1 /* Object file "section" support for the BFD library.
2 Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
3 Written by Cygnus Support.
5 This file is part of BFD, the Binary File Descriptor library.
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2 of the License, or
10 (at your option) any later version.
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program; if not, write to the Free Software
19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
25 The raw data contained within a BFD is maintained through the
26 section abstraction. A single BFD may have any number of
27 sections. It keeps hold of them by pointing to the first;
28 each one points to the next in the list.
30 Sections are supported in BFD in <<section.c>>.
36 @* section prototypes::
40 Section Input, Section Output, Sections, Sections
44 When a BFD is opened for reading, the section structures are
45 created and attached to the BFD.
47 Each section has a name which describes the section in the
48 outside world---for example, <<a.out>> would contain at least
49 three sections, called <<.text>>, <<.data>> and <<.bss>>.
51 Names need not be unique; for example a COFF file may have several
52 sections named <<.data>>.
54 Sometimes a BFD will contain more than the ``natural'' number of
55 sections. A back end may attach other sections containing
56 constructor data, or an application may add a section (using
57 <<bfd_make_section>>) to the sections attached to an already open
58 BFD. For example, the linker creates an extra section
59 <<COMMON>> for each input file's BFD to hold information about
62 The raw data is not necessarily read in when
63 the section descriptor is created. Some targets may leave the
64 data in place until a <<bfd_get_section_contents>> call is
65 made. Other back ends may read in all the data at once. For
66 example, an S-record file has to be read once to determine the
67 size of the data. An IEEE-695 file doesn't contain raw data in
68 sections, but data and relocation expressions intermixed, so
69 the data area has to be parsed to get out the data and
73 Section Output, typedef asection, Section Input, Sections
78 To write a new object style BFD, the various sections to be
79 written have to be created. They are attached to the BFD in
80 the same way as input sections; data is written to the
81 sections using <<bfd_set_section_contents>>.
83 Any program that creates or combines sections (e.g., the assembler
84 and linker) must use the <<asection>> fields <<output_section>> and
85 <<output_offset>> to indicate the file sections to which each
86 section must be written. (If the section is being created from
87 scratch, <<output_section>> should probably point to the section
88 itself and <<output_offset>> should probably be zero.)
90 The data to be written comes from input sections attached
91 (via <<output_section>> pointers) to
92 the output sections. The output section structure can be
93 considered a filter for the input section: the output section
94 determines the vma of the output data and the name, but the
95 input section determines the offset into the output section of
96 the data to be written.
98 E.g., to create a section "O", starting at 0x100, 0x123 long,
99 containing two subsections, "A" at offset 0x0 (i.e., at vma
100 0x100) and "B" at offset 0x20 (i.e., at vma 0x120) the <<asection>>
101 structures would look like:
106 | output_section -----------> section name "O"
108 | section name "B" | size 0x123
109 | output_offset 0x20 |
111 | output_section --------|
117 The data within a section is stored in a <<seclet>>. These
118 are much like the fixups in <<gas>>. The seclet abstraction
119 allows a section to grow and shrink within itself.
121 A seclet knows how big it is, and which is the next seclet and
122 where the raw data for it is; it also points to a list of
123 relocations which apply to it.
125 The seclet is used by the linker to perform relaxing on final
126 code. The compiler creates code which is as big as
127 necessary to make it work without relaxing, and the user can
128 select whether to relax. Sometimes relaxing takes a lot of
129 time. The linker runs around the relocations to see if any
130 are attached to data which can be shrunk, if so it does it on
131 a seclet by seclet basis.
144 typedef asection, section prototypes, Section Output, Sections
148 Here is the section structure:
154 . {* The name of the section; the name isn't a copy, the pointer is
155 . the same as that passed to bfd_make_section. *}
159 . {* Which section is it; 0..nth. *}
163 . {* The next section in the list belonging to the BFD, or NULL. *}
167 . {* The field flags contains attributes of the section. Some
168 . flags are read in from the object file, and some are
169 . synthesized from other information. *}
173 .#define SEC_NO_FLAGS 0x000
175 . {* Tells the OS to allocate space for this section when loading.
176 . This is clear for a section containing debug information
178 .#define SEC_ALLOC 0x001
180 . {* Tells the OS to load the section from the file when loading.
181 . This is clear for a .bss section. *}
182 .#define SEC_LOAD 0x002
184 . {* The section contains data still to be relocated, so there is
185 . some relocation information too. *}
186 .#define SEC_RELOC 0x004
188 .#if 0 {* Obsolete ? *}
189 .#define SEC_BALIGN 0x008
192 . {* A signal to the OS that the section contains read only
194 .#define SEC_READONLY 0x010
196 . {* The section contains code only. *}
197 .#define SEC_CODE 0x020
199 . {* The section contains data only. *}
200 .#define SEC_DATA 0x040
202 . {* The section will reside in ROM. *}
203 .#define SEC_ROM 0x080
205 . {* The section contains constructor information. This section
206 . type is used by the linker to create lists of constructors and
207 . destructors used by <<g++>>. When a back end sees a symbol
208 . which should be used in a constructor list, it creates a new
209 . section for the type of name (e.g., <<__CTOR_LIST__>>), attaches
210 . the symbol to it, and builds a relocation. To build the lists
211 . of constructors, all the linker has to do is catenate all the
212 . sections called <<__CTOR_LIST__>> and relocate the data
213 . contained within - exactly the operations it would peform on
215 .#define SEC_CONSTRUCTOR 0x100
217 . {* The section is a constuctor, and should be placed at the
218 . end of the text, data, or bss section(?). *}
219 .#define SEC_CONSTRUCTOR_TEXT 0x1100
220 .#define SEC_CONSTRUCTOR_DATA 0x2100
221 .#define SEC_CONSTRUCTOR_BSS 0x3100
223 . {* The section has contents - a data section could be
224 . <<SEC_ALLOC>> | <<SEC_HAS_CONTENTS>>; a debug section could be
225 . <<SEC_HAS_CONTENTS>> *}
226 .#define SEC_HAS_CONTENTS 0x200
228 . {* An instruction to the linker to not output the section
229 . even if it has information which would normally be written. *}
230 .#define SEC_NEVER_LOAD 0x400
232 . {* The section is a shared library section. The linker must leave
233 . these completely alone, as the vma and size are used when
234 . the executable is loaded. *}
235 .#define SEC_SHARED_LIBRARY 0x800
237 . {* The section is a common section (symbols may be defined
238 . multiple times, the value of a symbol is the amount of
239 . space it requires, and the largest symbol value is the one
240 . used). Most targets have exactly one of these (which we
241 . translate to bfd_com_section), but ECOFF has two. *}
242 .#define SEC_IS_COMMON 0x8000
244 . {* The section contains only debugging information. For
245 . example, this is set for ELF .debug and .stab sections.
246 . strip tests this flag to see if a section can be
248 .#define SEC_DEBUGGING 0x10000
250 . {* End of section flags. *}
252 . {* The virtual memory address of the section - where it will be
253 . at run time. The symbols are relocated against this. The
254 . user_set_vma flag is maintained by bfd; if it's not set, the
255 . backend can assign addresses (for example, in <<a.out>>, where
256 . the default address for <<.data>> is dependent on the specific
257 . target and various flags). *}
260 . boolean user_set_vma;
262 . {* The load address of the section - where it would be in a
263 . rom image; really only used for writing section header
268 . {* The size of the section in bytes, as it will be output.
269 . contains a value even if the section has no contents (e.g., the
270 . size of <<.bss>>). This will be filled in after relocation *}
272 . bfd_size_type _cooked_size;
274 . {* The original size on disk of the section, in bytes. Normally this
275 . value is the same as the size, but if some relaxing has
276 . been done, then this value will be bigger. *}
278 . bfd_size_type _raw_size;
280 . {* If this section is going to be output, then this value is the
281 . offset into the output section of the first byte in the input
282 . section. E.g., if this was going to start at the 100th byte in
283 . the output section, this value would be 100. *}
285 . bfd_vma output_offset;
287 . {* The output section through which to map on output. *}
289 . struct sec *output_section;
291 . {* The alignment requirement of the section, as an exponent of 2 -
292 . e.g., 3 aligns to 2^3 (or 8). *}
294 . unsigned int alignment_power;
296 . {* If an input section, a pointer to a vector of relocation
297 . records for the data in this section. *}
299 . struct reloc_cache_entry *relocation;
301 . {* If an output section, a pointer to a vector of pointers to
302 . relocation records for the data in this section. *}
304 . struct reloc_cache_entry **orelocation;
306 . {* The number of relocation records in one of the above *}
308 . unsigned reloc_count;
310 . {* Information below is back end specific - and not always used
313 . {* File position of section data *}
317 . {* File position of relocation info *}
319 . file_ptr rel_filepos;
321 . {* File position of line data *}
323 . file_ptr line_filepos;
325 . {* Pointer to data for applications *}
329 . struct lang_output_section *otheruserdata;
331 . {* Attached line number information *}
335 . {* Number of line number records *}
337 . unsigned int lineno_count;
339 . {* When a section is being output, this value changes as more
340 . linenumbers are written out *}
342 . file_ptr moving_line_filepos;
344 . {* What the section number is in the target world *}
350 . {* If this is a constructor section then here is a list of the
351 . relocations created to relocate items within it. *}
353 . struct relent_chain *constructor_chain;
355 . {* The BFD which owns the section. *}
359 . boolean reloc_done;
360 . {* A symbol which points at this section only *}
361 . struct symbol_cache_entry *symbol;
362 . struct symbol_cache_entry **symbol_ptr_ptr;
364 . struct bfd_seclet *seclets_head;
365 . struct bfd_seclet *seclets_tail;
369 . {* These sections are global, and are managed by BFD. The application
370 . and target back end are not permitted to change the values in
372 .#define BFD_ABS_SECTION_NAME "*ABS*"
373 .#define BFD_UND_SECTION_NAME "*UND*"
374 .#define BFD_COM_SECTION_NAME "*COM*"
375 .#define BFD_IND_SECTION_NAME "*IND*"
377 . {* the absolute section *}
378 .extern asection bfd_abs_section;
379 . {* Pointer to the undefined section *}
380 .extern asection bfd_und_section;
381 . {* Pointer to the common section *}
382 .extern asection bfd_com_section;
383 . {* Pointer to the indirect section *}
384 .extern asection bfd_ind_section;
386 .extern struct symbol_cache_entry *bfd_abs_symbol;
387 .extern struct symbol_cache_entry *bfd_com_symbol;
388 .extern struct symbol_cache_entry *bfd_und_symbol;
389 .extern struct symbol_cache_entry *bfd_ind_symbol;
390 .#define bfd_get_section_size_before_reloc(section) \
391 . (section->reloc_done ? (abort(),1): (section)->_raw_size)
392 .#define bfd_get_section_size_after_reloc(section) \
393 . ((section->reloc_done) ? (section)->_cooked_size: (abort(),1))
396 /* These symbols are global, not specific to any BFD. Therefore, anything
397 that tries to change them is broken, and should be repaired. */
398 static CONST asymbol global_syms
[] = {
399 /* the_bfd, name, value, attr, section [, udata] */
400 { 0, BFD_COM_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_com_section
},
401 { 0, BFD_UND_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_und_section
},
402 { 0, BFD_ABS_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_abs_section
},
403 { 0, BFD_IND_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_ind_section
},
406 #define STD_SECTION(SEC, FLAGS, SYM, NAME, IDX) \
407 asymbol *SYM = (asymbol *) &global_syms[IDX]; \
408 asection SEC = { NAME, 0, 0, FLAGS, 0, 0, (boolean) 0, 0, 0, 0, &SEC,\
409 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, (boolean) 0, \
410 (asymbol *) &global_syms[IDX], &SYM, }
412 STD_SECTION (bfd_com_section
, SEC_IS_COMMON
, bfd_com_symbol
, BFD_COM_SECTION_NAME
, 0);
413 STD_SECTION (bfd_und_section
, 0, bfd_und_symbol
, BFD_UND_SECTION_NAME
, 1);
414 STD_SECTION (bfd_abs_section
, 0, bfd_abs_symbol
, BFD_ABS_SECTION_NAME
, 2);
415 STD_SECTION (bfd_ind_section
, 0, bfd_ind_symbol
, BFD_IND_SECTION_NAME
, 3);
421 section prototypes, , typedef asection, Sections
425 These are the functions exported by the section handling part of
431 bfd_get_section_by_name
434 asection *bfd_get_section_by_name(bfd *abfd, CONST char *name);
437 Run through the provided @var{abfd} and return the one of the
438 <<asection>>s whose name matches @var{name}, otherwise NULL.
439 @xref{Sections}, for more information.
441 This should only be used in special cases; the normal way to process
442 all sections of a given name is to use bfd_map_over_sections and
443 strcmp on the name (or better yet, base it on the section flags
444 or something else) for each section.
448 DEFUN(bfd_get_section_by_name
,(abfd
, name
),
454 for (sect
= abfd
->sections
; sect
!= NULL
; sect
= sect
->next
)
455 if (!strcmp (sect
->name
, name
)) return sect
;
462 bfd_make_section_old_way
465 asection *bfd_make_section_old_way(bfd *abfd, CONST char *name);
468 Create a new empty section called @var{name}
469 and attach it to the end of the chain of sections for the
470 BFD @var{abfd}. An attempt to create a section with a name which
471 is already in use, returns its pointer without changing the
474 It has the funny name since this is the way it used to be
475 before it was rewritten....
478 o invalid_operation -
479 If output has already started for this BFD.
481 If obstack alloc fails.
487 DEFUN(bfd_make_section_old_way
,(abfd
, name
),
491 asection
*sec
= bfd_get_section_by_name(abfd
, name
);
492 if (sec
== (asection
*)NULL
)
494 sec
= bfd_make_section(abfd
, name
);
501 bfd_make_section_anyway
504 asection *bfd_make_section_anyway(bfd *abfd, CONST char *name);
507 Create a new empty section called @var{name} and attach it to the end of
508 the chain of sections for @var{abfd}. Create a new section even if there
509 is already a section with that name.
511 Returns NULL and sets bfd_error on error; possible errors are:
512 o invalid_operation - If output has already started for @var{abfd}.
513 o no_memory - If obstack alloc fails.
517 bfd_make_section_anyway (abfd
, name
)
522 asection
**prev
= &abfd
->sections
;
523 asection
* sect
= abfd
->sections
;
525 if (abfd
->output_has_begun
)
527 bfd_error
= invalid_operation
;
536 newsect
= (asection
*) bfd_zalloc(abfd
, sizeof (asection
));
537 if (newsect
== NULL
) {
538 bfd_error
= no_memory
;
542 newsect
->name
= name
;
543 newsect
->index
= abfd
->section_count
++;
544 newsect
->flags
= SEC_NO_FLAGS
;
546 newsect
->userdata
= 0;
547 newsect
->next
= (asection
*)NULL
;
548 newsect
->relocation
= (arelent
*)NULL
;
549 newsect
->reloc_count
= 0;
550 newsect
->line_filepos
=0;
551 newsect
->owner
= abfd
;
553 /* Create a symbol whos only job is to point to this section. This is
554 useful for things like relocs which are relative to the base of a
556 newsect
->symbol
= bfd_make_empty_symbol(abfd
);
557 newsect
->symbol
->name
= name
;
558 newsect
->symbol
->value
= 0;
559 newsect
->symbol
->section
= newsect
;
560 newsect
->symbol
->flags
= BSF_SECTION_SYM
;
562 newsect
->symbol_ptr_ptr
= &newsect
->symbol
;
564 if (BFD_SEND (abfd
, _new_section_hook
, (abfd
, newsect
)) != true) {
578 asection *bfd_make_section(bfd *, CONST char *name);
581 Like <<bfd_make_section_anyway>>, but return NULL (without setting
582 bfd_error) without changing the section chain if there is already a
583 section named @var{name}. If there is an error, return NULL and set
588 DEFUN(bfd_make_section
,(abfd
, name
),
592 asection
* sect
= abfd
->sections
;
594 if (strcmp(name
, BFD_ABS_SECTION_NAME
) == 0)
596 return &bfd_abs_section
;
598 if (strcmp(name
, BFD_COM_SECTION_NAME
) == 0)
600 return &bfd_com_section
;
602 if (strcmp(name
, BFD_UND_SECTION_NAME
) == 0)
604 return &bfd_und_section
;
607 if (strcmp(name
, BFD_IND_SECTION_NAME
) == 0)
609 return &bfd_ind_section
;
613 if (!strcmp(sect
->name
, name
)) return NULL
;
617 /* The name is not already used; go ahead and make a new section. */
618 return bfd_make_section_anyway (abfd
, name
);
624 bfd_set_section_flags
627 boolean bfd_set_section_flags(bfd *abfd, asection *sec, flagword flags);
630 Set the attributes of the section @var{sec} in the BFD
631 @var{abfd} to the value @var{flags}. Returns <<true>> on success,
632 <<false>> on error. Possible error returns are:
634 o invalid operation -
635 The section cannot have one or more of the attributes
636 requested. For example, a .bss section in <<a.out>> may not
637 have the <<SEC_HAS_CONTENTS>> field set.
642 DEFUN(bfd_set_section_flags
,(abfd
, section
, flags
),
648 /* If you try to copy a text section from an input file (where it
649 has the SEC_CODE flag set) to an output file, this loses big if
650 the bfd_applicable_section_flags (abfd) doesn't have the SEC_CODE
651 set - which it doesn't, at least not for a.out. FIXME */
653 if ((flags
& bfd_applicable_section_flags (abfd
)) != flags
) {
654 bfd_error
= invalid_operation
;
659 section
->flags
= flags
;
666 bfd_map_over_sections
669 void bfd_map_over_sections(bfd *abfd,
670 void (*func)(bfd *abfd,
676 Call the provided function @var{func} for each section
677 attached to the BFD @var{abfd}, passing @var{obj} as an
678 argument. The function will be called as if by
680 | func(abfd, the_section, obj);
682 This is the prefered method for iterating over sections; an
683 alternative would be to use a loop:
686 | for (p = abfd->sections; p != NULL; p = p->next)
694 DEFUN(bfd_map_over_sections
,(abfd
, operation
, user_storage
),
696 void (*operation
) PARAMS ((bfd
*abfd
, asection
*sect
, PTR obj
)) AND
702 for (sect
= abfd
->sections
; sect
!= NULL
; i
++, sect
= sect
->next
)
703 (*operation
) (abfd
, sect
, user_storage
);
705 if (i
!= abfd
->section_count
) /* Debugging */
715 boolean bfd_set_section_size(bfd *abfd, asection *sec, bfd_size_type val);
718 Set @var{sec} to the size @var{val}. If the operation is
719 ok, then <<true>> is returned, else <<false>>.
721 Possible error returns:
722 o invalid_operation -
723 Writing has started to the BFD, so setting the size is invalid
728 DEFUN(bfd_set_section_size
,(abfd
, ptr
, val
),
733 /* Once you've started writing to any section you cannot create or change
734 the size of any others. */
736 if (abfd
->output_has_begun
) {
737 bfd_error
= invalid_operation
;
741 ptr
->_cooked_size
= val
;
742 ptr
->_raw_size
= val
;
749 bfd_set_section_contents
752 boolean bfd_set_section_contents
757 bfd_size_type count);
761 Sets the contents of the section @var{section} in BFD
762 @var{abfd} to the data starting in memory at @var{data}. The
763 data is written to the output section starting at offset
764 @var{offset} for @var{count} bytes.
768 Normally <<true>> is returned, else <<false>>. Possible error
771 The output section does not have the <<SEC_HAS_CONTENTS>>
772 attribute, so nothing can be written to it.
775 This routine is front end to the back end function
776 <<_bfd_set_section_contents>>.
781 #define bfd_get_section_size_now(abfd,sec) \
783 ? bfd_get_section_size_after_reloc (sec) \
784 : bfd_get_section_size_before_reloc (sec))
787 DEFUN(bfd_set_section_contents
,(abfd
, section
, location
, offset
, count
),
796 if (!bfd_get_section_flags(abfd
, section
) & SEC_HAS_CONTENTS
)
798 bfd_error
= no_contents
;
805 bfd_error
= bad_value
;
808 sz
= bfd_get_section_size_now (abfd
, section
);
811 || offset
+ count
> sz
)
814 switch (abfd
->direction
)
818 bfd_error
= invalid_operation
;
821 case write_direction
:
825 /* File is opened for update. `output_has_begun' some time ago when
826 the file was created. Do not recompute sections sizes or alignments
827 in _bfd_set_section_content. */
828 abfd
->output_has_begun
= true;
832 if (BFD_SEND (abfd
, _bfd_set_section_contents
,
833 (abfd
, section
, location
, offset
, count
)))
835 abfd
->output_has_begun
= true;
844 bfd_get_section_contents
847 boolean bfd_get_section_contents
848 (bfd *abfd, asection *section, PTR location,
849 file_ptr offset, bfd_size_type count);
852 Read data from @var{section} in BFD @var{abfd}
853 into memory starting at @var{location}. The data is read at an
854 offset of @var{offset} from the start of the input section,
855 and is read for @var{count} bytes.
857 If the contents of a constuctor with the <<SEC_CONSTUCTOR>>
858 flag set are requested, then the @var{location} is filled with
859 zeroes. If no errors occur, <<true>> is returned, else
866 DEFUN(bfd_get_section_contents
,(abfd
, section
, location
, offset
, count
),
875 if (section
->flags
& SEC_CONSTRUCTOR
)
877 memset(location
, 0, (unsigned)count
);
884 bfd_error
= bad_value
;
887 sz
= bfd_get_section_size_now (abfd
, section
);
890 || offset
+ count
> sz
)
897 return BFD_SEND (abfd
, _bfd_get_section_contents
,
898 (abfd
, section
, location
, offset
, count
));