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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: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210226202256.116518-4-iii@linux.ibm.com
This commit is contained in:
Ilya Leoshkevich 2021-02-26 21:22:49 +01:00 committed by Alexei Starovoitov
parent 1b1ce92b24
commit 22541a9eeb
6 changed files with 94 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
tools/lib/bpf/btf.c
View File

@ -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:

6
tools/lib/bpf/btf.h
View File

@ -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));

4
tools/lib/bpf/btf_dump.c
View File

@ -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 @@ skip_mod:
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);

29
tools/lib/bpf/libbpf.c
View File

@ -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)

5
tools/lib/bpf/libbpf.map
View File

@ -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;

2
tools/lib/bpf/libbpf_internal.h
View File

@ -31,6 +31,8 @@
#define BTF_MEMBER_ENC(name, type, bits_offset) (name), (type), (bits_offset)
#define BTF_PARAM_ENC(name, type) (name), (type)
#define BTF_VAR_SECINFO_ENC(type, offset, size) (type), (offset), (size)
#define BTF_TYPE_FLOAT_ENC(name, sz) \
BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_FLOAT, 0, 0), sz)
#ifndef likely
#define likely(x) __builtin_expect(!!(x), 1)