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Subject[PATCH V2 1/4] hw_breakpoint: Add step_needed event attribute
Date
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 <panand@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;

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
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