bpftool: Add header guards to generated vmlinux.h

Add canonical #ifndef/#define/#endif guard for generated vmlinux.h header with
__VMLINUX_H__ symbol. __VMLINUX_H__ is also going to play double role of
identifying whether vmlinux.h is being used, versus, say, BCC or non-CO-RE
libbpf modes with dependency on kernel headers. This will make it possible to
write helper macro/functions, agnostic to exact BPF program set up.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200229231112.1240137-2-andriin@fb.com

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index b3745ed..bcaf55b 100644 (file)
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -389,6 +389,9 @@ static int dump_btf_c(const struct btf *btf,
        if (IS_ERR(d))
                return PTR_ERR(d);
 
+       printf("#ifndef __VMLINUX_H__\n");
+       printf("#define __VMLINUX_H__\n");
+       printf("\n");
        printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
        printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
        printf("#endif\n\n");
@@ -412,6 +415,8 @@ static int dump_btf_c(const struct btf *btf,
        printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
        printf("#pragma clang attribute pop\n");
        printf("#endif\n");
+       printf("\n");
+       printf("#endif /* __VMLINUX_H__ */\n");
 
 done:
        btf_dump__free(d);