On Tue, Nov 16, 2021 at 11:42 AM Mauricio Vásquez <mauricio@xxxxxxxxxx> wrote: > > BTFGen[0] requires access to the result of the CO-RE relocations without > actually loading the bpf programs. The current libbpf API doesn't allow > it because all the object preparation (subprogs, relocations: co-re, > elf, maps) happens inside bpf_object__load(). > > This commit introduces a new bpf_object__prepare() function to perform > all the preparation steps than an ebpf object requires, allowing users > to access the result of those preparation steps without having to load > the program. Almost all the steps that were done in bpf_object__load() > are now done in bpf_object__prepare(), except map creation and program > loading. > > Map relocations require a bit more attention as maps are only created in > bpf_object__load(). For this reason bpf_object__prepare() relocates maps > using BPF_PSEUDO_MAP_IDX, if someone dumps the instructions before > loading the program they get something meaningful. Map relocations are > completed in bpf_object__load() once the maps are created and we have > their fd to use with BPF_PSEUDO_MAP_FD. > > Users won’t see any visible changes if they’re using bpf_object__open() > + bpf_object__load() because this commit keeps backwards compatibility > by calling bpf_object__prepare() in bpf_object_load() if it wasn’t > called by the user. > > bpf_object__prepare_xattr() is not implemented as their counterpart > bpf_object__load_xattr() will be deprecated[1]. New options will be > added only to bpf_object_open_opts. > > [0]: https://github.com/kinvolk/btfgen/ > [1]: https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#libbpfh-high-level-apis > > Signed-off-by: Mauricio Vásquez <mauricio@xxxxxxxxxx> > Signed-off-by: Rafael David Tinoco <rafael.tinoco@xxxxxxxxxxx> > Signed-off-by: Lorenzo Fontana <lorenzo.fontana@xxxxxxxxxx> > Signed-off-by: Leonardo Di Donato <leonardo.didonato@xxxxxxxxxx> > --- > tools/lib/bpf/libbpf.c | 130 ++++++++++++++++++++++++++++----------- > tools/lib/bpf/libbpf.h | 2 + > tools/lib/bpf/libbpf.map | 1 + > 3 files changed, 98 insertions(+), 35 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 6ca76365c6da..f50f9428bb03 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -514,6 +514,7 @@ struct bpf_object { > int nr_extern; > int kconfig_map_idx; > > + bool prepared; > bool loaded; > bool has_subcalls; > bool has_rodata; > @@ -5576,34 +5577,19 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog) > > switch (relo->type) { > case RELO_LD64: > - if (obj->gen_loader) { > - insn[0].src_reg = BPF_PSEUDO_MAP_IDX; > - insn[0].imm = relo->map_idx; > - } else { > - insn[0].src_reg = BPF_PSEUDO_MAP_FD; > - insn[0].imm = obj->maps[relo->map_idx].fd; > - } > + insn[0].src_reg = BPF_PSEUDO_MAP_IDX; > + insn[0].imm = relo->map_idx; > break; > case RELO_DATA: > insn[1].imm = insn[0].imm + relo->sym_off; > - if (obj->gen_loader) { > - insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE; > - insn[0].imm = relo->map_idx; > - } else { > - insn[0].src_reg = BPF_PSEUDO_MAP_VALUE; > - insn[0].imm = obj->maps[relo->map_idx].fd; > - } > + insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE; > + insn[0].imm = relo->map_idx; > break; > case RELO_EXTERN_VAR: > ext = &obj->externs[relo->sym_off]; > if (ext->type == EXT_KCFG) { > - if (obj->gen_loader) { > - insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE; > - insn[0].imm = obj->kconfig_map_idx; > - } else { > - insn[0].src_reg = BPF_PSEUDO_MAP_VALUE; > - insn[0].imm = obj->maps[obj->kconfig_map_idx].fd; > - } > + insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE; > + insn[0].imm = obj->kconfig_map_idx; > insn[1].imm = ext->kcfg.data_off; > } else /* EXT_KSYM */ { > if (ext->ksym.type_id && ext->is_set) { /* typed ksyms */ > @@ -6144,8 +6130,50 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path) > return err; > } > } > - if (!obj->gen_loader) > - bpf_object__free_relocs(obj); > + > + return 0; > +} > + > +/* relocate instructions that refer to map fds */ > +static int > +bpf_object__finish_relocate(struct bpf_object *obj) > +{ > + int i, j; > + > + if (obj->gen_loader) > + return 0; > + > + for (i = 0; i < obj->nr_programs; i++) { > + struct bpf_program *prog = &obj->programs[i]; > + > + if (prog_is_subprog(obj, prog)) > + continue; > + for (j = 0; j < prog->nr_reloc; j++) { > + struct reloc_desc *relo = &prog->reloc_desc[j]; > + struct bpf_insn *insn = &prog->insns[relo->insn_idx]; > + struct extern_desc *ext; > + > + switch (relo->type) { > + case RELO_LD64: > + insn[0].src_reg = BPF_PSEUDO_MAP_FD; > + insn[0].imm = obj->maps[relo->map_idx].fd; > + break; > + case RELO_DATA: > + insn[0].src_reg = BPF_PSEUDO_MAP_VALUE; > + insn[0].imm = obj->maps[relo->map_idx].fd; > + break; > + case RELO_EXTERN_VAR: > + ext = &obj->externs[relo->sym_off]; > + if (ext->type == EXT_KCFG) { > + insn[0].src_reg = BPF_PSEUDO_MAP_VALUE; > + insn[0].imm = obj->maps[obj->kconfig_map_idx].fd; > + } > + default: > + break; > + } > + } > + } > + > return 0; > } > > @@ -6706,8 +6734,8 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level) > if (err) > return err; > } > - if (obj->gen_loader) > - bpf_object__free_relocs(obj); > + > + bpf_object__free_relocs(obj); > return 0; > } > > @@ -7258,6 +7286,39 @@ static int bpf_object__resolve_externs(struct bpf_object *obj, > return 0; > } > > +static int __bpf_object__prepare(struct bpf_object *obj, int log_level, > + const char *target_btf_path) > +{ > + int err; > + > + if (obj->prepared) { > + pr_warn("object '%s': prepare can't be attempted twice\n", obj->name); > + return libbpf_err(-EINVAL); > + } > + > + if (obj->gen_loader) > + bpf_gen__init(obj->gen_loader, log_level); > + > + err = bpf_object__probe_loading(obj); > + err = err ? : bpf_object__load_vmlinux_btf(obj, false); > + err = err ? : bpf_object__resolve_externs(obj, obj->kconfig); > + err = err ? : bpf_object__sanitize_and_load_btf(obj); > + err = err ? : bpf_object__sanitize_maps(obj); > + err = err ? : bpf_object__init_kern_struct_ops_maps(obj); > + err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path); > + > + obj->prepared = true; > + > + return err; > +} > + > +LIBBPF_API int bpf_object__prepare(struct bpf_object *obj) > +{ > + if (!obj) > + return libbpf_err(-EINVAL); > + return __bpf_object__prepare(obj, 0, NULL); > +} > + > int bpf_object__load_xattr(struct bpf_object_load_attr *attr) > { > struct bpf_object *obj; > @@ -7274,17 +7335,14 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr) > return libbpf_err(-EINVAL); > } > > - if (obj->gen_loader) > - bpf_gen__init(obj->gen_loader, attr->log_level); > + if (!obj->prepared) { > + err = __bpf_object__prepare(obj, attr->log_level, attr->target_btf_path); > + if (err) > + return err; > + } > > - err = bpf_object__probe_loading(obj); After sending the patches we realized they weren't working without root privileges in systems with unprivileged BPF disabled. This line should not be moved to bpf_object__prepare indeed. We'll fix it in the next iteration. > - err = err ? : bpf_object__load_vmlinux_btf(obj, false); > - err = err ? : bpf_object__resolve_externs(obj, obj->kconfig); > - err = err ? : bpf_object__sanitize_and_load_btf(obj); > - err = err ? : bpf_object__sanitize_maps(obj); > - err = err ? : bpf_object__init_kern_struct_ops_maps(obj); > - err = err ? : bpf_object__create_maps(obj); > - err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : attr->target_btf_path); > + err = bpf_object__create_maps(obj); > + err = err ? : bpf_object__finish_relocate(obj); > err = err ? : bpf_object__load_progs(obj, attr->log_level); > > if (obj->gen_loader) { > @@ -7940,6 +7998,8 @@ void bpf_object__close(struct bpf_object *obj) > bpf_object__elf_finish(obj); > bpf_object_unload(obj); > btf__free(obj->btf); > + if (!obj->user_provided_btf_vmlinux) > + btf__free(obj->btf_vmlinux_override); > btf_ext__free(obj->btf_ext); > > for (i = 0; i < obj->nr_maps; i++) > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > index 908ab04dc9bd..d206b4400a4d 100644 > --- a/tools/lib/bpf/libbpf.h > +++ b/tools/lib/bpf/libbpf.h > @@ -148,6 +148,8 @@ LIBBPF_API int bpf_object__unpin_programs(struct bpf_object *obj, > LIBBPF_API int bpf_object__pin(struct bpf_object *object, const char *path); > LIBBPF_API void bpf_object__close(struct bpf_object *object); > > +LIBBPF_API int bpf_object__prepare(struct bpf_object *obj); > + > struct bpf_object_load_attr { > struct bpf_object *obj; > int log_level; > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map > index c9555f8655af..459b41228933 100644 > --- a/tools/lib/bpf/libbpf.map > +++ b/tools/lib/bpf/libbpf.map > @@ -415,4 +415,5 @@ LIBBPF_0.6.0 { > perf_buffer__new_raw; > perf_buffer__new_raw_deprecated; > btf__save_raw; > + bpf_object__prepare; > } LIBBPF_0.5.0; > -- > 2.25.1 >
