linux-kernel - [PATCH 6/7] ftrace: Make DIRECT_CALLS work WITH_ARGS and !WITH

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Message-Id: <20230316173811.1223508-7-revest@chromium.org>
Date:   Thu, 16 Mar 2023 18:38:10 +0100
From:   Florent Revest <revest@...omium.org>
To:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Cc:     rostedt@...dmis.org, mhiramat@...nel.org, mark.rutland@....com,
        ast@...nel.org, daniel@...earbox.net, kpsingh@...nel.org,
        revest@...omium.org, jolsa@...nel.org
Subject: [PATCH 6/7] ftrace: Make DIRECT_CALLS work WITH_ARGS and !WITH_REGS

Direct called trampolines can be called in two ways:
- either from the ftrace callsite. In this case, they do not access any
  struct ftrace_regs nor pt_regs
- Or, if a ftrace ops is also attached, from the end of a ftrace
  trampoline. In this case, the call_direct_funcs ops is in charge of
  setting the direct call trampoline's address in a struct ftrace_regs

Since:

commit 9705bc709604 ("ftrace: pass fregs to arch_ftrace_set_direct_caller()")

The later case no longer requires a full pt_regs. It only needs a struct
ftrace_regs so DIRECT_CALLS can work with both WITH_ARGS or WITH_REGS.
With architectures like arm64 already abandoning WITH_REGS in favor of
WITH_ARGS, it's important to have DIRECT_CALLS work WITH_ARGS only.

Signed-off-by: Florent Revest <revest@...omium.org>
Co-developed-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Mark Rutland <mark.rutland@....com>
---
 include/linux/ftrace.h | 6 ++++++
 kernel/trace/Kconfig   | 2 +-
 kernel/trace/ftrace.c  | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 6a532dd6789e..31f1e1df2af3 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -241,6 +241,12 @@ enum {
 	FTRACE_OPS_FL_DIRECT			= BIT(17),
 };
 
+#ifndef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
+#define FTRACE_OPS_FL_SAVE_ARGS                        FTRACE_OPS_FL_SAVE_REGS
+#else
+#define FTRACE_OPS_FL_SAVE_ARGS                        0
+#endif
+
 /*
  * FTRACE_OPS_CMD_* commands allow the ftrace core logic to request changes
  * to a ftrace_ops. Note, the requests may fail.
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index a856d4a34c67..5b1e7fa41ca8 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -257,7 +257,7 @@ config DYNAMIC_FTRACE_WITH_REGS
 
 config DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	def_bool y
-	depends on DYNAMIC_FTRACE_WITH_REGS
+	depends on DYNAMIC_FTRACE_WITH_REGS || DYNAMIC_FTRACE_WITH_ARGS
 	depends on HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 
 config DYNAMIC_FTRACE_WITH_CALL_OPS
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 66c91fa4b6ab..7a0c7eddf25b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5287,7 +5287,7 @@ static LIST_HEAD(ftrace_direct_funcs);
 
 static int register_ftrace_function_nolock(struct ftrace_ops *ops);
 
-#define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS)
+#define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_ARGS)
 
 static int check_direct_multi(struct ftrace_ops *ops)
 {
-- 
2.40.0.rc2.332.ga46443480c-goog