Re: [PATCH bpf-next v3 1/3] bpf, riscv: introduce emit_store_stack_imm64() for trampoline
From: Pu Lehui
Date: Sat Feb 07 2026 - 20:58:34 EST
On 2026/2/7 18:53, Menglong Dong wrote:
On 2026/2/7 09:13, Pu Lehui wrote:
On 2026/2/6 20:20, Menglong Dong wrote:
Introduce a helper to store 64-bit immediate on the trampoline stack with
a help of a register.
Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
Tested-by: Björn Töpel <bjorn@xxxxxxxxxx>
Acked-by: Björn Töpel <bjorn@xxxxxxxxxx>
---
arch/riscv/net/bpf_jit_comp64.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 37888abee70c..e4f45e2e7e2f 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -926,6 +926,14 @@ static void restore_stack_args(int nr_stack_args, int args_off, int stk_arg_off,
}
}
+static void emit_store_stack_imm64(u8 reg, int stack_off, u64 imm64,
+ struct rv_jit_context *ctx)
Some nit. The first parameter can be removed by using a fixed RV_REG_T1.
Also, placing imm64 before stack_off might looks better.
Hi, Lehui. When I implement the emit_store_stack_imm64() in x86,
Andrii suggested that we'd better use the register explicitly to indicate
the register is used. So maybe it's better to keep this part still?
No problem, the impact is minimal. And in that case, just leave imm64 and stack_off as they are. :)
I can place the imm64 before stack_off.
Thanks!
Menglong Dong
+{
+ /* Load imm64 into reg and store it at [FP + stack_off]. */
+ emit_imm(reg, (s64)imm64, ctx);
+ emit_sd(RV_REG_FP, stack_off, reg, ctx);
+}
+
static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_off,
int run_ctx_off, bool save_ret, struct rv_jit_context *ctx)
{
@@ -933,12 +941,10 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
struct bpf_prog *p = l->link.prog;
int cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
- if (l->cookie) {
- emit_imm(RV_REG_T1, l->cookie, ctx);
- emit_sd(RV_REG_FP, -run_ctx_off + cookie_off, RV_REG_T1, ctx);
- } else {
+ if (l->cookie)
+ emit_store_stack_imm64(RV_REG_T1, -run_ctx_off + cookie_off, l->cookie, ctx);
+ else
emit_sd(RV_REG_FP, -run_ctx_off + cookie_off, RV_REG_ZERO, ctx);
- }
/* arg1: prog */
emit_imm(RV_REG_A0, (const s64)p, ctx);
@@ -1123,13 +1129,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
emit_sd(RV_REG_FP, -sreg_off, RV_REG_S1, ctx);
/* store ip address of the traced function */
- if (flags & BPF_TRAMP_F_IP_ARG) {
- emit_imm(RV_REG_T1, (const s64)func_addr, ctx);
- emit_sd(RV_REG_FP, -ip_off, RV_REG_T1, ctx);
- }
+ if (flags & BPF_TRAMP_F_IP_ARG)
+ emit_store_stack_imm64(RV_REG_T1, -ip_off, (u64)func_addr, ctx); >
- emit_li(RV_REG_T1, nr_arg_slots, ctx);
- emit_sd(RV_REG_FP, -nregs_off, RV_REG_T1, ctx);
+ emit_store_stack_imm64(RV_REG_T1, -nregs_off, nr_arg_slots, ctx);
store_args(nr_arg_slots, args_off, ctx);