[PATCH v6 36/39] fib: use C11 alignas

[Tyler Retzlaff]

The current location used for __rte_aligned(a) for alignment of types
and variables is not compatible with MSVC. There is only a single
location accepted by both toolchains.

For variables standard C11 offers alignas(a) supported by conformant
compilers i.e. both MSVC and GCC.

For types the standard offers no alignment facility that compatibly
interoperates with C and C++ but may be achieved by relocating the
placement of __rte_aligned(a) to the aforementioned location accepted
by all currently supported toolchains.

To allow alignment for both compilers do the following:

* Move __rte_aligned from the end of {struct,union} definitions to
  be between {struct,union} and tag.

  The placement between {struct,union} and the tag allows the desired
  alignment to be imparted on the type regardless of the toolchain being
  used for all of GCC, LLVM, MSVC compilers building both C and C++.

* Replace use of __rte_aligned(a) on variables/fields with alignas(a).

Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
Acked-by: Morten Brørup <mb at smartsharesystems.com>
---
 lib/fib/dir24_8.h | 4 +++-
 lib/fib/trie.h    | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/fib/dir24_8.h b/lib/fib/dir24_8.h
index b0d1a40..6d350f7 100644
--- a/lib/fib/dir24_8.h
+++ b/lib/fib/dir24_8.h
@@ -6,6 +6,8 @@
 #ifndef _DIR24_8_H_
 #define _DIR24_8_H_
 
+#include <stdalign.h>
+
 #include <rte_prefetch.h>
 #include <rte_branch_prediction.h>
 
@@ -32,7 +34,7 @@ struct dir24_8_tbl {
 	uint64_t	*tbl8;		/**< tbl8 table. */
 	uint64_t	*tbl8_idxes;	/**< bitmap containing free tbl8 idxes*/
 	/* tbl24 table. */
-	__extension__ uint64_t	tbl24[0] __rte_cache_aligned;
+	__extension__ alignas(RTE_CACHE_LINE_SIZE) uint64_t	tbl24[0];
 };
 
 static inline void *
diff --git a/lib/fib/trie.h b/lib/fib/trie.h
index 3cf161a..36ce1fd 100644
--- a/lib/fib/trie.h
+++ b/lib/fib/trie.h
@@ -6,6 +6,8 @@
 #ifndef _TRIE_H_
 #define _TRIE_H_
 
+#include <stdalign.h>
+
 /**
  * @file
  * RTE IPv6 Longest Prefix Match (LPM)
@@ -36,7 +38,7 @@ struct rte_trie_tbl {
 	uint32_t	*tbl8_pool;	/**< bitmap containing free tbl8 idxes*/
 	uint32_t	tbl8_pool_pos;
 	/* tbl24 table. */
-	__extension__ uint64_t	tbl24[0] __rte_cache_aligned;
+	__extension__ alignas(RTE_CACHE_LINE_SIZE) uint64_t	tbl24[0];
 };
 
 static inline uint32_t
-- 
1.8.3.1