Commit eaa266d8 authored by Toke Høiland-Jørgensen's avatar Toke Høiland-Jørgensen Committed by Andrii Nakryiko
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libbpf: Define BTF_KIND_* constants in btf.h to avoid compilation errors 

The btf.h header included with libbpf contains inline helper functions to
check for various BTF kinds. These helpers directly reference the
BTF_KIND_* constants defined in the kernel header, and because the header
file is included in user applications, this happens in the user application
compile units.

This presents a problem if a user application is compiled on a system with
older kernel headers because the constants are not available. To avoid
this, add #defines of the constants directly in btf.h before using them.

Since the kernel header moved to an enum for BTF_KIND_*, the #defines can
shadow the enum values without any errors, so we only need #ifndef guards
for the constants that predates the conversion to enum. We group these so
there's only one guard for groups of values that were added together.

  [0] Closes: https://github.com/libbpf/libbpf/issues/436



Fixes: 223f903e ("bpf: Rename BTF_KIND_TAG to BTF_KIND_DECL_TAG")
Fixes: 5b84bd10 ("libbpf: Add support for BTF_KIND_TAG")
Signed-off-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/bpf/20220118141327.34231-1-toke@redhat.com
parent 712d4793

tools/lib/bpf/btf.h

+21 −1
Original line number Diff line number Diff line
@@ -375,8 +375,28 @@ btf_dump__dump_type_data(struct btf_dump *d, __u32 id, 
			 const struct btf_dump_type_data_opts *opts);



/*

 * A set of helpers for easier BTF types handling

 * A set of helpers for easier BTF types handling.

 *

 * The inline functions below rely on constants from the kernel headers which

 * may not be available for applications including this header file. To avoid

 * compilation errors, we define all the constants here that were added after

 * the initial introduction of the BTF_KIND* constants.

 */

#ifndef BTF_KIND_FUNC

#define BTF_KIND_FUNC		12	/* Function	*/

#define BTF_KIND_FUNC_PROTO	13	/* Function Proto	*/

#endif

#ifndef BTF_KIND_VAR

#define BTF_KIND_VAR		14	/* Variable	*/

#define BTF_KIND_DATASEC	15	/* Section	*/

#endif

#ifndef BTF_KIND_FLOAT

#define BTF_KIND_FLOAT		16	/* Floating point	*/

#endif

/* The kernel header switched to enums, so these two were never #defined */

#define BTF_KIND_DECL_TAG	17	/* Decl Tag */

#define BTF_KIND_TYPE_TAG	18	/* Type Tag */



static inline __u16 btf_kind(const struct btf_type *t)

{

	return BTF_INFO_KIND(t->info);