Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190716222650.tk2coihjtsxszarf@ast-mbp.dhcp.thefacebook.com>
 <20190716224150.GC172157@google.com> <20190716235500.GA199237@google.com>
 <20190717012406.lugqemvubixfdd6v@ast-mbp.dhcp.thefacebook.com>
 <20190717130119.GA138030@google.com> <CAADnVQJY_=yeY0C3k1ZKpRFu5oNbB4zhQf5tQnLr=Mi8i6cgeQ@mail.gmail.com>
 <20190718025143.GB153617@google.com> <20190723221108.gamojemj5lorol7k@ast-mbp>
 <20190724135714.GA9945@google.com> <20190726183954.oxzhkrwt4uhgl4gl@ast-mbp.dhcp.thefacebook.com>
 <20190726191853.GA196514@google.com>
In-Reply-To: <20190726191853.GA196514@google.com>
From:   Joel Fernandes <joelaf@google.com>
Date:   Fri, 26 Jul 2019 15:49:30 -0400
Message-ID: <CAJWu+opEckc++G6btY6Muhi6ToJQYSW7HfxPYdrJkXiAoy4Fww@mail.gmail.com>
Subject: Re: [PATCH RFC 0/4] Add support to directly attach BPF program to ftrace
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Network Development <netdev@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Cc: Android Kernel" <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Jul 26, 2019 at 3:18 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> On Fri, Jul 26, 2019 at 11:39:56AM -0700, Alexei Starovoitov wrote:
[snip]
> > > For bpf program:
> > > https://android.googlesource.com/platform/system/bpfprogs/+/908f6cd718fab0de7a944f84628c56f292efeb17%5E%21/
> >
> > what is unsafe_bpf_map_update_elem() in there?
> > The verifier comment sounds odd.
> > Could you describe the issue you see with the verifier?
>
> Will dig out the verifier issue I was seeing. I was just trying to get a
> prototype working so I did not go into verifier details much.

This is actually slightly old code, the actual function name is
bpf_map_update_elem_unsafe() .
 https://android.googlesource.com/platform/system/bpf/+/refs/heads/master/progs/include/bpf_helpers.h#39

This function came about because someone added a DEFINE_BPF_MAP macro
which defines BPF map accessors based on the type of the key and
value. So that's the "safe" variant:
https://android.googlesource.com/platform/system/bpf/+/refs/heads/master/progs/include/bpf_helpers.h#54
(added in commit
https://android.googlesource.com/platform/system/bpf/+/6564b8eac46fc27dde807a39856386d98d2471c3)

So the "safe" variant of the bpf_map_update_elem for us became a map
specific version with a prototype:
static inline __always_inline __unused int
bpf_##the_map##_update_elem(TypeOfKey* k, TypeOfValue* v, unsigned
long long flags)

Since I had not upgraded my BPF program to the "safe" variant, I had
to use the internal "unsafe" variant of the API (if that makes
sense..).

thanks Alexei!

- Joel