On Tue, Jul 25, 2017 at 04:14:23PM +0200, Peter Zijlstra wrote: > 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.
Indeed. When I suggested this, I meant that it would be a kernel-internal flag, and not UAPI. Thanks, Mark.