Re: [PATCH bpf v3 1/2] bpf: Fix BTF_ID symbol generation collision

[Nathan Chancellor]

On Fri, Sep 15, 2023 at 10:34:27AM -0700, Nick Desaulniers wrote:
> From: Jiri Olsa <jolsa@xxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxx
> Reported-by: Satya Durga Srinivasu Prabhala <quic_satyap@xxxxxxxxxxx>
> Reported-by: Marcus Seyfarth <m.seyfarth@xxxxxxxxx>
> Closes: https://github.com/ClangBuiltLinux/linux/issues/1913
> Debugged-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Link: https://lore.kernel.org/bpf/CAEf4Bzb5KQ2_LmhN769ifMeSJaWfebccUasQOfQKaOd0nQ51tw@xxxxxxxxxxxxxx/
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
>  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
>