Re: [PATCH bpf] bpf: Fix BTF_ID symbol generation

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On Fri, Sep 15, 2023 at 3:32 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Marcus and Nick reported issue where BTF_ID macro generates same
> symbol in separate objects and that breaks final vmlinux link.
>
> Adding __LINE__ number suffix to make BTF_ID symbol more unique,
> which is not real fix, but it would help for now and meanwhile
> we can work on better solution as suggested by Andrii in [2].
>
> [1] https://github.com/ClangBuiltLinux/linux/issues/1913
> [2] https://lore.kernel.org/bpf/ZQQVr35crUtN1quS@krava/T/#m64d7c29c407d6adf0e7b420359958b3aafa7bf69
> Reported-by: Marcus Seyfarth <m.seyfarth@xxxxxxxxx>
> Reported-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@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__)

I think __COUNTER__ and __LINE__ both expand to string literals; you
can avoid another expansion via __PASTE by just putting them adjacent,
like so:
https://github.com/ClangBuiltLinux/linux/issues/1913#issuecomment-1710794319
I'll send that as a v2 and link back to your v1.

>
>  /*
>   * The BTF_ID defines unique symbol for each ID pointing
> --
> 2.41.0
>


-- 
Thanks,
~Nick Desaulniers





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