linux-kernel - [PATCH bpf-next v4 5/9] bpf,x86: introduce emit_st_r0

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Message-ID: <20251217095445.218428-6-dongml2@chinatelecom.cn>
Date: Wed, 17 Dec 2025 17:54:41 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
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Cc: davem@...emloft.net,
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Subject: [PATCH bpf-next v4 5/9] bpf,x86: introduce emit_st_r0_imm64() for trampoline

Introduce the helper emit_st_r0_imm64(), which is used to store a imm64 to
the stack with the help of r0.

Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
 arch/x86/net/bpf_jit_comp.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index b69dc7194e2c..8cbeefb26192 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1300,6 +1300,15 @@ static void emit_st_r12(u8 **pprog, u32 size, u32 dst_reg, int off, int imm)
 	emit_st_index(pprog, size, dst_reg, X86_REG_R12, off, imm);
 }
 
+static void emit_st_r0_imm64(u8 **pprog, u64 value, int off)
+{
+	/* mov rax, value
+	 * mov QWORD PTR [rbp - off], rax
+	 */
+	emit_mov_imm64(pprog, BPF_REG_0, value >> 32, (u32) value);
+	emit_stx(pprog, BPF_DW, BPF_REG_FP, BPF_REG_0, -off);
+}
+
 static int emit_atomic_rmw(u8 **pprog, u32 atomic_op,
 			   u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size)
 {
@@ -3341,16 +3350,14 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 	 *   mov rax, nr_regs
 	 *   mov QWORD PTR [rbp - nregs_off], rax
 	 */
-	emit_mov_imm64(&prog, BPF_REG_0, 0, (u32) nr_regs);
-	emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -nregs_off);
+	emit_st_r0_imm64(&prog, nr_regs, nregs_off);
 
 	if (flags & BPF_TRAMP_F_IP_ARG) {
 		/* Store IP address of the traced function:
 		 * movabsq rax, func_addr
 		 * mov QWORD PTR [rbp - ip_off], rax
 		 */
-		emit_mov_imm64(&prog, BPF_REG_0, (long) func_addr >> 32, (u32) (long) func_addr);
-		emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -ip_off);
+		emit_st_r0_imm64(&prog, (long)func_addr, ip_off);
 	}
 
 	save_args(m, &prog, regs_off, false, flags);
-- 
2.52.0