linux-kernel - [PATCH V4 07/13] ftrace: Add perf ksymbol events for ftrace trampolines

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Date:   Wed,  4 Mar 2020 11:06:27 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     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>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH V4 07/13] 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>
---
 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 9b38ac04c110..f80ce2e9f8b9 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1033,7 +1033,7 @@ 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 aa3149fd1fc2..fda0c9144642 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2794,8 +2794,13 @@ 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);
 }
@@ -6801,8 +6806,13 @@ 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