ARM unaligned memory access workaround

Question

I have to port source code from to an ARM platform that runs Linux. Unfortunately I have run into unaligned memory access problems. The source uses pointer casts and access

Answer 1

Wow, that's an unholy mess. Fiddling with the compiler isn't going to get you anywhere. The code is illegal on ALL architectures, but just happens to work on some (e.g x86). I would fix the code itself.

Sadly there's no pretty way to do that. However, you might get a long way with a long list of search-and-replaces, then manually fix up the rest. I'd start by removing the declarations of those data types, so if you compile any code you missed, it'll error. Then, search-and-replace snippets such as "*(IEC_DWORD OS_SPTR *)pSP =" with "set_dword(pSP, ". Make an inline function "set_dword" to do the right thing. Carry on for as many easily replaced snippets as you can imagine. There will still be a large amount to fix up by hand.

The only other way I can think of doing this would be a compiler plugin, as you suggest, and make every pointer in the entire compilation unit have alignment 1. The compiler will then byte load/store everything. It'll probably end up doing that for more than just the code you intended. This probably isn't as easy to achieve as it sounds.