Commit 68b08647 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

libbpf: Detect minimal BTF support and skip BTF loading, if missing 



Detect whether a kernel supports any BTF at all, and if not, don't even
attempt loading BTF to avoid unnecessary log messages like:

  libbpf: Error loading BTF: Invalid argument(22)
  libbpf: Error loading .BTF into kernel: -22. BTF is optional, ignoring.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200818213356.2629020-8-andriin@fb.com
parent 70785cfb

tools/lib/bpf/libbpf.c

+27 −0
Original line number Diff line number Diff line
@@ -170,6 +170,8 @@ enum kern_feature_id { 
	FEAT_PROG_NAME,

	/* v5.2: kernel support for global data sections. */

	FEAT_GLOBAL_DATA,

	/* BTF support */

	FEAT_BTF,

	/* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */

	FEAT_BTF_FUNC,

	/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
@@ -2533,6 +2535,15 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj) 
	if (!obj->btf)

		return 0;



	if (!kernel_supports(FEAT_BTF)) {

		if (kernel_needs_btf(obj)) {

			err = -EOPNOTSUPP;

			goto report;

		}

		pr_debug("Kernel doesn't support BTF, skipping uploading it.\n");

		return 0;

	}



	sanitize = btf_needs_sanitization(obj);

	if (sanitize) {

		const void *raw_data;
@@ -2558,6 +2569,7 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj) 
		}

		btf__free(kern_btf);

	}

report:

	if (err) {

		btf_mandatory = kernel_needs_btf(obj);

		pr_warn("Error loading .BTF into kernel: %d. %s\n", err,
@@ -3502,6 +3514,18 @@ static int probe_kern_global_data(void) 
	return probe_fd(ret);

}



static int probe_kern_btf(void)

{

	static const char strs[] = "\0int";

	__u32 types[] = {

		/* int */

		BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),

	};



	return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),

					     strs, sizeof(strs)));

}



static int probe_kern_btf_func(void)

{

	static const char strs[] = "\0int\0x\0a";
@@ -3633,6 +3657,9 @@ static struct kern_feature_desc { 
	[FEAT_GLOBAL_DATA] = {

		"global variables", probe_kern_global_data,

	},

	[FEAT_BTF] = {

		"minimal BTF", probe_kern_btf,

	},

	[FEAT_BTF_FUNC] = {

		"BTF functions", probe_kern_btf_func,

	},

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