2023-05-12 07:47 UTC-0700 ~ Yonghong Song <yhs@xxxxxxxx>
>
>
> On 5/12/23 3:33 AM, Quentin Monnet wrote:
>> From: Alexander Lobakin <alobakin@xxxxx>
>>
>> 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
>
> 'container_of() is not CO-REd' is incorrect.
>
> #define container_of(ptr, type, member) \
> ({ \
> void *__mptr = (void *)(ptr); \
> ((type *)(__mptr - offsetof(type, member))); \
> })
>
>
> offsetof() will do necessary CO-RE relocation if the field is specified
> with preserve_access_index attribute. So container_of will actually
> do CO-RE relocation as well.
Thanks! I'll amend the description for the next iteration.
Quentin
