Re: [PATCH 09/13] Move bp_type_idx to kernel/event/hw_breakpoint.c

[Arnd Bergmann <arnd@arndb.de>]

On Tuesday 15 September 2015 10:06:07 Peter Zijlstra wrote:
> > diff --git a/include/uapi/linux/hw_breakpoint.h b/include/uapi/linux/hw_breakpoint.h
> > index b04000a2296a..7a6a5a7f9511 100644
> > --- a/include/uapi/linux/hw_breakpoint.h
> > +++ b/include/uapi/linux/hw_breakpoint.h
> > @@ -17,14 +17,4 @@ enum {
> >       HW_BREAKPOINT_INVALID   = HW_BREAKPOINT_RW | HW_BREAKPOINT_X,
> >  };
> >  
> > -enum bp_type_idx {
> > -     TYPE_INST       = 0,
> > -#ifdef CONFIG_HAVE_MIXED_BREAKPOINTS_REGS
> > -     TYPE_DATA       = 0,
> > -#else
> > -     TYPE_DATA       = 1,
> > -#endif
> > -     TYPE_MAX
> > -};
> 
> This is rather unfortunate; you are correct that the naming is too
> generic (and I tend to agree), but I think these values are required by
> userspace to fill out:
> 
>   perf_event_attr::bp_type
> 
> So removing them will break things.
> 
> Frederic?

If user space actually relies on the definition from this header file,
then it will use the wrong one on x86 and get 'TYPE_DATA = 1', while the
kernel uses 'TYPE_DATA = 0'.

That seems unlikely to work, so I suspect it gets a different definition.
If it uses this definition and it does work, we can probably use

#if defined(__KERNEL__) && defined(CONFIG_HAVE_MIXED_BREAKPOINTS_REGS)

but that requires a comment explaining exactly why that works.

	Arnd