libbpf: BTF dumper support for typed data
authorAlan Maguire <alan.maguire@oracle.com>
Thu, 15 Jul 2021 15:15:24 +0000 (16:15 +0100)
committerAndrii Nakryiko <andrii@kernel.org>
Fri, 16 Jul 2021 20:46:59 +0000 (13:46 -0700)
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 data_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 user-specified indent string which will be printed once per
   indent level; if NULL, tab is chosen but any string <= 32 chars
   can be provided.
 - 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,
},
},
...

If the data structure is larger than the *data_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.  On success, the amount of data
dumped is returned.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1626362126-27775-2-git-send-email-alan.maguire@oracle.com
tools/lib/bpf/btf.h
tools/lib/bpf/btf_dump.c
tools/lib/bpf/libbpf.map

index b54f1c3..374e9f1 100644 (file)
@@ -184,6 +184,25 @@ LIBBPF_API int
 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;
+       const char *indent_str;
+       int indent_level;
+       /* below match "show" flags for bpf_show_snprintf() */
+       bool compact;           /* no newlines/indentation */
+       bool skip_names;        /* skip member/type names */
+       bool emit_zeroes;       /* show 0-valued fields */
+       size_t :0;
+};
+#define btf_dump_type_data_opts__last_field emit_zeroes
+
+LIBBPF_API int
+btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
+                        const void *data, size_t data_sz,
+                        const struct btf_dump_type_data_opts *opts);
+
 /*
  * A set of helpers for easier BTF types handling
  */
index 5dc6b51..929cf93 100644 (file)
@@ -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>
@@ -53,6 +55,26 @@ struct btf_dump_type_aux_state {
        __u8 referenced: 1;
 };
 
+/* indent string length; one indent string is added for each indent level */
+#define BTF_DATA_INDENT_STR_LEN                        32
+
+/*
+ * Common internal data for BTF type data dump operations.
+ */
+struct btf_dump_data {
+       const void *data_end;           /* end of valid data to show */
+       bool compact;
+       bool skip_names;
+       bool emit_zeroes;
+       __u8 indent_lvl;        /* base indent level */
+       char indent_str[BTF_DATA_INDENT_STR_LEN];
+       /* below are used during iteration */
+       int depth;
+       bool is_array_member;
+       bool is_array_terminated;
+       bool is_array_char;
+};
+
 struct btf_dump {
        const struct btf *btf;
        const struct btf_ext *btf_ext;
@@ -60,6 +82,7 @@ struct btf_dump {
        struct btf_dump_opts opts;
        int ptr_sz;
        bool strip_mods;
+       bool skip_anon_defs;
        int last_id;
 
        /* per-type auxiliary state */
@@ -89,6 +112,10 @@ struct btf_dump {
         * name occurrences
         */
        struct hashmap *ident_names;
+       /*
+        * data for typed display; allocated if needed.
+        */
+       struct btf_dump_data *typed_dump;
 };
 
 static size_t str_hash_fn(const void *key, void *ctx)
@@ -765,11 +792,11 @@ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
                break;
        case BTF_KIND_FUNC_PROTO: {
                const struct btf_param *p = btf_params(t);
-               __u16 vlen = btf_vlen(t);
+               __u16 n = btf_vlen(t);
                int i;
 
                btf_dump_emit_type(d, t->type, cont_id);
-               for (i = 0; i < vlen; i++, p++)
+               for (i = 0; i < n; i++, p++)
                        btf_dump_emit_type(d, p->type, cont_id);
 
                break;
@@ -852,8 +879,9 @@ static void btf_dump_emit_bit_padding(const struct btf_dump *d,
 static void btf_dump_emit_struct_fwd(struct btf_dump *d, __u32 id,
                                     const struct btf_type *t)
 {
-       btf_dump_printf(d, "%s %s",
+       btf_dump_printf(d, "%s%s%s",
                        btf_is_struct(t) ? "struct" : "union",
+                       t->name_off ? " " : "",
                        btf_dump_type_name(d, id));
 }
 
@@ -1259,7 +1287,7 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
                case BTF_KIND_UNION:
                        btf_dump_emit_mods(d, decls);
                        /* inline anonymous struct/union */
-                       if (t->name_off == 0)
+                       if (t->name_off == 0 && !d->skip_anon_defs)
                                btf_dump_emit_struct_def(d, id, t, lvl);
                        else
                                btf_dump_emit_struct_fwd(d, id, t);
@@ -1267,7 +1295,7 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
                case BTF_KIND_ENUM:
                        btf_dump_emit_mods(d, decls);
                        /* inline anonymous enum */
-                       if (t->name_off == 0)
+                       if (t->name_off == 0 && !d->skip_anon_defs)
                                btf_dump_emit_enum_def(d, id, t, lvl);
                        else
                                btf_dump_emit_enum_fwd(d, id, t);
@@ -1392,6 +1420,39 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
        btf_dump_emit_name(d, fname, last_was_ptr);
 }
 
+/* show type name as (type_name) */
+static void btf_dump_emit_type_cast(struct btf_dump *d, __u32 id,
+                                   bool top_level)
+{
+       const struct btf_type *t;
+
+       /* for array members, we don't bother emitting type name for each
+        * member to avoid the redundancy of
+        * .name = (char[4])[(char)'f',(char)'o',(char)'o',]
+        */
+       if (d->typed_dump->is_array_member)
+               return;
+
+       /* avoid type name specification for variable/section; it will be done
+        * for the associated variable value(s).
+        */
+       t = btf__type_by_id(d->btf, id);
+       if (btf_is_var(t) || btf_is_datasec(t))
+               return;
+
+       if (top_level)
+               btf_dump_printf(d, "(");
+
+       d->skip_anon_defs = true;
+       d->strip_mods = true;
+       btf_dump_emit_type_decl(d, id, "", 0);
+       d->strip_mods = false;
+       d->skip_anon_defs = false;
+
+       if (top_level)
+               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 +1503,751 @@ 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,
+                                  const void *data,
+                                  __u8 bits_offset,
+                                  __u8 bit_sz);
+
+static const char *btf_dump_data_newline(struct btf_dump *d)
+{
+       return d->typed_dump->compact || d->typed_dump->depth == 0 ? "" : "\n";
+}
+
+static const char *btf_dump_data_delim(struct btf_dump *d)
+{
+       return d->typed_dump->depth == 0 ? "" : ",";
+}
+
+static void btf_dump_data_pfx(struct btf_dump *d)
+{
+       int i, lvl = d->typed_dump->indent_lvl + d->typed_dump->depth;
+
+       if (d->typed_dump->compact)
+               return;
+
+       for (i = 0; i < lvl; i++)
+               btf_dump_printf(d, "%s", d->typed_dump->indent_str);
+}
+
+/* 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_unsupported_data(struct btf_dump *d,
+                                    const struct btf_type *t,
+                                    __u32 id)
+{
+       btf_dump_printf(d, "<unsupported kind:%u>", btf_kind(t));
+       return -ENOTSUP;
+}
+
+static void btf_dump_int128(struct btf_dump *d,
+                           const struct btf_type *t,
+                           const void *data)
+{
+       __int128 num = *(__int128 *)data;
+
+       if ((num >> 64) == 0)
+               btf_dump_type_values(d, "0x%llx", (long long)num);
+       else
+               btf_dump_type_values(d, "0x%llx%016llx", (long long)num >> 32,
+                                    (long long)num);
+}
+
+static unsigned __int128 btf_dump_bitfield_get_data(struct btf_dump *d,
+                                                   const struct btf_type *t,
+                                                   const void *data,
+                                                   __u8 bits_offset,
+                                                   __u8 bit_sz)
+{
+       __u16 left_shift_bits, right_shift_bits;
+       __u8 nr_copy_bits, nr_copy_bytes;
+       unsigned __int128 num = 0, ret;
+       const __u8 *bytes = data;
+       int i;
+
+       /* Bitfield value retrieval is done in two steps; first relevant bytes are
+        * stored in num, then we left/right shift num to eliminate irrelevant bits.
+        */
+       nr_copy_bits = bit_sz + bits_offset;
+       nr_copy_bytes = t->size;
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+       for (i = nr_copy_bytes - 1; i >= 0; i--)
+               num = num * 256 + bytes[i];
+#elif __BYTE_ORDER == __BIG_ENDIAN
+       for (i = 0; i < nr_copy_bytes; i++)
+               num = num * 256 + bytes[i];
+#else
+# error "Unrecognized __BYTE_ORDER__"
+#endif
+       left_shift_bits = 128 - nr_copy_bits;
+       right_shift_bits = 128 - bit_sz;
+
+       ret = (num << left_shift_bits) >> right_shift_bits;
+
+       return ret;
+}
+
+static int btf_dump_bitfield_check_zero(struct btf_dump *d,
+                                       const struct btf_type *t,
+                                       const void *data,
+                                       __u8 bits_offset,
+                                       __u8 bit_sz)
+{
+       __int128 check_num;
+
+       check_num = btf_dump_bitfield_get_data(d, t, data, bits_offset, bit_sz);
+       if (check_num == 0)
+               return -ENODATA;
+       return 0;
+}
+
+static int btf_dump_bitfield_data(struct btf_dump *d,
+                                 const struct btf_type *t,
+                                 const void *data,
+                                 __u8 bits_offset,
+                                 __u8 bit_sz)
+{
+       unsigned __int128 print_num;
+
+       print_num = btf_dump_bitfield_get_data(d, t, data, bits_offset, bit_sz);
+       btf_dump_int128(d, t, &print_num);
+
+       return 0;
+}
+
+/* ints, floats and ptrs */
+static int btf_dump_base_type_check_zero(struct btf_dump *d,
+                                        const struct btf_type *t,
+                                        __u32 id,
+                                        const void *data)
+{
+       static __u8 bytecmp[16] = {};
+       int nr_bytes;
+
+       /* For pointer types, pointer size is not defined on a per-type basis.
+        * On dump creation however, we store the pointer size.
+        */
+       if (btf_kind(t) == BTF_KIND_PTR)
+               nr_bytes = d->ptr_sz;
+       else
+               nr_bytes = t->size;
+
+       if (nr_bytes < 1 || nr_bytes > 16) {
+               pr_warn("unexpected size %d for id [%u]\n", nr_bytes, id);
+               return -EINVAL;
+       }
+
+       if (memcmp(data, bytecmp, nr_bytes) == 0)
+               return -ENODATA;
+       return 0;
+}
+
+static int btf_dump_int_data(struct btf_dump *d,
+                            const struct btf_type *t,
+                            __u32 type_id,
+                            const void *data,
+                            __u8 bits_offset)
+{
+       __u8 encoding = btf_int_encoding(t);
+       bool sign = encoding & BTF_INT_SIGNED;
+       int sz = t->size;
+
+       if (sz == 0) {
+               pr_warn("unexpected size %d for id [%u]\n", sz, type_id);
+               return -EINVAL;
+       }
+
+       /* handle packed int data - accesses of integers not aligned on
+        * int boundaries can cause problems on some platforms.
+        */
+       if (((uintptr_t)data) % sz)
+               return btf_dump_bitfield_data(d, t, data, 0, 0);
+
+       switch (sz) {
+       case 16:
+               btf_dump_int128(d, t, data);
+               break;
+       case 8:
+               if (sign)
+                       btf_dump_type_values(d, "%lld", *(long long *)data);
+               else
+                       btf_dump_type_values(d, "%llu", *(unsigned long long *)data);
+               break;
+       case 4:
+               if (sign)
+                       btf_dump_type_values(d, "%d", *(__s32 *)data);
+               else
+                       btf_dump_type_values(d, "%u", *(__u32 *)data);
+               break;
+       case 2:
+               if (sign)
+                       btf_dump_type_values(d, "%d", *(__s16 *)data);
+               else
+                       btf_dump_type_values(d, "%u", *(__u16 *)data);
+               break;
+       case 1:
+               if (d->typed_dump->is_array_char) {
+                       /* check for null terminator */
+                       if (d->typed_dump->is_array_terminated)
+                               break;
+                       if (*(char *)data == '\0') {
+                               d->typed_dump->is_array_terminated = true;
+                               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:
+               pr_warn("unexpected sz %d for id [%u]\n", sz, type_id);
+               return -EINVAL;
+       }
+       return 0;
+}
+
+union float_data {
+       long double ld;
+       double d;
+       float f;
+};
+
+static int btf_dump_float_data(struct btf_dump *d,
+                              const struct btf_type *t,
+                              __u32 type_id,
+                              const void *data)
+{
+       const union float_data *flp = data;
+       union float_data fl;
+       int sz = t->size;
+
+       /* handle unaligned data; copy to local union */
+       if (((uintptr_t)data) % sz) {
+               memcpy(&fl, data, sz);
+               flp = &fl;
+       }
+
+       switch (sz) {
+       case 16:
+               btf_dump_type_values(d, "%Lf", flp->ld);
+               break;
+       case 8:
+               btf_dump_type_values(d, "%lf", flp->d);
+               break;
+       case 4:
+               btf_dump_type_values(d, "%f", flp->f);
+               break;
+       default:
+               pr_warn("unexpected size %d for id [%u]\n", sz, type_id);
+               return -EINVAL;
+       }
+       return 0;
+}
+
+static int btf_dump_var_data(struct btf_dump *d,
+                            const struct btf_type *v,
+                            __u32 id,
+                            const 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:
+               l = "";
+               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_cast(d, type_id, 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, 0);
+}
+
+static int btf_dump_array_data(struct btf_dump *d,
+                              const struct btf_type *t,
+                              __u32 id,
+                              const void *data)
+{
+       const struct btf_array *array = btf_array(t);
+       const struct btf_type *elem_type;
+       __u32 i, elem_size = 0, elem_type_id;
+       bool is_array_member;
+
+       elem_type_id = array->type;
+       elem_type = skip_mods_and_typedefs(d->btf, elem_type_id, NULL);
+       elem_size = btf__resolve_size(d->btf, elem_type_id);
+       if (elem_size <= 0) {
+               pr_warn("unexpected elem size %d for array type [%u]\n", elem_size, id);
+               return -EINVAL;
+       }
+
+       if (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->typed_dump->is_array_char = true;
+       }
+
+       /* note that we increment depth before calling btf_dump_print() below;
+        * this is intentional.  btf_dump_data_newline() will not print a
+        * newline for depth 0 (since this leaves us with trailing newlines
+        * at the end of typed display), so depth is incremented first.
+        * For similar reasons, we decrement depth before showing the closing
+        * parenthesis.
+        */
+       d->typed_dump->depth++;
+       btf_dump_printf(d, "[%s", btf_dump_data_newline(d));
+
+       /* may be a multidimensional array, so store current "is array member"
+        * status so we can restore it correctly later.
+        */
+       is_array_member = d->typed_dump->is_array_member;
+       d->typed_dump->is_array_member = true;
+       for (i = 0; i < array->nelems; i++, data += elem_size) {
+               if (d->typed_dump->is_array_terminated)
+                       break;
+               btf_dump_dump_type_data(d, NULL, elem_type, elem_type_id, data, 0, 0);
+       }
+       d->typed_dump->is_array_member = is_array_member;
+       d->typed_dump->depth--;
+       btf_dump_data_pfx(d);
+       btf_dump_type_values(d, "]");
+
+       return 0;
+}
+
+static int btf_dump_struct_data(struct btf_dump *d,
+                               const struct btf_type *t,
+                               __u32 id,
+                               const void *data)
+{
+       const struct btf_member *m = btf_members(t);
+       __u16 n = btf_vlen(t);
+       int i, err;
+
+       /* note that we increment depth before calling btf_dump_print() below;
+        * this is intentional.  btf_dump_data_newline() will not print a
+        * newline for depth 0 (since this leaves us with trailing newlines
+        * at the end of typed display), so depth is incremented first.
+        * For similar reasons, we decrement depth before showing the closing
+        * parenthesis.
+        */
+       d->typed_dump->depth++;
+       btf_dump_printf(d, "{%s", btf_dump_data_newline(d));
+
+       for (i = 0; i < n; i++, m++) {
+               const struct btf_type *mtype;
+               const char *mname;
+               __u32 moffset;
+               __u8 bit_sz;
+
+               mtype = btf__type_by_id(d->btf, m->type);
+               mname = btf_name_of(d, m->name_off);
+               moffset = btf_member_bit_offset(t, i);
+
+               bit_sz = btf_member_bitfield_size(t, i);
+               err = btf_dump_dump_type_data(d, mname, mtype, m->type, data + moffset / 8,
+                                             moffset % 8, bit_sz);
+               if (err < 0)
+                       return err;
+       }
+       d->typed_dump->depth--;
+       btf_dump_data_pfx(d);
+       btf_dump_type_values(d, "}");
+       return err;
+}
+
+static int btf_dump_ptr_data(struct btf_dump *d,
+                             const struct btf_type *t,
+                             __u32 id,
+                             const void *data)
+{
+       btf_dump_type_values(d, "%p", *(void **)data);
+       return 0;
+}
+
+static int btf_dump_get_enum_value(struct btf_dump *d,
+                                  const struct btf_type *t,
+                                  const void *data,
+                                  __u32 id,
+                                  __s64 *value)
+{
+       int sz = t->size;
+
+       /* handle unaligned enum value */
+       if (((uintptr_t)data) % sz) {
+               *value = (__s64)btf_dump_bitfield_get_data(d, t, data, 0, 0);
+               return 0;
+       }
+       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;
+               return 0;
+       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,
+                             const void *data)
+{
+       const struct btf_enum *e;
+       __s64 value;
+       int i, err;
+
+       err = btf_dump_get_enum_value(d, 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,
+                                const 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, 0);
+               if (err < 0)
+                       return err;
+               btf_dump_printf(d, ";");
+       }
+       return 0;
+}
+
+/* return size of type, or if base type overflows, return -E2BIG. */
+static int btf_dump_type_data_check_overflow(struct btf_dump *d,
+                                            const struct btf_type *t,
+                                            __u32 id,
+                                            const void *data,
+                                            __u8 bits_offset)
+{
+       __s64 size = btf__resolve_size(d->btf, id);
+
+       if (size < 0 || size >= INT_MAX) {
+               pr_warn("unexpected size [%lld] for id [%u]\n",
+                       size, id);
+               return -EINVAL;
+       }
+
+       /* 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_kind(t)) {
+       case BTF_KIND_INT:
+       case BTF_KIND_FLOAT:
+       case BTF_KIND_PTR:
+       case BTF_KIND_ENUM:
+               if (data + bits_offset / 8 + size > d->typed_dump->data_end)
+                       return -E2BIG;
+               break;
+       default:
+               break;
+       }
+       return (int)size;
+}
+
+static int btf_dump_type_data_check_zero(struct btf_dump *d,
+                                        const struct btf_type *t,
+                                        __u32 id,
+                                        const void *data,
+                                        __u8 bits_offset,
+                                        __u8 bit_sz)
+{
+       __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->typed_dump->emit_zeroes || d->typed_dump->depth == 0 ||
+           (d->typed_dump->is_array_member &&
+            !d->typed_dump->is_array_char))
+               return 0;
+
+       t = skip_mods_and_typedefs(d->btf, id, NULL);
+
+       switch (btf_kind(t)) {
+       case BTF_KIND_INT:
+               if (bit_sz)
+                       return btf_dump_bitfield_check_zero(d, t, data, bits_offset, bit_sz);
+               return btf_dump_base_type_check_zero(d, t, id, data);
+       case BTF_KIND_FLOAT:
+       case BTF_KIND_PTR:
+               return btf_dump_base_type_check_zero(d, t, id, data);
+       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 = skip_mods_and_typedefs(d->btf, elem_type_id, NULL);
+
+               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, 0);
+                       if (err != -ENODATA)
+                               return err;
+               }
+               return -ENODATA;
+       }
+       case BTF_KIND_STRUCT:
+       case BTF_KIND_UNION: {
+               const struct btf_member *m = btf_members(t);
+               __u16 n = btf_vlen(t);
+
+               /* if any struct/union member is non-zero, the struct/union
+                * is considered non-zero and dumped.
+                */
+               for (i = 0; i < n; i++, m++) {
+                       const struct btf_type *mtype;
+                       __u32 moffset;
+
+                       mtype = btf__type_by_id(d->btf, m->type);
+                       moffset = btf_member_bit_offset(t, i);
+
+                       /* btf_int_bits() does not store member bitfield size;
+                        * bitfield size needs to be stored here so int display
+                        * of member can retrieve it.
+                        */
+                       bit_sz = btf_member_bitfield_size(t, i);
+                       err = btf_dump_type_data_check_zero(d, mtype, m->type, data + moffset / 8,
+                                                           moffset % 8, bit_sz);
+                       if (err != ENODATA)
+                               return err;
+               }
+               return -ENODATA;
+       }
+       case BTF_KIND_ENUM:
+               if (btf_dump_get_enum_value(d, t, data, id, &value))
+                       return 0;
+               if (value == 0)
+                       return -ENODATA;
+               return 0;
+       default:
+               return 0;
+       }
+}
+
+/* returns size of data dumped, or error. */
+static int btf_dump_dump_type_data(struct btf_dump *d,
+                                  const char *fname,
+                                  const struct btf_type *t,
+                                  __u32 id,
+                                  const void *data,
+                                  __u8 bits_offset,
+                                  __u8 bit_sz)
+{
+       int size, err;
+
+       size = btf_dump_type_data_check_overflow(d, t, id, data, bits_offset);
+       if (size < 0)
+               return size;
+       err = btf_dump_type_data_check_zero(d, t, id, data, bits_offset, bit_sz);
+       if (err) {
+               /* zeroed data is expected and not an error, so simply skip
+                * dumping such data.  Record other errors however.
+                */
+               if (err == -ENODATA)
+                       return size;
+               return err;
+       }
+       btf_dump_data_pfx(d);
+
+       if (!d->typed_dump->skip_names) {
+               if (fname && strlen(fname) > 0)
+                       btf_dump_printf(d, ".%s = ", fname);
+               btf_dump_emit_type_cast(d, id, true);
+       }
+
+       t = skip_mods_and_typedefs(d->btf, id, NULL);
+
+       switch (btf_kind(t)) {
+       case BTF_KIND_UNKN:
+       case BTF_KIND_FWD:
+       case BTF_KIND_FUNC:
+       case BTF_KIND_FUNC_PROTO:
+               err = btf_dump_unsupported_data(d, t, id);
+               break;
+       case BTF_KIND_INT:
+               if (bit_sz)
+                       err = btf_dump_bitfield_data(d, t, data, bits_offset, bit_sz);
+               else
+                       err = btf_dump_int_data(d, t, id, data, bits_offset);
+               break;
+       case BTF_KIND_FLOAT:
+               err = btf_dump_float_data(d, t, id, data);
+               break;
+       case BTF_KIND_PTR:
+               err = btf_dump_ptr_data(d, t, id, data);
+               break;
+       case BTF_KIND_ARRAY:
+               err = btf_dump_array_data(d, t, id, data);
+               break;
+       case BTF_KIND_STRUCT:
+       case BTF_KIND_UNION:
+               err = btf_dump_struct_data(d, t, id, data);
+               break;
+       case BTF_KIND_ENUM:
+               /* handle bitfield and int enum values */
+               if (bit_sz) {
+                       unsigned __int128 print_num;
+                       __s64 enum_val;
+
+                       print_num = btf_dump_bitfield_get_data(d, t, data, bits_offset, bit_sz);
+                       enum_val = (__s64)print_num;
+                       err = btf_dump_enum_data(d, t, id, &enum_val);
+               } else
+                       err = btf_dump_enum_data(d, t, id, data);
+               break;
+       case BTF_KIND_VAR:
+               err = btf_dump_var_data(d, t, id, data);
+               break;
+       case BTF_KIND_DATASEC:
+               err = btf_dump_datasec_data(d, t, id, data);
+               break;
+       default:
+               pr_warn("unexpected kind [%u] for id [%u]\n",
+                       BTF_INFO_KIND(t->info), id);
+               return -EINVAL;
+       }
+       if (err < 0)
+               return err;
+       return size;
+}
+
+int btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
+                            const void *data, size_t data_sz,
+                            const struct btf_dump_type_data_opts *opts)
+{
+       const struct btf_type *t;
+       int ret;
+
+       if (!OPTS_VALID(opts, btf_dump_type_data_opts))
+               return libbpf_err(-EINVAL);
+
+       t = btf__type_by_id(d->btf, id);
+       if (!t)
+               return libbpf_err(-ENOENT);
+
+       d->typed_dump = calloc(1, sizeof(struct btf_dump_data));
+       if (!d->typed_dump)
+               return libbpf_err(-ENOMEM);
+
+       d->typed_dump->data_end = data + data_sz;
+       d->typed_dump->indent_lvl = OPTS_GET(opts, indent_level, 0);
+       /* default indent string is a tab */
+       if (!opts->indent_str)
+               d->typed_dump->indent_str[0] = '\t';
+       else
+               strncat(d->typed_dump->indent_str, opts->indent_str,
+                       sizeof(d->typed_dump->indent_str) - 1);
+
+       d->typed_dump->compact = OPTS_GET(opts, compact, false);
+       d->typed_dump->skip_names = OPTS_GET(opts, skip_names, false);
+       d->typed_dump->emit_zeroes = OPTS_GET(opts, emit_zeroes, false);
+
+       ret = btf_dump_dump_type_data(d, NULL, t, id, data, 0, 0);
+
+       free(d->typed_dump);
+
+       return libbpf_err(ret);
+}
index 944c99d..5bfc107 100644 (file)
@@ -373,5 +373,6 @@ LIBBPF_0.5.0 {
                bpf_map__initial_value;
                bpf_map_lookup_and_delete_elem_flags;
                bpf_object__gen_loader;
+               btf_dump__dump_type_data;
                libbpf_set_strict_mode;
 } LIBBPF_0.4.0;