On Wed, Dec 20, 2023 at 03:19:52PM -0700, 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.
>
> 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.
>
> Example of encoding:
>
> $ bpftool btf dump file .tmp_vmlinux.btf | rg DECL_TAG | wc -l
> 388
>
> $ bpftool btf dump file .tmp_vmlinux.btf | rg 68940
> [68940] FUNC 'bpf_xdp_get_xfrm_state' type_id=68939 linkage=static
> [128124] DECL_TAG 'kfunc' type_id=68940 component_idx=-1
>
> Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
> ---
> btf_encoder.c | 202 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 202 insertions(+)
>
Hmm, looking more, seems like this will pick up non-kfunc functions as
well. For example, kernel/trace/bpf_trace.c:
BTF_SET_START(btf_allowlist_d_path)
#ifdef CONFIG_SECURITY
BTF_ID(func, security_file_permission)
BTF_ID(func, security_inode_getattr)
BTF_ID(func, security_file_open)
#endif
#ifdef CONFIG_SECURITY_PATH
BTF_ID(func, security_path_truncate)
#endif
BTF_ID(func, vfs_truncate)
BTF_ID(func, vfs_fallocate)
BTF_ID(func, dentry_open)
BTF_ID(func, vfs_getattr)
BTF_ID(func, filp_close)
BTF_SET_END(btf_allowlist_d_path)
Maybe we need a codemod from:
BTF_ID(func, ...
to:
BTF_ID(kfunc, ...
The change to resolve_btfids would be relatively small. Not sure what
the drawbacks are yet.
One way or another we'll need to annotate the kfuncs in source.
