linux-kernel - [PATCH v4 4/7] LoongArch: BPF: Save return address register ra to t0 before trampoline

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Message-Id: <20251217061435.802204-5-duanchenghao@kylinos.cn>
Date: Wed, 17 Dec 2025 14:14:32 +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 4/7] LoongArch: BPF: Save return address register ra to t0 before trampoline

Modify the build_prologue function to ensure the return address
register ra is saved to t0 before entering trampoline operations.
This change ensures accurate return address handling when a BPF
program calls another BPF program, preventing errors in the
BPF-to-BPF call chain.

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

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 76cd24646bec..c560d1e14b9d 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -139,6 +139,7 @@ static void build_prologue(struct jit_ctx *ctx)
 	stack_adjust = round_up(stack_adjust, 16);
 	stack_adjust += bpf_stack_adjust;
 
+	move_reg(ctx, LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);
 	/* Reserve space for the move_imm + jirl instruction */
 	for (i = 0; i < LOONGARCH_LONG_JUMP_NINSNS; i++)
 		emit_insn(ctx, nop);
-- 
2.25.1