Commit 22541a9e authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Alexei Starovoitov
Browse files

libbpf: Add BTF_KIND_FLOAT support 

The logic follows that of BTF_KIND_INT most of the time. Sanitization
replaces BTF_KIND_FLOATs with equally-sized empty BTF_KIND_STRUCTs on
older kernels, for example, the following:

    [4] FLOAT 'float' size=4

becomes the following:

    [4] STRUCT '(anon)' size=4 vlen=0

With dwarves patch [1] and this patch, the older kernels, which were
failing with the floating-point-related errors, will now start working
correctly.

[1] https://github.com/iii-i/dwarves/commit/btf-kind-float-v2



Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210226202256.116518-4-iii@linux.ibm.com
parent 1b1ce92b

tools/lib/bpf/btf.c

+49 −0
Original line number Diff line number Diff line
@@ -291,6 +291,7 @@ static int btf_type_size(const struct btf_type *t) 
	case BTF_KIND_PTR:

	case BTF_KIND_TYPEDEF:

	case BTF_KIND_FUNC:

	case BTF_KIND_FLOAT:

		return base_size;

	case BTF_KIND_INT:

		return base_size + sizeof(__u32);
@@ -338,6 +339,7 @@ static int btf_bswap_type_rest(struct btf_type *t) 
	case BTF_KIND_PTR:

	case BTF_KIND_TYPEDEF:

	case BTF_KIND_FUNC:

	case BTF_KIND_FLOAT:

		return 0;

	case BTF_KIND_INT:

		*(__u32 *)(t + 1) = bswap_32(*(__u32 *)(t + 1));
@@ -578,6 +580,7 @@ __s64 btf__resolve_size(const struct btf *btf, __u32 type_id) 
		case BTF_KIND_UNION:

		case BTF_KIND_ENUM:

		case BTF_KIND_DATASEC:

		case BTF_KIND_FLOAT:

			size = t->size;

			goto done;

		case BTF_KIND_PTR:
@@ -621,6 +624,7 @@ int btf__align_of(const struct btf *btf, __u32 id) 
	switch (kind) {

	case BTF_KIND_INT:

	case BTF_KIND_ENUM:

	case BTF_KIND_FLOAT:

		return min(btf_ptr_sz(btf), (size_t)t->size);

	case BTF_KIND_PTR:

		return btf_ptr_sz(btf);
@@ -1756,6 +1760,47 @@ int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding 
	return btf_commit_type(btf, sz);

}



/*

 * Append new BTF_KIND_FLOAT type with:

 *   - *name* - non-empty, non-NULL type name;

 *   - *sz* - size of the type, in bytes;

 * Returns:

 *   - >0, type ID of newly added BTF type;

 *   - <0, on error.

 */

int btf__add_float(struct btf *btf, const char *name, size_t byte_sz)

{

	struct btf_type *t;

	int sz, name_off;



	/* non-empty name */

	if (!name || !name[0])

		return -EINVAL;



	/* byte_sz must be one of the explicitly allowed values */

	if (byte_sz != 2 && byte_sz != 4 && byte_sz != 8 && byte_sz != 12 &&

	    byte_sz != 16)

		return -EINVAL;



	if (btf_ensure_modifiable(btf))

		return -ENOMEM;



	sz = sizeof(struct btf_type);

	t = btf_add_type_mem(btf, sz);

	if (!t)

		return -ENOMEM;



	name_off = btf__add_str(btf, name);

	if (name_off < 0)

		return name_off;



	t->name_off = name_off;

	t->info = btf_type_info(BTF_KIND_FLOAT, 0, 0);

	t->size = byte_sz;



	return btf_commit_type(btf, sz);

}



/* it's completely legal to append BTF types with type IDs pointing forward to

 * types that haven't been appended yet, so we only make sure that id looks

 * sane, we can't guarantee that ID will always be valid
@@ -3626,6 +3671,7 @@ static int btf_dedup_prep(struct btf_dedup *d) 
		case BTF_KIND_FWD:

		case BTF_KIND_TYPEDEF:

		case BTF_KIND_FUNC:

		case BTF_KIND_FLOAT:

			h = btf_hash_common(t);

			break;

		case BTF_KIND_INT:
@@ -3722,6 +3768,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id) 
		break;



	case BTF_KIND_FWD:

	case BTF_KIND_FLOAT:

		h = btf_hash_common(t);

		for_each_dedup_cand(d, hash_entry, h) {

			cand_id = (__u32)(long)hash_entry->value;
@@ -3983,6 +4030,7 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, 
			return btf_compat_enum(cand_type, canon_type);



	case BTF_KIND_FWD:

	case BTF_KIND_FLOAT:

		return btf_equal_common(cand_type, canon_type);



	case BTF_KIND_CONST:
@@ -4479,6 +4527,7 @@ static int btf_dedup_remap_type(struct btf_dedup *d, __u32 type_id) 
	switch (btf_kind(t)) {

	case BTF_KIND_INT:

	case BTF_KIND_ENUM:

	case BTF_KIND_FLOAT:

		break;



	case BTF_KIND_FWD:

tools/lib/bpf/btf.h

+6 −0
Original line number Diff line number Diff line
@@ -95,6 +95,7 @@ LIBBPF_API int btf__find_str(struct btf *btf, const char *s); 
LIBBPF_API int btf__add_str(struct btf *btf, const char *s);



LIBBPF_API int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding);

LIBBPF_API int btf__add_float(struct btf *btf, const char *name, size_t byte_sz);

LIBBPF_API int btf__add_ptr(struct btf *btf, int ref_type_id);

LIBBPF_API int btf__add_array(struct btf *btf,

			      int index_type_id, int elem_type_id, __u32 nr_elems);
@@ -294,6 +295,11 @@ static inline bool btf_is_datasec(const struct btf_type *t) 
	return btf_kind(t) == BTF_KIND_DATASEC;

}



static inline bool btf_is_float(const struct btf_type *t)

{

	return btf_kind(t) == BTF_KIND_FLOAT;

}



static inline __u8 btf_int_encoding(const struct btf_type *t)

{

	return BTF_INT_ENCODING(*(__u32 *)(t + 1));

tools/lib/bpf/btf_dump.c

+4 −0
Original line number Diff line number Diff line
@@ -279,6 +279,7 @@ static int btf_dump_mark_referenced(struct btf_dump *d) 
		case BTF_KIND_INT:

		case BTF_KIND_ENUM:

		case BTF_KIND_FWD:

		case BTF_KIND_FLOAT:

			break;



		case BTF_KIND_VOLATILE:
@@ -453,6 +454,7 @@ static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr) 


	switch (btf_kind(t)) {

	case BTF_KIND_INT:

	case BTF_KIND_FLOAT:

		tstate->order_state = ORDERED;

		return 0;
@@ -1133,6 +1135,7 @@ static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id, 
		case BTF_KIND_STRUCT:

		case BTF_KIND_UNION:

		case BTF_KIND_TYPEDEF:

		case BTF_KIND_FLOAT:

			goto done;

		default:

			pr_warn("unexpected type in decl chain, kind:%u, id:[%u]\n",
@@ -1247,6 +1250,7 @@ static void btf_dump_emit_type_chain(struct btf_dump *d, 


		switch (kind) {

		case BTF_KIND_INT:

		case BTF_KIND_FLOAT:

			btf_dump_emit_mods(d, decls);

			name = btf_name_of(d, t->name_off);

			btf_dump_printf(d, "%s", name);

tools/lib/bpf/libbpf.c

+28 −1
Original line number Diff line number Diff line
@@ -178,6 +178,8 @@ enum kern_feature_id { 
	FEAT_PROG_BIND_MAP,

	/* Kernel support for module BTFs */

	FEAT_MODULE_BTF,

	/* BTF_KIND_FLOAT support */

	FEAT_BTF_FLOAT,

	__FEAT_CNT,

};
@@ -1946,6 +1948,7 @@ static const char *btf_kind_str(const struct btf_type *t) 
	case BTF_KIND_FUNC_PROTO: return "func_proto";

	case BTF_KIND_VAR: return "var";

	case BTF_KIND_DATASEC: return "datasec";

	case BTF_KIND_FLOAT: return "float";

	default: return "unknown";

	}

}
@@ -2395,15 +2398,17 @@ static bool btf_needs_sanitization(struct bpf_object *obj) 
{

	bool has_func_global = kernel_supports(FEAT_BTF_GLOBAL_FUNC);

	bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);

	bool has_float = kernel_supports(FEAT_BTF_FLOAT);

	bool has_func = kernel_supports(FEAT_BTF_FUNC);



	return !has_func || !has_datasec || !has_func_global;

	return !has_func || !has_datasec || !has_func_global || !has_float;

}



static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)

{

	bool has_func_global = kernel_supports(FEAT_BTF_GLOBAL_FUNC);

	bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);

	bool has_float = kernel_supports(FEAT_BTF_FLOAT);

	bool has_func = kernel_supports(FEAT_BTF_FUNC);

	struct btf_type *t;

	int i, j, vlen;
@@ -2456,6 +2461,13 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf) 
		} else if (!has_func_global && btf_is_func(t)) {

			/* replace BTF_FUNC_GLOBAL with BTF_FUNC_STATIC */

			t->info = BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0);

		} else if (!has_float && btf_is_float(t)) {

			/* replace FLOAT with an equally-sized empty STRUCT;

			 * since C compilers do not accept e.g. "float" as a

			 * valid struct name, make it anonymous

			 */

			t->name_off = 0;

			t->info = BTF_INFO_ENC(BTF_KIND_STRUCT, 0, 0);

		}

	}

}
@@ -3927,6 +3939,18 @@ static int probe_kern_btf_datasec(void) 
					     strs, sizeof(strs)));

}



static int probe_kern_btf_float(void)

{

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

	__u32 types[] = {

		/* float */

		BTF_TYPE_FLOAT_ENC(1, 4),

	};



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

					     strs, sizeof(strs)));

}



static int probe_kern_array_mmap(void)

{

	struct bpf_create_map_attr attr = {
@@ -4106,6 +4130,9 @@ static struct kern_feature_desc { 
	[FEAT_MODULE_BTF] = {

		"module BTF support", probe_module_btf,

	},

	[FEAT_BTF_FLOAT] = {

		"BTF_KIND_FLOAT support", probe_kern_btf_float,

	},

};



static bool kernel_supports(enum kern_feature_id feat_id)

tools/lib/bpf/libbpf.map

+5 −0
Original line number Diff line number Diff line
@@ -350,3 +350,8 @@ LIBBPF_0.3.0 { 
		xsk_setup_xdp_prog;

		xsk_socket__update_xskmap;

} LIBBPF_0.2.0;



LIBBPF_0.4.0 {

	global:

		btf__add_float;

} LIBBPF_0.3.0;