On Tue, Jul 25, 2017 at 02:27:38PM +0100, Will Deacon wrote: > On Fri, Jul 07, 2017 at 05:33:57PM +0530, Pratyush Anand wrote: > > Architecture like ARM64 currently allows to use default hw breakpoint > > single step handler only to perf. However, some other users like few > > systemtap tests or kernel test in > > samples/hw_breakpoint/data_breakpoint.c can also work with default step > > handler implementation. At the same time, some other like GDB/ptrace may > > implement their own step handler. > > > > Therefore, this patch introduces a new perf_event_attr bit field, so > > that arch specific code(specially on arm64) can make a decision to > > enable single stepping. > > > > Any architecture which is not using this field will not have any > > side effect.
> > diff --git a/include/uapi/linux/perf_event.h > > b/include/uapi/linux/perf_event.h > > index b1c0b187acfe..00935808de0d 100644 > > --- a/include/uapi/linux/perf_event.h > > +++ b/include/uapi/linux/perf_event.h > > @@ -345,7 +345,8 @@ struct perf_event_attr { > > context_switch : 1, /* context switch data */ > > write_backward : 1, /* Write ring buffer from > > end to beginning */ > > namespaces : 1, /* include namespaces data > > */ > > - __reserved_1 : 35; > > + step_needed : 1, /* Use arch step handler */ > > + __reserved_1 : 34; > > This needs documenting properly, as I really have no idea how userspace is > going to use it sensibley, especially as you silently overwrite it in some > cases below. This is not something userspace _can_ use sensibly afaict. Therefore it should probably not live here.