netdev - Re: [PATCH bpf] bpf: fix "unresolved symbol" build error with resolve

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Message-ID: <20200930205847.7pj5pblqe6k6v64q@kafai-mbp.dhcp.thefacebook.com>
Date:   Wed, 30 Sep 2020 13:58:47 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Yonghong Song <yhs@...com>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH bpf] bpf: fix "unresolved symbol" build error with
 resolve_btfids

On Wed, Sep 30, 2020 at 09:41:09AM -0700, Yonghong Song wrote:
> 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 <mkubecek@...e.cz>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  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.

> +#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?

>  #undef BTF_SOCK_TYPE
>  MAX_BTF_SOCK_TYPE,
>  };
> -- 
> 2.24.1
>