Re: [RFC v2 3/3] atomic: Add alignment check to instrumented atomic operations

[Finn Thain <fthain@linux-m68k.org>]

On Mon, 22 Sep 2025, Arnd Bergmann wrote:

> 
> I don't think automated transformation is going to work well here, as 
> you may not want the same approach in each case, depending on what the 
> code is:
> 
> - it may be enough to annotate a single member as packed in order to 
>   make the entire structure compatible

Right, and that's the only transformation I mentioned.

> - some structures may have lots of misaligned members, but no holes, so 
>   a global __attribute__((packed, aligned(2))) on that struct is cleaner

That simplification should be amenable to further automation, if the first 
transformation is.

> - if there are holes, some strategic additions of explicit padding can 
>   be cleaner than annotating each misaligned member.

It's a matter of taste.

> - automation won't be able to tell whether a structure is ABI relevant 
>   or not

Right. That's why I said the list of struct members would need to be 
"manually pared down". But even that task may be too large to be feasible.

> - similarly, many files are not going to be interesting for m68k. E.g. 
>   if drivers/infiniband has an ABI that is different for -malign-int, 
>   that can likely be ignored because nobody cares in practice.
> 

Right. That's why I advocated running the plug-in on a "normal build" not 
a contrived mass of #includes and structs.