Re: [patch V3 01/13] entry: Provide generic syscall entry functionality

[Thomas Gleixner]

Andy Lutomirski <luto@xxxxxxxxxx> writes:
> On Fri, Jul 17, 2020 at 12:29 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>> The alternative is to play nasty games with TIF_IA32, TIF_ADDR32 and
>> TIF_X32 to free up bits for 32bit and make the flags field 64 bit on 64
>> bit kernels, but I prefer to do the above seperation.
>
> I'm all for cleaning it up, but I don't think any nasty games would be
> needed regardless.  IMO at least the following flags are nonsense and
> don't belong in TIF_anything at all:
>
> TIF_IA32, TIF_X32: can probably be deleted.  Someone would just need
> to finish the work.
> TIF_ADDR32: also probably removable, but I'm less confident.
> TIF_FORCED_TF: This is purely a ptrace artifact and could easily go
> somewhere else entirely.
>
> So getting those five bits back would be straightforward.
>
> FWIW, TIF_USER_RETURN_NOTIFY is a bit of an odd duck: it's an
> entry/exit word *and* a context switch word.  The latter is because
> it's logically a per-cpu flag, not a per-task flag, and the context
> switch code moves it around so it's always set on the running task.

Gah, I missed the context switch thing of that. That stuff is hideous.

Thanks,

       tglx