[RFC] eal/x86: disable array bounds checks in rte_memcpy_generic with gcc-12

[Stephen Hemminger <stephen@networkplumber.org>]

Gcc 12 adds more array bounds checking (good); but it is not smart
enough to realize that for small fixed sizes, the bigger move options
are not used.

An example is using rte_memcpy() on a RSS key of 40 bytes may trigger
rte_memcpy complaints from rte_mov128 reading past end of input.

In order to keep some of the checks add special case for calls
to rte_memcpy() with fixed size arguments to use the compiler
builtin instead. Don't want to give all the checking for
code that uses rte_memcpy() everywhere.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/eal/x86/include/rte_memcpy.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/lib/eal/x86/include/rte_memcpy.h b/lib/eal/x86/include/rte_memcpy.h
index 18aa4e43a743..b90cdd8d7326 100644
--- a/lib/eal/x86/include/rte_memcpy.h
+++ b/lib/eal/x86/include/rte_memcpy.h
@@ -27,6 +27,10 @@ extern "C" {
 #pragma GCC diagnostic ignored "-Wstringop-overflow"
 #endif
 
+#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 120000)
+#pragma GCC diagnostic ignored "-Warray-bounds"
+#endif
+
 /**
  * Copy bytes from one location to another. The locations must not overlap.
  *
@@ -842,19 +846,21 @@ rte_memcpy_aligned(void *dst, const void *src, size_t n)
 	return ret;
 }
 
+#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 100000)
+#pragma GCC diagnostic pop
+#endif
+
 static __rte_always_inline void *
 rte_memcpy(void *dst, const void *src, size_t n)
 {
-	if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK))
+	if (__builtin_constant_p(n))
+		return __builtin_memcpy(dst, src, n);
+	else if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK))
 		return rte_memcpy_aligned(dst, src, n);
 	else
 		return rte_memcpy_generic(dst, src, n);
 }
 
-#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 100000)
-#pragma GCC diagnostic pop
-#endif
-
 #ifdef __cplusplus
 }
 #endif
-- 
2.35.1