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.
>
> Signed-off-by: Pratyush Anand <pan...@redhat.com>
> ---
> include/linux/hw_breakpoint.h | 6 ++++++
> include/uapi/linux/perf_event.h | 3 ++-
> kernel/events/core.c | 2 ++
> tools/include/uapi/linux/perf_event.h | 3 ++-
> 4 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
> index 0464c85e63fd..6173ae048cbc 100644
> --- a/include/linux/hw_breakpoint.h
> +++ b/include/linux/hw_breakpoint.h
> @@ -38,6 +38,12 @@ static inline int hw_breakpoint_type(struct perf_event *bp)
> return bp->attr.bp_type;
> }
>
> +static inline bool
> +hw_breakpoint_needs_single_step(struct perf_event *bp)
> +{
> + return bp->attr.step_needed;
> +}
> +
> static inline unsigned long hw_breakpoint_len(struct perf_event *bp)
> {
> return bp->attr.bp_len;
> 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.
Will
>
> union {
> __u32 wakeup_events; /* wakeup every n events */
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 6c4e523dc1e2..220e26941475 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9444,9 +9444,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> } else if (is_write_backward(event)){
> event->overflow_handler = perf_event_output_backward;
> event->overflow_handler_context = NULL;
> + event->attr.step_needed = 1;
> } else {
> event->overflow_handler = perf_event_output_forward;
> event->overflow_handler_context = NULL;
> + event->attr.step_needed = 1;
> }
>
> perf_event__state_init(event);
> diff --git a/tools/include/uapi/linux/perf_event.h
> b/tools/include/uapi/linux/perf_event.h
> index b1c0b187acfe..00935808de0d 100644
> --- a/tools/include/uapi/linux/perf_event.h
> +++ b/tools/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;
>
> union {
> __u32 wakeup_events; /* wakeup every n events */
> --
> 2.9.3
>
