libbpf: Introduce BTF_KIND_FLOAT

iii-i · iii-i · commit b0f52066ab12 · 2021-02-16T00:41:46.000+01:00
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 to libbpf by representing them using
the new BTF_KIND_FLOAT.

Signed-off-by: Ilya Leoshkevich &lt;iii@linux.ibm.com&gt;
diff --git a/.gitmodules b/.gitmodules
@@ -1,3 +1,3 @@
 [submodule "lib/bpf"]
 	path = lib/bpf
-	url = https://github.com/libbpf/libbpf
+	url = https://github.com/iii-i/libbpf
diff --git a/btf_loader.c b/btf_loader.c
@@ -160,7 +160,7 @@ static struct variable *variable__new(strings_t name, uint32_t linkage)
 	return var;
 }
 
-static int create_new_base_type(struct btf_elf *btfe, const struct btf_type *tp, uint32_t id)
+static int create_new_int_type(struct btf_elf *btfe, const struct btf_type *tp, uint32_t id)
 {
 	uint32_t attrs = btf_int_encoding(tp);
 	strings_t name = tp->name_off;
@@ -175,6 +175,20 @@ static int create_new_base_type(struct btf_elf *btfe, const struct btf_type *tp,
 	return 0;
 }
 
+static int create_new_float_type(struct btf_elf *btfe, const struct btf_type *tp, uint32_t id)
+{
+	strings_t name = tp->name_off;
+	struct base_type *base = base_type__new(name, 0, BT_FP_SINGLE, tp->size * 8);
+
+	if (base == NULL)
+		return -ENOMEM;
+
+	base->tag.tag = DW_TAG_base_type;
+	cu__add_tag_with_id(btfe->priv, &base->tag, id);
+
+	return 0;
+}
+
 static int create_new_array(struct btf_elf *btfe, const struct btf_type *tp, uint32_t id)
 {
 	struct btf_array *ap = btf_array(tp);
@@ -397,7 +411,7 @@ static int btf_elf__load_types(struct btf_elf *btfe)
 
 		switch (type) {
 		case BTF_KIND_INT:
-			err = create_new_base_type(btfe, type_ptr, type_index);
+			err = create_new_int_type(btfe, type_ptr, type_index);
 			break;
 		case BTF_KIND_ARRAY:
 			err = create_new_array(btfe, type_ptr, type_index);
@@ -442,6 +456,9 @@ static int btf_elf__load_types(struct btf_elf *btfe)
 			// BTF_KIND_FUNC corresponding to a defined subprogram.
 			err = create_new_function(btfe, type_ptr, type_index);
 			break;
+		case BTF_KIND_FLOAT:
+			err = create_new_float_type(btfe, type_ptr, type_index);
+			break;
 		default:
 			fprintf(stderr, "BTF: idx: %d, Unknown kind %d\n", type_index, type);
 			fflush(stderr);
diff --git a/dwarf_loader.c b/dwarf_loader.c
@@ -461,6 +461,16 @@ static struct ptr_to_member_type *ptr_to_member_type__new(Dwarf_Die *die,
 	return ptr;
 }
 
+static uint8_t encoding_to_float_type(uint64_t encoding)
+{
+	switch (encoding) {
+	case DW_ATE_complex_float:	return BT_FP_CMPLX;
+	case DW_ATE_float:		return BT_FP_SINGLE;
+	case DW_ATE_imaginary_float:	return BT_FP_IMGRY;
+	default:			return 0;
+	}
+}
+
 static struct base_type *base_type__new(Dwarf_Die *die, struct cu *cu)
 {
 	struct base_type *bt = tag__alloc(cu, sizeof(*bt));
@@ -474,6 +484,7 @@ static struct base_type *base_type__new(Dwarf_Die *die, struct cu *cu)
 		bt->is_signed = encoding == DW_ATE_signed;
 		bt->is_varargs = false;
 		bt->name_has_encoding = true;
+		bt->float_type = encoding_to_float_type(encoding);
 	}
 
 	return bt;
diff --git a/lib/bpf b/lib/bpf
@@ -1 +1 @@
-Subproject commit 5af3d86b5a2c5fecdc3ab83822d083edd32b4396
+Subproject commit fd6c01735bc651391396760247c8f782b73d8d82
diff --git a/libbtf.c b/libbtf.c
@@ -227,6 +227,7 @@ 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_elf__printable_name(const struct btf_elf *btfe, uint32_t offset)
@@ -367,6 +368,27 @@ static void btf_log_func_param(const struct btf_elf *btfe,
 	}
 }
 
+static int32_t btf_elf__add_float_type(struct btf_elf *btfe,
+				       const struct base_type *bt,
+				       const char *name)
+{
+	int32_t id;
+
+	id = btf__add_float(btfe->btf, name, BITS_ROUNDUP_BYTES(bt->bit_size));
+	if (id < 0) {
+		btf_elf__log_err(btfe, BTF_KIND_FLOAT, name, true, "Error emitting BTF type");
+	} else {
+		const struct btf_type *t;
+
+		t = btf__type_by_id(btfe->btf, id);
+		btf_elf__log_type(btfe, t, false, true,
+				"size=%u nr_bits=%u",
+				t->size, bt->bit_size);
+	}
+
+	return id;
+}
+
 int32_t btf_elf__add_base_type(struct btf_elf *btfe, const struct base_type *bt,
 			       const char *name)
 {
@@ -380,7 +402,11 @@ int32_t btf_elf__add_base_type(struct btf_elf *btfe, const struct base_type *bt,
 	} else if (bt->is_bool) {
 		encoding = BTF_INT_BOOL;
 	} else if (bt->float_type) {
-		fprintf(stderr, "float_type is not supported\n");
+		if (bt->float_type == BT_FP_SINGLE ||
+		    bt->float_type == BT_FP_DOUBLE ||
+		    bt->float_type == BT_FP_LDBL)
+			return btf_elf__add_float_type(btfe, bt, name);
+		fprintf(stderr, "Complex, interval and imaginary float types are not supported\n");
 		return -1;
 	}
 
@@ -820,6 +846,8 @@ int btf_elf__encode(struct btf_elf *btfe, uint8_t flags)
 {
 	struct btf *btf = btfe->btf;
 
+	libbpf_set_print(libbpf_log);
+
 	/* Empty file, nothing to do, so... done! */
 	if (btf__get_nr_types(btf) == 0)
 		return 0;
