[PATCH 6/7] ftrace: Make DIRECT_CALLS work WITH_ARGS and !WITH_REGS

Florent Revest
2023-03-16T17:38:59Z

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@chromium.org>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.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