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

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Date:   Wed, 24 Mar 2021 12:24:59 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com, acme@...nel.org,
        mingo@...hat.com, jolsa@...hat.com, mark.rutland@....com,
        namhyung@...nel.org, tglx@...utronix.de
Cc:     glider@...gle.com, viro@...iv.linux.org.uk, arnd@...db.de,
        christian@...uner.io, dvyukov@...gle.com, jannh@...gle.com,
        axboe@...nel.dk, mascasa@...gle.com, pcc@...gle.com,
        irogers@...gle.com, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-kselftest@...r.kernel.org
Subject: [PATCH v3 07/11] perf: Add breakpoint information to siginfo on SIGTRAP

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@...gle.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