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::
39 @node Section Input, Section Output, Sections, Sections
43 When a BFD is opened for reading, the section structures are
44 created and attached to the BFD.
46 Each section has a name which describes the section in the
47 outside world - for example, <<a.out>> would contain at least
48 three sections, called <<.text>>, <<.data>> and <<.bss>>.
50 Sometimes a BFD will contain more than the 'natural' number of
51 sections. A back end may attach other sections containing
52 constructor data, or an application may add a section (using
53 bfd_make_section) to the sections attached to an already open
54 BFD. For example, the linker creates a supernumary section
55 <<COMMON>> for each input file's BFD to hold information about
58 The raw data is not necessarily read in at the same time as
59 the section descriptor is created. Some targets may leave the
60 data in place until a <<bfd_get_section_contents>> call is
61 made. Other back ends may read in all the data at once - For
62 example; an S-record file has to be read once to determine the
63 size of the data. An IEEE-695 file doesn't contain raw data in
64 sections, but data and relocation expressions intermixed, so
65 the data area has to be parsed to get out the data and
68 @node Section Output, typedef asection, Section Input, Sections
73 To write a new object style BFD, the various sections to be
74 written have to be created. They are attached to the BFD in
75 the same way as input sections, data is written to the
76 sections using <<bfd_set_section_contents>>.
78 The linker uses the fields <<output_section>> and
79 <<output_offset>> to create an output file.
81 The data to be written comes from input sections attached to
82 the output sections. The output section structure can be
83 considered a filter for the input section, the output section
84 determines the vma of the output data and the name, but the
85 input section determines the offset into the output section of
86 the data to be written.
88 Eg to create a section "O", starting at 0x100, 0x123 long,
89 containing two subsections, "A" at offset 0x0 (ie at vma
90 0x100) and "B" at offset 0x20 (ie at vma 0x120) the structures
96 | output_section -----------> section name "O"
98 | section name "B" | size 0x123
99 | output_offset 0x20 |
101 | output_section --------|
107 The data within a section is stored in a <<seglet>>. These
108 are much like the fixups in <<gas>>. The seglet abstraction
109 allows the a section to grow and shrink within itself.
111 A seglet knows how big it is, and which is the next seglet and
112 where the raw data for it is, and also points to a list of
113 relocations which apply to it.
115 The seglet is used by the linker to perform relaxing on final
116 code. The application creates code which is as big as
117 necessary to make it work without relaxing, and the user can
118 select whether to relax. Sometimes relaxing takes a lot of
119 time. The linker runs around the relocations to see if any
120 are attached to data which can be shrunk, if so it does it on
121 a seglet by seglet basis.
132 @node typedef asection, section prototypes, Section Output, Sections
136 The shape of a section struct:
142 . {* The name of the section, the name isn't a copy, the pointer is
143 . the same as that passed to bfd_make_section. *}
148 . {* Which section is it 0.nth *}
152 . {* The next section in the list belonging to the BFD, or NULL. *}
156 . {* The field flags contains attributes of the section. Some of
157 . flags are read in from the object file, and some are
158 . synthesized from other information. *}
162 .#define SEC_NO_FLAGS 0x000
164 . {* Tells the OS to allocate space for this section when loaded.
165 . This would clear for a section containing debug information
169 .#define SEC_ALLOC 0x001
170 . {* Tells the OS to load the section from the file when loading.
171 . This would be clear for a .bss section *}
173 .#define SEC_LOAD 0x002
174 . {* The section contains data still to be relocated, so there will
175 . be some relocation information too. *}
177 .#define SEC_RELOC 0x004
181 .#define SEC_BALIGN 0x008
183 . {* A signal to the OS that the section contains read only
185 .#define SEC_READONLY 0x010
187 . {* The section contains code only. *}
189 .#define SEC_CODE 0x020
191 . {* The section contains data only. *}
193 .#define SEC_DATA 0x040
195 . {* The section will reside in ROM. *}
197 .#define SEC_ROM 0x080
199 . {* The section contains constructor information. This section
200 . type is used by the linker to create lists of constructors and
201 . destructors used by <<g++>>. When a back end sees a symbol
202 . which should be used in a constructor list, it creates a new
203 . section for the type of name (eg <<__CTOR_LIST__>>), attaches
204 . the symbol to it and builds a relocation. To build the lists
205 . of constructors, all the linker has to to is catenate all the
206 . sections called <<__CTOR_LIST__>> and relocte the data
207 . contained within - exactly the operations it would peform on
210 .#define SEC_CONSTRUCTOR 0x100
212 . {* The section is a constuctor, and should be placed at the
216 .#define SEC_CONSTRUCTOR_TEXT 0x1100
218 .#define SEC_CONSTRUCTOR_DATA 0x2100
220 .#define SEC_CONSTRUCTOR_BSS 0x3100
223 . {* The section has contents - a bss section could be
224 . <<SEC_ALLOC>> | <<SEC_HAS_CONTENTS>>, a debug section could be
225 . <<SEC_HAS_CONTENTS>> *}
227 .#define SEC_HAS_CONTENTS 0x200
229 . {* An instruction to the linker not to output sections
230 . containing this flag even if they have information which
231 . would normally be written. *}
233 .#define SEC_NEVER_LOAD 0x400
239 . {* The size of the section in bytes, as it will be output.
240 . contains a value even if the section has no contents (eg, the
241 . size of <<.bss>>). This will be filled in after relocation *}
243 . bfd_size_type _cooked_size;
245 . {* The size on disk of the section in bytes originally. Normally this
246 . value is the same as the size, but if some relaxing has
247 . been done, then this value will be bigger. *}
249 . bfd_size_type _raw_size;
251 . {* If this section is going to be output, then this value is the
252 . offset into the output section of the first byte in the input
253 . section. Eg, if this was going to start at the 100th byte in
254 . the output section, this value would be 100. *}
256 . bfd_vma output_offset;
258 . {* The output section through which to map on output. *}
260 . struct sec *output_section;
262 . {* The alignment requirement of the section, as an exponent - eg
263 . 3 aligns to 2^3 (or 8) *}
265 . unsigned int alignment_power;
267 . {* If an input section, a pointer to a vector of relocation
268 . records for the data in this section. *}
270 . struct reloc_cache_entry *relocation;
272 . {* If an output section, a pointer to a vector of pointers to
273 . relocation records for the data in this section. *}
275 . struct reloc_cache_entry **orelocation;
277 . {* The number of relocation records in one of the above *}
279 . unsigned reloc_count;
281 . {* Information below is back end specific - and not always used
284 . File position of section data *}
288 . {* File position of relocation info *}
290 . file_ptr rel_filepos;
292 . {* File position of line data *}
294 . file_ptr line_filepos;
296 . {* Pointer to data for applications *}
300 . struct lang_output_section *otheruserdata;
302 . {* Attached line number information *}
306 . {* Number of line number records *}
308 . unsigned int lineno_count;
310 . {* When a section is being output, this value changes as more
311 . linenumbers are written out *}
313 . file_ptr moving_line_filepos;
315 . {* what the section number is in the target world *}
321 . {* If this is a constructor section then here is a list of the
322 . relocations created to relocate items within it. *}
324 . struct relent_chain *constructor_chain;
326 . {* The BFD which owns the section. *}
330 . boolean reloc_done;
331 . {* A symbol which points at this section only *}
332 . struct symbol_cache_entry *symbol;
333 . struct symbol_cache_entry **symbol_ptr_ptr;
334 . struct bfd_seclet_struct *seclets_head;
335 . struct bfd_seclet_struct *seclets_tail;
339 .#define BFD_ABS_SECTION_NAME "*ABS*"
340 .#define BFD_UND_SECTION_NAME "*UND*"
341 .#define BFD_COM_SECTION_NAME "*COM*"
343 . {* the absolute section *}
344 . extern asection bfd_abs_section;
345 . {* Pointer to the undefined section *}
346 . extern asection bfd_und_section;
347 . {* Pointer to the common section *}
348 . extern asection bfd_com_section;
350 . extern struct symbol_cache_entry *bfd_abs_symbol;
351 . extern struct symbol_cache_entry *bfd_com_symbol;
352 . extern struct symbol_cache_entry *bfd_und_symbol;
353 .#define bfd_get_section_size_before_reloc(section) \
354 . (section->reloc_done ? (abort(),1): (section)->_raw_size)
355 .#define bfd_get_section_size_after_reloc(section) \
356 . ((section->reloc_done) ? (section)->_cooked_size: (abort(),1))
361 asection bfd_com_section = { BFD_COM_SECTION_NAME ,0 };
362 asection bfd_und_section = { BFD_UND_SECTION_NAME ,0 };
363 asection bfd_abs_section = { BFD_ABS_SECTION_NAME ,0 };
365 struct symbol_cache_entry *bfd_abs_symbol;
366 struct symbol_cache_entry *bfd_com_symbol;
367 struct symbol_cache_entry *bfd_und_symbol;
370 @node section prototypes, , typedef asection, Sections
374 These are the functions exported by the section handling part of
380 bfd_get_section_by_name
383 asection *bfd_get_section_by_name(bfd *abfd, CONST char *name);
386 Runs through the provided @var{abfd} and returns the
387 <<asection>> who's name matches that provided, otherwise NULL.
388 @xref{Sections}, for more information.
393 DEFUN(bfd_get_section_by_name,(abfd, name),
399 for (sect = abfd->sections; sect != NULL; sect = sect->next)
400 if (!strcmp (sect->name, name)) return sect;
407 bfd_make_section_old_way
410 asection *bfd_make_section_old_way(bfd *, CONST char *name);
413 This function creates a new empty section called @var{name}
414 and attaches it to the end of the chain of sections for the
415 BFD supplied. An attempt to create a section with a name which
416 is already in use, returns its pointer without changing the
419 It has the funny name since this is the way it used to be
420 before is was rewritten...
424 If output has already started for this BFD.
426 If obstack alloc fails.
432 DEFUN(bfd_make_section_old_way,(abfd, name),
436 asection *sec = bfd_get_section_by_name(abfd, name);
437 if (sec == (asection *)NULL)
439 sec = bfd_make_section(abfd, name);
450 asection * bfd_make_section(bfd *, CONST char *name);
453 This function creates a new empty section called @var{name}
454 and attaches it to the end of the chain of sections for the
455 BFD supplied. An attempt to create a section with a name which
456 is already in use, returns NULL without changing the section
460 o invalid_operation - If output has already started for this BFD.
461 o no_memory - If obstack alloc fails.
467 DEFUN(bfd_make_section,(abfd, name),
472 asection ** prev = &abfd->sections;
473 asection * sect = abfd->sections;
475 if (abfd->output_has_begun) {
476 bfd_error = invalid_operation;
480 if (strcmp(name, BFD_ABS_SECTION_NAME) == 0)
482 return &bfd_abs_section;
484 if (strcmp(name, BFD_COM_SECTION_NAME) == 0)
486 return &bfd_com_section;
488 if (strcmp(name, BFD_UND_SECTION_NAME) == 0)
490 return &bfd_und_section;
494 if (!strcmp(sect->name, name)) return NULL;
499 newsect = (asection *) bfd_zalloc(abfd, sizeof (asection));
500 if (newsect == NULL) {
501 bfd_error = no_memory;
505 newsect->name = name;
506 newsect->index = abfd->section_count++;
507 newsect->flags = SEC_NO_FLAGS;
509 newsect->userdata = 0;
510 newsect->next = (asection *)NULL;
511 newsect->relocation = (arelent *)NULL;
512 newsect->reloc_count = 0;
513 newsect->line_filepos =0;
514 newsect->owner = abfd;
516 /* Create a symbol whos only job is to point to this section. This is
517 usfull for things like relocs which are relative to the base of a
520 newsect->symbol = bfd_make_empty_symbol(abfd);
521 newsect->symbol->name = name;
522 newsect->symbol->value = 0;
523 newsect->symbol->section = newsect;
524 newsect->symbol->flags = BSF_SECTION_SYM;
527 newsect->symbol_ptr_ptr = &newsect->symbol;
529 if (BFD_SEND (abfd, _new_section_hook, (abfd, newsect)) != true) {
541 bfd_set_section_flags
544 boolean bfd_set_section_flags(bfd *, asection *, flagword);
547 Attempts to set the attributes of the section named in the BFD
548 supplied to the value. Returns true on success, false on
549 error. Possible error returns are:
552 The section cannot have one or more of the attributes
553 requested. For example, a .bss section in <<a.out>> may not
554 have the <<SEC_HAS_CONTENTS>> field set.
559 DEFUN(bfd_set_section_flags,(abfd, section, flags),
564 if ((flags & bfd_applicable_section_flags (abfd)) != flags) {
565 bfd_error = invalid_operation;
569 section->flags = flags;
576 bfd_map_over_sections
579 void bfd_map_over_sections(bfd *abfd, void (*func)(), PTR obj);
582 Calls the provided function @var{func} for each section
583 attached to the BFD @var{abfd}, passing @var{obj} as an
584 argument. The function will be called as if by
586 | func(abfd, the_section, obj);
588 This is the prefered method for iterating over sections, an
589 alternative would be to use a loop:
592 | for (p = abfd->sections; p != NULL; p = p->next)
600 DEFUN(bfd_map_over_sections,(abfd, operation, user_storage),
602 void (*operation)() AND
608 for (sect = abfd->sections; sect != NULL; i++, sect = sect->next)
609 (*operation) (abfd, sect, user_storage);
611 if (i != abfd->section_count) /* Debugging */
621 boolean bfd_set_section_size(bfd *, asection *, bfd_size_type val);
624 Sets @var{section} to the size @var{val}. If the operation is
625 ok, then <<true>> is returned, else <<false>>.
627 Possible error returns:
629 Writing has started to the BFD, so setting the size is invalid
634 DEFUN(bfd_set_section_size,(abfd, ptr, val),
639 /* Once you've started writing to any section you cannot create or change
640 the size of any others. */
642 if (abfd->output_has_begun) {
643 bfd_error = invalid_operation;
647 ptr->_cooked_size = val;
648 ptr->_raw_size = val;
655 bfd_set_section_contents
658 boolean bfd_set_section_contents
663 bfd_size_type count);
667 Sets the contents of the section @var{section} in BFD
668 @var{abfd} to the data starting in memory at @var{data}. The
669 data is written to the output section starting at offset
670 @var{offset} for @var{count} bytes.
674 Normally <<true>> is returned, else <<false>>. Possible error
677 The output section does not have the <<SEC_HAS_CONTENTS>>
678 attribute, so nothing can be written to it.
681 This routine is front end to the back end function
682 <<_bfd_set_section_contents>>.
688 DEFUN(bfd_set_section_contents,(abfd, section, location, offset, count),
695 if (!(bfd_get_section_flags(abfd, section) & SEC_HAS_CONTENTS))
697 bfd_error = no_contents;
701 if (BFD_SEND (abfd, _bfd_set_section_contents,
702 (abfd, section, location, offset, count)))
704 abfd->output_has_begun = true;
713 bfd_get_section_contents
716 boolean bfd_get_section_contents
717 (bfd *abfd, asection *section, PTR location,
718 file_ptr offset, bfd_size_type count);
721 This function reads data from @var{section} in BFD @var{abfd}
722 into memory starting at @var{location}. The data is read at an
723 offset of @var{offset} from the start of the input section,
724 and is read for @var{count} bytes.
726 If the contents of a constuctor with the <<SEC_CONSTUCTOR>>
727 flag set are requested, then the @var{location} is filled with
728 zeroes. If no errors occur, <<true>> is returned, else
735 DEFUN(bfd_get_section_contents,(abfd, section, location, offset, count),
742 if (section->flags & SEC_CONSTRUCTOR)
744 memset(location, 0, (unsigned)count);
749 return (BFD_SEND (abfd, _bfd_get_section_contents,
750 (abfd, section, location, offset, count)));
755 /* Initialize the internal data structures */
756 DEFUN_VOID(bfd_section_init)
759 bfd_com_symbol = (asymbol *)zalloc(sizeof(asymbol));
760 bfd_com_symbol->name = BFD_COM_SECTION_NAME;
761 bfd_com_symbol->flags = BSF_SECTION_SYM;
762 bfd_com_symbol->section = &bfd_com_section;
763 bfd_com_section.symbol = bfd_com_symbol;
764 bfd_com_section.symbol_ptr_ptr = &bfd_com_symbol;
765 bfd_com_section.output_section = &bfd_com_section;
769 bfd_und_symbol = (asymbol *)zalloc(sizeof(asymbol));
770 bfd_und_symbol->name = BFD_UND_SECTION_NAME;
771 bfd_und_symbol->flags = BSF_SECTION_SYM;
772 bfd_und_symbol->section = &bfd_und_section;
773 bfd_und_section.symbol = bfd_und_symbol;
774 bfd_und_section.symbol_ptr_ptr = &bfd_und_symbol;
775 bfd_und_section.output_section = &bfd_und_section;
777 bfd_abs_symbol = (asymbol *)zalloc(sizeof(asymbol));
778 bfd_abs_symbol->name = BFD_ABS_SECTION_NAME;
779 bfd_abs_symbol->flags = BSF_SECTION_SYM;
780 bfd_abs_symbol->section = &bfd_abs_section;
781 bfd_abs_section.symbol = bfd_abs_symbol;
782 bfd_abs_section.symbol_ptr_ptr = &bfd_abs_symbol;
783 bfd_abs_section.output_section = &bfd_abs_section;