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Date:   Wed, 10 Mar 2021 11:41:37 +0100
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Subject: [PATCH RFC v2 6/8] perf/core: Add breakpoint information to siginfo
 on SIGTRAP
From:   Marco Elver <elver@google.com>
To:     elver@google.com, peterz@infradead.org,
        alexander.shishkin@linux.intel.com, acme@kernel.org,
        mingo@redhat.com, jolsa@redhat.com, mark.rutland@arm.com,
        namhyung@kernel.org, tglx@linutronix.de
Cc:     glider@google.com, viro@zeniv.linux.org.uk, arnd@arndb.de,
        christian@brauner.io, dvyukov@google.com, jannh@google.com,
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        irogers@google.com, kasan-dev@googlegroups.com,
        linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-kselftest@vger.kernel.org
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Precedence: bulk

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 <elver@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 e70c411b0b16..aa47e111435e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6336,6 +6336,22 @@ 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);
 }
 
-- 
2.30.1.766.gb4fecdf3b7-goog