[RFC PATCH 12/13] mm/kstackwatch: Add debug and test functions

[Jinchao Wang <wangjinchao600@gmail.com>]

This patch adds new helper functions to the kstackwatch module to aid in
debugging and testing.

- `ksw_watch_show()`: Displays information about the currently active hardware
  breakpoint, such as its address and length. This is useful for verifying
  that a breakpoint has been correctly installed.
- `ksw_watch_fire()`: Manually triggers the active hardware breakpoint. This
  function is for testing the breakpoint handler to ensure it correctly
  identifies and reports the stack corruption.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 mm/kstackwatch/kstackwatch.h |  4 ++++
 mm/kstackwatch/watch.c       | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index c24a651977c0..27c71a9391ac 100644
--- a/mm/kstackwatch/kstackwatch.h
+++ b/mm/kstackwatch/kstackwatch.h
@@ -2,6 +2,8 @@
 #ifndef _KSTACKWATCH_H
 #define _KSTACKWATCH_H
 
+#include <linux/kprobes.h>
+#include <linux/perf_event.h>
 #include <linux/types.h>
 
 #define MAX_FUNC_NAME_LEN 64
@@ -48,5 +50,7 @@ int ksw_watch_init(struct ksw_config *config);
 void ksw_watch_exit(void);
 int ksw_watch_on(u64 watch_addr, u64 watch_len);
 void ksw_watch_off(void);
+void ksw_watch_show(void);
+void ksw_watch_fire(void);
 
 #endif /* _KSTACKWATCH_H */
diff --git a/mm/kstackwatch/watch.c b/mm/kstackwatch/watch.c
index 1b4cf5d42db9..28ea24e4ae3a 100644
--- a/mm/kstackwatch/watch.c
+++ b/mm/kstackwatch/watch.c
@@ -218,3 +218,23 @@ void ksw_watch_off(void)
 	ksw_watch_on((unsigned long)&marker, sizeof(marker));
 	pr_info("KSW: All HWBPs disarmed\n");
 }
+
+/* Debug functions */
+void ksw_watch_show(void)
+{
+	struct perf_event *bp;
+
+	bp = *this_cpu_ptr(watch_events);
+	pr_info("KSW: HWBP info test - bp_addr: 0x%px len:%llu\n",
+		(void *)bp->attr.bp_addr, bp->attr.bp_len);
+}
+
+void ksw_watch_fire(void)
+{
+	struct perf_event *bp;
+	char *ptr;
+
+	bp = *this_cpu_ptr(watch_events);
+	ptr = (char *)READ_ONCE(bp->attr.bp_addr);
+	*ptr = 0x42; // This should trigger immediately
+}
-- 
2.43.0