|
| 1 | +#!/usr/bin/env python3 |
| 2 | + |
| 3 | +# Ad-hoc script to print BTF file in a readable format. |
| 4 | +# Follows the same printing conventions as bpftool with format 'raw'. |
| 5 | +# Usage: |
| 6 | +# |
| 7 | +# ./print_btf.py <btf_file> |
| 8 | +# |
| 9 | +# Parameters: |
| 10 | +# |
| 11 | +# <btf_file> :: a file name or '-' to read from stdin. |
| 12 | +# |
| 13 | +# Intended usage: |
| 14 | +# |
| 15 | +# llvm-objcopy --dump-section .BTF=- <input> | ./print_btf.py - |
| 16 | +# |
| 17 | +# Kernel documentation contains detailed format description: |
| 18 | +# https://www.kernel.org/doc/html/latest/bpf/btf.html |
| 19 | + |
| 20 | +import struct |
| 21 | +import ctypes |
| 22 | +import sys |
| 23 | + |
| 24 | +class SafeDict(dict): |
| 25 | + def __getitem__(self, key): |
| 26 | + try: |
| 27 | + return dict.__getitem__(self, key) |
| 28 | + except KeyError: |
| 29 | + return f'<BAD_KEY: {key}>' |
| 30 | + |
| 31 | +KINDS = SafeDict({ |
| 32 | + 0: 'UNKN', |
| 33 | + 1: 'INT', |
| 34 | + 2: 'PTR', |
| 35 | + 3: 'ARRAY', |
| 36 | + 4: 'STRUCT', |
| 37 | + 5: 'UNION', |
| 38 | + 6: 'ENUM', |
| 39 | + 7: 'FWD', |
| 40 | + 8: 'TYPEDEF', |
| 41 | + 9: 'VOLATILE', |
| 42 | + 10: 'CONST', |
| 43 | + 11: 'RESTRICT', |
| 44 | + 12: 'FUNC', |
| 45 | + 13: 'FUNC_PROTO', |
| 46 | + 14: 'VAR', |
| 47 | + 15: 'DATASEC', |
| 48 | + 16: 'FLOAT', |
| 49 | + 17: 'DECL_TAG', |
| 50 | + 18: 'TYPE_TAG', |
| 51 | + 19: 'ENUM64', |
| 52 | +}) |
| 53 | + |
| 54 | +INT_ENCODING = SafeDict({ |
| 55 | + 0 << 0: '(none)', |
| 56 | + 1 << 0: 'SIGNED', |
| 57 | + 1 << 1: 'CHAR', |
| 58 | + 1 << 2: 'BOOL' |
| 59 | +}) |
| 60 | + |
| 61 | +ENUM_ENCODING = SafeDict({ |
| 62 | + 0: 'UNSIGNED', |
| 63 | + 1: 'SIGNED' |
| 64 | +}) |
| 65 | + |
| 66 | +FUNC_LINKAGE = SafeDict({ |
| 67 | + 0: 'static', |
| 68 | + 1: 'global', |
| 69 | + 2: 'extern' |
| 70 | +}) |
| 71 | + |
| 72 | +VAR_LINKAGE = SafeDict({ |
| 73 | + 0: 'static', |
| 74 | + 1: 'global', |
| 75 | +}) |
| 76 | + |
| 77 | +FWD_KIND = SafeDict({ |
| 78 | + 0: 'struct', |
| 79 | + 1: 'union', |
| 80 | +}) |
| 81 | + |
| 82 | +for val, name in KINDS.items(): |
| 83 | + globals()['BTF_KIND_' + name] = val |
| 84 | + |
| 85 | +def warn(message): |
| 86 | + print(message, file=sys.stderr) |
| 87 | + |
| 88 | +def print_btf(filename): |
| 89 | + if filename == '-': |
| 90 | + buf = sys.stdin.buffer.read() |
| 91 | + else: |
| 92 | + with open(filename, 'rb') as file: |
| 93 | + buf = file.read() |
| 94 | + |
| 95 | + fmt_cache = {} |
| 96 | + endian_pfx = '' |
| 97 | + off = 0 |
| 98 | + |
| 99 | + def unpack(fmt): |
| 100 | + nonlocal off, endian_pfx |
| 101 | + fmt = endian_pfx + fmt |
| 102 | + if fmt not in fmt_cache: |
| 103 | + fmt_cache[fmt] = struct.Struct(fmt) |
| 104 | + st = fmt_cache[fmt] |
| 105 | + r = st.unpack_from(buf, off) |
| 106 | + off += st.size |
| 107 | + return r |
| 108 | + |
| 109 | + # Use magic number at the header start to determine endianness |
| 110 | + magic, = unpack('H') |
| 111 | + if magic == 0xeb9f: |
| 112 | + endian_pfx = '<' |
| 113 | + elif magic == 0x9feb: |
| 114 | + endian_pfx = '>' |
| 115 | + else: |
| 116 | + warn(f'Unexpected BTF magic: {magic:02x}') |
| 117 | + return |
| 118 | + |
| 119 | + # Rest of the header |
| 120 | + version, flags, hdr_len = unpack('BBI') |
| 121 | + type_off, type_len, str_off, str_len = unpack('IIII') |
| 122 | + |
| 123 | + # Offsets in the header are relative to the end of a header |
| 124 | + type_off += hdr_len |
| 125 | + str_off += hdr_len |
| 126 | + off = hdr_len |
| 127 | + type_end = type_off + type_len |
| 128 | + |
| 129 | + def string(rel_off): |
| 130 | + try: |
| 131 | + start = str_off + rel_off |
| 132 | + end = buf.index(b"\0", start); |
| 133 | + if start == end: |
| 134 | + return '(anon)' |
| 135 | + return buf[start:end].decode('utf8') |
| 136 | + except ValueError as e: |
| 137 | + warn(f"Can't get string at offset {str_off} + {rel_off}: {e}") |
| 138 | + return f'<BAD_STRING {rel_off}>' |
| 139 | + |
| 140 | + idx = 1 |
| 141 | + while off < type_end: |
| 142 | + name_off, info, size = unpack('III') |
| 143 | + kind = (info >> 24) & 0x1f |
| 144 | + vlen = info & 0xffff |
| 145 | + kflag = info >> 31 |
| 146 | + kind_name = KINDS[kind] |
| 147 | + name = string(name_off) |
| 148 | + |
| 149 | + def warn_nonzero(val, name): |
| 150 | + nonlocal idx |
| 151 | + if val != 0: |
| 152 | + warn(f'<{idx}> {name} should be 0 but is {val}') |
| 153 | + |
| 154 | + if kind == BTF_KIND_INT: |
| 155 | + info, = unpack('I') |
| 156 | + encoding = (info & 0x0f000000) >> 24 |
| 157 | + offset = (info & 0x00ff0000) >> 16 |
| 158 | + bits = info & 0x000000ff |
| 159 | + enc_name = INT_ENCODING[encoding] |
| 160 | + print(f"[{idx}] {kind_name} '{name}' size={size} " |
| 161 | + f"bits_offset={offset} " |
| 162 | + f"nr_bits={bits} encoding={enc_name}") |
| 163 | + warn_nonzero(kflag, 'kflag') |
| 164 | + warn_nonzero(vlen, 'vlen') |
| 165 | + |
| 166 | + elif kind in [BTF_KIND_PTR, BTF_KIND_CONST, BTF_KIND_VOLATILE, |
| 167 | + BTF_KIND_RESTRICT]: |
| 168 | + print(f"[{idx}] {kind_name} '{name}' type_id={size}") |
| 169 | + warn_nonzero(name_off, 'name_off') |
| 170 | + warn_nonzero(kflag, 'kflag') |
| 171 | + warn_nonzero(vlen, 'vlen') |
| 172 | + |
| 173 | + elif kind == BTF_KIND_ARRAY: |
| 174 | + warn_nonzero(name_off, 'name_off') |
| 175 | + warn_nonzero(kflag, 'kflag') |
| 176 | + warn_nonzero(vlen, 'vlen') |
| 177 | + warn_nonzero(size, 'size') |
| 178 | + type, index_type, nelems = unpack('III') |
| 179 | + print(f"[{idx}] {kind_name} '{name}' type_id={type} " |
| 180 | + f"index_type_id={index_type} nr_elems={nelems}") |
| 181 | + |
| 182 | + elif kind in [BTF_KIND_STRUCT, BTF_KIND_UNION]: |
| 183 | + print(f"[{idx}] {kind_name} '{name}' size={size} vlen={vlen}") |
| 184 | + if kflag not in [0, 1]: |
| 185 | + warn(f'<{idx}> kflag should 0 or 1: {kflag}') |
| 186 | + for _ in range(0, vlen): |
| 187 | + name_off, type, offset = unpack('III') |
| 188 | + if kflag == 0: |
| 189 | + print(f"\t'{string(name_off)}' type_id={type} " |
| 190 | + f"bits_offset={offset}") |
| 191 | + else: |
| 192 | + bits_offset = offset & 0xffffff |
| 193 | + bitfield_size = offset >> 24 |
| 194 | + print(f"\t'{string(name_off)}' type_id={type} " |
| 195 | + f"bits_offset={bits_offset} " |
| 196 | + f"bitfield_size={bitfield_size}") |
| 197 | + |
| 198 | + elif kind == BTF_KIND_ENUM: |
| 199 | + encoding=ENUM_ENCODING[kflag] |
| 200 | + print(f"[{idx}] {kind_name} '{name}' encoding={encoding} " |
| 201 | + f"size={size} vlen={vlen}") |
| 202 | + for _ in range(0, vlen): |
| 203 | + name_off, = unpack('I') |
| 204 | + val, = unpack('i' if kflag == 1 else 'I') |
| 205 | + print(f"\t'{string(name_off)}' val={val}") |
| 206 | + |
| 207 | + elif kind == BTF_KIND_ENUM64: |
| 208 | + encoding=ENUM_ENCODING[kflag] |
| 209 | + print(f"[{idx}] {kind_name} '{name}' encoding={encoding} " |
| 210 | + f"size={size} vlen={vlen}") |
| 211 | + for _ in range(0, vlen): |
| 212 | + name_off, lo, hi = unpack('III') |
| 213 | + val = hi << 32 | lo |
| 214 | + if kflag == 1: |
| 215 | + val = ctypes.c_long(val).value |
| 216 | + print(f"\t'{string(name_off)}' val={val}LL") |
| 217 | + |
| 218 | + elif kind == BTF_KIND_FWD: |
| 219 | + print(f"[{idx}] {kind_name} '{name}' fwd_kind={FWD_KIND[kflag]}") |
| 220 | + warn_nonzero(vlen, 'vlen') |
| 221 | + warn_nonzero(size, 'size') |
| 222 | + |
| 223 | + elif kind in [BTF_KIND_TYPEDEF, BTF_KIND_TYPE_TAG]: |
| 224 | + print(f"[{idx}] {kind_name} '{name}' type_id={size}") |
| 225 | + warn_nonzero(kflag, 'kflag') |
| 226 | + warn_nonzero(kflag, 'vlen') |
| 227 | + |
| 228 | + elif kind == BTF_KIND_FUNC: |
| 229 | + linkage = FUNC_LINKAGE[vlen] |
| 230 | + print(f"[{idx}] {kind_name} '{name}' type_id={size} " |
| 231 | + f"linkage={linkage}") |
| 232 | + warn_nonzero(kflag, 'kflag') |
| 233 | + |
| 234 | + elif kind == BTF_KIND_FUNC_PROTO: |
| 235 | + print(f"[{idx}] {kind_name} '{name}' ret_type_id={size} " |
| 236 | + f"vlen={vlen}") |
| 237 | + warn_nonzero(name_off, 'name_off') |
| 238 | + warn_nonzero(kflag, 'kflag') |
| 239 | + for _ in range(0, vlen): |
| 240 | + name_off, type = unpack('II') |
| 241 | + print(f"\t'{string(name_off)}' type_id={type}") |
| 242 | + |
| 243 | + elif kind == BTF_KIND_VAR: |
| 244 | + linkage, = unpack('I') |
| 245 | + linkage = VAR_LINKAGE[linkage] |
| 246 | + print(f"[{idx}] {kind_name} '{name}' type_id={size}, " |
| 247 | + f"linkage={linkage}") |
| 248 | + warn_nonzero(kflag, 'kflag') |
| 249 | + warn_nonzero(vlen, 'vlen') |
| 250 | + |
| 251 | + elif kind == BTF_KIND_DATASEC: |
| 252 | + print(f"[{idx}] {kind_name} '{name}' size={size} vlen={vlen}") |
| 253 | + warn_nonzero(kflag, 'kflag') |
| 254 | + warn_nonzero(size, 'size') |
| 255 | + for _ in range(0, vlen): |
| 256 | + type, offset, size = unpack('III') |
| 257 | + print(f"\ttype_id={type} offset={offset} size={size}") |
| 258 | + |
| 259 | + elif kind == BTF_KIND_FLOAT: |
| 260 | + print(f"[{idx}] {kind_name} '{name}' size={size}") |
| 261 | + warn_nonzero(kflag, 'kflag') |
| 262 | + warn_nonzero(vlen, 'vlen') |
| 263 | + |
| 264 | + elif kind == BTF_KIND_DECL_TAG: |
| 265 | + component_idx, = unpack('i') |
| 266 | + print(f"[{idx}] {kind_name} '{name}' type_id={size} " + |
| 267 | + f"component_idx={component_idx}") |
| 268 | + warn_nonzero(kflag, 'kflag') |
| 269 | + warn_nonzero(vlen, 'vlen') |
| 270 | + |
| 271 | + else: |
| 272 | + warn(f'<{idx}> Unexpected entry: kind={kind_name} ' |
| 273 | + f'name_off={name_off} ' |
| 274 | + f'vlen={vlen} kflag={kflag} size={size}') |
| 275 | + |
| 276 | + idx += 1 |
| 277 | + |
| 278 | +if __name__ == '__main__': |
| 279 | + if len(sys.argv) != 2: |
| 280 | + warn('Usage: {sys.argv[0]} <btf_file>') |
| 281 | + sys.exit(1) |
| 282 | + print_btf(sys.argv[1]) |
0 commit comments