Re: [PATCH v3 bpf-next 2/6] libbpf: Add BTF_KIND_FLOAT support

[Yonghong Song <yhs@fb.com>]

On 2/19/21 7:49 PM, Ilya Leoshkevich wrote:
> The logic follows that of BTF_KIND_INT most of the time. Sanitization
> replaces BTF_KIND_FLOATs with BTF_KIND_CONSTs pointing to
> equally-sized BTF_KIND_ARRAYs on older kernels.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>   tools/lib/bpf/btf.c             | 44 ++++++++++++++++++++++++++++++
>   tools/lib/bpf/btf.h             |  8 ++++++
>   tools/lib/bpf/btf_dump.c        |  4 +++
>   tools/lib/bpf/libbpf.c          | 48 ++++++++++++++++++++++++++++++++-
>   tools/lib/bpf/libbpf.map        |  5 ++++
>   tools/lib/bpf/libbpf_internal.h |  2 ++
>   6 files changed, 110 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index fdfff544f59a..1ebfcc687dab 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -292,6 +292,7 @@ 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);
> @@ -339,6 +340,7 @@ 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));
> @@ -579,6 +581,7 @@ __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:
> @@ -622,6 +625,7 @@ 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);
> @@ -2400,6 +2404,42 @@ int btf__add_datasec(struct btf *btf, const char *name, __u32 byte_sz)
>   	return btf_commit_type(btf, sz);
>   }
[...]

I skipped deduplication part, Andrii can take a look later.

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index d43cc3f29dae..b79a6a2e6faa 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -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,
>   };
>   
> @@ -1935,6 +1937,7 @@ 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";
>   	}
>   }
> @@ -2384,18 +2387,22 @@ 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 t_uchar = 0;
>   	int i, j, vlen;
> +	int t_uint = 0;
>   
>   	for (i = 1; i <= btf__get_nr_types(btf); i++) {
>   		t = (struct btf_type *)btf__type_by_id(btf, i);
> @@ -2445,6 +2452,26 @@ 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 TYPEDEF(u8[]) */

replace FLOAT with CONST(u8[]).

> +			int t_array;
> +			__u32 size;
> +
> +			size = t->size;
> +			if (!t_uchar)
> +				t_uchar = btf__add_int(btf, "unsigned char", 1,
> +						       0);
> +			if (!t_uint)
> +				t_uint = btf__add_int(btf, "unsigned int", 4,
> +						      0);
> +			t_array = btf__add_array(btf, t_uint, t_uchar, size);

Checking whether t_array is valid here or not?
We do not need to check t_uchar/t_uint. If they are invalid 
btf__add_array() will return -EINVAL.

> +
> +			/* adding new types may have invalidated t */
> +			t = (struct btf_type *)btf__type_by_id(btf, i);
> +
> +			t->name_off = 0;
> +			t->info = BTF_INFO_ENC(BTF_KIND_CONST, 0, 0);
> +			t->type = t_array;
>   		}
>   	}
>   }
> @@ -3882,6 +3909,18 @@ 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 = {
> @@ -4061,6 +4100,9 @@ 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)
> @@ -4940,6 +4982,8 @@ static int bpf_core_fields_are_compat(const struct btf *local_btf,
>   		local_id = btf_array(local_type)->type;
>   		targ_id = btf_array(targ_type)->type;
>   		goto recur;
> +	case BTF_KIND_FLOAT:
> +		return local_type->size == targ_type->size;
>   	default:
>   		pr_warn("unexpected kind %d relocated, local [%d], target [%d]\n",
>   			btf_kind(local_type), local_id, targ_id);
> @@ -5122,6 +5166,8 @@ static int bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id
>   		skip_mods_and_typedefs(targ_btf, targ_type->type, &targ_id);
>   		goto recur;
>   	}
> +	case BTF_KIND_FLOAT:
> +		return local_type->size == targ_type->size;
>   	default:
>   		pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
>   			btf_kind_str(local_type), local_id, targ_id);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 1c0fd2dd233a..ec898f464ab9 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -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;
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index 969d0ac592ba..343f6eb05637 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -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)
>