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Message-ID: <e7900b65-0d2d-48ef-b8fd-cea42ea99810@linux.dev>
Date: Sun, 4 Feb 2024 16:32:42 -0800
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Subject: Re: [PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const
 pointer
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To: Daniel Xu <dxu@dxuuu.xyz>, andrii@kernel.org, daniel@iogearbox.net,
 ast@kernel.org, olsajiri@gmail.com, quentin@isovalent.com,
 alan.maguire@oracle.com
Cc: martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org,
 john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
 haoluo@google.com, jolsa@kernel.org, bpf@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <cover.1707080349.git.dxu@dxuuu.xyz>
 <dfd3823f11ffd2d4c838e961d61ec9ae8a646773.1707080349.git.dxu@dxuuu.xyz>
From: Yonghong Song <yonghong.song@linux.dev>
In-Reply-To: <dfd3823f11ffd2d4c838e961d61ec9ae8a646773.1707080349.git.dxu@dxuuu.xyz>
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On 2/4/24 1:06 PM, Daniel Xu wrote:
> Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
> exporting a const arg version of bpf_rdonly_cast(). This causes the
> following conflicting type error when generating kfunc prototypes from
> BTF:
>
> In file included from skeleton/pid_iter.bpf.c:5:
> /home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
> extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
>               ^
> ./vmlinux.h:135625:14: note: previous declaration is here
> extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;
>
> This is b/c the kernel defines bpf_rdonly_cast() with non-const arg.
> Since const arg is more permissive and thus backwards compatible, we
> change the kernel definition as well to avoid conflicting type errors.
>
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>

Acked-by: Yonghong Song <yonghong.song@linux.dev>