netdev - Re: [PATCHv3 bpf-next 3/7] bpf: Add bpf_get_func

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Message-ID: <YOsEusl1MLaVJuF/@krava>
Date:   Sun, 11 Jul 2021 16:48:26 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCHv3 bpf-next 3/7] bpf: Add bpf_get_func_ip helper for
 tracing programs

On Wed, Jul 07, 2021 at 05:06:17PM -0700, Andrii Nakryiko wrote:
> On Wed, Jul 7, 2021 at 2:53 PM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > Adding bpf_get_func_ip helper for BPF_PROG_TYPE_TRACING programs,
> > specifically for all trampoline attach types.
> >
> > The trampoline's caller IP address is stored in (ctx - 8) address.
> > so there's no reason to actually call the helper, but rather fixup
> > the call instruction and return [ctx - 8] value directly (suggested
> > by Alexei).
> >
> > [fixed has_get_func_ip wrong return type]
> > Reported-by: kernel test robot <lkp@...el.com>
> > Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  include/uapi/linux/bpf.h       |  7 +++++
> >  kernel/bpf/verifier.c          | 53 ++++++++++++++++++++++++++++++++++
> >  kernel/trace/bpf_trace.c       | 15 ++++++++++
> >  tools/include/uapi/linux/bpf.h |  7 +++++
> >  4 files changed, 82 insertions(+)
> >
> 
> [...]
> 
> >  static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> >                              int *insn_idx_p)
> >  {
> > @@ -6225,6 +6256,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
> >         if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)
> >                 env->prog->call_get_stack = true;
> >
> > +       if (func_id == BPF_FUNC_get_func_ip) {
> > +               if (has_get_func_ip(env))
> 
> from has_xxx name I'd expect it returns true/false, so this reads
> super confusing. check_get_func_ip would be a bit more consistent with
> other cases like this (still reads confusing to me, but that's ok)

ok, will change

jirka

> 
> > +                       return -ENOTSUPP;
> > +               env->prog->call_get_func_ip = true;
> > +       }
> > +
> >         if (changes_data)
> >                 clear_all_pkt_pointers(env);
> >         return 0;
> 
> [...]
>