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libbpf: Add BTF_KIND_FLOAT support

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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 Andrii Nakryiko
parent 617f781804
commit 471e7c241d
6 changed files with 94 additions and 1 deletions
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29
src/libbpf.c
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@@ -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)