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
,
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 raise ELFRelocationError(
245 'Unexpected RELA relocation for MIPS: %s' % reloc
)
246 recipe
= self
._RELOCATION
_RECIPES
_MIPS
.get(reloc_type
, None)
247 elif self
.elffile
.get_machine_arch() == 'ARM':
249 raise ELFRelocationError(
250 'Unexpected RELA relocation for ARM: %s' % reloc
)
251 recipe
= self
._RELOCATION
_RECIPES
_ARM
.get(reloc_type
, None)
252 elif self
.elffile
.get_machine_arch() == 'AArch64':
253 recipe
= self
._RELOCATION
_RECIPES
_AARCH
64.get(reloc_type
, None)
254 elif self
.elffile
.get_machine_arch() == '64-bit PowerPC':
255 recipe
= self
._RELOCATION
_RECIPES
_PPC
64.get(reloc_type
, None)
258 raise ELFRelocationError(
259 'Unsupported relocation type: %s' % reloc_type
)
261 # So now we have everything we need to actually perform the relocation.
264 # 0. Find out which struct we're going to be using to read this value
265 # from the stream and write it back.
266 if recipe
.bytesize
== 4:
267 value_struct
= self
.elffile
.structs
.Elf_word('')
268 elif recipe
.bytesize
== 8:
269 value_struct
= self
.elffile
.structs
.Elf_word64('')
271 raise ELFRelocationError('Invalid bytesize %s for relocation' %
274 # 1. Read the value from the stream (with correct size and endianness)
275 original_value
= struct_parse(
278 stream_pos
=reloc
['r_offset'])
279 # 2. Apply the relocation to the value, acting according to the recipe
280 relocated_value
= recipe
.calc_func(
281 value
=original_value
,
283 offset
=reloc
['r_offset'],
284 addend
=reloc
['r_addend'] if recipe
.has_addend
else 0)
285 # 3. Write the relocated value back into the stream
286 stream
.seek(reloc
['r_offset'])
288 # Make sure the relocated value fits back by wrapping it around. This
289 # looks like a problem, but it seems to be the way this is done in
291 relocated_value
= relocated_value
% (2 ** (recipe
.bytesize
* 8))
292 value_struct
.build_stream(relocated_value
, stream
)
294 # Relocations are represented by "recipes". Each recipe specifies:
295 # bytesize: The number of bytes to read (and write back) to the section.
296 # This is the unit of data on which relocation is performed.
297 # has_addend: Does this relocation have an extra addend?
298 # calc_func: A function that performs the relocation on an extracted
299 # value, and returns the updated value.
301 _RELOCATION_RECIPE_TYPE
= namedtuple('_RELOCATION_RECIPE_TYPE',
302 'bytesize has_addend calc_func')
304 def _reloc_calc_identity(value
, sym_value
, offset
, addend
=0):
307 def _reloc_calc_sym_plus_value(value
, sym_value
, offset
, addend
=0):
308 return sym_value
+ value
310 def _reloc_calc_sym_plus_value_pcrel(value
, sym_value
, offset
, addend
=0):
311 return sym_value
+ value
- offset
313 def _reloc_calc_sym_plus_addend(value
, sym_value
, offset
, addend
=0):
314 return sym_value
+ addend
316 def _reloc_calc_sym_plus_addend_pcrel(value
, sym_value
, offset
, addend
=0):
317 return sym_value
+ addend
- offset
319 def _arm_reloc_calc_sym_plus_value_pcrel(value
, sym_value
, offset
, addend
=0):
320 return sym_value
// 4 + value
- offset
// 4
322 _RELOCATION_RECIPES_ARM
= {
323 ENUM_RELOC_TYPE_ARM
['R_ARM_ABS32']: _RELOCATION_RECIPE_TYPE(
324 bytesize
=4, has_addend
=False,
325 calc_func
=_reloc_calc_sym_plus_value
),
326 ENUM_RELOC_TYPE_ARM
['R_ARM_CALL']: _RELOCATION_RECIPE_TYPE(
327 bytesize
=4, has_addend
=False,
328 calc_func
=_arm_reloc_calc_sym_plus_value_pcrel
),
331 _RELOCATION_RECIPES_AARCH64
= {
332 ENUM_RELOC_TYPE_AARCH64
['R_AARCH64_ABS64']: _RELOCATION_RECIPE_TYPE(
333 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
334 ENUM_RELOC_TYPE_AARCH64
['R_AARCH64_ABS32']: _RELOCATION_RECIPE_TYPE(
335 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
336 ENUM_RELOC_TYPE_AARCH64
['R_AARCH64_PREL32']: _RELOCATION_RECIPE_TYPE(
337 bytesize
=4, has_addend
=True,
338 calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
341 # https://dmz-portal.mips.com/wiki/MIPS_relocation_types
342 _RELOCATION_RECIPES_MIPS
= {
343 ENUM_RELOC_TYPE_MIPS
['R_MIPS_NONE']: _RELOCATION_RECIPE_TYPE(
344 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
345 ENUM_RELOC_TYPE_MIPS
['R_MIPS_32']: _RELOCATION_RECIPE_TYPE(
346 bytesize
=4, has_addend
=False,
347 calc_func
=_reloc_calc_sym_plus_value
),
350 _RELOCATION_RECIPES_PPC64
= {
351 ENUM_RELOC_TYPE_PPC64
['R_PPC64_ADDR32']: _RELOCATION_RECIPE_TYPE(
352 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
353 ENUM_RELOC_TYPE_PPC64
['R_PPC64_REL32']: _RELOCATION_RECIPE_TYPE(
354 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
355 ENUM_RELOC_TYPE_PPC64
['R_PPC64_ADDR64']: _RELOCATION_RECIPE_TYPE(
356 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
359 _RELOCATION_RECIPES_X86
= {
360 ENUM_RELOC_TYPE_i386
['R_386_NONE']: _RELOCATION_RECIPE_TYPE(
361 bytesize
=4, has_addend
=False, calc_func
=_reloc_calc_identity
),
362 ENUM_RELOC_TYPE_i386
['R_386_32']: _RELOCATION_RECIPE_TYPE(
363 bytesize
=4, has_addend
=False,
364 calc_func
=_reloc_calc_sym_plus_value
),
365 ENUM_RELOC_TYPE_i386
['R_386_PC32']: _RELOCATION_RECIPE_TYPE(
366 bytesize
=4, has_addend
=False,
367 calc_func
=_reloc_calc_sym_plus_value_pcrel
),
370 _RELOCATION_RECIPES_X64
= {
371 ENUM_RELOC_TYPE_x64
['R_X86_64_NONE']: _RELOCATION_RECIPE_TYPE(
372 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_identity
),
373 ENUM_RELOC_TYPE_x64
['R_X86_64_64']: _RELOCATION_RECIPE_TYPE(
374 bytesize
=8, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
375 ENUM_RELOC_TYPE_x64
['R_X86_64_PC32']: _RELOCATION_RECIPE_TYPE(
376 bytesize
=4, has_addend
=True,
377 calc_func
=_reloc_calc_sym_plus_addend_pcrel
),
378 ENUM_RELOC_TYPE_x64
['R_X86_64_32']: _RELOCATION_RECIPE_TYPE(
379 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),
380 ENUM_RELOC_TYPE_x64
['R_X86_64_32S']: _RELOCATION_RECIPE_TYPE(
381 bytesize
=4, has_addend
=True, calc_func
=_reloc_calc_sym_plus_addend
),