> So here's basically what the kernel needs: > > - if we don't touch a field, the compiler doesn't touch it. > > This is the rule that gcc now violates with bitfields. > > This is a gcc bug. End of story. The "volatile" example proves it - > anybody who argues otherwise is simply wrong, and is just trying to > make excuses.
C historically didn't make this guarantee because a lot of processors couldn't make it because they didn't have things like byte accessors (In fact I suspect early ARM cannot make it for example). Not meeting it for types where you can do is a bit rude however and really ought to be an option (speed v sanity). > See above: it's not the "state" that is accessed concurrently. It's > the code. If you ever try to mark state, you've already lost. The same > "state" can be atomic or not depending on context. It's not about the > state or the data structures, and it never will be. There are optimisation cases - where you can prove access properties are safe (eg local variables some times) but they should be exactly that - optimisations. Alan
