linux-kernel - Re: [PATCH bpf-next v3 1/3] bpf, riscv: introduce emit_store_stack

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Message-ID: <3042323.e9J7NaK4W3@7950hx>
Date: Sat, 07 Feb 2026 18:53:17 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: Menglong Dong <menglong8.dong@...il.com>, Pu Lehui <pulehui@...wei.com>
Cc: bjorn@...nel.org, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, puranjay@...nel.org,
 pjw@...nel.org, palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr,
 bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, jiang.biao@...ux.dev
Subject: Re: [PATCH bpf-next v3 1/3] bpf,
 riscv: introduce emit_store_stack_imm64() for trampoline

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@...natelecom.cn>
> > Tested-by: Björn Töpel <bjorn@...nel.org>
> > Acked-by: Björn Töpel <bjorn@...nel.org>
> > ---
> >   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?

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);
> >   
> 
>