netdev - Re: [PATCH v2 bpf-next 3/4] libbpf: Introduce bpf_ksym

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Date:   Fri, 17 Mar 2023 15:53:45 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     davem@...emloft.net, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...nel.org, void@...ifault.com, davemarchevsky@...a.com,
        tj@...nel.org, memxor@...il.com, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v2 bpf-next 3/4] libbpf: Introduce bpf_ksym_exists() macro.

On Fri, Mar 17, 2023 at 1:19 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> From: Alexei Starovoitov <ast@...nel.org>
>
> Introduce bpf_ksym_exists() macro that can be used by BPF programs
> to detect at load time whether particular ksym (either variable or kfunc)
> is present in the kernel.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  tools/lib/bpf/bpf_helpers.h | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index 7d12d3e620cc..b49823117dae 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h
> @@ -177,6 +177,9 @@ enum libbpf_tristate {
>  #define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted")))
>  #define __kptr __attribute__((btf_type_tag("kptr")))
>
> +#define bpf_ksym_exists(sym) \
> +       ({ _Static_assert(!__builtin_constant_p(!!sym), #sym " should be marked as __weak"); !!sym; })
> +

I reformatted this to fit under 100 characters.

-#define bpf_ksym_exists(sym) \
-       ({ _Static_assert(!__builtin_constant_p(!!sym), #sym " should
be marked as __weak"); !!sym; })
+#define bpf_ksym_exists(sym) ({
                                 \
+       _Static_assert(!__builtin_constant_p(!!sym), #sym " should be
marked as __weak");       \
+       !!sym;
                         \
+})


Other than that, it looks great! Applied to bpf-next, thanks.



>  #ifndef ___bpf_concat
>  #define ___bpf_concat(a, b) a ## b
>  #endif
> --
> 2.34.1
>