linux-kernel - [PATCH] perf inject jit: Ignore memfd mmap events if jitdump present

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Message-Id: <20220802182502.85562-1-brianrob@linux.microsoft.com>
Date:   Tue,  2 Aug 2022 11:25:02 -0700
From:   Brian Robbins <brianrob@...ux.microsoft.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>
Cc:     linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        brianrob@...ux.microsoft.com
Subject: [PATCH] perf inject jit: Ignore memfd mmap events if jitdump present

Some processes store jitted code in memfd mappings to avoid having rwx
mappings.  These processes map the code with a writeable mapping and a
read-execute mapping.  They write the code using the writeable mapping
and then unmap the writeable mapping.  All subsequent execution is
through the read-execute mapping.

perf inject --jit ignores //anon* mappings for each process where a
jitdump is present because it expects to inject mmap events for each
jitted code range, and said jitted code ranges will overlap with the
//anon* mappings.

Ignore /memfd: mappings so that jitted code contained in /memfd:
mappings is treated the same way as jitted code contained in //anon*
mappings.

Signed-off-by: Brian Robbins <brianrob@...ux.microsoft.com>
---
 tools/perf/util/jitdump.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index a23255773c60..335a3c61940b 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -845,8 +845,12 @@ jit_process(struct perf_session *session,
 	if (jit_detect(filename, pid, nsi)) {
 		nsinfo__put(nsi);

-		// Strip //anon* mmaps if we processed a jitdump for this pid
-		if (jit_has_pid(machine, pid) && (strncmp(filename, "//anon", 6) == 0))
+		/*
+		 * Strip //anon* and /memfd:* mmaps if we processed a jitdump for this pid
+		 */
+		if (jit_has_pid(machine, pid) &&
+			((strncmp(filename, "//anon", 6) == 0) ||
+			 (strncmp(filename, "/memfd:", 7) == 0))
 			return 1;

 		return 0;
-- 
2.25.1