mi/mempool.c
@@ -25,7 +25,14 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
SOFTWARE.  */
 
 #include "libunwind_i.h"
 
-#define MAX_ALIGN      (sizeof (long double))
+/* From GCC docs: ``Gcc also provides a target specific macro
+ * __BIGGEST_ALIGNMENT__, which is the largest alignment ever used for any data
+ * type on the target machine you are compiling for.'' */
+#ifdef __BIGGEST_ALIGNMENT__
+# define MAX_ALIGN     __BIGGEST_ALIGNMENT__
+#else
+# define MAX_ALIGN     (sizeof (long double))
+#endif
 
 static char sos_memory[SOS_MEMORY_SIZE];
 static char *sos_memp;
-- 
1.7.9.5