libbpf: Support opting out from autoloading BPF programs declaratively
Establish SEC("?abc") naming convention (i.e., adding question mark in front of otherwise normal section name) that allows to set corresponding program's autoload property to false. This is effectively just a declarative way to do bpf_program__set_autoload(prog, false). Having a way to do this declaratively in BPF code itself is useful and convenient for various scenarios. E.g., for testing, when BPF object consists of multiple independent BPF programs that each needs to be tested separately. Opting out all of them by default and then setting autoload to true for just one of them at a time simplifies testing code (see next patch for few conversions in BPF selftests taking advantage of this new feature). Another real-world use case is in libbpf-tools for cases when different BPF programs have to be picked depending on particulars of the host kernel due to various incompatible changes (like kernel function renames or signature change, or to pick kprobe vs fentry depending on corresponding kernel support for the latter). Marking all the different BPF program candidates as non-autoloaded declaratively makes this more obvious in BPF source code and allows simpler code in user-space code. When BPF program marked as SEC("?abc") it is otherwise treated just like SEC("abc") and bpf_program__section_name() reported will be "abc". Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220419002452.632125-1-andrii@kernel.org
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@ -302,7 +302,7 @@ struct bpf_program {
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void *priv;
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bpf_program_clear_priv_t clear_priv;
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bool load;
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bool autoload;
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bool mark_btf_static;
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enum bpf_prog_type type;
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enum bpf_attach_type expected_attach_type;
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@ -672,7 +672,18 @@ bpf_object__init_prog(struct bpf_object *obj, struct bpf_program *prog,
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prog->insns_cnt = prog->sec_insn_cnt;
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prog->type = BPF_PROG_TYPE_UNSPEC;
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prog->load = true;
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/* libbpf's convention for SEC("?abc...") is that it's just like
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* SEC("abc...") but the corresponding bpf_program starts out with
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* autoload set to false.
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*/
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if (sec_name[0] == '?') {
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prog->autoload = false;
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/* from now on forget there was ? in section name */
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sec_name++;
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} else {
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prog->autoload = true;
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}
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prog->instances.fds = NULL;
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prog->instances.nr = -1;
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@ -2927,7 +2938,7 @@ static bool obj_needs_vmlinux_btf(const struct bpf_object *obj)
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}
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bpf_object__for_each_program(prog, obj) {
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if (!prog->load)
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if (!prog->autoload)
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continue;
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if (prog_needs_vmlinux_btf(prog))
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return true;
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@ -5702,7 +5713,7 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
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/* no need to apply CO-RE relocation if the program is
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* not going to be loaded
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*/
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if (!prog->load)
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if (!prog->autoload)
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continue;
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/* adjust insn_idx from section frame of reference to the local
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@ -6363,7 +6374,7 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
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*/
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if (prog_is_subprog(obj, prog))
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continue;
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if (!prog->load)
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if (!prog->autoload)
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continue;
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err = bpf_object__relocate_calls(obj, prog);
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@ -6378,7 +6389,7 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
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prog = &obj->programs[i];
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if (prog_is_subprog(obj, prog))
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continue;
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if (!prog->load)
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if (!prog->autoload)
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continue;
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err = bpf_object__relocate_data(obj, prog);
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if (err) {
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@ -6975,7 +6986,7 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
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prog = &obj->programs[i];
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if (prog_is_subprog(obj, prog))
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continue;
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if (!prog->load) {
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if (!prog->autoload) {
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pr_debug("prog '%s': skipped loading\n", prog->name);
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continue;
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}
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@ -8455,7 +8466,7 @@ const char *bpf_program__title(const struct bpf_program *prog, bool needs_copy)
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bool bpf_program__autoload(const struct bpf_program *prog)
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{
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return prog->load;
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return prog->autoload;
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}
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int bpf_program__set_autoload(struct bpf_program *prog, bool autoload)
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@ -8463,7 +8474,7 @@ int bpf_program__set_autoload(struct bpf_program *prog, bool autoload)
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if (prog->obj->loaded)
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return libbpf_err(-EINVAL);
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prog->load = autoload;
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prog->autoload = autoload;
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return 0;
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}
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@ -12665,7 +12676,7 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
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struct bpf_program *prog = *s->progs[i].prog;
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struct bpf_link **link = s->progs[i].link;
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if (!prog->load)
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if (!prog->autoload)
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continue;
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/* auto-attaching not supported for this program */
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