[PATCH v3 07/11] perf: Add breakpoint information to siginfo on SIGTRAP

[Marco Elver]

Encode information from breakpoint attributes into siginfo_t, which
helps disambiguate which breakpoint fired.

Note, providing the event fd may be unreliable, since the event may have
been modified (via PERF_EVENT_IOC_MODIFY_ATTRIBUTES) between the event
triggering and the signal being delivered to user space.

Signed-off-by: Marco Elver <el...@google.com>
---
v2:
* Add comment about si_perf==0.
---
 kernel/events/core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1e4c949bf75f..0316d39e8c8f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6399,6 +6399,22 @@ static void perf_sigtrap(struct perf_event *event)
        info.si_signo = SIGTRAP;
        info.si_code = TRAP_PERF;
        info.si_errno = event->attr.type;
+
+       switch (event->attr.type) {
+       case PERF_TYPE_BREAKPOINT:
+               info.si_addr = (void *)(unsigned long)event->attr.bp_addr;
+               info.si_perf = (event->attr.bp_len << 16) | 
(u64)event->attr.bp_type;
+               break;
+       default:
+               /*
+                * No additional info set (si_perf == 0).
+                *
+                * Adding new cases for event types to set si_perf to a
+                * non-constant value must ensure that si_perf != 0.
+                */
+               break;
+       }
+
        force_sig_info(&info);
 }
 
-- 
2.31.0.291.g576ba9dcdaf-goog