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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Fri, 8 Dec 2023 11:32:07 -0800
Message-ID: <CAADnVQJFB_CPtFS3=VV=RwnP=EQRL3yEsR8wXVcicb07P8NODw@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] x86/cfi,bpf: Fix BPF JIT call
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Jiri Olsa <olsajiri@gmail.com>, Song Liu <song@kernel.org>,
        Song Liu <songliubraving@meta.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        "David S. Miller" <davem@davemloft.net>,
        David Ahern <dsahern@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
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On Fri, Dec 8, 2023 at 5:41=E2=80=AFAM Peter Zijlstra <peterz@infradead.org=
> wrote:
>
> On Fri, Dec 08, 2023 at 11:29:40AM +0100, Peter Zijlstra wrote:
> > The only problem I now have is the one XXX, I'm not entirely sure what
> > signature to use there.
>
> > @@ -119,6 +119,7 @@ int bpf_struct_ops_test_run(struct bpf_p
> >       op_idx =3D prog->expected_attach_type;
> >       err =3D bpf_struct_ops_prepare_trampoline(tlinks, link,
> >                                               &st_ops->func_models[op_i=
dx],
> > +                                             /* XXX */ NULL,
> >                                               image, image + PAGE_SIZE)=
;
> >       if (err < 0)
> >               goto out;
>
> Duh, that should ofcourse be something of dummy_ops_test_ret_fn type.
> Let me go fix that.

Right. That should work.
A bit wasteful to generate real code just to read hash from it
via cfi_get_func_hash(), but it's a neat idea.
I guess it's hard to get kcfi from __ADDRESSABLE in plain C
and sprinkling asm("cfi_xxx: .long   __kcfi_typeid..."); is worse?
Even if it's a macro ?
That macro would be used to define cfi_bpf_hash and all other stubs?