Commit 0e6d0a9d authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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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: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240125205510.3642094-2-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent ced33f2c

tools/lib/bpf/features.c

+58 −0
Original line number Diff line number Diff line
@@ -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)

tools/lib/bpf/libbpf.c

+1 −64
Original line number Diff line number Diff line
@@ -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

tools/lib/bpf/libbpf_internal.h

+2 −0
Original line number Diff line number Diff line
@@ -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,

};