On 9/30/20 1:58 PM, Martin KaFai Lau wrote:

On Wed, Sep 30, 2020 at 09:41:09AM -0700, Yonghong Song wrote:

quoted

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
structs inet_timewait_sock and tcp_timewait_sock and hence vmlinux BTF
types are not generated for these two structures.

To fix the problem, omit the above two types for BTF_SOCK_TYPE_xxx
macro if CONFIG_INET is not defined.

Fixes: fce557bcef11 ("bpf: Make btf_sock_ids global")
Reported-by: Michal Kubecek <redacted>
Signed-off-by: Yonghong Song <redacted>
---
  include/linux/btf_ids.h | 20 ++++++++++++++++----
  1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 4867d549e3c1..d9a1e18d0921 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h

@@ -102,24 +102,36 @@ asm(							\
   * skc_to_*_sock() helpers. All these sockets should have
   * sock_common as the first argument in its memory layout.
   */
-#define BTF_SOCK_TYPE_xxx \
+
+#define __BTF_SOCK_TYPE_xxx \
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET, inet_sock)			\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_CONN, inet_connection_sock)	\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_REQ, inet_request_sock)	\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_TW, inet_timewait_sock)	\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_REQ, request_sock)			\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK, sock)				\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK_COMMON, sock_common)		\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP, tcp_sock)			\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_REQ, tcp_request_sock)		\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)		\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP6, tcp6_sock)			\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP, udp_sock)			\
  	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)
  
+#define __BTF_SOCK_TW_TYPE_xxx \
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_TW, inet_timewait_sock)	\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)
+
+#ifdef CONFIG_INET
+#define BTF_SOCK_TYPE_xxx						\
+	__BTF_SOCK_TYPE_xxx						\
+	__BTF_SOCK_TW_TYPE_xxx
+#else
+#define BTF_SOCK_TYPE_xxx	__BTF_SOCK_TYPE_xxx

BTF_SOCK_TYPE_xxx is used in BTF_ID_LIST_GLOBAL(btf_sock_ids) in filter.c
which does not include BTF_SOCK_TYPE_TCP_TW.
However, btf_sock_ids[BTF_SOCK_TYPE_TCP_TW] is still used
in bpf_skc_to_tcp_timewait_sock_proto.

quoted

+#endif
+
  enum {
  #define BTF_SOCK_TYPE(name, str) name,
-BTF_SOCK_TYPE_xxx
+__BTF_SOCK_TYPE_xxx
+__BTF_SOCK_TW_TYPE_xxx

BTF_SOCK_TYPE_TCP_TW is at the end of this enum.

Would btf_sock_ids[BTF_SOCK_TYPE_TCP_TW] always be 0?

No. If CONFIG_INET is y, the above BTF_SOCK_TYPE_xxx contains
   __BTF_SOCK_TW_TYPE_xxx
and
   btf_sock_ids[BTF_SOCK_TYPE_TCP_TW] will be calculated properly.

But if CONFIG_INET is n, then BTF_SOCK_TYPE_xxx will not contain
    __BTF_SOCK_TW_TYPE_xxx
so btf_sock_ids[BTF_SOCK_TYPE_TCP_TW] will have default value 0
as btf_sock_ids is a global.

Will send v2 to add some comments to make it easy to understand.

quoted

  #undef BTF_SOCK_TYPE
  MAX_BTF_SOCK_TYPE,
  };
-- 
2.24.1