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From: Menglong Dong <menglong.dong@linux.dev>
To: Menglong Dong <menglong8.dong@gmail.com>,
 Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>,
 Martin KaFai Lau <martin.lau@linux.dev>, Eduard <eddyz87@gmail.com>,
 Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>,
 John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>,
 Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
 Jiri Olsa <jolsa@kernel.org>, "David S. Miller" <davem@davemloft.net>,
 David Ahern <dsahern@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
 Ingo Molnar <mingo@redhat.com>, jiang.biao@linux.dev,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
 bpf <bpf@vger.kernel.org>, Network Development <netdev@vger.kernel.org>,
 LKML <linux-kernel@vger.kernel.org>
Subject:
 Re: [PATCH bpf-next v8 04/11] bpf: support fsession for bpf_session_is_return
Date: Sat, 10 Jan 2026 11:37:36 +0800
Message-ID: <5075208.31r3eYUQgx@7950hx>
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 <CAADnVQLj4c-nc6gLbBiaT24KXWEpG3AzFT=P1tszu_akXhyD=Q@mail.gmail.com>
References:
 <20260108022450.88086-1-dongml2@chinatelecom.cn>
 <20260108022450.88086-5-dongml2@chinatelecom.cn>
 <CAADnVQLj4c-nc6gLbBiaT24KXWEpG3AzFT=P1tszu_akXhyD=Q@mail.gmail.com>
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On 2026/1/10 10:40, Alexei Starovoitov wrote:
> On Wed, Jan 7, 2026 at 6:25=E2=80=AFPM Menglong Dong <menglong8.dong@gmai=
l.com> wrote:
> >
> > +       } else if (func_id =3D=3D special_kfunc_list[KF_bpf_session_is_=
return]) {
> > +               if (prog->expected_attach_type =3D=3D BPF_TRACE_FSESSIO=
N)
> > +                       addr =3D (unsigned long)bpf_fsession_is_return;
>=20
> ...
>=20
> > +bool bpf_fsession_is_return(void *ctx)
> > +{
> > +       /* This helper call is inlined by verifier. */
> > +       return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
> > +}
> > +
>=20
> Why do this specialization and introduce a global function
> that will never be called, since it will be inlined anyway?

Ah, the specialization and the definition of the global function
is not unnecessary. I thought that it's kinda fallback solution
that we define the function even if it is inlined by the verifier.

>=20
> Remove the first hunk and make the 2nd a comment instead of a real functi=
on?

Agree. So it will be:

+static bool bpf_fsession_is_return(void *ctx)
+{
+       /* This helper call is implemented and inlined by the verifier, and=
 the logic is:
+         *   return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
+         */
+        return false;
+}

>=20
>=20