linux-kernel - Re: [PATCH v2] bpf: Fix BTF_ID symbol generation collision

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Message-ID: <20230915171814.GA1721473@dev-arch.thelio-3990X>
Date:   Fri, 15 Sep 2023 10:18:14 -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>,
        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>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v2] bpf: Fix BTF_ID symbol generation collision

On Fri, Sep 15, 2023 at 09:42:20AM -0700, Nick Desaulniers wrote:
> 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
> Tested-by: Marcus Seyfarth <m.seyfarth@...il.com>
> Debugged-by: Nathan Chancellor <nathan@...nel.org>
> Co-developed-by: Jiri Olsa <jolsa@...nel.org>
> Link: https://lore.kernel.org/bpf/CAEf4Bzb5KQ2_LmhN769ifMeSJaWfebccUasQOfQKaOd0nQ51tw@mail.gmail.com/
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  tools/include/linux/btf_ids.h | 2 +-

Shouldn't this diff be in include/linux/btf_ids.h as well? Otherwise, I
don't think it will be used by the kernel build.

>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/include/linux/btf_ids.h b/tools/include/linux/btf_ids.h
> index 71e54b1e3796..30e920b96a18 100644
> --- a/tools/include/linux/btf_ids.h
> +++ b/tools/include/linux/btf_ids.h
> @@ -38,7 +38,7 @@ asm(							\
>  	____BTF_ID(symbol)
>  
>  #define __ID(prefix) \
> -	__PASTE(prefix, __COUNTER__)
> +	__PASTE(prefix, __COUNTER__ __LINE__)
>  
>  /*
>   * The BTF_ID defines unique symbol for each ID pointing
> 
> ---
> base-commit: 9fdfb15a3dbf818e06be514f4abbfc071004cbe7
> change-id: 20230915-bpf_collision-36889a391d44
> 
> Best regards,
> -- 
> Nick Desaulniers <ndesaulniers@...gle.com>
>