linux-kernel - [PATCH v4 6/7] LoongArch: BPF: Enhance the bpf_arch_text

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Message-Id: <20251217061435.802204-7-duanchenghao@kylinos.cn>
Date: Wed, 17 Dec 2025 14:14:34 +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 6/7] LoongArch: BPF: Enhance the bpf_arch_text_poke() function

Enhance the bpf_arch_text_poke() function to enable accurate location
of BPF program entry points.

When modifying the entry point of a BPF program, skip the move t0, ra
instruction to ensure the correct logic and copy of the jump address.

Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
---
 arch/loongarch/net/bpf_jit.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 3dbabacc8856..0c16a1b18e8f 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1290,6 +1290,10 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t,
 		       void *new_addr)
 {
 	int ret;
+	unsigned long size = 0;
+	unsigned long offset = 0;
+	char namebuf[KSYM_NAME_LEN];
+	void *image = NULL;
 	bool is_call;
 	u32 old_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
 	u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
@@ -1297,9 +1301,18 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t,
 	/* Only poking bpf text is supported. Since kernel function entry
 	 * is set up by ftrace, we rely on ftrace to poke kernel functions.
 	 */
-	if (!is_bpf_text_address((unsigned long)ip))
+	if (!__bpf_address_lookup((unsigned long)ip, &size, &offset, namebuf))
 		return -ENOTSUPP;
 
+	image = ip - offset;
+	/* zero offset means we're poking bpf prog entry */
+	if (offset == 0)
+		/* skip to the nop instruction in bpf prog entry:
+		 * move t0, ra
+		 * nop
+		 */
+		ip = image + LOONGARCH_INSN_SIZE;
+
 	is_call = old_t == BPF_MOD_CALL;
 	ret = emit_jump_or_nops(old_addr, ip, old_insns, is_call);
 	if (ret)
-- 
2.25.1