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

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Date:   Fri, 17 Mar 2023 13:19:19 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     davem@...emloft.net
Cc:     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: [PATCH v2 bpf-next 3/4] libbpf: Introduce bpf_ksym_exists() macro.

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; })
+
 #ifndef ___bpf_concat
 #define ___bpf_concat(a, b) a ## b
 #endif
-- 
2.34.1