1 // elfcpp_file.h -- file access for elfcpp -*- C++ -*-
3 // Copyright 2006, 2007, Free Software Foundation, Inc.
4 // Written by Ian Lance Taylor <iant@google.com>.
6 // This file is part of elfcpp.
8 // This program is free software; you can redistribute it and/or
9 // modify it under the terms of the GNU Library General Public License
10 // as published by the Free Software Foundation; either version 2, or
11 // (at your option) any later version.
13 // In addition to the permissions in the GNU Library General Public
14 // License, the Free Software Foundation gives you unlimited
15 // permission to link the compiled version of this file into
16 // combinations with other programs, and to distribute those
17 // combinations without any restriction coming from the use of this
18 // file. (The Library Public License restrictions do apply in other
19 // respects; for example, they cover modification of the file, and
20 /// distribution when not linked into a combined executable.)
22 // This program is distributed in the hope that it will be useful, but
23 // WITHOUT ANY WARRANTY; without even the implied warranty of
24 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
25 // Library General Public License for more details.
27 // You should have received a copy of the GNU Library General Public
28 // License along with this program; if not, write to the Free Software
29 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA
32 // This header file defines the class Elf_file which can be used to
33 // read useful data from an ELF file. The functions here are all
34 // templates which take a file interface object as a parameter. This
35 // type must have a subtype View. This type must support two methods:
36 // View view(off_t file_offset, off_t data_size)
37 // returns a View for the specified part of the file.
38 // void error(const char* printf_format, ...)
39 // prints an error message and does not return. The subtype View must
41 // const unsigned char* data()
42 // which returns a pointer to a buffer containing the requested data.
43 // This general interface is used to read data from the file. Objects
44 // of type View will never survive longer than the elfcpp function.
46 // Some of these functions must return a reference to part of the
47 // file. To use these, the file interface must support a subtype
49 // Location(off_t file_offset, off_t data_size)
50 // To use this in conjunction with the accessors types Shdr, etc., the
51 // file interface should support an overload of view:
52 // View view(Location)
53 // This permits writing
54 // elfcpp::Shdr shdr(file, ef.section_header(n));
68 // A simple helper class to recognize if a file has an ELF header.
73 // Maximum header size. The user should try to read this much of
74 // the file when using this class.
76 static const int max_header_size
= Elf_sizes
<64>::ehdr_size
;
78 // Checks if the file contains the ELF magic. Other header fields
82 is_elf_file(const unsigned char* ehdr_buf
, int size
);
84 // Check if EHDR_BUF/BUFSIZE is a valid header of a 32-bit or
85 // 64-bit, little-endian or big-endian ELF file. Assumes
86 // is_elf_file() has been checked to be true. If the header is not
87 // valid, *ERROR contains a human-readable error message. If is is,
88 // *SIZE is set to either 32 or 64, *BIG_ENDIAN is set to indicate
89 // whether the file is big-endian.
92 is_valid_header(const unsigned char* ehdr_buf
, off_t bufsize
,
93 int* size
, bool* big_endian
,
97 // This object is used to read an ELF file.
98 // SIZE: The size of file, 32 or 64.
99 // BIG_ENDIAN: Whether the file is in big-endian format.
100 // FILE: A file reading type as described above.
102 template<int size
, bool big_endian
, typename File
>
106 typedef Elf_file
<size
, big_endian
, File
> This
;
109 static const int ehdr_size
= Elf_sizes
<size
>::ehdr_size
;
110 static const int phdr_size
= Elf_sizes
<size
>::phdr_size
;
111 static const int shdr_size
= Elf_sizes
<size
>::shdr_size
;
112 static const int sym_size
= Elf_sizes
<size
>::sym_size
;
113 static const int rel_size
= Elf_sizes
<size
>::rel_size
;
114 static const int rela_size
= Elf_sizes
<size
>::rela_size
;
116 typedef Ehdr
<size
, big_endian
> Ef_ehdr
;
117 typedef Phdr
<size
, big_endian
> Ef_phdr
;
118 typedef Shdr
<size
, big_endian
> Ef_shdr
;
119 typedef Sym
<size
, big_endian
> Ef_sym
;
121 // Construct an Elf_file given an ELF file header.
122 Elf_file(File
* file
, const Ef_ehdr
& ehdr
)
123 { this->construct(file
, ehdr
); }
125 // Construct an ELF file.
127 Elf_file(File
* file
);
129 // Return the file offset to the section headers.
132 { return this->shoff_
; }
134 // Find the first section with an sh_type field equal to TYPE and
135 // return its index. Returns SHN_UNDEF if there is no such section.
137 find_section_by_type(unsigned int type
);
139 // Return the number of sections.
143 this->initialize_shnum();
147 // Return the section index of the section name string table.
151 this->initialize_shnum();
152 return this->shstrndx_
;
155 // Return the value to subtract from section indexes >=
156 // SHN_LORESERVE. See the comment in initialize_shnum.
160 this->initialize_shnum();
161 return this->large_shndx_offset_
;
164 // Return the location of the header of section SHNDX.
165 typename
File::Location
166 section_header(unsigned int shndx
)
168 return typename
File::Location(this->section_header_offset(shndx
),
172 // Return the name of section SHNDX.
174 section_name(unsigned int shndx
);
176 // Return the location of the contents of section SHNDX.
177 typename
File::Location
178 section_contents(unsigned int shndx
);
180 // Return the size of section SHNDX.
181 typename Elf_types
<size
>::Elf_WXword
182 section_size(unsigned int shndx
);
184 // Return the flags of section SHNDX.
185 typename Elf_types
<size
>::Elf_WXword
186 section_flags(unsigned int shndx
);
188 // Return the address of section SHNDX.
189 typename Elf_types
<size
>::Elf_Addr
190 section_addr(unsigned int shndx
);
192 // Return the type of section SHNDX.
194 section_type(unsigned int shndx
);
196 // Return the link field of section SHNDX.
198 section_link(unsigned int shndx
);
200 // Return the info field of section SHNDX.
202 section_info(unsigned int shndx
);
204 // Return the addralign field of section SHNDX.
205 typename Elf_types
<size
>::Elf_WXword
206 section_addralign(unsigned int shndx
);
209 // Shared constructor code.
211 construct(File
* file
, const Ef_ehdr
& ehdr
);
213 // Initialize shnum_ and shstrndx_.
217 // Return the file offset of the header of section SHNDX.
219 section_header_offset(unsigned int shndx
);
221 // The file we are reading.
223 // The file offset to the section headers.
225 // The number of sections.
227 // The section index of the section name string table.
228 unsigned int shstrndx_
;
229 // Offset to add to sections larger than SHN_LORESERVE.
230 int large_shndx_offset_
;
233 // A small wrapper around SHT_STRTAB data mapped to memory. It checks that the
234 // index is not out of bounds and the string is NULL-terminated.
239 // Construct an Elf_strtab for a section with contents *P and size SIZE.
240 Elf_strtab(const unsigned char* p
, size_t size
);
242 // Return the file offset to the section headers.
244 get_c_string(size_t offset
, const char** cstring
) const
246 if (offset
>= this->usable_size_
)
248 *cstring
= this->base_
+ offset
;
253 // Contents of the section mapped to memory.
255 // One larger that the position of the last NULL character in the section.
256 // For valid SHT_STRTAB sections, this is the size of the section.
260 // Inline function definitions.
262 // Check for presence of the ELF magic number.
265 Elf_recognizer::is_elf_file(const unsigned char* ehdr_buf
, int size
)
270 static unsigned char elfmagic
[4] =
272 elfcpp::ELFMAG0
, elfcpp::ELFMAG1
,
273 elfcpp::ELFMAG2
, elfcpp::ELFMAG3
275 return memcmp(ehdr_buf
, elfmagic
, 4) == 0;
281 // Print a number to a string.
284 internal_printf_int(const char* format
, int arg
)
287 snprintf(buf
, sizeof(buf
), format
, arg
);
288 return std::string(buf
);
291 } // End anonymous namespace.
293 // Check the validity of the ELF header.
296 Elf_recognizer::is_valid_header(
297 const unsigned char* ehdr_buf
,
303 if (bufsize
< elfcpp::EI_NIDENT
)
305 *error
= _("ELF file too short");
309 int v
= ehdr_buf
[elfcpp::EI_VERSION
];
310 if (v
!= elfcpp::EV_CURRENT
)
312 if (v
== elfcpp::EV_NONE
)
313 *error
= _("invalid ELF version 0");
315 *error
= internal_printf_int(_("unsupported ELF version %d"), v
);
319 int c
= ehdr_buf
[elfcpp::EI_CLASS
];
320 if (c
== elfcpp::ELFCLASSNONE
)
322 *error
= _("invalid ELF class 0");
325 else if (c
!= elfcpp::ELFCLASS32
326 && c
!= elfcpp::ELFCLASS64
)
328 *error
= internal_printf_int(_("unsupported ELF class %d"), c
);
332 int d
= ehdr_buf
[elfcpp::EI_DATA
];
333 if (d
== elfcpp::ELFDATANONE
)
335 *error
= _("invalid ELF data encoding");
338 else if (d
!= elfcpp::ELFDATA2LSB
339 && d
!= elfcpp::ELFDATA2MSB
)
341 *error
= internal_printf_int(_("unsupported ELF data encoding %d"), d
);
345 *big_endian
= (d
== elfcpp::ELFDATA2MSB
);
347 if (c
== elfcpp::ELFCLASS32
)
349 if (bufsize
< elfcpp::Elf_sizes
<32>::ehdr_size
)
351 *error
= _("ELF file too short");
358 if (bufsize
< elfcpp::Elf_sizes
<64>::ehdr_size
)
360 *error
= _("ELF file too short");
369 // Template function definitions.
371 // Construct an Elf_file given an ELF file header.
373 template<int size
, bool big_endian
, typename File
>
375 Elf_file
<size
, big_endian
, File
>::construct(File
* file
, const Ef_ehdr
& ehdr
)
378 this->shoff_
= ehdr
.get_e_shoff();
379 this->shnum_
= ehdr
.get_e_shnum();
380 this->shstrndx_
= ehdr
.get_e_shstrndx();
381 this->large_shndx_offset_
= 0;
382 if (ehdr
.get_e_ehsize() != This::ehdr_size
)
383 file
->error(_("bad e_ehsize (%d != %d)"),
384 ehdr
.get_e_ehsize(), This::ehdr_size
);
385 if (ehdr
.get_e_shentsize() != This::shdr_size
)
386 file
->error(_("bad e_shentsize (%d != %d)"),
387 ehdr
.get_e_shentsize(), This::shdr_size
);
390 // Construct an ELF file.
392 template<int size
, bool big_endian
, typename File
>
394 Elf_file
<size
, big_endian
, File
>::Elf_file(File
* file
)
396 typename
File::View
v(file
->view(file_header_offset
, This::ehdr_size
));
397 this->construct(file
, Ef_ehdr(v
.data()));
400 // Initialize the shnum_ and shstrndx_ fields, handling overflow.
402 template<int size
, bool big_endian
, typename File
>
404 Elf_file
<size
, big_endian
, File
>::initialize_shnum()
406 if ((this->shnum_
== 0 || this->shstrndx_
== SHN_XINDEX
)
407 && this->shoff_
!= 0)
409 typename
File::View
v(this->file_
->view(this->shoff_
, This::shdr_size
));
410 Ef_shdr
shdr(v
.data());
412 if (this->shnum_
== 0)
413 this->shnum_
= shdr
.get_sh_size();
415 if (this->shstrndx_
== SHN_XINDEX
)
417 this->shstrndx_
= shdr
.get_sh_link();
419 // Versions of the GNU binutils between 2.12 and 2.18 did
420 // not handle objects with more than SHN_LORESERVE sections
421 // correctly. All large section indexes were offset by
422 // 0x100. Some information can be found here:
423 // http://sourceware.org/bugzilla/show_bug.cgi?id=5900 .
424 // Fortunately these object files are easy to detect, as the
425 // GNU binutils always put the section header string table
426 // near the end of the list of sections. Thus if the
427 // section header string table index is larger than the
428 // number of sections, then we know we have to subtract
429 // 0x100 to get the real section index.
430 if (this->shstrndx_
>= this->shnum_
)
432 if (this->shstrndx_
>= elfcpp::SHN_LORESERVE
+ 0x100)
434 this->large_shndx_offset_
= - 0x100;
435 this->shstrndx_
-= 0x100;
437 if (this->shstrndx_
>= this->shnum_
)
438 this->file_
->error(_("bad shstrndx: %u >= %u"),
439 this->shstrndx_
, this->shnum_
);
445 // Find section with sh_type equal to TYPE and return its index.
446 // Returns SHN_UNDEF if not found.
448 template<int size
, bool big_endian
, typename File
>
450 Elf_file
<size
, big_endian
, File
>::find_section_by_type(unsigned int type
)
452 unsigned int shnum
= this->shnum();
453 typename
File::View
v(this->file_
->view(this->shoff_
,
454 This::shdr_size
* shnum
));
455 for (unsigned int i
= 0; i
< shnum
; i
++)
457 Ef_shdr
shdr(v
.data() + This::shdr_size
* i
);
458 if (shdr
.get_sh_type() == type
)
464 // Return the file offset of the section header of section SHNDX.
466 template<int size
, bool big_endian
, typename File
>
468 Elf_file
<size
, big_endian
, File
>::section_header_offset(unsigned int shndx
)
470 if (shndx
>= this->shnum())
471 this->file_
->error(_("section_header_offset: bad shndx %u >= %u"),
472 shndx
, this->shnum());
473 return this->shoff_
+ This::shdr_size
* shndx
;
476 // Return the name of section SHNDX.
478 template<int size
, bool big_endian
, typename File
>
480 Elf_file
<size
, big_endian
, File
>::section_name(unsigned int shndx
)
482 File
* const file
= this->file_
;
484 // Get the section name offset.
485 unsigned int sh_name
;
487 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
489 Ef_shdr
shdr(v
.data());
490 sh_name
= shdr
.get_sh_name();
493 // Get the file offset for the section name string table data.
495 typename Elf_types
<size
>::Elf_WXword shstr_size
;
497 const unsigned int shstrndx
= this->shstrndx_
;
498 typename
File::View
v(file
->view(this->section_header_offset(shstrndx
),
500 Ef_shdr
shstr_shdr(v
.data());
501 shstr_off
= shstr_shdr
.get_sh_offset();
502 shstr_size
= shstr_shdr
.get_sh_size();
505 if (sh_name
>= shstr_size
)
506 file
->error(_("bad section name offset for section %u: %u"),
509 typename
File::View
v(file
->view(shstr_off
, shstr_size
));
511 const unsigned char* datau
= v
.data();
512 const char* data
= reinterpret_cast<const char*>(datau
);
513 const void* p
= ::memchr(data
+ sh_name
, '\0', shstr_size
- sh_name
);
515 file
->error(_("missing null terminator for name of section %u"),
518 size_t len
= static_cast<const char*>(p
) - (data
+ sh_name
);
520 return std::string(data
+ sh_name
, len
);
523 // Return the contents of section SHNDX.
525 template<int size
, bool big_endian
, typename File
>
526 typename
File::Location
527 Elf_file
<size
, big_endian
, File
>::section_contents(unsigned int shndx
)
529 File
* const file
= this->file_
;
531 if (shndx
>= this->shnum())
532 file
->error(_("section_contents: bad shndx %u >= %u"),
533 shndx
, this->shnum());
535 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
537 Ef_shdr
shdr(v
.data());
538 return typename
File::Location(shdr
.get_sh_offset(), shdr
.get_sh_size());
541 // Get the size of section SHNDX.
543 template<int size
, bool big_endian
, typename File
>
544 typename Elf_types
<size
>::Elf_WXword
545 Elf_file
<size
, big_endian
, File
>::section_size(unsigned int shndx
)
547 File
* const file
= this->file_
;
549 if (shndx
>= this->shnum())
550 file
->error(_("section_size: bad shndx %u >= %u"),
551 shndx
, this->shnum());
553 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
556 Ef_shdr
shdr(v
.data());
557 return shdr
.get_sh_size();
560 // Return the section flags of section SHNDX.
562 template<int size
, bool big_endian
, typename File
>
563 typename Elf_types
<size
>::Elf_WXword
564 Elf_file
<size
, big_endian
, File
>::section_flags(unsigned int shndx
)
566 File
* const file
= this->file_
;
568 if (shndx
>= this->shnum())
569 file
->error(_("section_flags: bad shndx %u >= %u"),
570 shndx
, this->shnum());
572 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
575 Ef_shdr
shdr(v
.data());
576 return shdr
.get_sh_flags();
579 // Return the address of section SHNDX.
581 template<int size
, bool big_endian
, typename File
>
582 typename Elf_types
<size
>::Elf_Addr
583 Elf_file
<size
, big_endian
, File
>::section_addr(unsigned int shndx
)
585 File
* const file
= this->file_
;
587 if (shndx
>= this->shnum())
588 file
->error(_("section_flags: bad shndx %u >= %u"),
589 shndx
, this->shnum());
591 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
594 Ef_shdr
shdr(v
.data());
595 return shdr
.get_sh_addr();
598 // Return the type of section SHNDX.
600 template<int size
, bool big_endian
, typename File
>
602 Elf_file
<size
, big_endian
, File
>::section_type(unsigned int shndx
)
604 File
* const file
= this->file_
;
606 if (shndx
>= this->shnum())
607 file
->error(_("section_type: bad shndx %u >= %u"),
608 shndx
, this->shnum());
610 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
613 Ef_shdr
shdr(v
.data());
614 return shdr
.get_sh_type();
617 // Return the sh_link field of section SHNDX.
619 template<int size
, bool big_endian
, typename File
>
621 Elf_file
<size
, big_endian
, File
>::section_link(unsigned int shndx
)
623 File
* const file
= this->file_
;
625 if (shndx
>= this->shnum())
626 file
->error(_("section_link: bad shndx %u >= %u"),
627 shndx
, this->shnum());
629 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
632 Ef_shdr
shdr(v
.data());
633 return shdr
.get_sh_link();
636 // Return the sh_info field of section SHNDX.
638 template<int size
, bool big_endian
, typename File
>
640 Elf_file
<size
, big_endian
, File
>::section_info(unsigned int shndx
)
642 File
* const file
= this->file_
;
644 if (shndx
>= this->shnum())
645 file
->error(_("section_info: bad shndx %u >= %u"),
646 shndx
, this->shnum());
648 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
651 Ef_shdr
shdr(v
.data());
652 return shdr
.get_sh_info();
655 // Return the sh_addralign field of section SHNDX.
657 template<int size
, bool big_endian
, typename File
>
658 typename Elf_types
<size
>::Elf_WXword
659 Elf_file
<size
, big_endian
, File
>::section_addralign(unsigned int shndx
)
661 File
* const file
= this->file_
;
663 if (shndx
>= this->shnum())
664 file
->error(_("section_addralign: bad shndx %u >= %u"),
665 shndx
, this->shnum());
667 typename
File::View
v(file
->view(this->section_header_offset(shndx
),
670 Ef_shdr
shdr(v
.data());
671 return shdr
.get_sh_addralign();
675 Elf_strtab::Elf_strtab(const unsigned char* p
, size_t size
)
677 // Check if the section is NUL-terminated. If it isn't, we ignore
678 // the last part to make sure we don't return non-NUL-terminated
680 while (size
> 0 && p
[size
- 1] != 0)
682 this->base_
= reinterpret_cast<const char*>(p
);
683 this->usable_size_
= size
;
686 } // End namespace elfcpp.
688 #endif // !defined(ELFCPP_FILE_H)
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