linux-kernel - Re: [PATCH bpf v3 1/2] bpf: Fix BTF

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Date:   Fri, 15 Sep 2023 11:30:08 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        KP Singh <kpsingh@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, stable@...r.kernel.org,
        Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        Marcus Seyfarth <m.seyfarth@...il.com>
Subject: Re: [PATCH  bpf  v3 1/2] bpf: Fix BTF_ID symbol generation collision

On Fri, Sep 15, 2023 at 10:34:27AM -0700, Nick Desaulniers wrote:
> From: Jiri Olsa <jolsa@...nel.org>
> 
> Marcus and Satya reported an issue where BTF_ID macro generates same
> symbol in separate objects and that breaks final vmlinux link.
> 
> ld.lld: error: ld-temp.o <inline asm>:14577:1: symbol
> '__BTF_ID__struct__cgroup__624' is already defined
> 
> This can be triggered under specific configs when __COUNTER__ happens to
> be the same for the same symbol in two different translation units,
> which is already quite unlikely to happen.
> 
> Add __LINE__ number suffix to make BTF_ID symbol more unique, which is
> not a complete fix, but it would help for now and meanwhile we can work
> on better solution as suggested by Andrii.
> 
> Cc: stable@...r.kernel.org
> Reported-by: Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
> Reported-by: Marcus Seyfarth <m.seyfarth@...il.com>
> Closes: https://github.com/ClangBuiltLinux/linux/issues/1913
> Debugged-by: Nathan Chancellor <nathan@...nel.org>
> Link: https://lore.kernel.org/bpf/CAEf4Bzb5KQ2_LmhN769ifMeSJaWfebccUasQOfQKaOd0nQ51tw@mail.gmail.com/
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  include/linux/btf_ids.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
> index a3462a9b8e18..a9cb10b0e2e9 100644
> --- a/include/linux/btf_ids.h
> +++ b/include/linux/btf_ids.h
> @@ -49,7 +49,7 @@ word							\
>  	____BTF_ID(symbol, word)
>  
>  #define __ID(prefix) \
> -	__PASTE(prefix, __COUNTER__)
> +	__PASTE(__PASTE(prefix, __COUNTER__), __LINE__)
>  
>  /*
>   * The BTF_ID defines unique symbol for each ID pointing
> 
> -- 
> 2.42.0.459.ge4e396fd5e-goog
>