bpftool: Use __typeof__() instead of typeof() in BPF skeleton

When generated BPF skeleton header is included in C++ code base, some
compiler setups will emit warning about using language extensions due to
typeof() usage, resulting in something like:

  error: extension used [-Werror,-Wlanguage-extension-token]
  obj->struct_ops.empty_tcp_ca = (typeof(obj->struct_ops.empty_tcp_ca))
                                  ^

It looks like __typeof__() is a preferred way to do typeof() with better
C++ compatibility behavior, so switch to that. With __typeof__() we get
no such warning.

Fixes: c2a0257c1edf ("bpftool: Cast pointers for shadow types explicitly.")
Fixes: 00389c58ffe9 ("bpftool: Add support for subskeletons")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kui-Feng Lee <thinker.li@gmail.com>
Acked-by: Quentin Monnet <qmo@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20240401170713.2081368-1-andrii@kernel.org

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 786268f1a483560999021c00ea66dbe7273a15b9..b3979ddc01895abb571d54ba2e2f2779f0b31b17 100644 (file)
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -386,7 +386,7 @@ static int codegen_subskel_datasecs(struct bpf_object *obj, const char *obj_name
                         */
                        needs_typeof = btf_is_array(var) || btf_is_ptr_to_func_proto(btf, var);
                        if (needs_typeof)
-                               printf("typeof(");
+                               printf("__typeof__(");
 
                        err = btf_dump__emit_type_decl(d, var_type_id, &opts);
                        if (err)
@@ -1131,7 +1131,7 @@ static void gen_st_ops_shadow_init(struct btf *btf, struct bpf_object *obj)
                        continue;
                codegen("\
                        \n\
-                               obj->struct_ops.%1$s = (typeof(obj->struct_ops.%1$s))\n\
+                               obj->struct_ops.%1$s = (__typeof__(obj->struct_ops.%1$s))\n\
                                        bpf_map__initial_value(obj->maps.%1$s, NULL);\n\
                        \n\
                        ", ident);