[PATCH v2] eal: force compilation of RTE_ASSERT expression

[Stephen Hemminger <stephen@networkplumber.org>]

Even if RTE_ENABLE_ASSERT is not enabled, the expression used should
still be checked for compiler warnings. Use sizeof()
and ternary operator in same manner as the assert() macro to
cause the expression to be evaluated but not generate code.

This was motivated by detection of problems in a driver submission
that was not detected until compiled with non default flags.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
v2 - reduce checkpatch complaints and reword comment

 lib/eal/include/rte_debug.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/lib/eal/include/rte_debug.h b/lib/eal/include/rte_debug.h
index 74593cd4d4..204e6db017 100644
--- a/lib/eal/include/rte_debug.h
+++ b/lib/eal/include/rte_debug.h
@@ -46,8 +46,16 @@ void rte_dump_stack(void);
 #ifdef RTE_ENABLE_ASSERT
 #define RTE_ASSERT(exp)	RTE_VERIFY(exp)
 #else
-#define RTE_ASSERT(exp) do {} while (0)
+/*
+ * If RTE_ENABLE_ASSERT is not set, the exp is not checked but not evaluated because
+ * of the use of sizeof(). The ternary operator is to allow function pointers
+ * and bit fields, and to suppress the evaluation of any variable length arrays.
+ */
+#define RTE_ASSERT(exp)	do {		\
+	(void)sizeof((exp) ? 1 : 0);	\
+} while (0)
 #endif
+
 #define	RTE_VERIFY(exp)	do {                                                  \
 	if (unlikely(!(exp)))                                                           \
 		rte_panic("line %d\tassert \"%s\" failed\n", __LINE__, #exp); \
-- 
2.47.2