linux-kernel - [PATCH 1/8] ftrace: add ftrace_init

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Message-Id: <20191021163426.9408-2-mark.rutland@arm.com>
Date:   Mon, 21 Oct 2019 17:34:19 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     amit.kachhap@....com, ard.biesheuvel@...aro.org,
        catalin.marinas@....com, deller@....de, duwe@...e.de,
        james.morse@....com, jeyu@...nel.org, jpoimboe@...hat.com,
        jthierry@...hat.com, mark.rutland@....com, mingo@...hat.com,
        peterz@...radead.org, rostedt@...dmis.org, svens@...ckframe.org,
        takahiro.akashi@...aro.org, will@...nel.org
Subject: [PATCH 1/8] ftrace: add ftrace_init_nop()

Architectures may need to perform special initialization of ftrace
callsites, and today they do so by special-casing ftrace_make_nop() when
the expected branch address is MCOUNT_ADDR. In some cases (e.g. for
patchable-function-entry), we don't have an mcount-like symbol and don't
want a synthetic MCOUNT_ADDR, but we may need to perform some
initialization of callsites.

To make it possible to separate initialization from runtime
modification, and to handle cases without an mcount-like symbol, this
patch adds an optional ftrace_init_nop() function that architectures can
implement, which does not pass a branch address.

Where an architecture does not provide ftrace_init_nop(), we will fall
back to the existing behaviour of calling ftrace_make_nop() with
MCOUNT_ADDR.

At the same time, ftrace_code_disable() is renamed to
ftrace_code_init_disabled() to make it clearer that it is intended to
intialize a callsite into a disabled state, and is not for disabling a
callsite that has been runtime enabled.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Torsten Duwe <duwe@...e.de>
---
 kernel/trace/ftrace.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f296d89be757..afd7e210e595 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2493,15 +2493,22 @@ struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter)
 	return &iter->pg->records[iter->index];
 }

+#ifndef ftrace_init_nop
+static int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
+{
+	return ftrace_make_nop(mod, rec, MCOUNT_ADDR);
+}
+#endif
+
 static int
-ftrace_code_disable(struct module *mod, struct dyn_ftrace *rec)
+ftrace_code_init_disabled(struct module *mod, struct dyn_ftrace *rec)
 {
 	int ret;

 	if (unlikely(ftrace_disabled))
 		return 0;

-	ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
+	ret = ftrace_init_nop(mod, rec);
 	if (ret) {
 		ftrace_bug_type = FTRACE_BUG_INIT;
 		ftrace_bug(ret, rec);
@@ -2943,7 +2950,7 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
 			 * to the NOP instructions.
 			 */
 			if (!__is_defined(CC_USING_NOP_MCOUNT) &&
-			    !ftrace_code_disable(mod, p))
+			    !ftrace_code_init_disabled(mod, p))
 				break;

 			update_cnt++;
-- 
2.11.0