1 /* Object file "section" support for the BFD library.
2 Copyright (C) 1990-1991 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 Sections are supported in BFD in <<section.c>>.
27 The raw data contained within a BFD is maintained through the
28 section abstraction. A single BFD may have any number of
29 sections, and keeps hold of them by pointing to the first,
30 each one points to the next in the list.
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 Sometimes a BFD will contain more than the 'natural' number of
52 sections. A back end may attach other sections containing
53 constructor data, or an application may add a section (using
54 bfd_make_section) to the sections attached to an already open
55 BFD. For example, the linker creates a supernumary section
56 <<COMMON>> for each input file's BFD to hold information about
59 The raw data is not necessarily read in at the same time as
60 the section descriptor is created. Some targets may leave the
61 data in place until a <<bfd_get_section_contents>> call is
62 made. Other back ends may read in all the data at once - For
63 example; an S-record file has to be read once to determine the
64 size of the data. An IEEE-695 file doesn't contain raw data in
65 sections, but data and relocation expressions intermixed, so
66 the data area has to be parsed to get out the data and
70 Section Output, typedef asection, Section Input, Sections
75 To write a new object style BFD, the various sections to be
76 written have to be created. They are attached to the BFD in
77 the same way as input sections, data is written to the
78 sections using <<bfd_set_section_contents>>.
80 Any program that creates or combines sections (e.g., the assembler
81 and linker) must use the fields <<output_section>> and
82 <<output_offset>> to indicate the file sections to which each
83 section must be written. (If the section is being created from
84 scratch, <<output_section>> should probably point to the section
85 itself, and <<output_offset>> should probably be zero.)
87 The data to be written comes from input sections attached to
88 the output sections. The output section structure can be
89 considered a filter for the input section, the output section
90 determines the vma of the output data and the name, but the
91 input section determines the offset into the output section of
92 the data to be written.
94 E.g., to create a section "O", starting at 0x100, 0x123 long,
95 containing two subsections, "A" at offset 0x0 (ie at vma
96 0x100) and "B" at offset 0x20 (ie at vma 0x120) the structures
102 | output_section -----------> section name "O"
104 | section name "B" | size 0x123
105 | output_offset 0x20 |
107 | output_section --------|
113 The data within a section is stored in a <<seglet>>. These
114 are much like the fixups in <<gas>>. The seglet abstraction
115 allows the a section to grow and shrink within itself.
117 A seglet knows how big it is, and which is the next seglet and
118 where the raw data for it is, and also points to a list of
119 relocations which apply to it.
121 The seglet is used by the linker to perform relaxing on final
122 code. The application creates code which is as big as
123 necessary to make it work without relaxing, and the user can
124 select whether to relax. Sometimes relaxing takes a lot of
125 time. The linker runs around the relocations to see if any
126 are attached to data which can be shrunk, if so it does it on
127 a seglet by seglet basis.
140 typedef asection, section prototypes, Section Output, Sections
144 The shape of a section struct:
150 . {* The name of the section, the name isn't a copy, the pointer is
151 . the same as that passed to bfd_make_section. *}
156 . {* Which section is it 0.nth *}
160 . {* The next section in the list belonging to the BFD, or NULL. *}
164 . {* The field flags contains attributes of the section. Some of
165 . flags are read in from the object file, and some are
166 . synthesized from other information. *}
170 .#define SEC_NO_FLAGS 0x000
172 . {* Tells the OS to allocate space for this section when loaded.
173 . This would clear for a section containing debug information
177 .#define SEC_ALLOC 0x001
178 . {* Tells the OS to load the section from the file when loading.
179 . This would be clear for a .bss section *}
181 .#define SEC_LOAD 0x002
182 . {* The section contains data still to be relocated, so there will
183 . be some relocation information too. *}
185 .#define SEC_RELOC 0x004
189 .#define SEC_BALIGN 0x008
191 . {* A signal to the OS that the section contains read only
193 .#define SEC_READONLY 0x010
195 . {* The section contains code only. *}
197 .#define SEC_CODE 0x020
199 . {* The section contains data only. *}
201 .#define SEC_DATA 0x040
203 . {* The section will reside in ROM. *}
205 .#define SEC_ROM 0x080
207 . {* The section contains constructor information. This section
208 . type is used by the linker to create lists of constructors and
209 . destructors used by <<g++>>. When a back end sees a symbol
210 . which should be used in a constructor list, it creates a new
211 . section for the type of name (eg <<__CTOR_LIST__>>), attaches
212 . the symbol to it and builds a relocation. To build the lists
213 . of constructors, all the linker has to to is catenate all the
214 . sections called <<__CTOR_LIST__>> and relocte the data
215 . contained within - exactly the operations it would peform on
218 .#define SEC_CONSTRUCTOR 0x100
220 . {* The section is a constuctor, and should be placed at the
224 .#define SEC_CONSTRUCTOR_TEXT 0x1100
226 .#define SEC_CONSTRUCTOR_DATA 0x2100
228 .#define SEC_CONSTRUCTOR_BSS 0x3100
231 . {* The section has contents - a bss section could be
232 . <<SEC_ALLOC>> | <<SEC_HAS_CONTENTS>>, a debug section could be
233 . <<SEC_HAS_CONTENTS>> *}
235 .#define SEC_HAS_CONTENTS 0x200
237 . {* An instruction to the linker not to output sections
238 . containing this flag even if they have information which
239 . would normally be written. *}
241 .#define SEC_NEVER_LOAD 0x400
246 . boolean user_set_vma;
248 . {* The size of the section in bytes, as it will be output.
249 . contains a value even if the section has no contents (eg, the
250 . size of <<.bss>>). This will be filled in after relocation *}
252 . bfd_size_type _cooked_size;
254 . {* The size on disk of the section in bytes originally. Normally this
255 . value is the same as the size, but if some relaxing has
256 . been done, then this value will be bigger. *}
258 . bfd_size_type _raw_size;
260 . {* If this section is going to be output, then this value is the
261 . offset into the output section of the first byte in the input
262 . section. Eg, if this was going to start at the 100th byte in
263 . the output section, this value would be 100. *}
265 . bfd_vma output_offset;
267 . {* The output section through which to map on output. *}
269 . struct sec *output_section;
271 . {* The alignment requirement of the section, as an exponent - eg
272 . 3 aligns to 2^3 (or 8) *}
274 . unsigned int alignment_power;
276 . {* If an input section, a pointer to a vector of relocation
277 . records for the data in this section. *}
279 . struct reloc_cache_entry *relocation;
281 . {* If an output section, a pointer to a vector of pointers to
282 . relocation records for the data in this section. *}
284 . struct reloc_cache_entry **orelocation;
286 . {* The number of relocation records in one of the above *}
288 . unsigned reloc_count;
290 . {* Information below is back end specific - and not always used
293 . File position of section data *}
297 . {* File position of relocation info *}
299 . file_ptr rel_filepos;
301 . {* File position of line data *}
303 . file_ptr line_filepos;
305 . {* Pointer to data for applications *}
309 . struct lang_output_section *otheruserdata;
311 . {* Attached line number information *}
315 . {* Number of line number records *}
317 . unsigned int lineno_count;
319 . {* When a section is being output, this value changes as more
320 . linenumbers are written out *}
322 . file_ptr moving_line_filepos;
324 . {* what the section number is in the target world *}
330 . {* If this is a constructor section then here is a list of the
331 . relocations created to relocate items within it. *}
333 . struct relent_chain *constructor_chain;
335 . {* The BFD which owns the section. *}
339 . boolean reloc_done;
340 . {* A symbol which points at this section only *}
341 . struct symbol_cache_entry *symbol;
342 . struct symbol_cache_entry **symbol_ptr_ptr;
343 . struct bfd_seclet *seclets_head;
344 . struct bfd_seclet *seclets_tail;
348 .#define BFD_ABS_SECTION_NAME "*ABS*"
349 .#define BFD_UND_SECTION_NAME "*UND*"
350 .#define BFD_COM_SECTION_NAME "*COM*"
352 . {* the absolute section *}
353 . extern asection bfd_abs_section;
354 . {* Pointer to the undefined section *}
355 . extern asection bfd_und_section;
356 . {* Pointer to the common section *}
357 . extern asection bfd_com_section;
359 . extern struct symbol_cache_entry *bfd_abs_symbol;
360 . extern struct symbol_cache_entry *bfd_com_symbol;
361 . extern struct symbol_cache_entry *bfd_und_symbol;
362 .#define bfd_get_section_size_before_reloc(section) \
363 . (section->reloc_done ? (abort(),1): (section)->_raw_size)
364 .#define bfd_get_section_size_after_reloc(section) \
365 . ((section->reloc_done) ? (section)->_cooked_size: (abort(),1))
368 /* These symbols are global, not specific to any BFD. Therefore, anything
369 that tries to change them is broken, and should be repaired. */
370 static CONST asymbol global_syms
[] = {
371 /* bfd, name, value, attr, section [, udata] */
372 { 0, BFD_COM_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_com_section
},
373 { 0, BFD_UND_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_und_section
},
374 { 0, BFD_ABS_SECTION_NAME
, 0, BSF_SECTION_SYM
, &bfd_abs_section
},
377 #define STD_SECTION(SEC,SYM,NAME, IDX) \
378 asymbol *SYM = (asymbol *) &global_syms[IDX]; \
379 asection SEC = { NAME, 0, 0, 0, 0, (boolean) 0, 0, 0, 0, &SEC,\
380 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, (boolean) 0, \
381 (asymbol *) &global_syms[IDX], &SYM, }
383 STD_SECTION (bfd_com_section
, bfd_com_symbol
, BFD_COM_SECTION_NAME
, 0);
384 STD_SECTION (bfd_und_section
, bfd_und_symbol
, BFD_UND_SECTION_NAME
, 1);
385 STD_SECTION (bfd_abs_section
, bfd_abs_symbol
, BFD_ABS_SECTION_NAME
, 2);
391 section prototypes, , typedef asection, Sections
395 These are the functions exported by the section handling part of
401 bfd_get_section_by_name
404 asection *bfd_get_section_by_name(bfd *abfd, CONST char *name);
407 Runs through the provided @var{abfd} and returns the
408 <<asection>> who's name matches that provided, otherwise NULL.
409 @xref{Sections}, for more information.
414 DEFUN(bfd_get_section_by_name
,(abfd
, name
),
420 for (sect
= abfd
->sections
; sect
!= NULL
; sect
= sect
->next
)
421 if (!strcmp (sect
->name
, name
)) return sect
;
428 bfd_make_section_old_way
431 asection *bfd_make_section_old_way(bfd *, CONST char *name);
434 This function creates a new empty section called @var{name}
435 and attaches it to the end of the chain of sections for the
436 BFD supplied. An attempt to create a section with a name which
437 is already in use, returns its pointer without changing the
440 It has the funny name since this is the way it used to be
441 before is was rewritten...
444 o invalid_operation -
445 If output has already started for this BFD.
447 If obstack alloc fails.
453 DEFUN(bfd_make_section_old_way
,(abfd
, name
),
457 asection
*sec
= bfd_get_section_by_name(abfd
, name
);
458 if (sec
== (asection
*)NULL
)
460 sec
= bfd_make_section(abfd
, name
);
471 asection * bfd_make_section(bfd *, CONST char *name);
474 This function creates a new empty section called @var{name}
475 and attaches it to the end of the chain of sections for the
476 BFD supplied. An attempt to create a section with a name which
477 is already in use, returns NULL without changing the section
481 o invalid_operation - If output has already started for this BFD.
482 o no_memory - If obstack alloc fails.
488 DEFUN(bfd_make_section
,(abfd
, name
),
493 asection
** prev
= &abfd
->sections
;
494 asection
* sect
= abfd
->sections
;
496 if (abfd
->output_has_begun
) {
497 bfd_error
= invalid_operation
;
501 if (strcmp(name
, BFD_ABS_SECTION_NAME
) == 0)
503 return &bfd_abs_section
;
505 if (strcmp(name
, BFD_COM_SECTION_NAME
) == 0)
507 return &bfd_com_section
;
509 if (strcmp(name
, BFD_UND_SECTION_NAME
) == 0)
511 return &bfd_und_section
;
515 if (!strcmp(sect
->name
, name
)) return NULL
;
520 newsect
= (asection
*) bfd_zalloc(abfd
, sizeof (asection
));
521 if (newsect
== NULL
) {
522 bfd_error
= no_memory
;
526 newsect
->name
= name
;
527 newsect
->index
= abfd
->section_count
++;
528 newsect
->flags
= SEC_NO_FLAGS
;
530 newsect
->userdata
= 0;
531 newsect
->next
= (asection
*)NULL
;
532 newsect
->relocation
= (arelent
*)NULL
;
533 newsect
->reloc_count
= 0;
534 newsect
->line_filepos
=0;
535 newsect
->owner
= abfd
;
537 /* Create a symbol whos only job is to point to this section. This is
538 useful for things like relocs which are relative to the base of a
540 newsect
->symbol
= bfd_make_empty_symbol(abfd
);
541 newsect
->symbol
->name
= name
;
542 newsect
->symbol
->value
= 0;
543 newsect
->symbol
->section
= newsect
;
544 newsect
->symbol
->flags
= BSF_SECTION_SYM
;
547 newsect
->symbol_ptr_ptr
= &newsect
->symbol
;
549 if (BFD_SEND (abfd
, _new_section_hook
, (abfd
, newsect
)) != true) {
561 bfd_set_section_flags
564 boolean bfd_set_section_flags(bfd *, asection *, flagword);
567 Attempts to set the attributes of the section named in the BFD
568 supplied to the value. Returns true on success, false on
569 error. Possible error returns are:
571 o invalid operation -
572 The section cannot have one or more of the attributes
573 requested. For example, a .bss section in <<a.out>> may not
574 have the <<SEC_HAS_CONTENTS>> field set.
579 DEFUN(bfd_set_section_flags
,(abfd
, section
, flags
),
585 /* If you try to copy a text section from an input file (where it
586 has the SEC_CODE flag set) to an output file, this loses big if
587 the bfd_applicable_section_flags (abfd) doesn't have the SEC_CODE
588 set - which it doesn't, at least not for a.out. FIXME */
590 if ((flags
& bfd_applicable_section_flags (abfd
)) != flags
) {
591 bfd_error
= invalid_operation
;
596 section
->flags
= flags
;
603 bfd_map_over_sections
606 void bfd_map_over_sections(bfd *abfd,
607 void (*func)(bfd *abfd,
613 Calls the provided function @var{func} for each section
614 attached to the BFD @var{abfd}, passing @var{obj} as an
615 argument. The function will be called as if by
617 | func(abfd, the_section, obj);
619 This is the prefered method for iterating over sections, an
620 alternative would be to use a loop:
623 | for (p = abfd->sections; p != NULL; p = p->next)
631 DEFUN(bfd_map_over_sections
,(abfd
, operation
, user_storage
),
633 void (*operation
) PARAMS ((bfd
*abfd
, asection
*sect
, PTR obj
)) AND
639 for (sect
= abfd
->sections
; sect
!= NULL
; i
++, sect
= sect
->next
)
640 (*operation
) (abfd
, sect
, user_storage
);
642 if (i
!= abfd
->section_count
) /* Debugging */
652 boolean bfd_set_section_size(bfd *, asection *, bfd_size_type val);
655 Sets @var{section} to the size @var{val}. If the operation is
656 ok, then <<true>> is returned, else <<false>>.
658 Possible error returns:
659 o invalid_operation -
660 Writing has started to the BFD, so setting the size is invalid
665 DEFUN(bfd_set_section_size
,(abfd
, ptr
, val
),
670 /* Once you've started writing to any section you cannot create or change
671 the size of any others. */
673 if (abfd
->output_has_begun
) {
674 bfd_error
= invalid_operation
;
678 ptr
->_cooked_size
= val
;
679 ptr
->_raw_size
= val
;
686 bfd_set_section_contents
689 boolean bfd_set_section_contents
694 bfd_size_type count);
698 Sets the contents of the section @var{section} in BFD
699 @var{abfd} to the data starting in memory at @var{data}. The
700 data is written to the output section starting at offset
701 @var{offset} for @var{count} bytes.
705 Normally <<true>> is returned, else <<false>>. Possible error
708 The output section does not have the <<SEC_HAS_CONTENTS>>
709 attribute, so nothing can be written to it.
712 This routine is front end to the back end function
713 <<_bfd_set_section_contents>>.
718 #define bfd_get_section_size_now(abfd,sec) \
720 ? bfd_get_section_size_after_reloc (sec) \
721 : bfd_get_section_size_before_reloc (sec))
724 DEFUN(bfd_set_section_contents
,(abfd
, section
, location
, offset
, count
),
733 if (!(bfd_get_section_flags(abfd
, section
) & SEC_HAS_CONTENTS
))
735 bfd_error
= no_contents
;
739 if (offset
< 0 || count
< 0)
742 bfd_error
= bad_value
;
745 sz
= bfd_get_section_size_now (abfd
, section
);
748 || offset
+ count
> sz
)
751 if (BFD_SEND (abfd
, _bfd_set_section_contents
,
752 (abfd
, section
, location
, offset
, count
)))
754 abfd
->output_has_begun
= true;
763 bfd_get_section_contents
766 boolean bfd_get_section_contents
767 (bfd *abfd, asection *section, PTR location,
768 file_ptr offset, bfd_size_type count);
771 This function reads data from @var{section} in BFD @var{abfd}
772 into memory starting at @var{location}. The data is read at an
773 offset of @var{offset} from the start of the input section,
774 and is read for @var{count} bytes.
776 If the contents of a constuctor with the <<SEC_CONSTUCTOR>>
777 flag set are requested, then the @var{location} is filled with
778 zeroes. If no errors occur, <<true>> is returned, else
785 DEFUN(bfd_get_section_contents
,(abfd
, section
, location
, offset
, count
),
794 if (section
->flags
& SEC_CONSTRUCTOR
)
796 memset(location
, 0, (unsigned)count
);
800 if (offset
< 0 || count
< 0)
803 bfd_error
= bad_value
;
806 sz
= bfd_get_section_size_now (abfd
, section
);
809 || offset
+ count
> sz
)
816 return BFD_SEND (abfd
, _bfd_get_section_contents
,
817 (abfd
, section
, location
, offset
, count
));