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From:   Matteo Croce <mcroce@linux.microsoft.com>
Date:   Fri, 28 Jan 2022 19:51:22 +0100
Message-ID: <CAFnufp3ybOFMY=ObZFvbmr+c70CPUrL2uYp1oZQmffQBTyVy_A@mail.gmail.com>
Subject: Re: [PATCH bpf-next] bpf: limit bpf_core_types_are_compat() recursion
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Yonghong Song <yhs@fb.com>, bpf <bpf@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Jan 28, 2022 at 6:31 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Dec 20, 2021 at 10:34 PM Yonghong Song <yhs@fb.com> wrote:
> >
> >
> > https://reviews.llvm.org/D116063 improved the error message as below
> > to make it a little bit more evident what is the problem:
> >
> > $ clang -target bpf -O2 -g -c bug.c
> >
> > fatal error: error in backend: SubroutineType not supported for
> > BTF_TYPE_ID_REMOTE reloc
>
> Hi Matteo,
>
> Are you still working on a test?
> What's a timeline to repost the patch set?
>
> Thanks!

Hi Alexei,

The change itself is ready, I'm just stuck at writing a test which
will effectively calls __bpf_core_types_are_compat() with some
recursion.
I guess that I have to generate a BTF_KIND_FUNC_PROTO type somehow, so
__bpf_core_types_are_compat() is called again to check the prototipe
arguments type.
I tried with these two, with no luck:

// 1
typedef int (*func_proto_typedef)(struct sk_buff *);
bpf_core_type_exists(func_proto_typedef);

// 2
void func_proto(int, unsigned int);
bpf_core_type_id_kernel(func_proto);

Which is a simple way to generate a BTF_KIND_FUNC_PROTO BTF field?

Regards,
-- 
per aspera ad upstream