libbpf: integrate __arg_ctx feature detector into kernel_supports()

Now that feature detection code is in bpf-next tree, integrate __arg_ctx
kernel-side support into kernel_supports() framework.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240125205510.3642094-2-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index 5a5c766bf61590aa5beb12967e02c0d094f6e634..6b0738ad7063674e34f0e1229149f4c5615d5fd0 100644 (file)
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -407,6 +407,61 @@ static int probe_kern_btf_enum64(int token_fd)
                                             strs, sizeof(strs), token_fd));
 }
 
+static int probe_kern_arg_ctx_tag(int token_fd)
+{
+       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,
+               .token_fd = token_fd,
+               .prog_flags = token_fd ? BPF_F_TOKEN_FD : 0,
+       );
+       int prog_fd, btf_fd, insn_cnt = ARRAY_SIZE(insns);
+
+       btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs), token_fd);
+       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);
+
+       return probe_fd(prog_fd);
+}
+
 typedef int (*feature_probe_fn)(int /* token_fd */);
 
 static struct kern_feature_cache feature_cache;
@@ -476,6 +531,9 @@ static struct kern_feature_desc {
        [FEAT_UPROBE_MULTI_LINK] = {
                "BPF multi-uprobe link support", probe_uprobe_multi_link,
        },
+       [FEAT_ARG_CTX_TAG] = {
+               "kernel-side __arg_ctx tag", probe_kern_arg_ctx_tag,
+       },
 };
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fa7094ff3e6614ec1dfb501b0a43d96ead993829..41ab7a21f868b7222acb9ca389743e261fa3e551 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6462,69 +6462,6 @@ 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 internally.
-        * 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), 0);
-       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
@@ -6549,7 +6486,7 @@ static int bpf_program_fixup_func_info(struct bpf_object *obj, struct bpf_progra
                return 0;
 
        /* don't do any fix ups if kernel natively supports __arg_ctx */
-       if (probe_kern_arg_ctx_tag() > 0)
+       if (kernel_supports(obj, FEAT_ARG_CTX_TAG))
                return 0;
 
        /* some BPF program types just don't have named context structs, so

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 5b30f3b67a0278c7f20b4655c439fd7ddd1127c6..ad936ac5e6397b8121673451dd880aec2eee1295 100644 (file)
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -372,6 +372,8 @@ 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,
 };