[PATCH bpf-next] libbpf: handle invalid typedef emitted by old GCC

[Andrii Nakryiko]

Old GCC versions are producing invalid typedef for __gnuc_va_list
pointing to void. Special-case this and emit valid:

typedef __builtin_va_list __gnuc_va_list;

Reported-by: John Fastabend <john.fastab...@gmail.com>
Signed-off-by: Andrii Nakryiko <andr...@fb.com>
---
 tools/lib/bpf/btf_dump.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 87f27e2664c5..139812b46c7b 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -975,6 +975,17 @@ static void btf_dump_emit_typedef_def(struct btf_dump *d, 
__u32 id,
 {
        const char *name = btf_dump_ident_name(d, id);
 
+       /*
+        * Old GCC versions are emitting invalid typedef for __gnuc_va_list
+        * pointing to VOID. This generates warnings from btf_dump() and
+        * results in uncompilable header file, so we are fixing it up here
+        * with valid typedef into __builtin_va_list.
+        */
+       if (t->type == 0 && strcmp(name, "__gnuc_va_list") == 0) {
+               btf_dump_printf(d, "typedef __builtin_va_list __gnuc_va_list");
+               return;
+       }
+
        btf_dump_printf(d, "typedef ");
        btf_dump_emit_type_decl(d, t->type, name, lvl);
 }
-- 
2.17.1