bpf: Fix "unresolved symbol" build error with resolve_btfids

Michal reported a build failure likes below:

   BTFIDS  vmlinux
   FAILED unresolved symbol tcp_timewait_sock
   make[1]: *** [/.../linux-5.9-rc7/Makefile:1176: vmlinux] Error 255

This error can be triggered when config has CONFIG_NET enabled
but CONFIG_INET disabled. In this case, there is no user of
istructs inet_timewait_sock and tcp_timewait_sock and hence
vmlinux BTF types are not generated for these two structures.

To fix the problem, let us force BTF generation for these two
structures with BTF_TYPE_EMIT.

Fixes: fce557bcef11 ("bpf: Make btf_sock_ids global")
Reported-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201001051339.2549085-1-yhs@fb.com

diff --git a/net/core/filter.c b/net/core/filter.c
index 21eaf3b182f2fb5a3c1d128ab737a8282125f9fd..b5f3faac5e3b6c217a48ca90d733ed095bcbf92f 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -9558,6 +9558,12 @@ const struct bpf_func_proto bpf_skc_to_tcp_sock_proto = {
 
 BPF_CALL_1(bpf_skc_to_tcp_timewait_sock, struct sock *, sk)
 {
+       /* BTF types for tcp_timewait_sock and inet_timewait_sock are not
+        * generated if CONFIG_INET=n. Trigger an explicit generation here.
+        */
+       BTF_TYPE_EMIT(struct inet_timewait_sock);
+       BTF_TYPE_EMIT(struct tcp_timewait_sock);
+
 #ifdef CONFIG_INET
        if (sk && sk->sk_prot == &tcp_prot && sk->sk_state == TCP_TIME_WAIT)
                return (unsigned long)sk;