libbpf: Skip forward declaration when counting duplicated type names

Currently if a declaration appears in the BTF before the definition, the
definition is dumped as a conflicting name, e.g.:

    $ bpftool btf dump file vmlinux format raw | grep "'unix_sock'"
    [81287] FWD 'unix_sock' fwd_kind=struct
    [89336] STRUCT 'unix_sock' size=1024 vlen=14

    $ bpftool btf dump file vmlinux format c | grep "struct unix_sock"
    struct unix_sock;
    struct unix_sock___2 {	<--- conflict, the "___2" is unexpected
		    struct unix_sock___2 *unix_sk;

This causes a compilation error if the dump output is used as a header file.

Fix it by skipping declaration when counting duplicated type names.

Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion")
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20220301053250.1464204-2-xukuohai@huawei.com

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 07ebe70d3a309624127870fc1fb59ec20e4f5944..6b1bc1f43728c78be7fe5f8849c3aed5ab90d7a8 100644 (file)
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1505,6 +1505,11 @@ static const char *btf_dump_resolve_name(struct btf_dump *d, __u32 id,
        if (s->name_resolved)
                return *cached_name ? *cached_name : orig_name;
 
+       if (btf_is_fwd(t) || (btf_is_enum(t) && btf_vlen(t) == 0)) {
+               s->name_resolved = 1;
+               return orig_name;
+       }
+
        dup_cnt = btf_dump_name_dups(d, name_map, orig_name);
        if (dup_cnt > 1) {
                const size_t max_len = 256;