linux-kernel - [PATCH V7 07/15] ftrace: Add perf ksymbol events for ftrace trampolines

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Date:   Tue, 12 May 2020 15:19:14 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>, Jiri Olsa <jolsa@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH V7 07/15] ftrace: Add perf ksymbol events for ftrace trampolines

Symbols are needed for tools to describe instruction addresses. Pages
allocated for ftrace's purposes need symbols to be created for them.
Add such symbols to be visible via perf ksymbol events.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/uapi/linux/perf_event.h |  2 +-
 kernel/trace/ftrace.c           | 14 ++++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index e1a4179144a1..52ca2093831c 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1051,7 +1051,7 @@ enum perf_record_ksymbol_type {
 	PERF_RECORD_KSYMBOL_TYPE_BPF		= 1,
 	/*
 	 * Out of line code such as kprobe-replaced instructions or optimized
-	 * kprobes.
+	 * kprobes or ftrace trampolines.
 	 */
 	PERF_RECORD_KSYMBOL_TYPE_OOL		= 2,
 	PERF_RECORD_KSYMBOL_TYPE_MAX		/* non-ABI */
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9b0baeb4f0bb..1103a8fcf142 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2801,8 +2801,13 @@ static void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops)
 static void ftrace_trampoline_free(struct ftrace_ops *ops)
 {
 	if (ops && (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP) &&
-	    ops->trampoline)
+	    ops->trampoline) {
+		perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_OOL,
+				   ops->trampoline, ops->trampoline_size,
+				   true, FTRACE_TRAMPOLINE_SYM);
+		/* Remove from kallsyms after the perf events */
 		ftrace_remove_trampoline_from_kallsyms(ops);
+	}
 
 	arch_ftrace_trampoline_free(ops);
 }
@@ -6815,8 +6820,13 @@ static void ftrace_update_trampoline(struct ftrace_ops *ops)
 
 	arch_ftrace_update_trampoline(ops);
 	if (ops->trampoline && ops->trampoline != trampoline &&
-	    (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
+	    (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP)) {
+		/* Add to kallsyms before the perf events */
 		ftrace_add_trampoline_to_kallsyms(ops);
+		perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_OOL,
+				   ops->trampoline, ops->trampoline_size, false,
+				   FTRACE_TRAMPOLINE_SYM);
+	}
 }
 
 void ftrace_init_trace_array(struct trace_array *tr)
-- 
2.17.1