netdev - [PATCH bpf-next v10 06/12] bpf,x86: introduce emit_store_stack

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Message-ID: <20260115112246.221082-7-dongml2@chinatelecom.cn>
Date: Thu, 15 Jan 2026 19:22:40 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
	andrii@...nel.org
Cc: daniel@...earbox.net,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
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	dave.hansen@...ux.intel.com,
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Subject: [PATCH bpf-next v10 06/12] bpf,x86: introduce emit_store_stack_imm64() for trampoline

Introduce the helper emit_store_stack_imm64(), which is used to store a
imm64 to the stack with the help of a register.

Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
v10:
- add the "reg" to the function arguments of emit_store_stack_imm64()
- use the positive offset in emit_store_stack_imm64()
- remove some unnecessary comment, as we already have proper comment in
  emit_store_stack_imm64()

v9:
- rename emit_st_r0_imm64() to emit_store_stack_imm64()
---
 arch/x86/net/bpf_jit_comp.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index e3b1c4b1d550..2f31331955b5 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1300,6 +1300,16 @@ 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_store_stack_imm64(u8 **pprog, int reg, int stack_off, u64 imm64)
+{
+	/*
+	 * mov reg, imm64
+	 * mov QWORD PTR [rbp + stack_off], reg
+	 */
+	emit_mov_imm64(pprog, reg, imm64 >> 32, (u32) imm64);
+	emit_stx(pprog, BPF_DW, BPF_REG_FP, reg, stack_off);
+}
+
 static int emit_atomic_rmw(u8 **pprog, u32 atomic_op,
 			   u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size)
 {
@@ -3348,20 +3358,12 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 	/* mov QWORD PTR [rbp - rbx_off], rbx */
 	emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_6, -rbx_off);
 
-	/* Store number of argument registers of the traced function:
-	 *   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);
+	/* Store number of argument registers of the traced function */
+	emit_store_stack_imm64(&prog, BPF_REG_0, -nregs_off, nr_regs);
 
 	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);
+		/* Store IP address of the traced function */
+		emit_store_stack_imm64(&prog, BPF_REG_0, -ip_off, (long)func_addr);
 	}
 
 	save_args(m, &prog, regs_off, false, flags);
-- 
2.52.0