On Wed, Sep 3, 2025 at 10:52 PM Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
>
> Hi, Hengqi,
>
> On Wed, Sep 3, 2025 at 8:06 PM Hengqi Chen <hengqi.chen@xxxxxxxxx> wrote:
> >
> > The current implementation of bpf_arch_text_poke() requires 5 nops
> > at patch site which is not applicable for kernel/module functions.
> > With CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=y, this can be done
> > by ftrace instead.
> Does this mean BPF trampoline can only work with FTRACE enabled?
>
IIUC, with CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=n, we could still trace
BPF progs with BPF trampoline.
> Huacai
>
> >
> > See the following commit for details:
> > * commit b91e014f078e ("bpf: Make BPF trampoline use register_ftrace_direct() API")
> > * commit 9cdc3b6a299c ("LoongArch: ftrace: Add direct call support")
> >
> > Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
> > ---
> > arch/loongarch/net/bpf_jit.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> > index 7b7e449b9ea9..35b13d91a979 100644
> > --- a/arch/loongarch/net/bpf_jit.c
> > +++ b/arch/loongarch/net/bpf_jit.c
> > @@ -1294,8 +1294,11 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
> > u32 old_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
> > u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
> >
> > - if (!is_kernel_text((unsigned long)ip) &&
> > - !is_bpf_text_address((unsigned long)ip))
> > + if (!is_bpf_text_address((unsigned long)ip))
> > + /* Only poking bpf text is supported. Since kernel function
> > + * entry is set up by ftrace, we reply on ftrace to poke kernel
> > + * functions.
> > + */
> > return -ENOTSUPP;
> >
> > ret = emit_jump_or_nops(old_addr, ip, old_insns, is_call);
> > --
> > 2.43.5
> >
