Merge branch 'btf-dump'

Andrii Nakryiko says:

====================
This patch set adds a new `bpftool btf dump` sub-command, which allows to dump
BTF contents (only types for now). Currently it only outputs low-level
content, almost 1:1 with binary BTF format, but follow up patches will add
ability to dump BTF types as a compilable C header file. JSON output is
supported as well.

Patch #1 adds `btf` sub-command, dumping BTF types in human-readable format.
It also implements reading .BTF data from ELF file.
Patch #2 adds minimal documentation with output format examples and different
ways to specify source of BTF data.
Patch #3 adds support for btf command in bash-completion/bpftool script.
Patch #4 fixes minor indentation issue in bash-completion script.

Output format is mostly following existing format of BPF verifier log, but
deviates from it in few places. More details are in commit message for patch 1.

Example of output for all supported BTF kinds are in patch #2 as part of
documentation. Some field names are quite verbose and I'd rather shorten them,
if we don't feel like being very close to BPF verifier names is a necessity,
but in this patch I left them exactly the same as in verifier log.

v3->v4:
  - reverse Christmas tree (Quentin)
  - better docs (Quentin)

v2->v3:
  - make map's key|value|kv|all suggestion more precise (Quentin)
  - fix default case indentations (Quentin)

v1->v2:
  - fix unnecessary trailing whitespaces in bpftool-btf.rst (Yonghong)
  - add btf in main.c for a list of possible OBJECTs
  - handle unknown keyword under `bpftool btf dump` (Yonghong)
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/Documentation/bpftool-btf.rst

+================
+bpftool-btf
+================
+-------------------------------------------------------------------------------
+tool for inspection of BTF data
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+	**bpftool** [*OPTIONS*] **btf** *COMMAND*
+
+	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] }
+
+	*COMMANDS* := { **dump** | **help** }
+
+BTF COMMANDS
+=============
+
+|	**bpftool** **btf dump** *BTF_SRC*
+|	**bpftool** **btf help**
+|
+|	*BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
+|	*MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
+|	*PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* }
+
+DESCRIPTION
+===========
+	**bpftool btf dump** *BTF_SRC*
+		  Dump BTF entries from a given *BTF_SRC*.
+
+                  When **id** is specified, BTF object with that ID will be
+                  loaded and all its BTF types emitted.
+
+                  When **map** is provided, it's expected that map has
+                  associated BTF object with BTF types describing key and
+                  value. It's possible to select whether to dump only BTF
+                  type(s) associated with key (**key**), value (**value**),
+                  both key and value (**kv**), or all BTF types present in
+                  associated BTF object (**all**). If not specified, **kv**
+                  is assumed.
+
+                  When **prog** is provided, it's expected that program has
+                  associated BTF object with BTF types.
+
+                  When specifying *FILE*, an ELF file is expected, containing
+                  .BTF section with well-defined BTF binary format data,
+                  typically produced by clang or pahole.
+
+	**bpftool btf help**
+		  Print short help message.
+
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-V, --version
+		  Print version number (similar to **bpftool version**).
+
+	-j, --json
+		  Generate JSON output. For commands that cannot produce JSON, this
+		  option has no effect.
+
+	-p, --pretty
+		  Generate human-readable JSON output. Implies **-j**.
+
+EXAMPLES
+========
+**# bpftool btf dump id 1226**
+::
+
+  [1] PTR '(anon)' type_id=2
+  [2] STRUCT 'dummy_tracepoint_args' size=16 vlen=2
+          'pad' type_id=3 bits_offset=0
+          'sock' type_id=4 bits_offset=64
+  [3] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
+  [4] PTR '(anon)' type_id=5
+  [5] FWD 'sock' fwd_kind=union
+
+This gives an example of default output for all supported BTF kinds.
+
+**$ cat prog.c**
+::
+
+  struct fwd_struct;
+
+  enum my_enum {
+          VAL1 = 3,
+          VAL2 = 7,
+  };
+
+  typedef struct my_struct my_struct_t;
+
+  struct my_struct {
+          const unsigned int const_int_field;
+          int bitfield_field: 4;
+          char arr_field[16];
+          const struct fwd_struct *restrict fwd_field;
+          enum my_enum enum_field;
+          volatile my_struct_t *typedef_ptr_field;
+  };
+
+  union my_union {
+          int a;
+          struct my_struct b;
+  };
+
+  struct my_struct struct_global_var __attribute__((section("data_sec"))) = {
+          .bitfield_field = 3,
+          .enum_field = VAL1,
+  };
+  int global_var __attribute__((section("data_sec"))) = 7;
+
+  __attribute__((noinline))
+  int my_func(union my_union *arg1, int arg2)
+  {
+          static int static_var __attribute__((section("data_sec"))) = 123;
+          static_var++;
+          return static_var;
+  }
+
+**$ bpftool btf dump file prog.o**
+::
+
+  [1] PTR '(anon)' type_id=2
+  [2] UNION 'my_union' size=48 vlen=2
+          'a' type_id=3 bits_offset=0
+          'b' type_id=4 bits_offset=0
+  [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
+  [4] STRUCT 'my_struct' size=48 vlen=6
+          'const_int_field' type_id=5 bits_offset=0
+          'bitfield_field' type_id=3 bits_offset=32 bitfield_size=4
+          'arr_field' type_id=8 bits_offset=40
+          'fwd_field' type_id=10 bits_offset=192
+          'enum_field' type_id=14 bits_offset=256
+          'typedef_ptr_field' type_id=15 bits_offset=320
+  [5] CONST '(anon)' type_id=6
+  [6] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
+  [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
+  [8] ARRAY '(anon)' type_id=7 index_type_id=9 nr_elems=16
+  [9] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
+  [10] RESTRICT '(anon)' type_id=11
+  [11] PTR '(anon)' type_id=12
+  [12] CONST '(anon)' type_id=13
+  [13] FWD 'fwd_struct' fwd_kind=union
+  [14] ENUM 'my_enum' size=4 vlen=2
+          'VAL1' val=3
+          'VAL2' val=7
+  [15] PTR '(anon)' type_id=16
+  [16] VOLATILE '(anon)' type_id=17
+  [17] TYPEDEF 'my_struct_t' type_id=4
+  [18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=2
+          'arg1' type_id=1
+          'arg2' type_id=3
+  [19] FUNC 'my_func' type_id=18
+  [20] VAR 'struct_global_var' type_id=4, linkage=global-alloc
+  [21] VAR 'global_var' type_id=3, linkage=global-alloc
+  [22] VAR 'my_func.static_var' type_id=3, linkage=static
+  [23] DATASEC 'data_sec' size=0 vlen=3
+          type_id=20 offset=0 size=48
+          type_id=21 offset=0 size=4
+          type_id=22 offset=52 size=4
+
+The following commands print BTF types associated with specified map's key,
+value, both key and value, and all BTF types, respectively. By default, both
+key and value types will be printed.
+
+**# bpftool btf dump map id 123 key**
+
+::
+
+  [39] TYPEDEF 'u32' type_id=37
+
+**# bpftool btf dump map id 123 value**
+
+::
+
+  [86] PTR '(anon)' type_id=87
+
+**# bpftool btf dump map id 123 kv**
+
+::
+
+  [39] TYPEDEF 'u32' type_id=37
+  [86] PTR '(anon)' type_id=87
+
+**# bpftool btf dump map id 123 all**
+
+::
+
+  [1] PTR '(anon)' type_id=0
+  .
+  .
+  .
+  [2866] ARRAY '(anon)' type_id=52 index_type_id=51 nr_elems=4
+
+All the standard ways to specify map or program are supported:
+
+**# bpftool btf dump map id 123**
+
+**# bpftool btf dump map pinned /sys/fs/bpf/map_name**
+
+**# bpftool btf dump prog id 456**
+
+**# bpftool btf dump prog tag b88e0a09b1d9759d**
+
+**# bpftool btf dump prog pinned /sys/fs/bpf/prog_name**
+
+SEE ALSO
+========
+	**bpf**\ (2),
+	**bpf-helpers**\ (7),
+	**bpftool**\ (8),
+	**bpftool-map**\ (8),
+	**bpftool-prog**\ (8),
+	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
+	**bpftool-net**\ (8),
+	**bpftool-perf**\ (8)

tools/bpf/bpftool/Documentation/bpftool-cgroup.rst

@@ -145,4 +145,5 @@ SEE ALSO
 	**bpftool-map**\ (8),
 	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
-	**bpftool-perf**\ (8)
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/Documentation/bpftool-feature.rst

@@ -82,4 +82,5 @@ SEE ALSO
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
 	**bpftool-net**\ (8),
-	**bpftool-perf**\ (8)
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/Documentation/bpftool-map.rst

@@ -258,4 +258,5 @@ SEE ALSO
 	**bpftool-cgroup**\ (8),
 	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
-	**bpftool-perf**\ (8)
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/Documentation/bpftool-net.rst

@@ -143,4 +143,5 @@ SEE ALSO
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
 	**bpftool-feature**\ (8),
-	**bpftool-perf**\ (8)
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/Documentation/bpftool-perf.rst

@@ -85,4 +85,5 @@ SEE ALSO
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
 	**bpftool-feature**\ (8),
-	**bpftool-net**\ (8)
+	**bpftool-net**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/Documentation/bpftool-prog.rst

@@ -271,4 +271,5 @@ SEE ALSO
 	**bpftool-cgroup**\ (8),
 	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
-	**bpftool-perf**\ (8)
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/Documentation/bpftool.rst

@@ -76,4 +76,5 @@ SEE ALSO
 	**bpftool-cgroup**\ (8),
 	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
-	**bpftool-perf**\ (8)
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)

tools/bpf/bpftool/bash-completion/bpftool

@@ -217,6 +217,7 @@ _bpftool()
     done
     cur=${words[cword]}
     prev=${words[cword - 1]}
+    pprev=${words[cword - 2]}
 
     local object=${words[1]} command=${words[2]}
 
@@ -272,17 +273,17 @@ _bpftool()
                                 "$cur" ) )
                             return 0
                             ;;
-                    *)
-                        _bpftool_once_attr 'file'
-                        if _bpftool_search_list 'xlated'; then
-                            COMPREPLY+=( $( compgen -W 'opcodes visual linum' -- \
-                                "$cur" ) )
-                        else
-                            COMPREPLY+=( $( compgen -W 'opcodes linum' -- \
-                                "$cur" ) )
-                        fi
-                        return 0
-                        ;;
+                        *)
+                            _bpftool_once_attr 'file'
+                            if _bpftool_search_list 'xlated'; then
+                                COMPREPLY+=( $( compgen -W 'opcodes visual linum' -- \
+                                    "$cur" ) )
+                            else
+                                COMPREPLY+=( $( compgen -W 'opcodes linum' -- \
+                                    "$cur" ) )
+                            fi
+                            return 0
+                            ;;
                     esac
                     ;;
                 pin)
@@ -607,6 +608,51 @@ _bpftool()
                     ;;
             esac
             ;;
+        btf)
+            local PROG_TYPE='id pinned tag'
+            local MAP_TYPE='id pinned'
+            case $command in
+                dump)
+                    case $prev in
+                        $command)
+                            COMPREPLY+=( $( compgen -W "id map prog file" -- \
+                                "$cur" ) )
+                            return 0
+                            ;;
+                        prog)
+                            COMPREPLY=( $( compgen -W "$PROG_TYPE" -- "$cur" ) )
+                            return 0
+                            ;;
+                        map)
+                            COMPREPLY=( $( compgen -W "$MAP_TYPE" -- "$cur" ) )
+                            return 0
+                            ;;
+                        id)
+                            case $pprev in
+                                prog)
+                                    _bpftool_get_prog_ids
+                                    ;;
+                                map)
+                                    _bpftool_get_map_ids
+                                    ;;
+                            esac
+                            return 0
+                            ;;
+                        *)
+                            if [[ $cword == 6 ]] && [[ ${words[3]} == "map" ]]; then
+                                 COMPREPLY+=( $( compgen -W 'key value kv all' -- \
+                                     "$cur" ) )
+                            fi
+                            return 0
+                            ;;
+                    esac
+                    ;;
+                *)
+                    [[ $prev == $object ]] && \
+                        COMPREPLY=( $( compgen -W 'dump help' -- "$cur" ) )
+                    ;;
+            esac
+            ;;
         cgroup)
             case $command in
                 show|list)

tools/bpf/bpftool/btf.c

+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/* Copyright (C) 2019 Facebook */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/err.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <gelf.h>
+#include <bpf.h>
+#include <linux/btf.h>
+
+#include "btf.h"
+#include "json_writer.h"
+#include "main.h"
+
+static const char * const btf_kind_str[NR_BTF_KINDS] = {
+	[BTF_KIND_UNKN]		= "UNKNOWN",
+	[BTF_KIND_INT]		= "INT",
+	[BTF_KIND_PTR]		= "PTR",
+	[BTF_KIND_ARRAY]	= "ARRAY",
+	[BTF_KIND_STRUCT]	= "STRUCT",
+	[BTF_KIND_UNION]	= "UNION",
+	[BTF_KIND_ENUM]		= "ENUM",
+	[BTF_KIND_FWD]		= "FWD",
+	[BTF_KIND_TYPEDEF]	= "TYPEDEF",
+	[BTF_KIND_VOLATILE]	= "VOLATILE",
+	[BTF_KIND_CONST]	= "CONST",
+	[BTF_KIND_RESTRICT]	= "RESTRICT",
+	[BTF_KIND_FUNC]		= "FUNC",
+	[BTF_KIND_FUNC_PROTO]	= "FUNC_PROTO",
+	[BTF_KIND_VAR]		= "VAR",
+	[BTF_KIND_DATASEC]	= "DATASEC",
+};
+
+static const char *btf_int_enc_str(__u8 encoding)
+{
+	switch (encoding) {
+	case 0:
+		return "(none)";
+	case BTF_INT_SIGNED:
+		return "SIGNED";
+	case BTF_INT_CHAR:
+		return "CHAR";
+	case BTF_INT_BOOL:
+		return "BOOL";
+	default:
+		return "UNKN";
+	}
+}
+
+static const char *btf_var_linkage_str(__u32 linkage)
+{
+	switch (linkage) {
+	case BTF_VAR_STATIC:
+		return "static";
+	case BTF_VAR_GLOBAL_ALLOCATED:
+		return "global-alloc";
+	default:
+		return "(unknown)";
+	}
+}
+
+static const char *btf_str(const struct btf *btf, __u32 off)
+{
+	if (!off)
+		return "(anon)";
+	return btf__name_by_offset(btf, off) ? : "(invalid)";
+}
+
+static int dump_btf_type(const struct btf *btf, __u32 id,
+			 const struct btf_type *t)
+{
+	json_writer_t *w = json_wtr;
+	int kind, safe_kind;
+
+	kind = BTF_INFO_KIND(t->info);
+	safe_kind = kind <= BTF_KIND_MAX ? kind : BTF_KIND_UNKN;
+
+	if (json_output) {
+		jsonw_start_object(w);
+		jsonw_uint_field(w, "id", id);
+		jsonw_string_field(w, "kind", btf_kind_str[safe_kind]);
+		jsonw_string_field(w, "name", btf_str(btf, t->name_off));
+	} else {
+		printf("[%u] %s '%s'", id, btf_kind_str[safe_kind],
+		       btf_str(btf, t->name_off));
+	}
+
+	switch (BTF_INFO_KIND(t->info)) {
+	case BTF_KIND_INT: {
+		__u32 v = *(__u32 *)(t + 1);
+		const char *enc;
+
+		enc = btf_int_enc_str(BTF_INT_ENCODING(v));
+
+		if (json_output) {
+			jsonw_uint_field(w, "size", t->size);
+			jsonw_uint_field(w, "bits_offset", BTF_INT_OFFSET(v));
+			jsonw_uint_field(w, "nr_bits", BTF_INT_BITS(v));
+			jsonw_string_field(w, "encoding", enc);
+		} else {
+			printf(" size=%u bits_offset=%u nr_bits=%u encoding=%s",
+			       t->size, BTF_INT_OFFSET(v), BTF_INT_BITS(v),
+			       enc);
+		}
+		break;
+	}
+	case BTF_KIND_PTR:
+	case BTF_KIND_CONST:
+	case BTF_KIND_VOLATILE:
+	case BTF_KIND_RESTRICT:
+	case BTF_KIND_TYPEDEF:
+		if (json_output)
+			jsonw_uint_field(w, "type_id", t->type);
+		else
+			printf(" type_id=%u", t->type);
+		break;
+	case BTF_KIND_ARRAY: {
+		const struct btf_array *arr = (const void *)(t + 1);
+
+		if (json_output) {
+			jsonw_uint_field(w, "type_id", arr->type);
+			jsonw_uint_field(w, "index_type_id", arr->index_type);
+			jsonw_uint_field(w, "nr_elems", arr->nelems);
+		} else {
+			printf(" type_id=%u index_type_id=%u nr_elems=%u",
+			       arr->type, arr->index_type, arr->nelems);
+		}
+		break;
+	}
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION: {
+		const struct btf_member *m = (const void *)(t + 1);
+		__u16 vlen = BTF_INFO_VLEN(t->info);
+		int i;
+
+		if (json_output) {
+			jsonw_uint_field(w, "size", t->size);
+			jsonw_uint_field(w, "vlen", vlen);
+			jsonw_name(w, "members");
+			jsonw_start_array(w);
+		} else {
+			printf(" size=%u vlen=%u", t->size, vlen);
+		}
+		for (i = 0; i < vlen; i++, m++) {
+			const char *name = btf_str(btf, m->name_off);
+			__u32 bit_off, bit_sz;
+
+			if (BTF_INFO_KFLAG(t->info)) {
+				bit_off = BTF_MEMBER_BIT_OFFSET(m->offset);
+				bit_sz = BTF_MEMBER_BITFIELD_SIZE(m->offset);
+			} else {
+				bit_off = m->offset;
+				bit_sz = 0;
+			}
+
+			if (json_output) {
+				jsonw_start_object(w);
+				jsonw_string_field(w, "name", name);
+				jsonw_uint_field(w, "type_id", m->type);
+				jsonw_uint_field(w, "bits_offset", bit_off);
+				if (bit_sz) {
+					jsonw_uint_field(w, "bitfield_size",
+							 bit_sz);
+				}
+				jsonw_end_object(w);
+			} else {
+				printf("\n\t'%s' type_id=%u bits_offset=%u",
+				       name, m->type, bit_off);
+				if (bit_sz)
+					printf(" bitfield_size=%u", bit_sz);
+			}
+		}
+		if (json_output)
+			jsonw_end_array(w);
+		break;
+	}
+	case BTF_KIND_ENUM: {
+		const struct btf_enum *v = (const void *)(t + 1);
+		__u16 vlen = BTF_INFO_VLEN(t->info);
+		int i;
+
+		if (json_output) {
+			jsonw_uint_field(w, "size", t->size);
+			jsonw_uint_field(w, "vlen", vlen);
+			jsonw_name(w, "values");
+			jsonw_start_array(w);
+		} else {
+			printf(" size=%u vlen=%u", t->size, vlen);
+		}
+		for (i = 0; i < vlen; i++, v++) {
+			const char *name = btf_str(btf, v->name_off);
+
+			if (json_output) {
+				jsonw_start_object(w);
+				jsonw_string_field(w, "name", name);
+				jsonw_uint_field(w, "val", v->val);
+				jsonw_end_object(w);
+			} else {
+				printf("\n\t'%s' val=%u", name, v->val);
+			}
+		}
+		if (json_output)
+			jsonw_end_array(w);
+		break;
+	}
+	case BTF_KIND_FWD: {
+		const char *fwd_kind = BTF_INFO_KIND(t->info) ? "union"
+							      : "struct";
+
+		if (json_output)
+			jsonw_string_field(w, "fwd_kind", fwd_kind);
+		else
+			printf(" fwd_kind=%s", fwd_kind);
+		break;
+	}
+	case BTF_KIND_FUNC:
+		if (json_output)
+			jsonw_uint_field(w, "type_id", t->type);
+		else
+			printf(" type_id=%u", t->type);
+		break;
+	case BTF_KIND_FUNC_PROTO: {
+		const struct btf_param *p = (const void *)(t + 1);
+		__u16 vlen = BTF_INFO_VLEN(t->info);
+		int i;
+
+		if (json_output) {
+			jsonw_uint_field(w, "ret_type_id", t->type);
+			jsonw_uint_field(w, "vlen", vlen);
+			jsonw_name(w, "params");
+			jsonw_start_array(w);
+		} else {
+			printf(" ret_type_id=%u vlen=%u", t->type, vlen);
+		}
+		for (i = 0; i < vlen; i++, p++) {
+			const char *name = btf_str(btf, p->name_off);
+
+			if (json_output) {
+				jsonw_start_object(w);
+				jsonw_string_field(w, "name", name);
+				jsonw_uint_field(w, "type_id", p->type);
+				jsonw_end_object(w);
+			} else {
+				printf("\n\t'%s' type_id=%u", name, p->type);
+			}
+		}
+		if (json_output)
+			jsonw_end_array(w);
+		break;
+	}
+	case BTF_KIND_VAR: {
+		const struct btf_var *v = (const void *)(t + 1);
+		const char *linkage;
+
+		linkage = btf_var_linkage_str(v->linkage);
+
+		if (json_output) {
+			jsonw_uint_field(w, "type_id", t->type);
+			jsonw_string_field(w, "linkage", linkage);
+		} else {
+			printf(" type_id=%u, linkage=%s", t->type, linkage);
+		}
+		break;
+	}
+	case BTF_KIND_DATASEC: {
+		const struct btf_var_secinfo *v = (const void *)(t+1);
+		__u16 vlen = BTF_INFO_VLEN(t->info);
+		int i;
+
+		if (json_output) {
+			jsonw_uint_field(w, "size", t->size);
+			jsonw_uint_field(w, "vlen", vlen);
+			jsonw_name(w, "vars");
+			jsonw_start_array(w);
+		} else {
+			printf(" size=%u vlen=%u", t->size, vlen);
+		}
+		for (i = 0; i < vlen; i++, v++) {
+			if (json_output) {
+				jsonw_start_object(w);
+				jsonw_uint_field(w, "type_id", v->type);
+				jsonw_uint_field(w, "offset", v->offset);
+				jsonw_uint_field(w, "size", v->size);
+				jsonw_end_object(w);
+			} else {
+				printf("\n\ttype_id=%u offset=%u size=%u",
+				       v->type, v->offset, v->size);
+			}
+		}
+		if (json_output)
+			jsonw_end_array(w);
+		break;
+	}
+	default:
+		break;
+	}
+
+	if (json_output)
+		jsonw_end_object(json_wtr);
+	else
+		printf("\n");
+
+	return 0;
+}
+
+static int dump_btf_raw(const struct btf *btf,
+			__u32 *root_type_ids, int root_type_cnt)
+{
+	const struct btf_type *t;
+	int i;
+
+	if (json_output) {
+		jsonw_start_object(json_wtr);
+		jsonw_name(json_wtr, "types");
+		jsonw_start_array(json_wtr);
+	}
+
+	if (root_type_cnt) {
+		for (i = 0; i < root_type_cnt; i++) {
+			t = btf__type_by_id(btf, root_type_ids[i]);
+			dump_btf_type(btf, root_type_ids[i], t);
+		}
+	} else {
+		int cnt = btf__get_nr_types(btf);
+
+		for (i = 1; i <= cnt; i++) {
+			t = btf__type_by_id(btf, i);
+			dump_btf_type(btf, i, t);
+		}
+	}
+
+	if (json_output) {
+		jsonw_end_array(json_wtr);
+		jsonw_end_object(json_wtr);
+	}
+	return 0;
+}
+
+static bool check_btf_endianness(GElf_Ehdr *ehdr)
+{
+	static unsigned int const endian = 1;
+
+	switch (ehdr->e_ident[EI_DATA]) {
+	case ELFDATA2LSB:
+		return *(unsigned char const *)&endian == 1;
+	case ELFDATA2MSB:
+		return *(unsigned char const *)&endian == 0;
+	default:
+		return 0;
+	}
+}
+
+static int btf_load_from_elf(const char *path, struct btf **btf)
+{
+	int err = -1, fd = -1, idx = 0;
+	Elf_Data *btf_data = NULL;
+	Elf_Scn *scn = NULL;
+	Elf *elf = NULL;
+	GElf_Ehdr ehdr;
+
+	if (elf_version(EV_CURRENT) == EV_NONE) {
+		p_err("failed to init libelf for %s", path);
+		return -1;
+	}
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0) {
+		p_err("failed to open %s: %s", path, strerror(errno));
+		return -1;
+	}
+
+	elf = elf_begin(fd, ELF_C_READ, NULL);
+	if (!elf) {
+		p_err("failed to open %s as ELF file", path);
+		goto done;
+	}
+	if (!gelf_getehdr(elf, &ehdr)) {
+		p_err("failed to get EHDR from %s", path);
+		goto done;
+	}
+	if (!check_btf_endianness(&ehdr)) {
+		p_err("non-native ELF endianness is not supported");
+		goto done;
+	}
+	if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
+		p_err("failed to get e_shstrndx from %s\n", path);
+		goto done;
+	}
+
+	while ((scn = elf_nextscn(elf, scn)) != NULL) {
+		GElf_Shdr sh;
+		char *name;
+
+		idx++;
+		if (gelf_getshdr(scn, &sh) != &sh) {
+			p_err("failed to get section(%d) header from %s",
+			      idx, path);
+			goto done;
+		}
+		name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);
+		if (!name) {
+			p_err("failed to get section(%d) name from %s",
+			      idx, path);
+			goto done;
+		}
+		if (strcmp(name, BTF_ELF_SEC) == 0) {
+			btf_data = elf_getdata(scn, 0);
+			if (!btf_data) {
+				p_err("failed to get section(%d, %s) data from %s",
+				      idx, name, path);
+				goto done;
+			}
+			break;
+		}
+	}
+
+	if (!btf_data) {
+		p_err("%s ELF section not found in %s", BTF_ELF_SEC, path);
+		goto done;
+	}
+
+	*btf = btf__new(btf_data->d_buf, btf_data->d_size);
+	if (IS_ERR(*btf)) {
+		err = PTR_ERR(*btf);
+		*btf = NULL;
+		p_err("failed to load BTF data from %s: %s",
+		      path, strerror(err));
+		goto done;
+	}
+
+	err = 0;
+done:
+	if (err) {
+		if (*btf) {
+			btf__free(*btf);
+			*btf = NULL;
+		}
+	}
+	if (elf)
+		elf_end(elf);
+	close(fd);
+	return err;
+}
+
+static int do_dump(int argc, char **argv)
+{
+	struct btf *btf = NULL;
+	__u32 root_type_ids[2];
+	int root_type_cnt = 0;
+	__u32 btf_id = -1;
+	const char *src;
+	int fd = -1;
+	int err;
+
+	if (!REQ_ARGS(2)) {
+		usage();
+		return -1;
+	}
+	src = GET_ARG();
+
+	if (is_prefix(src, "map")) {
+		struct bpf_map_info info = {};
+		__u32 len = sizeof(info);
+
+		if (!REQ_ARGS(2)) {
+			usage();
+			return -1;
+		}
+
+		fd = map_parse_fd_and_info(&argc, &argv, &info, &len);
+		if (fd < 0)
+			return -1;
+
+		btf_id = info.btf_id;
+		if (argc && is_prefix(*argv, "key")) {
+			root_type_ids[root_type_cnt++] = info.btf_key_type_id;
+			NEXT_ARG();
+		} else if (argc && is_prefix(*argv, "value")) {
+			root_type_ids[root_type_cnt++] = info.btf_value_type_id;
+			NEXT_ARG();
+		} else if (argc && is_prefix(*argv, "all")) {
+			NEXT_ARG();
+		} else if (argc && is_prefix(*argv, "kv")) {
+			root_type_ids[root_type_cnt++] = info.btf_key_type_id;
+			root_type_ids[root_type_cnt++] = info.btf_value_type_id;
+			NEXT_ARG();
+		} else {
+			root_type_ids[root_type_cnt++] = info.btf_key_type_id;
+			root_type_ids[root_type_cnt++] = info.btf_value_type_id;
+		}
+	} else if (is_prefix(src, "prog")) {
+		struct bpf_prog_info info = {};
+		__u32 len = sizeof(info);
+
+		if (!REQ_ARGS(2)) {
+			usage();
+			return -1;
+		}
+
+		fd = prog_parse_fd(&argc, &argv);
+		if (fd < 0)
+			return -1;
+
+		err = bpf_obj_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			p_err("can't get prog info: %s", strerror(errno));
+			goto done;
+		}
+
+		btf_id = info.btf_id;
+	} else if (is_prefix(src, "id")) {
+		char *endptr;
+
+		btf_id = strtoul(*argv, &endptr, 0);
+		if (*endptr) {
+			p_err("can't parse %s as ID", **argv);
+			return -1;
+		}
+		NEXT_ARG();
+	} else if (is_prefix(src, "file")) {
+		err = btf_load_from_elf(*argv, &btf);
+		if (err)
+			goto done;
+		NEXT_ARG();
+	} else {
+		err = -1;
+		p_err("unrecognized BTF source specifier: '%s'", src);
+		goto done;
+	}
+
+	if (!btf) {
+		err = btf__get_from_id(btf_id, &btf);
+		if (err) {
+			p_err("get btf by id (%u): %s", btf_id, strerror(err));
+			goto done;
+		}
+		if (!btf) {
+			err = ENOENT;
+			p_err("can't find btf with ID (%u)", btf_id);
+			goto done;
+		}
+	}
+
+	dump_btf_raw(btf, root_type_ids, root_type_cnt);
+
+done:
+	close(fd);
+	btf__free(btf);
+	return err;
+}
+
+static int do_help(int argc, char **argv)
+{
+	if (json_output) {
+		jsonw_null(json_wtr);
+		return 0;
+	}
+
+	fprintf(stderr,
+		"Usage: %s btf dump BTF_SRC\n"
+		"       %s btf help\n"
+		"\n"
+		"       BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE }\n"
+		"       " HELP_SPEC_MAP "\n"
+		"       " HELP_SPEC_PROGRAM "\n"
+		"       " HELP_SPEC_OPTIONS "\n"
+		"",
+		bin_name, bin_name);
+
+	return 0;
+}
+
+static const struct cmd cmds[] = {
+	{ "help",	do_help },
+	{ "dump",	do_dump },
+	{ 0 }
+};
+
+int do_btf(int argc, char **argv)
+{
+	return cmd_select(cmds, argc, argv, do_help);
+}

tools/bpf/bpftool/main.c

@@ -56,7 +56,7 @@ static int do_help(int argc, char **argv)
 		"       %s batch file FILE\n"
 		"       %s version\n"
 		"\n"
-		"       OBJECT := { prog | map | cgroup | perf | net | feature }\n"
+		"       OBJECT := { prog | map | cgroup | perf | net | feature | btf }\n"
 		"       " HELP_SPEC_OPTIONS "\n"
 		"",
 		bin_name, bin_name, bin_name);
@@ -188,6 +188,7 @@ static const struct cmd cmds[] = {
 	{ "perf",	do_perf },
 	{ "net",	do_net },
 	{ "feature",	do_feature },
+	{ "btf",	do_btf },
 	{ "version",	do_version },
 	{ 0 }
 };

tools/bpf/bpftool/main.h

@@ -150,6 +150,7 @@ int do_perf(int argc, char **arg);
 int do_net(int argc, char **arg);
 int do_tracelog(int argc, char **arg);
 int do_feature(int argc, char **argv);
+int do_btf(int argc, char **argv);
 
 int parse_u32_arg(int *argc, char ***argv, __u32 *val, const char *what);
 int prog_parse_fd(int *argc, char ***argv);