Hello,
On Thu, Apr 21, 2022 at 12:38:58AM +0000, Alexander Lobakin wrote:
> When building bpftool with !CONFIG_PERF_EVENTS:
>
> skeleton/pid_iter.bpf.c:47:14: error: incomplete definition of type 'struct bpf_perf_link'
> perf_link = container_of(link, struct bpf_perf_link, link);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:74:22: note: expanded from macro 'container_of'
> ((type *)(__mptr - offsetof(type, member))); \
> ^~~~~~~~~~~~~~~~~~~~~~
> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:68:60: note: expanded from macro 'offsetof'
> #define offsetof(TYPE, MEMBER) ((unsigned long)&((TYPE *)0)->MEMBER)
> ~~~~~~~~~~~^
> skeleton/pid_iter.bpf.c:44:9: note: forward declaration of 'struct bpf_perf_link'
> struct bpf_perf_link *perf_link;
> ^
>
> &bpf_perf_link is being defined and used only under the ifdef.
> Define struct bpf_perf_link___local with the `preserve_access_index`
> attribute inside the pid_iter BPF prog to allow compiling on any
> configs. CO-RE will substitute it with the real struct bpf_perf_link
> accesses later on.
> container_of() is not CO-REd, but it is a noop for
> bpf_perf_link <-> bpf_link and the local copy is a full mirror of
> the original structure.
>
> Fixes: cbdaf71f7e65 ("bpftool: Add bpf_cookie to link output")
This does not solve the problem completely. Kernels that don't have
CONFIG_PERF_EVENTS in the first place are also missing the enum value
BPF_LINK_TYPE_PERF_EVENT which is used as the condition for handling the
cookie.
Thanks
Michal
