Merge branch 'Add BTF_KIND_FLOAT support'

Ilya Leoshkevich says:

====================

Some BPF programs compiled on s390 fail to load, because s390
arch-specific linux headers contain float and double types.

Introduce support for such types by representing them using the new
BTF_KIND_FLOAT. This series deals with libbpf, bpftool, in-kernel BTF
parser as well as selftests and documentation.

There are also pahole and LLVM parts:

* https://github.com/iii-i/dwarves/commit/btf-kind-float-v2
* https://reviews.llvm.org/D83289

but they should go in after the libbpf part is integrated.
---

v0: https://lore.kernel.org/bpf/20210210030317.78820-1-iii@linux.ibm.com/
v0 -> v1: Per Andrii's suggestion, remove the unnecessary trailing u32.

v1: https://lore.kernel.org/bpf/20210216011216.3168-1-iii@linux.ibm.com/
v1 -> v2: John noticed that sanitization corrupts BTF, because new and
          old sizes don't match. Per Yonghong's suggestion, use a
          modifier type (which has the same size as the float type) as
          a replacement.
          Per Yonghong's suggestion, add size and alignment checks to
          the kernel BTF parser.

v2: https://lore.kernel.org/bpf/20210219022543.20893-1-iii@linux.ibm.com/
v2 -> v3: Based on Yonghong's suggestions: Use BTF_KIND_CONST instead of
          BTF_KIND_TYPEDEF and make sure that the C code generated from
          the sanitized BTF is well-formed; fix size calculation in
          tests and use NAME_TBD everywhere; limit allowed sizes to 2,
          4, 8, 12 and 16 (this should also fix m68k and nds32le
          builds).

v3: https://lore.kernel.org/bpf/20210220034959.27006-1-iii@linux.ibm.com/
v3 -> v4: More fixes for the Yonghong's findings: fix the outdated
          comment in bpf_object__sanitize_btf() and add the error
          handling there (I've decided to check uint_id and uchar_id
          too in order to simplify debugging); add bpftool output
          example; use div64_u64_rem() instead of % in order to fix the
          linker error.
          Also fix the "invalid BTF_INFO" test (new commit, #4).

v4: https://lore.kernel.org/bpf/20210222214917.83629-1-iii@linux.ibm.com/
v4 -> v5: Fixes for the Andrii's findings: Use BTF_KIND_STRUCT instead
          of BTF_KIND_TYPEDEF for sanitization; check byte_sz in
          libbpf; move btf__add_float; remove relo support; add a dedup
          test (new commit, #7).

v5: https://lore.kernel.org/bpf/20210223231459.99664-1-iii@linux.ibm.com/
v5 -> v6: Fixes for further findings by Andrii: split whitespace issue
          fix into a separate patch; add 12-byte float to "float test #1,
          well-formed".

v6: https://lore.kernel.org/bpf/20210224234535.106970-1-iii@linux.ibm.com/
v6 -> v7: John suggested to add a comment explaining why sanitization
          does not preserve the type name, as well as what effect it has
          on running the code on the older kernels.
          Yonghong has asked to add a comment explaining why we are not
          checking the alignment very precisely in the kernel.
          John suggested to add a bpf_core_field_size test (commit #9).

Based on Alexei's feedback [1] I'm proceeding with the BTF_KIND_FLOAT
approach.

[1] https://lore.kernel.org/bpf/CAADnVQKWPODWZ2RSJ5FJhfYpxkuV0cvSAL1O+FSr9oP1ercoBg@mail.gmail.com/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/bpf/btf.rst

@@ -84,6 +84,7 @@ sequentially and type id is assigned to each recognized type starting from id
     #define BTF_KIND_FUNC_PROTO     13      /* Function Proto       */
     #define BTF_KIND_VAR            14      /* Variable     */
     #define BTF_KIND_DATASEC        15      /* Section      */
+    #define BTF_KIND_FLOAT          16      /* Floating point       */
 
 Note that the type section encodes debug info, not just pure types.
 ``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram.
@@ -95,8 +96,8 @@ Each type contains the following common data::
         /* "info" bits arrangement
          * bits  0-15: vlen (e.g. # of struct's members)
          * bits 16-23: unused
-         * bits 24-27: kind (e.g. int, ptr, array...etc)
-         * bits 28-30: unused
+         * bits 24-28: kind (e.g. int, ptr, array...etc)
+         * bits 29-30: unused
          * bit     31: kind_flag, currently used by
          *             struct, union and fwd
          */
@@ -452,6 +453,18 @@ map definition.
   * ``offset``: the in-section offset of the variable
   * ``size``: the size of the variable in bytes
 
+2.2.16 BTF_KIND_FLOAT
+~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+ * ``name_off``: any valid offset
+ * ``info.kind_flag``: 0
+ * ``info.kind``: BTF_KIND_FLOAT
+ * ``info.vlen``: 0
+ * ``size``: the size of the float type in bytes: 2, 4, 8, 12 or 16.
+
+No additional type data follow ``btf_type``.
+
 3. BTF Kernel API
 *****************
 

include/uapi/linux/btf.h

@@ -52,7 +52,7 @@ struct btf_type {
 	};
 };
 
-#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x0f)
+#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x1f)
 #define BTF_INFO_VLEN(info)	((info) & 0xffff)
 #define BTF_INFO_KFLAG(info)	((info) >> 31)
 
@@ -72,7 +72,8 @@ struct btf_type {
 #define BTF_KIND_FUNC_PROTO	13	/* Function Proto	*/
 #define BTF_KIND_VAR		14	/* Variable	*/
 #define BTF_KIND_DATASEC	15	/* Section	*/
-#define BTF_KIND_MAX		BTF_KIND_DATASEC
+#define BTF_KIND_FLOAT		16	/* Floating point	*/
+#define BTF_KIND_MAX		BTF_KIND_FLOAT
 #define NR_BTF_KINDS		(BTF_KIND_MAX + 1)
 
 /* For some specific BTF_KIND, "struct btf_type" is immediately

kernel/bpf/btf.c

@@ -173,7 +173,7 @@
 #define BITS_ROUNDUP_BYTES(bits) \
 	(BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
 
-#define BTF_INFO_MASK 0x8f00ffff
+#define BTF_INFO_MASK 0x9f00ffff
 #define BTF_INT_MASK 0x0fffffff
 #define BTF_TYPE_ID_VALID(type_id) ((type_id) <= BTF_MAX_TYPE)
 #define BTF_STR_OFFSET_VALID(name_off) ((name_off) <= BTF_MAX_NAME_OFFSET)
@@ -280,6 +280,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
 	[BTF_KIND_FUNC_PROTO]	= "FUNC_PROTO",
 	[BTF_KIND_VAR]		= "VAR",
 	[BTF_KIND_DATASEC]	= "DATASEC",
+	[BTF_KIND_FLOAT]	= "FLOAT",
 };
 
 static const char *btf_type_str(const struct btf_type *t)
@@ -574,6 +575,7 @@ static bool btf_type_has_size(const struct btf_type *t)
 	case BTF_KIND_UNION:
 	case BTF_KIND_ENUM:
 	case BTF_KIND_DATASEC:
+	case BTF_KIND_FLOAT:
 		return true;
 	}
 
@@ -1704,6 +1706,7 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		case BTF_KIND_STRUCT:
 		case BTF_KIND_UNION:
 		case BTF_KIND_ENUM:
+		case BTF_KIND_FLOAT:
 			size = type->size;
 			goto resolved;
 
@@ -1849,7 +1852,7 @@ static int btf_df_check_kflag_member(struct btf_verifier_env *env,
 	return -EINVAL;
 }
 
-/* Used for ptr, array and struct/union type members.
+/* Used for ptr, array struct/union and float type members.
  * int, enum and modifier types have their specific callback functions.
  */
 static int btf_generic_check_kflag_member(struct btf_verifier_env *env,
@@ -3675,6 +3678,81 @@ static const struct btf_kind_operations datasec_ops = {
 	.show			= btf_datasec_show,
 };
 
+static s32 btf_float_check_meta(struct btf_verifier_env *env,
+				const struct btf_type *t,
+				u32 meta_left)
+{
+	if (btf_type_vlen(t)) {
+		btf_verifier_log_type(env, t, "vlen != 0");
+		return -EINVAL;
+	}
+
+	if (btf_type_kflag(t)) {
+		btf_verifier_log_type(env, t, "Invalid btf_info kind_flag");
+		return -EINVAL;
+	}
+
+	if (t->size != 2 && t->size != 4 && t->size != 8 && t->size != 12 &&
+	    t->size != 16) {
+		btf_verifier_log_type(env, t, "Invalid type_size");
+		return -EINVAL;
+	}
+
+	btf_verifier_log_type(env, t, NULL);
+
+	return 0;
+}
+
+static int btf_float_check_member(struct btf_verifier_env *env,
+				  const struct btf_type *struct_type,
+				  const struct btf_member *member,
+				  const struct btf_type *member_type)
+{
+	u64 start_offset_bytes;
+	u64 end_offset_bytes;
+	u64 misalign_bits;
+	u64 align_bytes;
+	u64 align_bits;
+
+	/* Different architectures have different alignment requirements, so
+	 * here we check only for the reasonable minimum. This way we ensure
+	 * that types after CO-RE can pass the kernel BTF verifier.
+	 */
+	align_bytes = min_t(u64, sizeof(void *), member_type->size);
+	align_bits = align_bytes * BITS_PER_BYTE;
+	div64_u64_rem(member->offset, align_bits, &misalign_bits);
+	if (misalign_bits) {
+		btf_verifier_log_member(env, struct_type, member,
+					"Member is not properly aligned");
+		return -EINVAL;
+	}
+
+	start_offset_bytes = member->offset / BITS_PER_BYTE;
+	end_offset_bytes = start_offset_bytes + member_type->size;
+	if (end_offset_bytes > struct_type->size) {
+		btf_verifier_log_member(env, struct_type, member,
+					"Member exceeds struct_size");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void btf_float_log(struct btf_verifier_env *env,
+			  const struct btf_type *t)
+{
+	btf_verifier_log(env, "size=%u", t->size);
+}
+
+static const struct btf_kind_operations float_ops = {
+	.check_meta = btf_float_check_meta,
+	.resolve = btf_df_resolve,
+	.check_member = btf_float_check_member,
+	.check_kflag_member = btf_generic_check_kflag_member,
+	.log_details = btf_float_log,
+	.show = btf_df_show,
+};
+
 static int btf_func_proto_check(struct btf_verifier_env *env,
 				const struct btf_type *t)
 {
@@ -3808,6 +3886,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = {
 	[BTF_KIND_FUNC_PROTO] = &func_proto_ops,
 	[BTF_KIND_VAR] = &var_ops,
 	[BTF_KIND_DATASEC] = &datasec_ops,
+	[BTF_KIND_FLOAT] = &float_ops,
 };
 
 static s32 btf_check_meta(struct btf_verifier_env *env,

tools/bpf/bpftool/btf.c

@@ -36,6 +36,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
 	[BTF_KIND_FUNC_PROTO]	= "FUNC_PROTO",
 	[BTF_KIND_VAR]		= "VAR",
 	[BTF_KIND_DATASEC]	= "DATASEC",
+	[BTF_KIND_FLOAT]	= "FLOAT",
 };
 
 struct btf_attach_table {
@@ -327,6 +328,13 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
 			jsonw_end_array(w);
 		break;
 	}
+	case BTF_KIND_FLOAT: {
+		if (json_output)
+			jsonw_uint_field(w, "size", t->size);
+		else
+			printf(" size=%u", t->size);
+		break;
+	}
 	default:
 		break;
 	}

tools/bpf/bpftool/btf_dumper.c

@@ -596,6 +596,7 @@ static int __btf_dumper_type_only(const struct btf *btf, __u32 type_id,
 	switch (BTF_INFO_KIND(t->info)) {
 	case BTF_KIND_INT:
 	case BTF_KIND_TYPEDEF:
+	case BTF_KIND_FLOAT:
 		BTF_PRINT_ARG("%s ", btf__name_by_offset(btf, t->name_off));
 		break;
 	case BTF_KIND_STRUCT:

tools/include/uapi/linux/btf.h

@@ -52,7 +52,7 @@ struct btf_type {
 	};
 };
 
-#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x0f)
+#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x1f)
 #define BTF_INFO_VLEN(info)	((info) & 0xffff)
 #define BTF_INFO_KFLAG(info)	((info) >> 31)
 
@@ -72,7 +72,8 @@ struct btf_type {
 #define BTF_KIND_FUNC_PROTO	13	/* Function Proto	*/
 #define BTF_KIND_VAR		14	/* Variable	*/
 #define BTF_KIND_DATASEC	15	/* Section	*/
-#define BTF_KIND_MAX		BTF_KIND_DATASEC
+#define BTF_KIND_FLOAT		16	/* Floating point	*/
+#define BTF_KIND_MAX		BTF_KIND_FLOAT
 #define NR_BTF_KINDS		(BTF_KIND_MAX + 1)
 
 /* For some specific BTF_KIND, "struct btf_type" is immediately

tools/lib/bpf/btf.c

@@ -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
@@ -1883,7 +1928,7 @@ static int btf_add_composite(struct btf *btf, int kind, const char *name, __u32
  *   - *byte_sz* - size of the struct, in bytes;
  *
  * Struct initially has no fields in it. Fields can be added by
- * btf__add_field() right after btf__add_struct() succeeds. 
+ * btf__add_field() right after btf__add_struct() succeeds.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
@@ -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

@@ -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));