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

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Message-ID: <9830ef1c-d9cc-46ce-b292-07c8222d72ac@huawei.com>
Date: Sun, 8 Feb 2026 09:58:03 +0800
From: Pu Lehui <pulehui@...wei.com>
To: Menglong Dong <menglong.dong@...ux.dev>, Menglong Dong
	<menglong8.dong@...il.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 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@...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?

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);
>>>    
>>
>>
> 
> 
> 
> 
> 
>