linux-kernel - Re: [PATCH v4 6/7] LoongArch: BPF: Enhance the bpf_arch_text

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Message-ID: <CAEyhmHRbacxpfTkPJq4MerBupH0bJkFfx8xGUvHMvGOzDDJUow@mail.gmail.com>
Date: Sat, 20 Dec 2025 22:07:25 +0800
From: Hengqi Chen <hengqi.chen@...il.com>
To: Chenghao Duan <duanchenghao@...inos.cn>
Cc: yangtiezhu@...ngson.cn, rostedt@...dmis.org, mhiramat@...nel.org, 
	mark.rutland@....com, chenhuacai@...nel.org, kernel@...0n.name, 
	zhangtianyang@...ngson.cn, masahiroy@...nel.org, linux-kernel@...r.kernel.org, 
	loongarch@...ts.linux.dev, bpf@...r.kernel.org, youling.tang@...ux.dev, 
	jianghaoran@...inos.cn, vincent.mc.li@...il.com, 
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/7] LoongArch: BPF: Enhance the bpf_arch_text_poke() function

On Wed, Dec 17, 2025 at 2:15 PM Chenghao Duan <duanchenghao@...inos.cn> wrote:
>
> Enhance the bpf_arch_text_poke() function to enable accurate location
> of BPF program entry points.
>
> When modifying the entry point of a BPF program, skip the move t0, ra
> instruction to ensure the correct logic and copy of the jump address.
>
> Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
> ---
>  arch/loongarch/net/bpf_jit.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 3dbabacc8856..0c16a1b18e8f 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -1290,6 +1290,10 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t,
>                        void *new_addr)

The signature of bpf_arch_text_poke() was changed in v6.19 ([1]), please rebase.

  [1]: https://github.com/torvalds/linux/commit/ae4a3160d19cd16b874737ebc1798c7bc2fe3c9e

>  {
>         int ret;
> +       unsigned long size = 0;
> +       unsigned long offset = 0;
> +       char namebuf[KSYM_NAME_LEN];
> +       void *image = NULL;
>         bool is_call;
>         u32 old_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
>         u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
> @@ -1297,9 +1301,18 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t,
>         /* Only poking bpf text is supported. Since kernel function entry
>          * is set up by ftrace, we rely on ftrace to poke kernel functions.
>          */
> -       if (!is_bpf_text_address((unsigned long)ip))
> +       if (!__bpf_address_lookup((unsigned long)ip, &size, &offset, namebuf))
>                 return -ENOTSUPP;
>
> +       image = ip - offset;
> +       /* zero offset means we're poking bpf prog entry */
> +       if (offset == 0)
> +               /* skip to the nop instruction in bpf prog entry:
> +                * move t0, ra
> +                * nop
> +                */
> +               ip = image + LOONGARCH_INSN_SIZE;
> +
>         is_call = old_t == BPF_MOD_CALL;
>         ret = emit_jump_or_nops(old_addr, ip, old_insns, is_call);
>         if (ret)
> --
> 2.25.1
>