build: add -Wa,-mbranches-within-32B-boundaries compiler flag

CMakeLists.txt

@@ -147,6 +147,7 @@ target_compile_options(${PROJECT_NAME} PRIVATE
 
     # Assembler Options
     -Wa,--noexecstack
+    ${BRANCH_ALIGN_FLAG}
 
     # Suppressed Warnings
     -Wno-deprecated-declarations
@@ -373,6 +374,12 @@ if (NOT S2N_EXECINFO_AVAILABLE)
 endif()
 feature_probe_result(S2N_STACKTRACE ${S2N_STACKTRACE})
 
+if (SN_BRANCH_ALIGN AND NOT S2N_FUZZ_TEST)
+    set (BRANCH_ALIGN_FLAG "-Wa,-mbranches-within-32B-boundaries")
+else()
+    set (BRANCH_ALIGN_FLAG "")
+endif()
+
 if (S2N_INTERN_LIBCRYPTO)
 
     # Check if the AWS::crypto target has beeen added and handle it

tests/features/S2N_BRANCH_ALIGN.c

@@ -0,0 +1,19 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+ int main() {
+     return 0;
+ }
+

tests/features/S2N_BRANCH_ALIGN.flags

@@ -0,0 +1 @@
+-Wa,-mbranches-within-32B-boundaries