On Tuesday 25 July 2017 06:57 PM, 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. 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.
I too had thought to put it under include/linux/perf_event.h : struct perf_event. But, see hw_break_module_init() which does not have knowledge of this structure, and we need to have some way so that none-perf kernel module implementation can tell that it needs default arch step handler.
Do you see any alternative? -- Regards Pratyush
