[PATCH v4 6/6] eal: replace out of bounds VLA with static_assert

[Stephen Hemminger]

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().

Need to add brackets {} around the static_assert() to workaround
a bug in clang. Clang was not handling static_assert() in
a switch case properly.

Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
Acked-by: Morten Brørup <mb at smartsharesystems.com>
Acked-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>

---
 lib/eal/include/rte_common.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
index 33680e818bfb..f63119b444fa 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>
 
@@ -495,7 +496,7 @@ rte_is_aligned(const void * const __rte_restrict ptr, const unsigned int align)
 /**
  * Triggers an error at compilation time if the condition is true.
  */
-#define RTE_BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#define RTE_BUILD_BUG_ON(condition) { static_assert(!(condition), #condition); }
 
 /*********** Cache line related macros ********/
 
-- 
2.43.0