[PATCH v5 6/6] eal: replace out of bounds VLA with static_assert

[Stephen Hemminger <stephen@networkplumber.org>]

Both Gcc, clang and MSVC have better way to do compile time
assertions rather than using out of bounds array access.
The old method would fail if -Wvla is enabled because compiler
can't determine size in that code.  Also, the use of new
_Static_assert will catch broken code that is passing non-constant
expression to RTE_BUILD_BUG_ON().

Add workaround for clang static_assert in switch,
and missing static_assert in older FreeBSD.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
---
 lib/eal/include/rte_common.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
index 33680e818bfb..aa066125b6cd 100644
--- a/lib/eal/include/rte_common.h
+++ b/lib/eal/include/rte_common.h
@@ -16,6 +16,7 @@
 extern "C" {
 #endif
 
+#include <assert.h>
 #include <stdint.h>
 #include <limits.h>
 
@@ -492,10 +493,18 @@ rte_is_aligned(const void * const __rte_restrict ptr, const unsigned int align)
 
 /*********** Macros for compile type checks ********/
 
+/* Workaround for toolchain issues with missing C11 macro in FreeBSD */
+#if !defined(static_assert) && !defined(__cplusplus)
+#define	static_assert	_Static_assert
+#endif
+
 /**
  * Triggers an error at compilation time if the condition is true.
+ *
+ * The do { } while(0) exists to workaround a bug in clang (#55821)
+ * where it would not handle _Static_assert in a switch case.
  */
-#define RTE_BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#define RTE_BUILD_BUG_ON(condition) do { static_assert(!(condition), #condition); } while (0)
 
 /*********** Cache line related macros ********/
 
-- 
2.43.0