Provide cmake test if alignment requirement is strict

This is based on AX_CHECK_ALIGNED_ACCESS_REQUIRED from autoconf-archive.

Note, that on some arches unaligned access behavior could be changed at
runtime via prctl(1). Also, unaligned memory access is still slower (and
very slow on some arches) even if it's not strictly required.

(cherry picked from commit d2810d23a9f30ae885f9bf0783f0847a12972ff3)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 91c99a117809feb687c78661efef691ff3900951..112bbec7b7e2c3a1070c713d79143929e2db66e1 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -66,6 +66,18 @@ if (ADDCARRY_U64)
   add_definitions(-DHAVE_ADDCARRY_U64)
 endif()
 
+check_c_source_runs("
+  int main(void) {
+    char buf[16] = { 0, 1, 2 };
+    int *p = buf + 1;
+    int *q = buf + 2;
+    return (*p == *q);
+  }
+  " RELAXED_ALIGNMENT)
+if (NOT RELAXED_ALIGNMENT)
+  add_definitions(-DSTRICT_ALIGNMENT)
+endif()
+
 set(BIN_DIRECTORY bin)
 
 # Same soversion as OpenSSL