On Wed, Dec 20, 2023 at 11:37:01PM -0700, Daniel Xu wrote: > 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) you need to pick up only 'BTF_ID(func, ...)' IDs that belongs to SET8 lists, which are bounded by __BTF_ID__set8__<name> symbols, which also provide size __BTF_ID__func_* symbol that has address inside the SET8 list is kfunc > > Maybe we need a codemod from: > > BTF_ID(func, ... > > to: > > BTF_ID(kfunc, ... I think it's better to keep just 'func' and not to do anything special for kfuncs in resolve_btfids logic to keep it simple also it's going to be already in pahole so if we want to make a fix in future you need to change pahole, resolve_btfids and possibly also kernel jirka > > > 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.
