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

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Date:   Wed, 30 Sep 2020 12:44:20 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <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 12:25 PM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 9/30/20 11:40 AM, Andrii Nakryiko wrote:
> > On Wed, Sep 30, 2020 at 9:41 AM Yonghong Song <yhs@...com> 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
> >> +#endif
> >> +
> >>   enum {
> >>   #define BTF_SOCK_TYPE(name, str) name,
> >> -BTF_SOCK_TYPE_xxx
> >> +__BTF_SOCK_TYPE_xxx
> >> +__BTF_SOCK_TW_TYPE_xxx
> >
> > Why BTF_SOCK_TYPE_xxx doesn't still work here after the above changes?
>
> The macro, e.g., BTF_SOCK_TYPE_TCP_TW, still needed to be defined as
> it is used to get the location for btf_id.

Ah, right, so you want those here unconditionally, even if CONFIG_INET
is not defined. Missed that. Might be worth leaving a short comment.

Otherwise LGTM.

Acked-by: Andrii Nakryiko <andriin@...com>

>
> const struct bpf_func_proto bpf_skc_to_tcp_timewait_sock_proto = {
>          .func                   = bpf_skc_to_tcp_timewait_sock,
>          .gpl_only               = false,
>          .ret_type               = RET_PTR_TO_BTF_ID_OR_NULL,
>          .arg1_type              = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
>          .ret_btf_id             = &btf_sock_ids[BTF_SOCK_TYPE_TCP_TW],
> };
>
> If CONFIG_INET is not defined, bpf_sock_ids[BTF_SOCK_TYPE_TCP_TW]
> will be 0.
>
> >
> >>   #undef BTF_SOCK_TYPE
> >>   MAX_BTF_SOCK_TYPE,
> >>   };
> >> --
> >> 2.24.1
> >>