selftests/bpf: Add a C test for btf_type_tag
The following is the main btf_type_tag usage in the
C test:
#define __tag1 __attribute__((btf_type_tag("tag1")))
#define __tag2 __attribute__((btf_type_tag("tag2")))
struct btf_type_tag_test {
int __tag1 * __tag1 __tag2 *p;
} g;
The bpftool raw dump with related types:
[4] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[11] STRUCT 'btf_type_tag_test' size=8 vlen=1
'p' type_id=14 bits_offset=0
[12] TYPE_TAG 'tag1' type_id=16
[13] TYPE_TAG 'tag2' type_id=12
[14] PTR '(anon)' type_id=13
[15] TYPE_TAG 'tag1' type_id=4
[16] PTR '(anon)' type_id=15
[17] VAR 'g' type_id=11, linkage=global
With format C dump, we have
struct btf_type_tag_test {
int __attribute__((btf_type_tag("tag1"))) * __attribute__((btf_type_tag("tag1"))) __attribute__((btf_type_tag("tag2"))) *p;
};
The result C code is identical to the original definition except macro's are gone.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211112012646.1508231-1-yhs@fb.com