Add comments about gcc-5
Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/sha256.c b/library/sha256.c
index 81c011b..bf9af6b 100644
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -54,7 +54,10 @@
# pragma clang attribute push (__attribute__((target("crypto"))), apply_to=function)
# define MBEDTLS_POP_TARGET_PRAGMA
# elif defined(__GNUC__)
-# if __GNUC__ < 6 /* TODO: check sha256 compatible for GCC */
+ /* FIXME: GCC-5 annouce crypto extension, but some intrinsic are missed.
+ * Known miss intrinsic can be workaround.
+ */
+# if __GNUC__ < 6
# error "A more recent GCC is required for MBEDTLS_SHA256_USE_A64_CRYPTO_*"
# else
# pragma GCC push_options