Intel vs. ARM memory alignment

ARM64 correctly handles unaligned loads and stores at most widths, but that doesn't usually matter for most programmers, because C requires pointers to be adequately aligned for their type regardless of the underlying processor, and programs that violate this rule have undefined behavior. The fact that the code will appear to work if the compiler emits a normal load or store doesn't change the fact that it's not allowed and that the behavior isn't guaranteed. You need to tell the compiler that you're accessing unaligned memory.

There are several ways to tell the compiler that, and the best approach depends on how you're doing the access. If you're reading from a struct, you can simply make the struct packed to tell the compiler that its fields aren't required to be aligned. If you're reading from a pointer, you can make sure that the pointer is to a typedef declared with attribute((aligned(1))), e.g.:

Code Block 
typedef uint32_t unaligned_int32 attribute((aligned(1)));

(Apologies, attribute is supposed to be surrounded by double underscores, but the forum software appears to mangle it.)

Similarly, 64-bit loads and stores are guaranteed by the processor to be done without tearing, but the compiler does not make such a guarantee. If you need this guarantee, you should use relaxed atomics.