Re: [PATCH dwarves v8 3/3] pahole: Inject kfunc decl tags into BTF

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2024-04-25 at 18:28 -0600, Daniel Xu wrote:
> This commit teaches pahole to parse symbols in .BTF_ids section in
> vmlinux and discover exported kfuncs. Pahole then takes the list of
> kfuncs and injects a BTF_KIND_DECL_TAG for each kfunc.
> 
> Example of encoding:
> 
>         $ bpftool btf dump file .tmp_vmlinux.btf | rg "DECL_TAG 'bpf_kfunc'" | wc -l
>         121
> 
>         $ bpftool btf dump file .tmp_vmlinux.btf | rg 56337
>         [56337] FUNC 'bpf_ct_change_timeout' type_id=56336 linkage=static
>         [127861] DECL_TAG 'bpf_kfunc' type_id=56337 component_idx=-1
> 
> This enables downstream users and tools to dynamically discover which
> kfuncs are available on a system by parsing vmlinux or module BTF, both
> available in /sys/kernel/btf.
> 
> This feature is enabled with --btf_features=decl_tag,decl_tag_kfuncs.

I tried to double-check results produced by this patch and found that
decl_tag for one kfunc is missing, namely, the following function:

[66020] FUNC 'update_socket_protocol' type_id=66018 linkage=static

And it is present in symbols table (15 is a number of the .BTF_ids section):

60433: ffffffff8293a7fc     4 OBJECT  LOCAL  DEFAULT   15 __BTF_ID__func__update_socket_protocol__78624

Interestingly, this is the last symbol printed for the section.
I'll try to debug this issue.