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Subject[PATCH] sample/hw_breakpoint: avoid sample hw_breakpoint recursion for arm/arm64
Date
From: Wang Xu <wangxu72@huawei.com>

For x86/ppc, hw_breakpoint is triggered after the instruction is
executed.

For arm/arm64, which is triggered before the instruction executed.
Arm/arm64 skips the instruction by using single step. But it only
supports default overflow_handler.

This patch provides a chance to avoid sample hw_breakpoint recursion
for arm/arm64 by adding 'struct perf_event_attr.bp_step'.

Signed-off-by: Wang Xu <wangxu72@huawei.com>
---
include/linux/perf_event.h | 3 +++
include/uapi/linux/perf_event.h | 3 ++-
samples/hw_breakpoint/data_breakpoint.c | 1 +
3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 61448c1..f270eb7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1024,6 +1024,9 @@ extern int perf_event_output(struct perf_event *event,
return true;
if (unlikely(event->overflow_handler == perf_event_output_backward))
return true;
+ /* avoid sample hw_breakpoint recursion */
+ if (unlikely(event->attr.bp_step))
+ return true;
return false;
}

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index bb7b271..95b81c2 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -375,7 +375,8 @@ struct perf_event_attr {
ksymbol : 1, /* include ksymbol events */
bpf_event : 1, /* include bpf events */
aux_output : 1, /* generate AUX records instead of events */
- __reserved_1 : 32;
+ bp_step : 1,
+ __reserved_1 : 31;

union {
__u32 wakeup_events; /* wakeup every n events */
diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
index c585047..9fe1351 100644
--- a/samples/hw_breakpoint/data_breakpoint.c
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -46,6 +46,7 @@ static int __init hw_break_module_init(void)
attr.bp_addr = kallsyms_lookup_name(ksym_name);
attr.bp_len = HW_BREAKPOINT_LEN_4;
attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
+ attr.bp_step = true;

sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
if (IS_ERR((void __force *)sample_hbp)) {
--
1.8.5.6
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