Some BPF programs compiled on s390 fail to load, because s390
arch-specific linux headers contain float and double types.
Fix as follows:
- Make the DWARF loader fill base_type.float_type.
- Introduce the --btf_gen_floats command-line parameter, so that
pahole could be used to build both the older and the newer kernels.
- libbpf introduced the support for the floating-point types in commit
986962fade5, so update the libbpf submodule to that version and use
the new btf__add_float() function in order to emit the floating-point
types when not in the compatibility mode.
- Make the BTF loader recognize the new BTF kind.
Example of the resulting entry in the vmlinux BTF:
[7164] FLOAT 'double' size=8
when building with:
LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} --btf_gen_floats
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
v1: https://lore.kernel.org/dwarves/20210306022203.152930-1-iii@xxxxxxxxxxxxx/
v1 -> v2: Introduce libbpf compatibility level command-line parameter.
The code should now work for both bpf-next/master and
v5.12-rc2.
v2: https://lore.kernel.org/dwarves/20210308235913.162038-1-iii@xxxxxxxxxxxxx/
v2 -> v3: Use the feature flag (--encode_btf_kind_float) instead of the
libbpf version flag.
v3: https://lore.kernel.org/dwarves/20210310141517.169698-1-iii@xxxxxxxxxxxxx/
v3 -> v4: Rename the flag to --btf_gen_floats.
btf_loader.c | 21 +++++++++++++++++++--
dwarf_loader.c | 11 +++++++++++
lib/bpf | 2 +-
libbtf.c | 36 ++++++++++++++++++++++++++++++++++--
libbtf.h | 1 +
man-pages/pahole.1 | 5 +++++
pahole.c | 8 ++++++++
7 files changed, 79 insertions(+), 5 deletions(-)
diff --git a/btf_loader.c b/btf_loader.c
index ec286f4..7cc39aa 100644
--- 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
index b73d786..c5e6681 100644
--- 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
index 5af3d86..986962f 160000
--- a/lib/bpf
+++ b/lib/bpf
@@ -1 +1 @@
-Subproject commit 5af3d86b5a2c5fecdc3ab83822d083edd32b4396
+Subproject commit 986962fade5dfa89c2890f3854eb040d2a64ab38
diff --git a/libbtf.c b/libbtf.c
index 9f76283..7ad7e9c 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -30,6 +30,7 @@
struct btf *base_btf;
uint8_t btf_elf__verbose;
uint8_t btf_elf__force;
+bool btf_gen_floats = false;
static int btf_var_secinfo_cmp(const void *a, const void *b)
{
@@ -227,6 +228,7 @@ 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 +369,27 @@ 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)
{
@@ -379,8 +402,17 @@ int32_t btf_elf__add_base_type(struct btf_elf *btfe, const struct base_type *bt,
encoding = BTF_INT_SIGNED;
} else if (bt->is_bool) {
encoding = BTF_INT_BOOL;
- } else if (bt->float_type) {
- fprintf(stderr, "float_type is not supported\n");
+ } else if (bt->float_type && btf_gen_floats) {
+ /*
+ * Encode floats as BTF_KIND_FLOAT if allowed, otherwise (in
+ * compatibility mode) encode them as BTF_KIND_INT - that's not
+ * fully correct, but that's what it used to be.
+ */
+ 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;
}
diff --git a/libbtf.h b/libbtf.h
index 191f586..c7cbe6e 100644
--- a/libbtf.h
+++ b/libbtf.h
@@ -35,6 +35,7 @@ extern struct btf *base_btf;
extern uint8_t btf_elf__verbose;
extern uint8_t btf_elf__force;
#define btf_elf__verbose_log(fmt, ...) { if (btf_elf__verbose) printf(fmt, __VA_ARGS__); }
+extern bool btf_gen_floats;
#define PERCPU_SECTION ".data..percpu"
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 352bb5e..e292b2c 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -199,6 +199,11 @@ Path to the base BTF file, for instance: vmlinux when encoding kernel module BTF
This may be inferred when asking for a /sys/kernel/btf/MODULE, when it will be autoconfigured
to "/sys/kernel/btf/vmlinux".
+.TP
+.B \-\-btf_gen_floats
+Allow producing BTF_KIND_FLOAT entries in systems where the vmlinux DWARF
+information has float types.
+
.TP
.B \-l, \-\-show_first_biggest_size_base_type_member
Show first biggest size base_type member.
diff --git a/pahole.c b/pahole.c
index 4a34ba5..c8d38f5 100644
--- a/pahole.c
+++ b/pahole.c
@@ -825,6 +825,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
#define ARGP_just_packed_structs 319
#define ARGP_numeric_version 320
#define ARGP_btf_base 321
+#define ARGP_btf_gen_floats 322
static const struct argp_option pahole__options[] = {
{
@@ -1119,6 +1120,11 @@ static const struct argp_option pahole__options[] = {
.key = ARGP_btf_encode_force,
.doc = "Ignore those symbols found invalid when encoding BTF."
},
+ {
+ .name = "btf_gen_floats",
+ .key = ARGP_btf_gen_floats,
+ .doc = "Allow producing BTF_KIND_FLOAT entries."
+ },
{
.name = "structs",
.key = ARGP_just_structs,
@@ -1254,6 +1260,8 @@ static error_t pahole__options_parser(int key, char *arg,
base_btf_file = arg; break;
case ARGP_numeric_version:
print_numeric_version = true; break;
+ case ARGP_btf_gen_floats:
+ btf_gen_floats = true; break;
default:
return ARGP_ERR_UNKNOWN;
}
--
2.29.2
