Re: [PATCH v3 bpf-next 1/2] libbpf: BTF dumper support for typed data
From: Andrii Nakryiko
Date: Thu May 27 2021 - 21:25:12 EST
On Thu, May 27, 2021 at 9:00 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Add a BTF dumper for typed data, so that the user can dump a typed
> version of the data provided.
>
> The API is
>
> int btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
> void *data, size_t byte_sz,
> const struct btf_dump_type_data_opts *opts);
>
> ...where the id is the BTF id of the data pointed to by the "void *"
> argument; for example the BTF id of "struct sk_buff" for a
> "struct skb *" data pointer. Options supported are
>
> - a starting indent level (indent_lvl)
> - a set of boolean options to control dump display, similar to those
> used for BPF helper bpf_snprintf_btf(). Options are
> - compact : omit newlines and other indentation
> - skip_names: omit member names
> - emit_zeroes: show zero-value members
>
> Default output format is identical to that dumped by bpf_snprintf_btf(),
> for example a "struct sk_buff" representation would look like this:
>
> struct sk_buff){
> (union){
> (struct){
> .next = (struct sk_buff *)0xffffffffffffffff,
> .prev = (struct sk_buff *)0xffffffffffffffff,
> (union){
> .dev = (struct net_device *)0xffffffffffffffff,
> .dev_scratch = (long unsigned int)18446744073709551615,
> },
> },
> ...
Is the '\t' as a default indentation filler a requirement? With 8
spaces per tab this gets wide really fast. 2 or 4 spaces might be a
better default? And it probably would be good to let users specify
this as a string (e.g., "indent_str"), which could be anything the
user wants, from empty string to multiple tabs to "..." to whatever
else. If I needed to dump something with this API, I'd probably use 2
spaces, for instance. But I can see how other users might want
something else, so making this customizable seems like a good thing?
>
> If the data structure is larger than the *byte_sz*
> number of bytes that are available in *data*, as much
> of the data as possible will be dumped and -E2BIG will
> be returned. This is useful as tracers will sometimes
> not be able to capture all of the data associated with
> a type; for example a "struct task_struct" is ~16k.
> Being able to specify that only a subset is available is
> important for such cases.
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
I'll do another pass next week, I ran out of time, it's a bit of a big
patch, sorry. But left few comments, please take a look.
> tools/lib/bpf/btf.h | 17 +
> tools/lib/bpf/btf_dump.c | 901 +++++++++++++++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.map | 5 +
> 3 files changed, 923 insertions(+)
>
> diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> index b54f1c3..234aa97 100644
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -184,6 +184,23 @@ struct btf_dump_emit_type_decl_opts {
> btf_dump__emit_type_decl(struct btf_dump *d, __u32 id,
> const struct btf_dump_emit_type_decl_opts *opts);
>
> +
> +struct btf_dump_type_data_opts {
> + /* size of this struct, for forward/backward compatibility */
> + size_t sz;
> + int indent_level;
> + /* below match "show" flags for bpf_show_snprintf() */
> + bool compact; /* no newlines/tabs */
> + bool skip_names; /* skip member/type names */
> + bool emit_zeroes; /* show 0-valued fields */
please add size_t: 0; as the last member to avoid various issues with
non-zero padding. We've been doing it for a few not perfectly aligned
opts recently and that seems to work good in practice.
> +};
> +#define btf_dump_type_data_opts__last_field emit_zeroes
> +
> +LIBBPF_API int
> +btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
> + void *data, size_t byte_sz,
can't get over data vs byte_sz naming inconsistency.... why not data
and data_sz?
also, const void *data?
> + const struct btf_dump_type_data_opts *opts);
> +
> /*
> * A set of helpers for easier BTF types handling
> */
> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index 5e2809d..27baa6a 100644
> --- a/tools/lib/bpf/btf_dump.c
> +++ b/tools/lib/bpf/btf_dump.c
> @@ -10,6 +10,8 @@
> #include <stddef.h>
> #include <stdlib.h>
> #include <string.h>
> +#include <ctype.h>
> +#include <endian.h>
> #include <errno.h>
> #include <linux/err.h>
> #include <linux/btf.h>
> @@ -19,6 +21,13 @@
> #include "libbpf.h"
> #include "libbpf_internal.h"
>
> +#define BITS_PER_BYTE 8
> +#define BITS_PER_U128 128
> +#define BITS_PER_BYTE_MASK (BITS_PER_BYTE - 1)
> +#define BITS_PER_BYTE_MASKED(bits) ((bits) & BITS_PER_BYTE_MASK)
> +#define BITS_ROUNDDOWN_BYTES(bits) ((bits) / 8)
> +#define BITS_ROUNDUP_BYTES(bits) (roundup(bits, 8))
> +
> static const char PREFIXES[] = "\t\t\t\t\t\t\t\t\t\t\t\t\t";
> static const size_t PREFIX_CNT = sizeof(PREFIXES) - 1;
>
> @@ -53,6 +62,25 @@ struct btf_dump_type_aux_state {
> __u8 referenced: 1;
> };
>
> +/*
> + * Common internal data for BTF type data dump operations.
> + */
> +struct btf_dump_data {
> + void *data_end; /* end of valid data to show */
> + bool compact;
> + bool skip_names;
> + bool emit_zeroes;
> + __u8 indent_lvl; /* base indent level */
> + /* below are used during iteration */
> + struct {
> + __u8 depth;
> + __u8 array_member:1,
> + array_terminated:1,
> + array_ischar:1;
> + __u32 bitfield_size;
> + } state;
> +};
> +
> struct btf_dump {
> const struct btf *btf;
> const struct btf_ext *btf_ext;
> @@ -89,6 +117,10 @@ struct btf_dump {
> * name occurrences
> */
> struct hashmap *ident_names;
> + /*
> + * data for typed display.
> + */
> + struct btf_dump_data data;
given it's not always used, should this be allocated lazily only if necessary?
> };
>
> static size_t str_hash_fn(const void *key, void *ctx)
> @@ -1392,6 +1424,91 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
> btf_dump_emit_name(d, fname, last_was_ptr);
> }
>
> +/* show type name as [.fname =] (type_name) */
> +static void btf_dump_emit_type_name(struct btf_dump *d, __u32 id,
> + const char *fname, int lvl, bool toplevel)
Sorry, I didn't get from your cover letter why
btf_dump__emit_type_decl() doesn't do what you need it to do. Can you
please elaborate with a simple example?
> +{
> +
> + const struct btf_type *t, *child;
> + const char *name;
> + __u16 kind;
> +
> + /* for array members, we don't bother emitting type name for each
> + * member to avoid the redundancy of
> + * .name = (char[])[(char)'f',(char)'o',(char)'o',]
> + */
> + if (d->data.state.array_member)
> + return;
> +
> + t = btf__type_by_id(d->btf, id);
> + kind = btf_kind(t);
> +
> + /* avoid type name specification for variable/section; it will be done
> + * for the associated variable value(s). Also skip for function
> + * prototypes.
> + */
> + switch (kind) {
> + case BTF_KIND_VAR:
> + case BTF_KIND_DATASEC:
> + case BTF_KIND_FUNC_PROTO:
hm... why skipping func_proto? seems useful when printing all kinds of
opts struct?
> + return;
> + default:
> + break;
> + }
> +
> + if (toplevel) {
> + if (fname && strlen(fname) > 0)
> + btf_dump_printf(d, ".%s = ", fname);
> + btf_dump_printf(d, "(");
> + }
".field = " part is not really a type name, can't it be done outside?
> +
> + switch (kind) {
> + case BTF_KIND_INT:
> + name = btf_name_of(d, t->name_off);
> + btf_dump_printf(d, "%s", name);
> + break;
> + case BTF_KIND_STRUCT:
> + case BTF_KIND_UNION:
> + name = btf_dump_type_name(d, id);
> + btf_dump_printf(d, "%s%s%s",
> + btf_is_struct(t) ? "struct" : "union",
> + strlen(name) > 0 ? " " : "",
> + name);
> + break;
> + case BTF_KIND_ENUM:
> + btf_dump_emit_enum_fwd(d, id, t);
> + break;
> + case BTF_KIND_TYPEDEF:
> + btf_dump_printf(d, "%s", btf_dump_ident_name(d, id));
> + break;
> + case BTF_KIND_VOLATILE:
> + case BTF_KIND_CONST:
> + case BTF_KIND_RESTRICT:
> + /* modifiers are omitted from the cast to save space */
> + btf_dump_emit_type_name(d, t->type, NULL, lvl, false);
> + break;
> + case BTF_KIND_PTR:
> + btf_dump_emit_type_name(d, t->type, NULL, lvl, false);
> + child = btf__type_by_id(d->btf, t->type);
> + btf_dump_printf(d,
> + btf_kind(child) == BTF_KIND_PTR ? "*" : " *");
> + break;
> + case BTF_KIND_ARRAY: {
> + const struct btf_array *a = btf_array(t);
> +
> + btf_dump_emit_type_name(d, a->type, NULL, lvl, false);
> + btf_dump_printf(d, "[]");
> + break;
> + }
> + default:
> + pr_warn("unexpected type when emitting type name, kind %u, id:[%u]\n",
> + kind, id);
> + break;
> + }
> + if (toplevel)
> + btf_dump_printf(d, ")");
> +}
> +
> /* return number of duplicates (occurrences) of a given name */
> static size_t btf_dump_name_dups(struct btf_dump *d, struct hashmap *name_map,
> const char *orig_name)
> @@ -1442,3 +1559,787 @@ static const char *btf_dump_ident_name(struct btf_dump *d, __u32 id)
> {
> return btf_dump_resolve_name(d, id, d->ident_names);
> }
> +
> +static int btf_dump_dump_type_data(struct btf_dump *d,
> + const char *fname,
> + const struct btf_type *t,
> + __u32 id,
> + void *data,
> + __u8 bits_offset);
> +
> +static const char *btf_dump_data_newline(struct btf_dump *d)
> +{
> + return d->data.compact ? "" : "\n";
> +}
> +
> +static const char *btf_dump_data_delim(struct btf_dump *d)
> +{
> + if (d->data.state.depth == 0)
> + return "";
> +
> + return ",";
nit: use ternary like for newline?
> +}
> +
> +static const char *btf_dump_data_pfx(struct btf_dump *d)
> +{
> + int lvl = d->data.indent_lvl + d->data.state.depth;
> +
> + if (d->data.compact)
> + lvl = 0;
> + return pfx(lvl);
> +}
> +
> +/* A macro is used here as btf_type_value[s]() appends format specifiers
> + * to the format specifier passed in; these do the work of appending
> + * delimiters etc while the caller simply has to specify the type values
> + * in the format specifier + value(s).
> + */
> +#define btf_dump_type_values(d, fmt, ...) \
> + btf_dump_printf(d, fmt "%s%s", \
> + __VA_ARGS__, \
> + btf_dump_data_delim(d), \
> + btf_dump_data_newline(d))
> +
> +static int btf_dump_df_data(struct btf_dump *d,
what does "df" stand for?
> + const struct btf_type *t,
> + __u32 id,
> + void *data)
> +{
> + btf_dump_printf(d, "<unsupported kind:%u>",
> + BTF_INFO_KIND(t->info));
> + return -ENOTSUP;
> +}
> +
> +static void btf_dump_int128(struct btf_dump *d,
> + const struct btf_type *t,
> + void *data)
> +{
> + /* data points to a __int128 number.
> + * Suppose
> + * int128_num = *(__int128 *)data;
> + * The below formulas shows what upper_num and lower_num represents:
> + * upper_num = int128_num >> 64;
> + * lower_num = int128_num & 0xffffffffFFFFFFFFULL;
> + */
> + __u64 upper_num, lower_num;
> +
> +#ifdef __BIG_ENDIAN_BITFIELD
> + upper_num = *(__u64 *)data;
> + lower_num = *(__u64 *)(data + 8);
> +#else
> + upper_num = *(__u64 *)(data + 8);
> + lower_num = *(__u64 *)data;
> +#endif
> + if (upper_num == 0)
> + btf_dump_type_values(d, "0x%llx", (long long)lower_num);
> + else
> + btf_dump_type_values(d, "0x%llx%016llx", (long long)upper_num,
> + (long long)lower_num);
> +}
> +
> +static void btf_int128_shift(__u64 *print_num, __u16 left_shift_bits,
> + __u16 right_shift_bits)
> +{
> + __u64 upper_num, lower_num;
> +
> +#ifdef __BIG_ENDIAN_BITFIELD
> + upper_num = print_num[0];
> + lower_num = print_num[1];
> +#else
> + upper_num = print_num[1];
> + lower_num = print_num[0];
> +#endif
> +
> + /* shake out un-needed bits by shift/or operations */
> + if (left_shift_bits >= 64) {
> + upper_num = lower_num << (left_shift_bits - 64);
> + lower_num = 0;
> + } else {
> + upper_num = (upper_num << left_shift_bits) |
> + (lower_num >> (64 - left_shift_bits));
> + lower_num = lower_num << left_shift_bits;
> + }
> +
> + if (right_shift_bits >= 64) {
> + lower_num = upper_num >> (right_shift_bits - 64);
> + upper_num = 0;
> + } else {
> + lower_num = (lower_num >> right_shift_bits) |
> + (upper_num << (64 - right_shift_bits));
> + upper_num = upper_num >> right_shift_bits;
> + }
> +
> +#ifdef __BIG_ENDIAN_BITFIELD
> + print_num[0] = upper_num;
> + print_num[1] = lower_num;
> +#else
> + print_num[0] = lower_num;
> + print_num[1] = upper_num;
> +#endif
> +}
> +
> +static int btf_dump_bitfield_get_data(struct btf_dump *d,
> + void *data,
> + __u8 bits_offset,
> + __u8 nr_bits,
> + __u64 *print_num)
> +{
> + __u16 left_shift_bits, right_shift_bits;
> + __u8 nr_copy_bytes;
> + __u8 nr_copy_bits;
> +
> + nr_copy_bits = nr_bits + bits_offset;
> + nr_copy_bytes = BITS_ROUNDUP_BYTES(nr_copy_bits);
> +
> + memcpy(print_num, data, nr_copy_bytes);
> +
> +#ifdef __BIG_ENDIAN_BITFIELD
> + left_shift_bits = bits_offset;
> +#else
> + left_shift_bits = BITS_PER_U128 - nr_copy_bits;
> +#endif
> + right_shift_bits = BITS_PER_U128 - nr_bits;
> +
> + btf_int128_shift(print_num, left_shift_bits, right_shift_bits);
> +
> + return 0;
> +}
> +
> +static int btf_dump_bitfield_data(struct btf_dump *d,
> + const struct btf_type *t,
> + void *data,
> + __u8 bits_offset,
> + __u8 nr_bits)
> +{
> + __u64 print_num[2] = {};
= {} is unnecessary as you always initialize it anyways?
> +
> + btf_dump_bitfield_get_data(d, data, bits_offset, nr_bits, print_num);
> + btf_dump_int128(d, t, print_num);
> +
> + return 0;
> +}
> +
> +static int btf_dump_int_bits(struct btf_dump *d,
> + const struct btf_type *t,
> + void *data,
> + __u8 bits_offset)
> +{
> + __u8 nr_bits = d->data.state.bitfield_size ?: btf_int_bits(t);
> + __u8 total_bits_offset;
> +
> + /*
> + * bits_offset is at most 7.
> + * BTF_INT_OFFSET() cannot exceed 128 bits.
> + */
> + total_bits_offset = bits_offset + btf_int_offset(t);
BTF_INT_OFFSET() is long deprecated, pahole doesn't generate such
INTs, many versions of Clang don't generate such int, so I don't think
we should bother supporting it.
> + data += BITS_ROUNDDOWN_BYTES(total_bits_offset);
> + bits_offset = BITS_PER_BYTE_MASKED(total_bits_offset);
> + return btf_dump_bitfield_data(d, t, data, bits_offset, nr_bits);
> +}
> +
> +static int btf_dump_int_bits_check_zero(struct btf_dump *d,
> + const struct btf_type *t,
> + void *data,
> + __u8 bits_offset)
> +{
> + __u64 print_num[2], zero[2] = { };
> + __u8 nr_bits = d->data.state.bitfield_size ?: btf_int_bits(t);
> + __u8 total_bits_offset;
> +
> + total_bits_offset = bits_offset + btf_int_offset(t);
> + data += BITS_ROUNDDOWN_BYTES(total_bits_offset);
> + bits_offset = BITS_PER_BYTE_MASKED(total_bits_offset);
> + btf_dump_bitfield_get_data(d, data, bits_offset, nr_bits,
> + (__u64 *)&print_num);
> + if (memcmp(print_num, zero, sizeof(zero)) == 0)
> + return -ENODATA;
> + return 0;
> +}
> +
> +static int btf_dump_int_check_zero(struct btf_dump *d,
> + const struct btf_type *t,
> + void *data,
> + __u8 bits_offset)
> +{
> + __u8 encoding = btf_int_encoding(t);
> + bool sign = encoding & BTF_INT_SIGNED;
> + __u8 nr_bits = btf_int_bits(t);
> + bool zero = false;
> +
> + if (bits_offset || btf_int_offset(t) ||
> + BITS_PER_BYTE_MASKED(nr_bits))
> + return btf_dump_int_bits_check_zero(d, t, data, bits_offset);
> +
> + switch (nr_bits) {
> + case 128:
> + zero = sign ? (*(__int128 *)data) == 0 :
> + (*(unsigned __int128 *)data) == 0;
> + break;
> + case 64:
> + zero = sign ? (*(__s64 *)data) == 0 :
> + (*(__u64 *)data) == 0;
> + break;
> + case 32:
> + zero = sign ? (*(__s32 *)data) == 0 :
> + (*(__u32 *)data) == 0;
> + break;
> + case 16:
> + zero = sign ? (*(__s16 *)data) == 0 :
> + (*(__u16 *)data) == 0;
> + break;
> + case 8:
> + zero = sign ? (*(__s8 *)data) == 0 :
> + (*(__u8 *)data) == 0;
for zero checks sign doesn't matter
> + break;
> + default:
> + break;
> + }
> + if (zero)
> + return -ENODATA;
> + return 0;
> +}
> +
> +static int btf_dump_int_data(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 type_id,
> + void *data,
> + __u8 bits_offset)
> +{
> + __u8 encoding = btf_int_encoding(t);
> + bool sign = encoding & BTF_INT_SIGNED;
> + __u8 nr_bits = btf_int_bits(t);
> +
> + if (bits_offset || btf_int_offset(t) ||
> + BITS_PER_BYTE_MASKED(nr_bits))
> + return btf_dump_int_bits(d, t, data, bits_offset);
> +
> + switch (nr_bits) {
> + case 128:
> + btf_dump_int128(d, t, data);
> + break;
> + case 64:
> + if (sign)
> + btf_dump_type_values(d, "%lld", *(long long *)data);
> + else
> + btf_dump_type_values(d, "%llu",
> + *(unsigned long long *)data);
> + break;
> + case 32:
> + if (sign)
> + btf_dump_type_values(d, "%d", *(__s32 *)data);
> + else
> + btf_dump_type_values(d, "%u", *(__u32 *)data);
> + break;
> + case 16:
> + if (sign)
> + btf_dump_type_values(d, "%d", *(__s16 *)data);
> + else
> + btf_dump_type_values(d, "%u", *(__u16 *)data);
> + break;
> + case 8:
> + if (d->data.state.array_ischar) {
> + /* check for null terminator */
> + if (d->data.state.array_terminated)
> + break;
> + if (*(char *)data == '\0') {
> + d->data.state.array_terminated = 1;
> + break;
> + }
> + if (isprint(*(char *)data)) {
> + btf_dump_type_values(d, "'%c'",
> + *(char *)data);
> + break;
> + }
> + }
> + if (sign)
> + btf_dump_type_values(d, "%d", *(__s8 *)data);
> + else
> + btf_dump_type_values(d, "%u", *(__u8 *)data);
> + break;
> + default:
> + return btf_dump_int_bits(d, t, data, bits_offset);
error out in such case?
> + }
> + return 0;
> +}
> +
> +static int btf_dump_var_data(struct btf_dump *d,
> + const struct btf_type *v,
> + __u32 id,
> + void *data)
> +{
> + enum btf_func_linkage linkage = btf_var(v)->linkage;
> + const struct btf_type *t;
> + const char *l = "";
> + __u32 type_id;
> +
> + switch (linkage) {
> + case BTF_FUNC_STATIC:
> + l = "static ";
> + break;
> + case BTF_FUNC_EXTERN:
> + l = "extern ";
> + break;
> + case BTF_FUNC_GLOBAL:
> + default:
> + break;
> + }
> +
> + /* format of output here is [linkage] [type] [varname] = (type)value,
> + * for example "static int cpu_profile_flip = (int)1"
> + */
> + btf_dump_printf(d, "%s", l);
> + type_id = v->type;
> + t = btf__type_by_id(d->btf, type_id);
> + btf_dump_emit_type_name(d, type_id, NULL, 0, false);
> + btf_dump_printf(d, " %s = ", btf_name_of(d, v->name_off));
> + return btf_dump_dump_type_data(d, NULL,
> + t, type_id, data, 0);
> +}
> +
> +static int btf_dump_array_data(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data)
> +{
> + const struct btf_array *array = btf_array(t);
> + const struct btf_type *elem_type;
> + __u32 i, elem_size = 0, elem_type_id;
> + int array_member;
> +
> + elem_type_id = array->type;
> + elem_type = skip_mods_and_typedefs(d->btf, elem_type_id, NULL);
> + if (!elem_type) {
can't really happen in well-formed BTF, I don't think libbpf ever
checks this for NULL
> + pr_warn("unexpected error skipping mods/typedefs for id [%u]\n",
> + elem_type_id);
> + return -EINVAL;
> + }
> + elem_size = btf__resolve_size(d->btf, elem_type_id);
this can actually fail and return -Exxx, so I'd check <= 0 case here,
otherwise it might get confusing later
> +
> + if (elem_type && btf_is_int(elem_type)) {
> + /*
> + * BTF_INT_CHAR encoding never seems to be set for
> + * char arrays, so if size is 1 and element is
> + * printable as a char, we'll do that.
> + */
> + if (elem_size == 1)
> + d->data.state.array_ischar = true;
> + }
> +
> + if (!elem_type)
> + return 0;
already checked above
> +
> + btf_dump_printf(d, "[%s",
> + btf_dump_data_newline(d));
nit: keep on single line, it's not that long
> + d->data.state.depth++;
> +
> + /* may be a multidimemsional array, so store current "is array member"
typo: multidimensional
> + * status so we can restore it correctly later.
> + */
> + array_member = d->data.state.array_member;
> + d->data.state.array_member = 1;
> + for (i = 0; i < array->nelems && !d->data.state.array_terminated; i++) {
> +
> + btf_dump_dump_type_data(d, NULL, elem_type, elem_type_id,
> + data, 0);
> + data += elem_size;
> + }
> + d->data.state.array_member = array_member;
> + d->data.state.depth--;
> + btf_dump_printf(d, "%s]%s%s",
> + btf_dump_data_pfx(d),
> + btf_dump_data_delim(d),
> + btf_dump_data_newline(d));
> +
> + return 0;
> +}
> +
> +static int btf_dump_struct_data(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data)
> +{
> + const struct btf_member *member;
> + __u32 i;
> + int err;
> +
> + btf_dump_printf(d, "{%s",
> + btf_dump_data_newline(d));
> + d->data.state.depth++;
> + for (i = 0, member = btf_members(t);
> + i < btf_vlen(t);
> + i++, member++) {
> + const struct btf_type *member_type;
> + __u32 bytes_offset, member_offset;
> + const char *member_name;
> + __u8 bits8_offset;
> +
> + member_type = btf__type_by_id(d->btf, member->type);
> + member_name = btf_name_of(d, member->name_off);
> + member_offset = btf_member_bit_offset(t, i);
> + bytes_offset = BITS_ROUNDDOWN_BYTES(member_offset);
> + bits8_offset = BITS_PER_BYTE_MASKED(member_offset);
> +
> + /* btf_int_bits() does not store member bitfield size;
> + * bitfield size needs to be stored here so int display
> + * of member can retrieve it.
> + */
> + d->data.state.bitfield_size =
> + btf_member_bitfield_size(t, i);
> + err = btf_dump_dump_type_data(d,
> + member_name,
> + member_type,
> + member->type,
> + data + bytes_offset,
> + bits8_offset);
> + d->data.state.bitfield_size = 0;
> + if (err)
> + return err;
> + }
> + d->data.state.depth--;
> + btf_dump_printf(d, "%s}%s%s",
> + btf_dump_data_pfx(d),
> + btf_dump_data_delim(d),
> + btf_dump_data_newline(d));
> + return err;
> +}
> +
> +static int btf_dump_ptr_data(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data)
> +{
> + btf_dump_type_values(d, "%p", *(void **)data);
> + return 0;
> +}
> +
> +static int btf_dump_get_enum_value(const struct btf_type *t,
> + void *data,
> + __u32 id,
> + __s64 *value)
> +{
> + switch (t->size) {
> + case 8:
> + *value = *(__s64 *)data;
> + return 0;
> + case 4:
> + *value = *(__s32 *)data;
> + return 0;
> + case 2:
> + *value = *(__s16 *)data;
> + return 0;
> + case 1:
> + *value = *(__s8 *)data;
> + default:
> + pr_warn("unexpected size %d for enum, id:[%u]\n",
> + t->size, id);
> + return -EINVAL;
> + }
> +}
> +
> +static int btf_dump_enum_data(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data)
> +{
> + const struct btf_enum *e;
> + __s64 value;
> + int i, err;
> +
> + err = btf_dump_get_enum_value(t, data, id, &value);
> + if (err)
> + return err;
> +
> + for (i = 0, e = btf_enum(t); i < btf_vlen(t); i++, e++) {
> + if (value != e->val)
> + continue;
> + btf_dump_type_values(d, "%s",
> + btf_name_of(d, e->name_off));
> + return 0;
> + }
> +
> + btf_dump_type_values(d, "%d", value);
> + return 0;
> +}
> +
> +static int btf_dump_datasec_data(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data)
> +{
> + const struct btf_var_secinfo *vsi;
> + const struct btf_type *var;
> + __u32 i;
> + int err;
> +
> + btf_dump_type_values(d, "SEC(\"%s\") ",
> + btf_name_of(d, t->name_off));
> + for (i = 0, vsi = btf_var_secinfos(t);
> + i < btf_vlen(t);
> + i++, vsi++) {
> + var = btf__type_by_id(d->btf, vsi->type);
> + err = btf_dump_dump_type_data(d, NULL, var,
> + vsi->type,
> + data + vsi->offset,
> + 0);
> + if (err)
> + return err;
> + btf_dump_printf(d, ";");
> + }
> + return 0;
> +}
> +
> +static int btf_dump_type_data_check_overflow(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data,
> + __u8 bits_offset)
> +{
> + __s64 size;
> +
> + /* Only do overflow checking for base types; we do not want to
> + * avoid showing part of a struct, union or array, even if we
> + * do not have enough data to show the full object. By
> + * restricting overflow checking to base types we can ensure
> + * that partial display succeeds, while avoiding overflowing
> + * and using bogus data for display.
> + */
> + t = skip_mods_and_typedefs(d->btf, id, NULL);
> + if (!t) {
> + pr_warn("unexpected error skipping mods/typedefs for id [%u]\n",
> + id);
> + return -EINVAL;
> + }
> +
> + switch (BTF_INFO_KIND(t->info)) {
> + case BTF_KIND_INT:
> + case BTF_KIND_PTR:
> + case BTF_KIND_ENUM:
> + size = btf__resolve_size(d->btf, id);
> + if (size < 0) {
> + pr_warn("unexpected size [%llu] for id [%u]\n",
> + size, id);
> + return -EINVAL;
> + }
> + if (data + (bits_offset >> 3) + size > d->data.data_end)
bits_offset / 8...
and considering you have a whole dedicated BITS_PER_BYTE (btw, why?..
are we expecting it to ever change?), it's surprising to see bit
shifts instead of division
> + return -E2BIG;
> + return 0;
> + default:
> + return 0;
> + }
> +}
> +
> +static int btf_dump_type_data_check_zero(struct btf_dump *d,
> + const struct btf_type *t,
> + __u32 id,
> + void *data,
> + __u8 bits_offset)
> +{
> + __s64 value;
> + int i, err;
> +
> + /* toplevel exceptions; we show zero values if
> + * - we ask for them (emit_zeros)
> + * - if we are at top-level so we see "struct empty { }"
> + * - or if we are an array member and the array is non-empty and
> + * not a char array; we don't want to be in a situation where we
> + * have an integer array 0, 1, 0, 1 and only show non-zero values.
> + * If the array contains zeroes only, or is a char array starting
> + * with a '\0', the array-level check_zero() will prevent showing it;
> + * we are concerned with determining zero value at the array member
> + * level here.
> + */
> + if (d->data.emit_zeroes || d->data.state.depth == 0 ||
> + (d->data.state.array_member && !d->data.state.array_ischar))
> + return 0;
> +
> + t = skip_mods_and_typedefs(d->btf, id, NULL);
> + if (!t) {
don't check, if anything btf_dump_type_data_check_overflow() already
validated that it's ok
> + pr_warn("unexpected error skipping mods/typedefs for id [%u]\n",
> + id);
> + return -EINVAL;
> + }
> +
> +
> + switch (BTF_INFO_KIND(t->info)) {
> + case BTF_KIND_INT:
> + if (d->data.state.bitfield_size)
> + return btf_dump_int_bits_check_zero(d, t, data,
> + bits_offset);
> + return btf_dump_int_check_zero(d, t, data, bits_offset);
> + case BTF_KIND_PTR:
> + if (*((void **)data) == NULL)
> + return -ENODATA;
> + return 0;
> + case BTF_KIND_ARRAY: {
> + const struct btf_array *array = btf_array(t);
> + const struct btf_type *elem_type;
> + __u32 elem_type_id, elem_size;
> + bool ischar;
> +
> + elem_type_id = array->type;
> + elem_size = btf__resolve_size(d->btf, elem_type_id);
> + elem_type = btf__type_by_id(d->btf, elem_type_id);
> +
> + ischar = btf_is_int(elem_type) && elem_size == 1;
> +
> + /* check all elements; if _any_ element is nonzero, all
> + * of array is displayed. We make an exception however
> + * for char arrays where the first element is 0; these
> + * are considered zeroed also, even if later elements are
> + * non-zero because the string is terminated.
> + */
> + for (i = 0; i < array->nelems; i++) {
> + if (i == 0 && ischar && *(char *)data == 0)
> + return -ENODATA;
> + err = btf_dump_type_data_check_zero(d, elem_type,
> + elem_type_id,
> + data +
> + (i * elem_size),
> + bits_offset);
> + if (err != -ENODATA)
> + return err;
> + }
> + return -ENODATA;
> + }
> + case BTF_KIND_STRUCT:
> + case BTF_KIND_UNION: {
> + const struct btf_member *member;
> +
> + /* if any struct/union member is non-zero, the struct/union
> + * is considered non-zero and dumped.
> + */
> + for (i = 0, member = btf_members(t);
> + i < btf_vlen(t);
> + i++, member++) {
in a lot of other places in libbpf we use more succinct names and this pattern
n = btf_vlen(t);
m = btf_members(t);
for (i = 0; i < n; i++, m++) {
it's nice, short, and familiar in libbpf code base
> + const struct btf_type *member_type;
> + __u32 bytes_offset, member_offset;
> + __u8 bits8_offset;
> +
> + member_type = btf__type_by_id(d->btf, member->type);
> + member_offset = btf_member_bit_offset(t, i);
> + bytes_offset = BITS_ROUNDDOWN_BYTES(member_offset);
> + bits8_offset = BITS_PER_BYTE_MASKED(member_offset);
> +
> + /* btf_int_bits() does not store member bitfield size;
> + * bitfield size needs to be stored here so int display
> + * of member can retrieve it.
> + */
> + d->data.state.bitfield_size =
> + btf_member_bitfield_size(t, i);
> +
> + err = btf_dump_type_data_check_zero(d, member_type,
> + member->type,
> + data + bytes_offset,
> + bits8_offset);
> + d->data.state.bitfield_size = 0;
> + if (err != ENODATA)
> + return err;
> + }
> + return -ENODATA;
> + }
> + case BTF_KIND_ENUM:
> + if (btf_dump_get_enum_value(t, data, id, &value))
> + return 0;
> + if (value == 0)
> + return -ENODATA;
> + return 0;
> + default:
> + return 0;
> + }
> +}
> +
> +static int btf_dump_dump_type_data(struct btf_dump *d,
> + const char *fname,
> + const struct btf_type *t,
> + __u32 id,
> + void *data,
> + __u8 bits_offset)
> +{
> + int err;
> +
> + err = btf_dump_type_data_check_overflow(d, t, id, data, bits_offset);
> + if (err)
> + return err;
> + err = btf_dump_type_data_check_zero(d, t, id, data, bits_offset);
> + if (err) {
> + /* zeroed data is expected and not an error, so simply skip
> + * dumping such data. Record other errors however.
> + */
> + if (err == -ENODATA)
> + return 0;
> + return err;
> + }
> + btf_dump_printf(d, "%s", btf_dump_data_pfx(d));
> + if (!d->data.skip_names)
> + btf_dump_emit_type_name(d, id, fname, 0, true);
> +
> + t = skip_mods_and_typedefs(d->btf, id, NULL);
> + if (!t) {
> + pr_warn("unexpected error skipping mods/typedefs for id [%u]\n",
> + id);
> + return -EINVAL;
> + }
> +
> + switch (BTF_INFO_KIND(t->info)) {
> + case BTF_KIND_UNKN:
> + case BTF_KIND_FWD:
> + case BTF_KIND_FUNC:
> + case BTF_KIND_FUNC_PROTO:
> + return btf_dump_df_data(d, t, id, data);
> + case BTF_KIND_INT:
> + if (d->data.state.bitfield_size)
btw, enum can be part of bitfields as well
> + return btf_dump_bitfield_data(d, t, data,
> + bits_offset,
> + d->data.state.bitfield_size);
> + return btf_dump_int_data(d, t, id, data, bits_offset);
> + case BTF_KIND_PTR:
> + return btf_dump_ptr_data(d, t, id, data);
> + case BTF_KIND_ARRAY:
> + return btf_dump_array_data(d, t, id, data);
> + case BTF_KIND_STRUCT:
> + case BTF_KIND_UNION:
> + return btf_dump_struct_data(d, t, id, data);
> + case BTF_KIND_ENUM:
> + return btf_dump_enum_data(d, t, id, data);
> + case BTF_KIND_VAR:
> + return btf_dump_var_data(d, t, id, data);
> + case BTF_KIND_DATASEC:
> + return btf_dump_datasec_data(d, t, id, data);
> + default:
since last time we also added BTF_KIND_FLOAT
> + pr_warn("unexpected kind [%u] for id [%u]\n",
> + BTF_INFO_KIND(t->info), id);
> + return -EINVAL;
> + }
> +}
> +
> +int btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
> + void *data, size_t byte_sz,
> + const struct btf_dump_type_data_opts *opts)
> +{
> + const struct btf_type *t;
> + int err;
> +
> + if (!OPTS_VALID(opts, btf_dump_type_data_opts))
> + return -EINVAL;
> +
> + t = btf__type_by_id(d->btf, id);
> + if (!t)
> + return -ENOENT;
public APIs should use libbpf_err() to ensure errno is set properly,
see my recent patch set. This should be
return libbpf_err(-ENOENT);
> +
> + d->data.data_end = data + byte_sz;
> + d->data.indent_lvl = OPTS_GET(opts, indent_level, 0);
> + d->data.compact = OPTS_GET(opts, compact, false);
> + d->data.skip_names = OPTS_GET(opts, skip_names, false);
> + d->data.emit_zeroes = OPTS_GET(opts, emit_zeroes, false);
> + memset(&d->data.state, 0, sizeof(d->data.state));
> +
> + err = btf_dump_dump_type_data(d, NULL, t, id, data, 0);
> +
> + /* We reported all the data; return size of data we reported. */
> + if (err == 0)
> + err = btf__resolve_size(d->btf, id);
hm.. why can't btf_dump_dump_type_data() return the consumed amount of bytes?
> +
> + memset(&d->data, 0, sizeof(d->data));
> +
> + return err;
> +}
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 0229e01..76cfac6 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -370,3 +370,8 @@ LIBBPF_0.4.0 {
> bpf_tc_hook_destroy;
> bpf_tc_query;
> } LIBBPF_0.3.0;
> +
> +LIBBPF_0.5.0 {
> + global:
> + btf_dump__dump_type_data;
> +} LIBBPF_0.4.0;
> --
> 1.8.3.1
>