linux-kernel - [PATCH v4 1/7] LoongArch: ftrace: Refactor register restoration in ftrace_common

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Message-Id: <20251217061435.802204-2-duanchenghao@kylinos.cn>
Date: Wed, 17 Dec 2025 14:14:29 +0800
From: Chenghao Duan <duanchenghao@...inos.cn>
To: yangtiezhu@...ngson.cn,
	rostedt@...dmis.org,
	mhiramat@...nel.org,
	mark.rutland@....com,
	hengqi.chen@...il.com,
	chenhuacai@...nel.org
Cc: kernel@...0n.name,
	zhangtianyang@...ngson.cn,
	masahiroy@...nel.org,
	linux-kernel@...r.kernel.org,
	loongarch@...ts.linux.dev,
	bpf@...r.kernel.org,
	duanchenghao@...inos.cn,
	youling.tang@...ux.dev,
	jianghaoran@...inos.cn,
	vincent.mc.li@...il.com,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH v4 1/7] LoongArch: ftrace: Refactor register restoration in ftrace_common_return

Refactor the register restoration sequence in the ftrace_common_return
function to clearly distinguish between the logic of normal returns and
direct call returns in function tracing scenarios. The logic is as
follows:
1. In the case of a normal return, the execution flow returns to the
traced function, and ftrace must ensure that the register data is
consistent with the state when the function was entered.
ra = parent return address; t0 = traced function return address.

2. In the case of a direct call return, the execution flow jumps to the
custom trampoline function, and ftrace must ensure that the register
data is consistent with the state when ftrace was entered.
ra = traced function return address; t0 = parent return address.

Fixes: 9cdc3b6a299c ("LoongArch: ftrace: Add direct call support")
Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
---
 arch/loongarch/kernel/mcount_dyn.S | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/loongarch/kernel/mcount_dyn.S b/arch/loongarch/kernel/mcount_dyn.S
index d6b474ad1d5e..5729c20e5b8b 100644
--- a/arch/loongarch/kernel/mcount_dyn.S
+++ b/arch/loongarch/kernel/mcount_dyn.S
@@ -94,7 +94,6 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL)
  * at the callsite, so there is no need to restore the T series regs.
  */
 ftrace_common_return:
-	PTR_L		ra, sp, PT_R1
 	PTR_L		a0, sp, PT_R4
 	PTR_L		a1, sp, PT_R5
 	PTR_L		a2, sp, PT_R6
@@ -104,12 +103,17 @@ ftrace_common_return:
 	PTR_L		a6, sp, PT_R10
 	PTR_L		a7, sp, PT_R11
 	PTR_L		fp, sp, PT_R22
-	PTR_L		t0, sp, PT_ERA
 	PTR_L		t1, sp, PT_R13
-	PTR_ADDI	sp, sp, PT_SIZE
 	bnez		t1, .Ldirect
+
+	PTR_L		ra, sp, PT_R1
+	PTR_L		t0, sp, PT_ERA
+	PTR_ADDI	sp, sp, PT_SIZE
 	jr		t0
 .Ldirect:
+	PTR_L		t0, sp, PT_R1
+	PTR_L		ra, sp, PT_ERA
+	PTR_ADDI	sp, sp, PT_SIZE
 	jr		t1
 SYM_CODE_END(ftrace_common)
 
@@ -161,6 +165,8 @@ SYM_CODE_END(return_to_handler)
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 SYM_CODE_START(ftrace_stub_direct_tramp)
 	UNWIND_HINT_UNDEFINED
-	jr		t0
+	move		t1, ra
+	move		ra, t0
+	jr		t1
 SYM_CODE_END(ftrace_stub_direct_tramp)
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
-- 
2.25.1