[PATCH v5 2/2] arm64/ftrace: Make function graph use ftrace directly

Chengming Zhou
2022-04-20T16:01:56Z

As we do in commit 0c0593b45c9b ("x86/ftrace: Make function graph
use ftrace directly"), we don't need special hook for graph tracer,
but instead we use graph_ops:func function to install return_hooker.

Since commit 3b23e4991fb6 ("arm64: implement ftrace with regs") add
implementation for FTRACE_WITH_REGS on arm64, we can easily adopt
the same cleanup on arm64.

And this cleanup only changes the FTRACE_WITH_REGS implementation,
so the mcount-based implementation is unaffected.

While in theory it would be possible to make a similar cleanup for
!FTRACE_WITH_REGS, this will require rework of the core code, and
so for now we only change the FTRACE_WITH_REGS implementation.

Tested-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
v5:
- Add reason why this patch only changed FTRACE_WITH_REGS
implementation in the commit message as suggested by Mark.
- Change to use nicer comment in ftrace_graph_func() as suggested
by Mark, because the previous comment sounds like there's an bug
to be fixed.
- Add Tested-by and Reviewed-by tags from Mark, thanks.

v3:
- Add comments in ftrace_graph_func() as suggested by Steve. Thanks.

v2:
- Remove FTRACE_WITH_REGS ftrace_graph_caller asm, thanks Mark.
---
arch/arm64/include/asm/ftrace.h | 7 +++++++
arch/arm64/kernel/entry-ftrace.S | 17 -----------------
arch/arm64/kernel/ftrace.c | 17 +++++++++++++++++
3 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 1494cfa8639b..dbc45a4157fa 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -80,8 +80,15 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
struct dyn_ftrace;
+struct ftrace_ops;
+struct ftrace_regs;
+
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
#define ftrace_init_nop ftrace_init_nop
+
+void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
+ struct ftrace_ops *op, struct ftrace_regs *fregs);
+#define ftrace_graph_func ftrace_graph_func
#endif

#define ftrace_return_address(n) return_address(n)
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index e535480a4069..d42a205ef625 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -97,12 +97,6 @@ SYM_CODE_START(ftrace_common)
SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
bl ftrace_stub

-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
- nop // If enabled, this will be replaced
- // "b ftrace_graph_caller"
-#endif
-
/*
* At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
* x19-x29 per the AAPCS, and we created frame records upon entry, so we need
@@ -127,17 +121,6 @@ ftrace_common_return:
ret x9
SYM_CODE_END(ftrace_common)

-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-SYM_CODE_START(ftrace_graph_caller)
- ldr x0, [sp, #S_PC]
- sub x0, x0, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
- add x1, sp, #S_LR // parent_ip (callsite's LR)
- ldr x2, [sp, #PT_REGS_SIZE] // parent fp (callsite's FP)
- bl prepare_ftrace_return
- b ftrace_common_return
-SYM_CODE_END(ftrace_graph_caller)
-#endif
-
#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */

/*
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 4506c4a90ac1..f447c4a36f69 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -268,6 +268,22 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
}

#ifdef CONFIG_DYNAMIC_FTRACE
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
+ struct ftrace_ops *op, struct ftrace_regs *fregs)
+{
+ /*
+ * When DYNAMIC_FTRACE_WITH_REGS is selected, `fregs` can never be NULL
+ * and arch_ftrace_get_regs(fregs) will always give a non-NULL pt_regs
+ * in which we can safely modify the LR.
+ */
+ struct pt_regs *regs = arch_ftrace_get_regs(fregs);
+ unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs);
+
+ prepare_ftrace_return(ip, parent, frame_pointer(regs));
+}
+#else
/*
* Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
* depending on @enable.
@@ -297,5 +313,6 @@ int ftrace_disable_ftrace_graph_caller(void)
{
return ftrace_modify_graph_caller(false);
}
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
--
2.35.2