netdev - [PATCH bpf-next 1/2] libbpf: Do not use btf_dump_

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Date:   Thu, 23 Dec 2021 14:17:35 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     netdev@...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>
Subject: [PATCH bpf-next 1/2] libbpf: Do not use btf_dump__new macro for c++ objects

As reported in here [0], C++ compilers don't support __builtin_types_compatible_p(),
so at least don't screw up compilation for them and let C++ users
pick btf_dump__new vs btf_dump__new_deprecated explicitly.

[0] https://github.com/libbpf/libbpf/issues/283#issuecomment-986100727
Fixes: 6084f5dc928f ("libbpf: Ensure btf_dump__new() and btf_dump_opts are future-proof")
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/lib/bpf/btf.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 742a2bf71c5e..061839f04525 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -313,12 +313,18 @@ LIBBPF_API struct btf_dump *btf_dump__new_deprecated(const struct btf *btf,
  *
  * The rest works just like in case of ___libbpf_override() usage with symbol
  * versioning.
+ *
+ * C++ compilers don't support __builtin_types_compatible_p(), so at least
+ * don't screw up compilation for them and let C++ users pick btf_dump__new
+ * vs btf_dump__new_deprecated explicitly.
  */
+#ifndef __cplusplus
 #define btf_dump__new(a1, a2, a3, a4) __builtin_choose_expr(				\
 	__builtin_types_compatible_p(typeof(a4), btf_dump_printf_fn_t) ||		\
 	__builtin_types_compatible_p(typeof(a4), void(void *, const char *, va_list)),	\
 	btf_dump__new_deprecated((void *)a1, (void *)a2, (void *)a3, (void *)a4),	\
 	btf_dump__new((void *)a1, (void *)a2, (void *)a3, (void *)a4))
+#endif
 
 LIBBPF_API void btf_dump__free(struct btf_dump *d);
 
-- 
2.33.1