On Thu, Dec 21, 2023 at 09:35:20AM +0100, Jiri Olsa 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>
>
> SNIP
>
> > +
> > +static int btf_encoder__tag_kfunc(struct btf_encoder *encoder, const char *kfunc)
> > +{
> > + int nr_types, type_id, err = -1;
> > + struct btf *btf = encoder->btf;
>
> could we store the kuncs in sorted array (by name) and iterate all IDs
> just once while doing the bsearch for the name over the kfuncs array
Ack, will take a look.
>
> > +
> > + nr_types = btf__type_cnt(btf);
> > + for (type_id = 1; type_id < nr_types; type_id++) {
> > + const struct btf_type *type;
> > + const char *name;
> > +
> > + type = btf__type_by_id(btf, type_id);
> > + if (!type) {
> > + fprintf(stderr, "%s: malformed BTF, can't resolve type for ID %d\n",
> > + __func__, type_id);
> > + goto out;
> > + }
> > +
> > + if (!btf_is_func(type))
> > + continue;
> > +
> > + name = btf__name_by_offset(btf, type->name_off);
> > + if (!name) {
> > + fprintf(stderr, "%s: malformed BTF, can't resolve name for ID %d\n",
> > + __func__, type_id);
> > + goto out;
> > + }
> > +
> > + if (strcmp(name, kfunc))
> > + continue;
> > +
> > + err = btf__add_decl_tag(btf, BTF_KFUNC_TYPE_TAG, type_id, -1);
> > + if (err < 0) {
> > + fprintf(stderr, "%s: failed to insert kfunc decl tag for '%s': %d\n",
> > + __func__, kfunc, err);
> > + goto out;
> > + }
> > +
> > + err = 0;
> > + break;
> > + }
> > +
> > +out:
> > + return err;
> > +}
> > +
> > +static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder)
> > +{
> > + const char *filename = encoder->filename;
> > + GElf_Shdr shdr_mem, *shdr;
> > + int symbols_shndx = -1;
> > + int idlist_shndx = -1;
> > + Elf_Scn *scn = NULL;
> > + Elf_Data *symbols;
> > + int fd, err = -1;
> > + size_t strtabidx;
> > + Elf *elf = NULL;
> > + size_t strndx;
> > + char *secname;
> > + int nr_syms;
> > + int i = 0;
> > +
> > + fd = open(filename, O_RDONLY);
> > + if (fd < 0) {
> > + fprintf(stderr, "Cannot open %s\n", filename);
> > + goto out;
> > + }
> > +
> > + if (elf_version(EV_CURRENT) == EV_NONE) {
> > + elf_error("Cannot set libelf version");
> > + goto out;
> > + }
> > +
> > + elf = elf_begin(fd, ELF_C_READ, NULL);
> > + if (elf == NULL) {
> > + elf_error("Cannot update ELF file");
> > + goto out;
> > + }
>
> SNIP
>
> > + }
> > + free(kfunc);
> > + }
> > +
> > + err = 0;
> > +out:
>
> leaking fd and elf object (elf_end)
Good catch thanks. Been writing too much rust...
Thanks,
Daniel
