1 #-------------------------------------------------------------------------------
2 # elftools: elf/relocation.py
6 # Eli Bendersky (eliben@gmail.com)
7 # This code is in the public domain
8 #-------------------------------------------------------------------------------
9 from collections
import namedtuple
11 from ..common
.exceptions
import ELFRelocationError
12 from ..common
.utils
import elf_assert
, struct_parse
13 from .sections
import Section
15 ENUM_RELOC_TYPE_i386
, ENUM_RELOC_TYPE_x64
, ENUM_RELOC_TYPE_MIPS
,
16 ENUM_RELOC_TYPE_ARM
, ENUM_RELOC_TYPE_AARCH64
, ENUM_RELOC_TYPE_PPC64
,
17 ENUM_RELOC_TYPE_BPF
, ENUM_RELOC_TYPE_LOONGARCH
, ENUM_D_TAG
)
18 from ..construct
import Container
21 class Relocation(object):
22 """ Relocation object - representing a single relocation entry. Allows
23 dictionary-like access to the entry's fields.
25 Can be either a REL or RELA relocation.
27 def __init__(self
, entry
, elffile
):
29 self
.elffile
= elffile
32 """ Is this a RELA relocation? If not, it's REL.
34 return 'r_addend' in self
.entry
36 def __getitem__(self
, name
):
37 """ Dict-like access to entries
39 return self
.entry
[name
]
42 return '<Relocation (%s): %s>' % (
43 'RELA' if self
.is_RELA() else 'REL',
47 return self
.__repr
__()
50 class RelocationTable(object):
51 """ Shared functionality between relocation sections and relocation tables
54 def __init__(self
, elffile
, offset
, size
, is_rela
):
55 self
._stream
= elffile
.stream
56 self
._elffile
= elffile
57 self
._elfstructs
= elffile
.structs
60 self
._is
_rela
= is_rela
63 self
.entry_struct
= self
._elfstructs
.Elf_Rela
65 self
.entry_struct
= self
._elfstructs
.Elf_Rel
67 self
.entry_size
= self
.entry_struct
.sizeof()
70 """ Is this a RELA relocation section? If not, it's REL.
74 def num_relocations(self
):
75 """ Number of relocations in the section
77 return self
._size
// self
.entry_size
79 def get_relocation(self
, n
):
80 """ Get the relocation at index #n from the section (Relocation object)
82 entry_offset
= self
._offset
+ n
* self
.entry_size
86 stream_pos
=entry_offset
)
87 return Relocation(entry
, self
._elffile
)
89 def iter_relocations(self
):
90 """ Yield all the relocations in the section
92 for i
in range(self
.num_relocations()):
93 yield self
.get_relocation(i
)
96 class RelocationSection(Section
, RelocationTable
):
97 """ ELF relocation section. Serves as a collection of Relocation entries.
99 def __init__(self
, header
, name
, elffile
):
100 Section
.__init
__(self
, header
, name
, elffile
)
101 RelocationTable
.__init
__(self
, self
.elffile
,
102 self
['sh_offset'], self
['sh_size'], header
['sh_type'] == 'SHT_RELA')
104 elf_assert(header
['sh_type'] in ('SHT_REL', 'SHT_RELA'),
105 'Unknown relocation type section')
106 elf_assert(header
['sh_entsize'] == self
.entry_size
,
107 'Expected sh_entsize of %s section to be %s' % (
108 header
['sh_type'], self
.entry_size
))
110 class RelrRelocationSection(Section
):
111 """ RELR compressed relocation section. This stores relative relocations
112 in a compressed format. An entry with an even value serves as an
113 'anchor' that defines a base address. Following this entry are one or
114 more bitmaps for consecutive addresses after the anchor which determine
115 if the corresponding relocation exists (if the bit is 1) or if it is
116 skipped. Addends are stored at the respective addresses (as in REL
119 def __init__(self
, header
, name
, elffile
):
120 Section
.__init
__(self
, header
, name
, elffile
)
121 self
._offset
= self
['sh_offset']
122 self
._size
= self
['sh_size']
123 self
._relr
_struct
= self
.elffile
.structs
.Elf_Relr
124 self
._entrysize
= self
._relr
_struct
.sizeof()
125 self
._cached
_relocations
= None
127 def iter_relocations(self
):
128 """ Yield all the relocations in the section
130 limit
= self
._offset
+ self
._size
132 # The addresses of relocations in a bitmap are calculated from a base
133 # value provided in an initial 'anchor' relocation.
136 entry
= struct_parse(self
._relr
_struct
,
139 entry_offset
= entry
['r_offset']
140 if (entry_offset
& 1) == 0:
141 # We found an anchor, take the current value as the base address
142 # for the following bitmaps and move the 'where' pointer to the
143 # beginning of the first bitmap.
145 base
+= self
._entrysize
146 yield Relocation(entry
, self
.elffile
)
148 # We're processing a bitmap.
149 elf_assert(base
is not None, 'RELR bitmap without base address')
152 # Iterate over all bits except the least significant one.
153 entry_offset
= (entry_offset
>> 1)
154 if entry_offset
== 0:
156 # if the current LSB is set, we have a relocation at the
157 # corresponding address so generate a Relocation with the
159 if (entry_offset
& 1) != 0:
160 calc_offset
= base
+ i
* self
._entrysize
161 yield Relocation(Container(r_offset
= calc_offset
),
164 # Advance 'base' past the current bitmap (8 == CHAR_BIT). There
165 # are 63 (or 31 for 32-bit ELFs) entries in each bitmap, and
166 # every bit corresponds to an ELF_addr-sized relocation.
167 base
+= (8 * self
._entrysize
- 1) * self
.elffile
.structs
.Elf_addr('').sizeof()
168 # Advance to the next entry
169 relr
+= self
._entrysize
171 def num_relocations(self
):
172 """ Number of relocations in the section
174 if self
._cached
_relocations
is None:
175 self
._cached
_relocations
= list(self
.iter_relocations())
176 return len(self
._cached
_relocations
)
178 def get_relocation(self
, n
):
179 """ Get the relocation at index #n from the section (Relocation object)
181 if self
._cached
_relocations
is None:
182 self
._cached
_relocations
= list(self
.iter_relocations())
183 return self
._cached
_relocations
[n
]
185 class RelocationHandler(object):
186 """ Handles the logic of relocations in ELF files.
188 def __init__(self
, elffile
):
189 self
.elffile
= elffile
191 def find_relocations_for_section(self
, section
):
192 """ Given a section, find the relocation section for it in the ELF
193 file. Return a RelocationSection object, or None if none was
196 reloc_section_names
= (
197 '.rel' + section
.name
,
198 '.rela' + section
.name
)
199 # Find the relocation section aimed at this one. Currently assume
200 # that either .rel or .rela section exists for this section, but
202 for relsection
in self
.elffile
.iter_sections():
203 if ( isinstance(relsection
, RelocationSection
) and
204 relsection
.name
in reloc_section_names
):
208 def apply_section_relocations(self
, stream
, reloc_section
):
209 """ Apply all relocations in reloc_section (a RelocationSection object)
210 to the given stream, that contains the data of the section that is
211 being relocated. The stream is modified as a result.
213 # The symbol table associated with this relocation section
214 symtab
= self
.elffile
.get_section(reloc_section
['sh_link'])
215 for reloc
in reloc_section
.iter_relocations():
216 self
._do
_apply
_relocation
(stream
, reloc
, symtab
)
218 def _do_apply_relocation(self
, stream
, reloc
, symtab
):
219 # Preparations for performing the relocation: obtain the value of
220 # the symbol mentioned in the relocation, as well as the relocation
221 # recipe which tells us how to actually perform it.
222 # All peppered with some sanity checking.
223 if reloc
['r_info_sym'] >= symtab
.num_symbols():
224 raise ELFRelocationError(
225 'Invalid symbol reference in relocation: index %s' % (
226 reloc
['r_info_sym']))
227 sym_value
= symtab
.get_symbol(reloc
['r_info_sym'])['st_value']
229 reloc_type
= reloc
['r_info_type']
232 if self
.elffile
.get_machine_arch() == 'x86':
234 raise ELFRelocationError(
235 'Unexpected RELA relocation for x86: %s' % reloc
)
236 recipe
= self
._RELOCATION
_RECIPES
_X
86.get(reloc_type
, None)
237 elif self
.elffile
.get_machine_arch() == 'x64':
238 if not reloc
.is_RELA():
239 raise ELFRelocationError(
240 'Unexpected REL relocation for x64: %s' % reloc
)
241 recipe
= self
._RELOCATION
_RECIPES
_X
64.get(reloc_type
, None)
242 elif self
.elffile
.get_machine_arch() == 'MIPS':
244 if reloc_type
== ENUM_RELOC_TYPE_MIPS
['R_MIPS_64']:
245 if reloc
['r_type2'] != 0 or reloc
['r_type3'] != 0 or reloc
['r_ssym'] != 0:
246 raise ELFRelocationError(
247 'Multiple relocations in R_MIPS_64 are not implemented: %s' % reloc
)
248 recipe
= self
._RELOCATION
_RECIPES
_MIPS
_RELA
.get(reloc_type
, None)
250 recipe
= self
._RELOCATION
_RECIPES
_MIPS
_REL
.get(reloc_type
, None)
251 elif self
.elffile
.get_machine_arch() == 'ARM':
253 raise ELFRelocationError(
254 'Unexpected RELA relocation for ARM: %s' % reloc
)
255 recipe
= self
._RELOCATION
_RECIPES
_ARM
.get(reloc_type
, None)
256 elif self
.elffile
.get_machine_arch() == 'AArch64':
257 recipe
= self
._RELOCATION
_RECIPES
_AARCH
64.get(reloc_type
, None)
258 elif self
.elffile
.get_machine_arch() == '64-bit PowerPC':
259 recipe
= self
._RELOCATION
_RECIPES
_PPC
64.get(reloc_type
, None)
260 elif self
.elffile
.get_machine_arch() == 'Linux BPF - in-kernel virtual machine':
261 recipe
= self
._RELOCATION
_RECIPES
_EBPF
.get(reloc_type
, None)
262 elif self
.elffile
.get_machine_arch() == 'LoongArch':
263 if not reloc
.is_RELA():
264 raise ELFRelocationError(
265 'Unexpected REL relocation for LoongArch: %s' % reloc
)
266 recipe
= self
._RELOCATION
_RECIPES
_LOONGARCH
.get(reloc_type
, None)
269 raise ELFRelocationError(
270 'Unsupported relocation type: %s' % reloc_type
)
272 # So now we have everything we need to actually perform the relocation.
275 # 0. Find out which struct we're going to be using to read this value
276 # from the stream and write it back.
277 if recipe
.bytesize
== 4:
278 value_struct
= self
.elffile
.structs
.Elf_word('')
279 elif recipe
.bytesize
== 8:
280 value_struct
= self
.elffile
.structs
.Elf_word64('')
281 elif recipe
.bytesize
== 1:
282 value_struct
= self
.elffile
.structs
.Elf_byte('')
283 elif recipe
.bytesize
== 2:
284 value_struct
= self
.elffile
.structs
.Elf_half('')
286 raise ELFRelocationError('Invalid bytesize %s for relocation' %
289 # 1. Read the value from the stream (with correct size and endianness)
290 original_value
= struct_parse(
293 stream_pos
=reloc
['r_offset'])
294 # 2. Apply the relocation to the value, acting according to the recipe
295 relocated_value
= recipe
.calc_func(
296 value
=original_value
,
298 offset
=reloc
['r_offset'],
299 addend
=reloc
['r_addend'] if recipe
.has_addend
else 0)
300 # 3. Write the relocated value back into the stream
301 stream
.seek(reloc
['r_offset'])
303 # Make sure the relocated value fits back by wrapping it around. This
304 # looks like a problem, but it seems to be the way this is done in
306 relocated_value
= relocated_value
% (2 ** (recipe
.bytesize
* 8))
307 value_struct
.build_stream(relocated_value
, stream
)
309 # Relocations are represented by "recipes". Each recipe specifies:
310 # bytesize: The number of bytes to read (and write back) to the section.
311 # This is the unit of data on which relocation is performed.
312 # has_addend: Does this relocation have an extra addend?
313 # calc_func: A function that performs the relocation on an extracted
314 # value, and returns the updated value.
316 _RELOCATION_RECIPE_TYPE
= namedtuple('_RELOCATION_RECIPE_TYPE',
317 'bytesize has_addend calc_func')
319 def _reloc_calc_identity(value
, sym_value
, offset
, addend
=0):
322 def _reloc_calc_sym_plus_value(value
, sym_value
, offset
, addend
=0):
323 return sym_value
+ value
+ addend
325 def _reloc_calc_sym_plus_value_pcrel(value
, sym_value
, offset
, addend
=0):
326 return sym_value
+ value
- offset
328 def _reloc_calc_sym_plus_addend(value
, sym_value
, offset
, addend
=0):
329 return sym_value
+ addend
331 def _reloc_calc_sym_plus_addend_pcrel(value
, sym_value
, offset
, addend
=0):
332 return sym_value
+ addend
- offset
334 def _reloc_calc_value_minus_sym_addend(value
, sym_value
, offset
, addend
=0):
335 return value
- sym_value
- addend
337 def _arm_reloc_calc_sym_plus_value_pcrel(value
, sym_value
, offset
, addend
=0):
338 return sym_value
// 4 + value
- offset
// 4
340 def _bpf_64_32_reloc_calc_sym_plus_addend(value
, sym_value
, offset
, addend
=0):
341 return (sym_value
+ addend
) // 8 - 1
343 _RELOCATION_RECIPES_ARM
= {
344 ENUM_RELOC_TYPE_ARM
['R_ARM_ABS32']: _RELOCATION_RECIPE_TYPE(
345 bytesize
=4, has_addend
=False,
346 calc_func
=_reloc_calc_sym_plus_value
),
347 ENUM_RELOC_TYPE_ARM
['R_ARM_CALL']: _RELOCATION_RECIPE_TYPE(
348 bytesize
=4, has_addend
=False,
349 calc_func
=_arm_reloc_calc_sym_plus_value_pcrel
),
352 _RELOCATION_RECIPES_AARCH64
= {
353 ENUM_RELOC_TYPE_AARCH64
['R_AARCH64_ABS64']: _RELOCATION_RECIPE_TYPE(
354 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
355 ENUM_RELOC_TYPE_AARCH64
['R_AARCH64_ABS32']: _RELOCATION_RECIPE_TYPE(
356 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
357 ENUM_RELOC_TYPE_AARCH64
['R_AARCH64_PREL32']: _RELOCATION_RECIPE_TYPE(
358 bytesize
=4, has_addend
=True,
359 calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
362 # https://dmz-portal.mips.com/wiki/MIPS_relocation_types
363 _RELOCATION_RECIPES_MIPS_REL
= {
364 ENUM_RELOC_TYPE_MIPS
['R_MIPS_NONE']: _RELOCATION_RECIPE_TYPE(
365 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
366 ENUM_RELOC_TYPE_MIPS
['R_MIPS_32']: _RELOCATION_RECIPE_TYPE(
367 bytesize
=4, has_addend
=False,
368 calc_func
=_reloc_calc_sym_plus_value
),
370 _RELOCATION_RECIPES_MIPS_RELA
= {
371 ENUM_RELOC_TYPE_MIPS
['R_MIPS_NONE']: _RELOCATION_RECIPE_TYPE(
372 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_identity
),
373 ENUM_RELOC_TYPE_MIPS
['R_MIPS_32']: _RELOCATION_RECIPE_TYPE(
374 bytesize
=4, has_addend
=True,
375 calc_func
=_reloc_calc_sym_plus_value
),
376 ENUM_RELOC_TYPE_MIPS
['R_MIPS_64']: _RELOCATION_RECIPE_TYPE(
377 bytesize
=8, has_addend
=True,
378 calc_func
=_reloc_calc_sym_plus_value
),
381 _RELOCATION_RECIPES_PPC64
= {
382 ENUM_RELOC_TYPE_PPC64
['R_PPC64_ADDR32']: _RELOCATION_RECIPE_TYPE(
383 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
384 ENUM_RELOC_TYPE_PPC64
['R_PPC64_REL32']: _RELOCATION_RECIPE_TYPE(
385 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
386 ENUM_RELOC_TYPE_PPC64
['R_PPC64_ADDR64']: _RELOCATION_RECIPE_TYPE(
387 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
390 _RELOCATION_RECIPES_X86
= {
391 ENUM_RELOC_TYPE_i386
['R_386_NONE']: _RELOCATION_RECIPE_TYPE(
392 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
393 ENUM_RELOC_TYPE_i386
['R_386_32']: _RELOCATION_RECIPE_TYPE(
394 bytesize
=4, has_addend
=False,
395 calc_func
=_reloc_calc_sym_plus_value
),
396 ENUM_RELOC_TYPE_i386
['R_386_PC32']: _RELOCATION_RECIPE_TYPE(
397 bytesize
=4, has_addend
=False,
398 calc_func
=_reloc_calc_sym_plus_value_pcrel
),
401 _RELOCATION_RECIPES_X64
= {
402 ENUM_RELOC_TYPE_x64
['R_X86_64_NONE']: _RELOCATION_RECIPE_TYPE(
403 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_identity
),
404 ENUM_RELOC_TYPE_x64
['R_X86_64_64']: _RELOCATION_RECIPE_TYPE(
405 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
406 ENUM_RELOC_TYPE_x64
['R_X86_64_PC32']: _RELOCATION_RECIPE_TYPE(
407 bytesize
=4, has_addend
=True,
408 calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
409 ENUM_RELOC_TYPE_x64
['R_X86_64_32']: _RELOCATION_RECIPE_TYPE(
410 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
411 ENUM_RELOC_TYPE_x64
['R_X86_64_32S']: _RELOCATION_RECIPE_TYPE(
412 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
415 # https://www.kernel.org/doc/html/latest/bpf/llvm_reloc.html#different-relocation-types
416 _RELOCATION_RECIPES_EBPF
= {
417 ENUM_RELOC_TYPE_BPF
['R_BPF_NONE']: _RELOCATION_RECIPE_TYPE(
418 bytesize
=8, has_addend
=False, calc_func
=_reloc_calc_identity
),
419 ENUM_RELOC_TYPE_BPF
['R_BPF_64_64']: _RELOCATION_RECIPE_TYPE(
420 bytesize
=8, has_addend
=False, calc_func
=_reloc_calc_identity
),
421 ENUM_RELOC_TYPE_BPF
['R_BPF_64_32']: _RELOCATION_RECIPE_TYPE(
422 bytesize
=8, has_addend
=False, calc_func
=_bpf_64_32_reloc_calc_sym_plus_addend
),
423 ENUM_RELOC_TYPE_BPF
['R_BPF_64_NODYLD32']: _RELOCATION_RECIPE_TYPE(
424 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
425 ENUM_RELOC_TYPE_BPF
['R_BPF_64_ABS64']: _RELOCATION_RECIPE_TYPE(
426 bytesize
=8, has_addend
=False, calc_func
=_reloc_calc_identity
),
427 ENUM_RELOC_TYPE_BPF
['R_BPF_64_ABS32']: _RELOCATION_RECIPE_TYPE(
428 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
431 # https://github.com/loongson/la-abi-specs/blob/release/laelf.adoc
432 _RELOCATION_RECIPES_LOONGARCH
= {
433 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_NONE']: _RELOCATION_RECIPE_TYPE(
434 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
435 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_32']: _RELOCATION_RECIPE_TYPE(
436 bytesize
=4, has_addend
=True,
437 calc_func
=_reloc_calc_sym_plus_addend
),
438 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_64']: _RELOCATION_RECIPE_TYPE(
439 bytesize
=8, has_addend
=True,
440 calc_func
=_reloc_calc_sym_plus_addend
),
441 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_ADD8']: _RELOCATION_RECIPE_TYPE(
442 bytesize
=1, has_addend
=True,
443 calc_func
=_reloc_calc_sym_plus_value
),
444 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_SUB8']: _RELOCATION_RECIPE_TYPE(
445 bytesize
=1, has_addend
=True,
446 calc_func
=_reloc_calc_value_minus_sym_addend
),
447 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_ADD16']: _RELOCATION_RECIPE_TYPE(
448 bytesize
=2, has_addend
=True,
449 calc_func
=_reloc_calc_sym_plus_value
),
450 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_SUB16']: _RELOCATION_RECIPE_TYPE(
451 bytesize
=2, has_addend
=True,
452 calc_func
=_reloc_calc_value_minus_sym_addend
),
453 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_ADD32']: _RELOCATION_RECIPE_TYPE(
454 bytesize
=4, has_addend
=True,
455 calc_func
=_reloc_calc_sym_plus_value
),
456 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_SUB32']: _RELOCATION_RECIPE_TYPE(
457 bytesize
=4, has_addend
=True,
458 calc_func
=_reloc_calc_value_minus_sym_addend
),
459 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_ADD64']: _RELOCATION_RECIPE_TYPE(
460 bytesize
=8, has_addend
=True,
461 calc_func
=_reloc_calc_sym_plus_value
),
462 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_SUB64']: _RELOCATION_RECIPE_TYPE(
463 bytesize
=8, has_addend
=True,
464 calc_func
=_reloc_calc_value_minus_sym_addend
),
465 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_32_PCREL']: _RELOCATION_RECIPE_TYPE(
466 bytesize
=4, has_addend
=True,
467 calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
468 ENUM_RELOC_TYPE_LOONGARCH
['R_LARCH_64_PCREL']: _RELOCATION_RECIPE_TYPE(
469 bytesize
=8, has_addend
=True,
470 calc_func
=_reloc_calc_sym_plus_addend_pcrel
),