Add feature detector of kernel-side arg:ctx (__arg_ctx) tag support. If this is detected, libbpf will avoid doing any __arg_ctx-related BTF rewriting and checks in favor of letting kernel handle this completely. test_global_funcs/ctx_arg_rewrite subtest is adjusted to do the same feature detection (albeit in much simpler, though round-about and inefficient, way), and skip the tests. This is done to still be able to execute this test on older kernels (like in libbpf CI). Note, BPF token series ([0]) does a major refactor and code moving of libbpf-internal feature detection "framework", so to avoid unnecessary conflicts we keep newly added feature detection stand-alone with ad-hoc result caching. Once things settle, there will be a small follow up to re-integrate everything back and move code into its final place in newly-added (by BPF token series) features.c file. [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=814209&state=* Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> --- tools/lib/bpf/libbpf.c | 67 +++++++++++++++++++ tools/lib/bpf/libbpf_internal.h | 2 + .../bpf/prog_tests/test_global_funcs.c | 13 ++++ 3 files changed, 82 insertions(+) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index c5a42ac309fd..4a266c475cb9 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -6757,6 +6757,69 @@ static int clone_func_btf_info(struct btf *btf, int orig_fn_id, struct bpf_progr return fn_id; } +static int probe_kern_arg_ctx_tag(void) +{ + /* To minimize merge conflicts with BPF token series that refactors + * feature detection code a lot, we don't integrate + * probe_kern_arg_ctx_tag() into kernel_supports() feature-detection + * framework yet, doing our own caching internatlly. + * This will be cleaned up a bit later when bpf/bpf-next trees settle. + */ + static int cached_result = -1; + static const char strs[] = "\0a\0b\0arg:ctx\0"; + const __u32 types[] = { + /* [1] INT */ + BTF_TYPE_INT_ENC(1 /* "a" */, BTF_INT_SIGNED, 0, 32, 4), + /* [2] PTR -> VOID */ + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_PTR, 0, 0), 0), + /* [3] FUNC_PROTO `int(void *a)` */ + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 1), + BTF_PARAM_ENC(1 /* "a" */, 2), + /* [4] FUNC 'a' -> FUNC_PROTO (main prog) */ + BTF_TYPE_ENC(1 /* "a" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 3), + /* [5] FUNC_PROTO `int(void *b __arg_ctx)` */ + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 1), + BTF_PARAM_ENC(3 /* "b" */, 2), + /* [6] FUNC 'b' -> FUNC_PROTO (subprog) */ + BTF_TYPE_ENC(3 /* "b" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 5), + /* [7] DECL_TAG 'arg:ctx' -> func 'b' arg 'b' */ + BTF_TYPE_DECL_TAG_ENC(5 /* "arg:ctx" */, 6, 0), + }; + const struct bpf_insn insns[] = { + /* main prog */ + BPF_CALL_REL(+1), + BPF_EXIT_INSN(), + /* global subprog */ + BPF_EMIT_CALL(BPF_FUNC_get_func_ip), /* needs PTR_TO_CTX */ + BPF_EXIT_INSN(), + }; + const struct bpf_func_info_min func_infos[] = { + { 0, 4 }, /* main prog -> FUNC 'a' */ + { 2, 6 }, /* subprog -> FUNC 'b' */ + }; + LIBBPF_OPTS(bpf_prog_load_opts, opts); + int prog_fd, btf_fd, insn_cnt = ARRAY_SIZE(insns); + + if (cached_result >= 0) + return cached_result; + + btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs)); + if (btf_fd < 0) + return 0; + + opts.prog_btf_fd = btf_fd; + opts.func_info = &func_infos; + opts.func_info_cnt = ARRAY_SIZE(func_infos); + opts.func_info_rec_size = sizeof(func_infos[0]); + + prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, "det_arg_ctx", + "GPL", insns, insn_cnt, &opts); + close(btf_fd); + + cached_result = probe_fd(prog_fd); + return cached_result; +} + /* Check if main program or global subprog's function prototype has `arg:ctx` * argument tags, and, if necessary, substitute correct type to match what BPF * verifier would expect, taking into account specific program type. This @@ -6780,6 +6843,10 @@ static int bpf_program_fixup_func_info(struct bpf_object *obj, struct bpf_progra if (!obj->btf_ext || !prog->func_info) return 0; + /* don't do any fix ups if kernel natively supports __arg_ctx */ + if (probe_kern_arg_ctx_tag() > 0) + return 0; + /* some BPF program types just don't have named context structs, so * this fallback mechanism doesn't work for them */ diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h index 27e4e320e1a6..4ec8c43b81af 100644 --- a/tools/lib/bpf/libbpf_internal.h +++ b/tools/lib/bpf/libbpf_internal.h @@ -357,6 +357,8 @@ enum kern_feature_id { FEAT_SYSCALL_WRAPPER, /* BPF multi-uprobe link support */ FEAT_UPROBE_MULTI_LINK, + /* Kernel supports arg:ctx tag (__arg_ctx) for global subprogs natively */ + FEAT_ARG_CTX_TAG, __FEAT_CNT, }; diff --git a/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c b/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c index 67d4ef9e62b3..e905cbaf6b3d 100644 --- a/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c +++ b/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c @@ -47,6 +47,19 @@ static void subtest_ctx_arg_rewrite(void) struct btf *btf = NULL; __u32 info_len = sizeof(info); int err, fd, i; + struct btf *kern_btf = NULL; + + kern_btf = btf__load_vmlinux_btf(); + if (!ASSERT_OK_PTR(kern_btf, "kern_btf_load")) + return; + + /* simple detection of kernel native arg:ctx tag support */ + if (btf__find_by_name_kind(kern_btf, "bpf_subprog_arg_info", BTF_KIND_STRUCT) > 0) { + test__skip(); + btf__free(kern_btf); + return; + } + btf__free(kern_btf); skel = test_global_func_ctx_args__open(); if (!ASSERT_OK_PTR(skel, "skel_open")) -- 2.34.1
