[PATCH 1/8] ftrace: add ftrace_init_nop()

From: Mark Rutland
Date: Mon Oct 21 2019 - 12:35:07 EST

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

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@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Torsten Duwe <duwe@xxxxxxx>
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);
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))