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

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Message-ID: <20251222015010.GA119291@chenghao-pc>
Date: Mon, 22 Dec 2025 09:50:10 +0800
From: Chenghao Duan <duanchenghao@...inos.cn>
To: Hengqi Chen <hengqi.chen@...il.com>
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 Sat, Dec 20, 2025 at 10:07:25PM +0800, Hengqi Chen wrote:
> 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

Thank you for your review and for pointing out the API change in v6.19.

I believe my patch series already accounts for this. It was developed on
top of commit ae4a3160d19c ("bpf: specify the old and new poke_type for bpf_arch_text_poke"),
so all modifications to bpf_arch_text_poke() call sites within my
patches should already be using the updated signature.

Please let me know if you find any inconsistencies or if further
adjustments are needed.

Best regards,
Chenghao

> 
> >  {
> >         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
> >