Update C11 atomic support to rely on just the compiler version

CMakeLists.txt

@@ -68,16 +68,7 @@ if(CMAKE_VERSION VERSION_GREATER "3.1.0")
   endif()
   set(CMAKE_CXX_STANDARD_REQUIRED ON)
   if (NOT DEFINED CMAKE_C_STANDARD)
-    try_compile(
-            RESULT
-            ${PROJECT_BINARY_DIR}
-            SOURCES "${CMAKE_CURRENT_LIST_DIR}/tests/compiler_features_tests/simple_main.c"
-            CMAKE_FLAGS "-DCMAKE_C_FLAGS=\"-std=c11\"")
-    if(RESULT)
-      set(CMAKE_C_STANDARD 11)
-    else()
-      set(CMAKE_C_STANDARD 99)
-    endif()
+    set(CMAKE_C_STANDARD 99)
   endif ()
   set(CMAKE_C_STANDARD_REQUIRED ON)
 endif ()
@@ -364,11 +355,8 @@ if(GCC OR CLANG)
   # Note clang-cl is odd and sets both CLANG and MSVC. We base our configuration
   # primarily on our normal Clang one.
   if (NOT CMAKE_C_STANDARD)
-    message(STATUS "Adding CMAKE_C_FLAGS -std=c99")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99")
-  else()
-    message(STATUS "Setting CMAKE_C_STANDARD=${CMAKE_C_STANDARD}")
-  endif()
+  endif ()
 
   # TODO(CryptoAlg-759): enable '-Wpedantic' if awslc has to follow c99 spec.
   if(CLANG OR (GCC AND CMAKE_C_COMPILER_VERSION VERSION_GREATER "4.1.3"))

crypto/internal.h

@@ -564,12 +564,15 @@ OPENSSL_EXPORT void CRYPTO_once(CRYPTO_once_t *once, void (*init)(void));
 
 // Reference counting.
 
-// Automatically enable C11 atomics if implemented.
+// Automatically enable C11 atomics if the compiler supports it (Clang or GCC > 4.8)
 #if !defined(OPENSSL_C11_ATOMIC) && defined(OPENSSL_THREADS) &&   \
-    !defined(__STDC_NO_ATOMICS__) && defined(__STDC_VERSION__) && \
-    __STDC_VERSION__ >= 201112L
+    !defined(OPENSSL_WINDOWS) && !defined(__STDC_NO_ATOMICS__) && \
+    !(defined(__GNUC__) && (__GNUC__ < 4 || __GNUC__ == 4 && __GNUC_MINOR__ < 7) && !defined(__clang__))
+#include <stdatomic.h>
+#if ATOMIC_LONG_LOCK_FREE > 0
 #define OPENSSL_C11_ATOMIC
 #endif
+#endif
 
 // Older MSVC does not support C11 atomics, so we fallback to the Windows APIs.
 // This can be removed once we can rely on

crypto/refcount_c11.c

@@ -25,14 +25,14 @@
 #include <openssl/type_check.h>
 
 
-// See comment above the typedef of CRYPTO_refcount_t about these tests.
-static_assert(alignof(CRYPTO_refcount_t) == alignof(_Atomic CRYPTO_refcount_t),
-              "_Atomic alters the needed alignment of a reference count");
-static_assert(sizeof(CRYPTO_refcount_t) == sizeof(_Atomic CRYPTO_refcount_t),
-              "_Atomic alters the size of a reference count");
+//// See comment above the typedef of CRYPTO_refcount_t about these tests.
+OPENSSL_STATIC_ASSERT(alignof(CRYPTO_refcount_t) == alignof(_Atomic CRYPTO_refcount_t),
+              _Atomic_alters_the_needed_alignment_of_a_reference_count);
+OPENSSL_STATIC_ASSERT(sizeof(CRYPTO_refcount_t) == sizeof(_Atomic CRYPTO_refcount_t),
+              _Atomic_alters_the_size_of_a_reference_count);
 
-static_assert((CRYPTO_refcount_t)-1 == CRYPTO_REFCOUNT_MAX,
-              "CRYPTO_REFCOUNT_MAX is incorrect");
+OPENSSL_STATIC_ASSERT((CRYPTO_refcount_t)-1 == CRYPTO_REFCOUNT_MAX,
+              CRYPTO_REFCOUNT_MAX_is_incorrect);
 
 void CRYPTO_refcount_inc(CRYPTO_refcount_t *in_count) {
   _Atomic CRYPTO_refcount_t *count = (_Atomic CRYPTO_refcount_t *) in_count;