section.texi revision 1.1.1.6
1@section Sections
2The raw data contained within a BFD is maintained through the
3section abstraction.  A single BFD may have any number of
4sections.  It keeps hold of them by pointing to the first;
5each one points to the next in the list.
6
7Sections are supported in BFD in @code{section.c}.
8
9@menu
10* Section Input::
11* Section Output::
12* typedef asection::
13* section prototypes::
14@end menu
15
16@node Section Input, Section Output, Sections, Sections
17@subsection Section input
18When a BFD is opened for reading, the section structures are
19created and attached to the BFD.
20
21Each section has a name which describes the section in the
22outside world---for example, @code{a.out} would contain at least
23three sections, called @code{.text}, @code{.data} and @code{.bss}.
24
25Names need not be unique; for example a COFF file may have several
26sections named @code{.data}.
27
28Sometimes a BFD will contain more than the ``natural'' number of
29sections. A back end may attach other sections containing
30constructor data, or an application may add a section (using
31@code{bfd_make_section}) to the sections attached to an already open
32BFD. For example, the linker creates an extra section
33@code{COMMON} for each input file's BFD to hold information about
34common storage.
35
36The raw data is not necessarily read in when
37the section descriptor is created. Some targets may leave the
38data in place until a @code{bfd_get_section_contents} call is
39made. Other back ends may read in all the data at once.  For
40example, an S-record file has to be read once to determine the
41size of the data. An IEEE-695 file doesn't contain raw data in
42sections, but data and relocation expressions intermixed, so
43the data area has to be parsed to get out the data and
44relocations.
45
46@node Section Output, typedef asection, Section Input, Sections
47@subsection Section output
48To write a new object style BFD, the various sections to be
49written have to be created. They are attached to the BFD in
50the same way as input sections; data is written to the
51sections using @code{bfd_set_section_contents}.
52
53Any program that creates or combines sections (e.g., the assembler
54and linker) must use the @code{asection} fields @code{output_section} and
55@code{output_offset} to indicate the file sections to which each
56section must be written.  (If the section is being created from
57scratch, @code{output_section} should probably point to the section
58itself and @code{output_offset} should probably be zero.)
59
60The data to be written comes from input sections attached
61(via @code{output_section} pointers) to
62the output sections.  The output section structure can be
63considered a filter for the input section: the output section
64determines the vma of the output data and the name, but the
65input section determines the offset into the output section of
66the data to be written.
67
68E.g., to create a section "O", starting at 0x100, 0x123 long,
69containing two subsections, "A" at offset 0x0 (i.e., at vma
700x100) and "B" at offset 0x20 (i.e., at vma 0x120) the @code{asection}
71structures would look like:
72
73@example
74   section name          "A"
75     output_offset   0x00
76     size            0x20
77     output_section ----------->  section name    "O"
78                             |    vma             0x100
79   section name          "B" |    size            0x123
80     output_offset   0x20    |
81     size            0x103   |
82     output_section  --------|
83@end example
84
85@subsection Link orders
86The data within a section is stored in a @dfn{link_order}.
87These are much like the fixups in @code{gas}.  The link_order
88abstraction allows a section to grow and shrink within itself.
89
90A link_order knows how big it is, and which is the next
91link_order and where the raw data for it is; it also points to
92a list of relocations which apply to it.
93
94The link_order is used by the linker to perform relaxing on
95final code.  The compiler creates code which is as big as
96necessary to make it work without relaxing, and the user can
97select whether to relax.  Sometimes relaxing takes a lot of
98time.  The linker runs around the relocations to see if any
99are attached to data which can be shrunk, if so it does it on
100a link_order by link_order basis.
101
102
103@node typedef asection, section prototypes, Section Output, Sections
104@subsection typedef asection
105Here is the section structure:
106
107
108@example
109
110typedef struct bfd_section
111@{
112  /* The name of the section; the name isn't a copy, the pointer is
113     the same as that passed to bfd_make_section.  */
114  const char *name;
115
116  /* A unique sequence number.  */
117  unsigned int id;
118
119  /* Which section in the bfd; 0..n-1 as sections are created in a bfd.  */
120  unsigned int index;
121
122  /* The next section in the list belonging to the BFD, or NULL.  */
123  struct bfd_section *next;
124
125  /* The previous section in the list belonging to the BFD, or NULL.  */
126  struct bfd_section *prev;
127
128  /* The field flags contains attributes of the section. Some
129     flags are read in from the object file, and some are
130     synthesized from other information.  */
131  flagword flags;
132
133#define SEC_NO_FLAGS                      0x0
134
135  /* Tells the OS to allocate space for this section when loading.
136     This is clear for a section containing debug information only.  */
137#define SEC_ALLOC                         0x1
138
139  /* Tells the OS to load the section from the file when loading.
140     This is clear for a .bss section.  */
141#define SEC_LOAD                          0x2
142
143  /* The section contains data still to be relocated, so there is
144     some relocation information too.  */
145#define SEC_RELOC                         0x4
146
147  /* A signal to the OS that the section contains read only data.  */
148#define SEC_READONLY                      0x8
149
150  /* The section contains code only.  */
151#define SEC_CODE                         0x10
152
153  /* The section contains data only.  */
154#define SEC_DATA                         0x20
155
156  /* The section will reside in ROM.  */
157#define SEC_ROM                          0x40
158
159  /* The section contains constructor information. This section
160     type is used by the linker to create lists of constructors and
161     destructors used by @code{g++}. When a back end sees a symbol
162     which should be used in a constructor list, it creates a new
163     section for the type of name (e.g., @code{__CTOR_LIST__}), attaches
164     the symbol to it, and builds a relocation. To build the lists
165     of constructors, all the linker has to do is catenate all the
166     sections called @code{__CTOR_LIST__} and relocate the data
167     contained within - exactly the operations it would peform on
168     standard data.  */
169#define SEC_CONSTRUCTOR                  0x80
170
171  /* The section has contents - a data section could be
172     @code{SEC_ALLOC} | @code{SEC_HAS_CONTENTS}; a debug section could be
173     @code{SEC_HAS_CONTENTS}  */
174#define SEC_HAS_CONTENTS                0x100
175
176  /* An instruction to the linker to not output the section
177     even if it has information which would normally be written.  */
178#define SEC_NEVER_LOAD                  0x200
179
180  /* The section contains thread local data.  */
181#define SEC_THREAD_LOCAL                0x400
182
183  /* The section has GOT references.  This flag is only for the
184     linker, and is currently only used by the elf32-hppa back end.
185     It will be set if global offset table references were detected
186     in this section, which indicate to the linker that the section
187     contains PIC code, and must be handled specially when doing a
188     static link.  */
189#define SEC_HAS_GOT_REF                 0x800
190
191  /* The section contains common symbols (symbols may be defined
192     multiple times, the value of a symbol is the amount of
193     space it requires, and the largest symbol value is the one
194     used).  Most targets have exactly one of these (which we
195     translate to bfd_com_section_ptr), but ECOFF has two.  */
196#define SEC_IS_COMMON                  0x1000
197
198  /* The section contains only debugging information.  For
199     example, this is set for ELF .debug and .stab sections.
200     strip tests this flag to see if a section can be
201     discarded.  */
202#define SEC_DEBUGGING                  0x2000
203
204  /* The contents of this section are held in memory pointed to
205     by the contents field.  This is checked by bfd_get_section_contents,
206     and the data is retrieved from memory if appropriate.  */
207#define SEC_IN_MEMORY                  0x4000
208
209  /* The contents of this section are to be excluded by the
210     linker for executable and shared objects unless those
211     objects are to be further relocated.  */
212#define SEC_EXCLUDE                    0x8000
213
214  /* The contents of this section are to be sorted based on the sum of
215     the symbol and addend values specified by the associated relocation
216     entries.  Entries without associated relocation entries will be
217     appended to the end of the section in an unspecified order.  */
218#define SEC_SORT_ENTRIES              0x10000
219
220  /* When linking, duplicate sections of the same name should be
221     discarded, rather than being combined into a single section as
222     is usually done.  This is similar to how common symbols are
223     handled.  See SEC_LINK_DUPLICATES below.  */
224#define SEC_LINK_ONCE                 0x20000
225
226  /* If SEC_LINK_ONCE is set, this bitfield describes how the linker
227     should handle duplicate sections.  */
228#define SEC_LINK_DUPLICATES           0xc0000
229
230  /* This value for SEC_LINK_DUPLICATES means that duplicate
231     sections with the same name should simply be discarded.  */
232#define SEC_LINK_DUPLICATES_DISCARD       0x0
233
234  /* This value for SEC_LINK_DUPLICATES means that the linker
235     should warn if there are any duplicate sections, although
236     it should still only link one copy.  */
237#define SEC_LINK_DUPLICATES_ONE_ONLY  0x40000
238
239  /* This value for SEC_LINK_DUPLICATES means that the linker
240     should warn if any duplicate sections are a different size.  */
241#define SEC_LINK_DUPLICATES_SAME_SIZE 0x80000
242
243  /* This value for SEC_LINK_DUPLICATES means that the linker
244     should warn if any duplicate sections contain different
245     contents.  */
246#define SEC_LINK_DUPLICATES_SAME_CONTENTS \
247  (SEC_LINK_DUPLICATES_ONE_ONLY | SEC_LINK_DUPLICATES_SAME_SIZE)
248
249  /* This section was created by the linker as part of dynamic
250     relocation or other arcane processing.  It is skipped when
251     going through the first-pass output, trusting that someone
252     else up the line will take care of it later.  */
253#define SEC_LINKER_CREATED           0x100000
254
255  /* This section should not be subject to garbage collection.
256     Also set to inform the linker that this section should not be
257     listed in the link map as discarded.  */
258#define SEC_KEEP                     0x200000
259
260  /* This section contains "short" data, and should be placed
261     "near" the GP.  */
262#define SEC_SMALL_DATA               0x400000
263
264  /* Attempt to merge identical entities in the section.
265     Entity size is given in the entsize field.  */
266#define SEC_MERGE                    0x800000
267
268  /* If given with SEC_MERGE, entities to merge are zero terminated
269     strings where entsize specifies character size instead of fixed
270     size entries.  */
271#define SEC_STRINGS                 0x1000000
272
273  /* This section contains data about section groups.  */
274#define SEC_GROUP                   0x2000000
275
276  /* The section is a COFF shared library section.  This flag is
277     only for the linker.  If this type of section appears in
278     the input file, the linker must copy it to the output file
279     without changing the vma or size.  FIXME: Although this
280     was originally intended to be general, it really is COFF
281     specific (and the flag was renamed to indicate this).  It
282     might be cleaner to have some more general mechanism to
283     allow the back end to control what the linker does with
284     sections.  */
285#define SEC_COFF_SHARED_LIBRARY     0x4000000
286
287  /* This input section should be copied to output in reverse order
288     as an array of pointers.  This is for ELF linker internal use
289     only.  */
290#define SEC_ELF_REVERSE_COPY        0x4000000
291
292  /* This section contains data which may be shared with other
293     executables or shared objects. This is for COFF only.  */
294#define SEC_COFF_SHARED             0x8000000
295
296  /* This section should be compressed.  This is for ELF linker
297     internal use only.  */
298#define SEC_ELF_COMPRESS            0x8000000
299
300  /* When a section with this flag is being linked, then if the size of
301     the input section is less than a page, it should not cross a page
302     boundary.  If the size of the input section is one page or more,
303     it should be aligned on a page boundary.  This is for TI
304     TMS320C54X only.  */
305#define SEC_TIC54X_BLOCK           0x10000000
306
307  /* This section should be renamed.  This is for ELF linker
308     internal use only.  */
309#define SEC_ELF_RENAME             0x10000000
310
311  /* Conditionally link this section; do not link if there are no
312     references found to any symbol in the section.  This is for TI
313     TMS320C54X only.  */
314#define SEC_TIC54X_CLINK           0x20000000
315
316  /* This section contains vliw code.  This is for Toshiba MeP only.  */
317#define SEC_MEP_VLIW               0x20000000
318
319  /* Indicate that section has the no read flag set. This happens
320     when memory read flag isn't set. */
321#define SEC_COFF_NOREAD            0x40000000
322
323  /* Indicate that section has the purecode flag set.  */
324#define SEC_ELF_PURECODE           0x80000000
325
326  /*  End of section flags.  */
327
328  /* Some internal packed boolean fields.  */
329
330  /* See the vma field.  */
331  unsigned int user_set_vma : 1;
332
333  /* A mark flag used by some of the linker backends.  */
334  unsigned int linker_mark : 1;
335
336  /* Another mark flag used by some of the linker backends.  Set for
337     output sections that have an input section.  */
338  unsigned int linker_has_input : 1;
339
340  /* Mark flag used by some linker backends for garbage collection.  */
341  unsigned int gc_mark : 1;
342
343  /* Section compression status.  */
344  unsigned int compress_status : 2;
345#define COMPRESS_SECTION_NONE    0
346#define COMPRESS_SECTION_DONE    1
347#define DECOMPRESS_SECTION_SIZED 2
348
349  /* The following flags are used by the ELF linker. */
350
351  /* Mark sections which have been allocated to segments.  */
352  unsigned int segment_mark : 1;
353
354  /* Type of sec_info information.  */
355  unsigned int sec_info_type:3;
356#define SEC_INFO_TYPE_NONE      0
357#define SEC_INFO_TYPE_STABS     1
358#define SEC_INFO_TYPE_MERGE     2
359#define SEC_INFO_TYPE_EH_FRAME  3
360#define SEC_INFO_TYPE_JUST_SYMS 4
361#define SEC_INFO_TYPE_TARGET    5
362#define SEC_INFO_TYPE_EH_FRAME_ENTRY 6
363
364  /* Nonzero if this section uses RELA relocations, rather than REL.  */
365  unsigned int use_rela_p:1;
366
367  /* Bits used by various backends.  The generic code doesn't touch
368     these fields.  */
369
370  unsigned int sec_flg0:1;
371  unsigned int sec_flg1:1;
372  unsigned int sec_flg2:1;
373  unsigned int sec_flg3:1;
374  unsigned int sec_flg4:1;
375  unsigned int sec_flg5:1;
376
377  /* End of internal packed boolean fields.  */
378
379  /*  The virtual memory address of the section - where it will be
380      at run time.  The symbols are relocated against this.  The
381      user_set_vma flag is maintained by bfd; if it's not set, the
382      backend can assign addresses (for example, in @code{a.out}, where
383      the default address for @code{.data} is dependent on the specific
384      target and various flags).  */
385  bfd_vma vma;
386
387  /*  The load address of the section - where it would be in a
388      rom image; really only used for writing section header
389      information.  */
390  bfd_vma lma;
391
392  /* The size of the section in *octets*, as it will be output.
393     Contains a value even if the section has no contents (e.g., the
394     size of @code{.bss}).  */
395  bfd_size_type size;
396
397  /* For input sections, the original size on disk of the section, in
398     octets.  This field should be set for any section whose size is
399     changed by linker relaxation.  It is required for sections where
400     the linker relaxation scheme doesn't cache altered section and
401     reloc contents (stabs, eh_frame, SEC_MERGE, some coff relaxing
402     targets), and thus the original size needs to be kept to read the
403     section multiple times.  For output sections, rawsize holds the
404     section size calculated on a previous linker relaxation pass.  */
405  bfd_size_type rawsize;
406
407  /* The compressed size of the section in octets.  */
408  bfd_size_type compressed_size;
409
410  /* Relaxation table. */
411  struct relax_table *relax;
412
413  /* Count of used relaxation table entries. */
414  int relax_count;
415
416
417  /* If this section is going to be output, then this value is the
418     offset in *bytes* into the output section of the first byte in the
419     input section (byte ==> smallest addressable unit on the
420     target).  In most cases, if this was going to start at the
421     100th octet (8-bit quantity) in the output section, this value
422     would be 100.  However, if the target byte size is 16 bits
423     (bfd_octets_per_byte is "2"), this value would be 50.  */
424  bfd_vma output_offset;
425
426  /* The output section through which to map on output.  */
427  struct bfd_section *output_section;
428
429  /* The alignment requirement of the section, as an exponent of 2 -
430     e.g., 3 aligns to 2^3 (or 8).  */
431  unsigned int alignment_power;
432
433  /* If an input section, a pointer to a vector of relocation
434     records for the data in this section.  */
435  struct reloc_cache_entry *relocation;
436
437  /* If an output section, a pointer to a vector of pointers to
438     relocation records for the data in this section.  */
439  struct reloc_cache_entry **orelocation;
440
441  /* The number of relocation records in one of the above.  */
442  unsigned reloc_count;
443
444  /* Information below is back end specific - and not always used
445     or updated.  */
446
447  /* File position of section data.  */
448  file_ptr filepos;
449
450  /* File position of relocation info.  */
451  file_ptr rel_filepos;
452
453  /* File position of line data.  */
454  file_ptr line_filepos;
455
456  /* Pointer to data for applications.  */
457  void *userdata;
458
459  /* If the SEC_IN_MEMORY flag is set, this points to the actual
460     contents.  */
461  unsigned char *contents;
462
463  /* Attached line number information.  */
464  alent *lineno;
465
466  /* Number of line number records.  */
467  unsigned int lineno_count;
468
469  /* Entity size for merging purposes.  */
470  unsigned int entsize;
471
472  /* Points to the kept section if this section is a link-once section,
473     and is discarded.  */
474  struct bfd_section *kept_section;
475
476  /* When a section is being output, this value changes as more
477     linenumbers are written out.  */
478  file_ptr moving_line_filepos;
479
480  /* What the section number is in the target world.  */
481  int target_index;
482
483  void *used_by_bfd;
484
485  /* If this is a constructor section then here is a list of the
486     relocations created to relocate items within it.  */
487  struct relent_chain *constructor_chain;
488
489  /* The BFD which owns the section.  */
490  bfd *owner;
491
492  /* A symbol which points at this section only.  */
493  struct bfd_symbol *symbol;
494  struct bfd_symbol **symbol_ptr_ptr;
495
496  /* Early in the link process, map_head and map_tail are used to build
497     a list of input sections attached to an output section.  Later,
498     output sections use these fields for a list of bfd_link_order
499     structs.  */
500  union @{
501    struct bfd_link_order *link_order;
502    struct bfd_section *s;
503  @} map_head, map_tail;
504@} asection;
505
506/* Relax table contains information about instructions which can
507   be removed by relaxation -- replacing a long address with a
508   short address.  */
509struct relax_table @{
510  /* Address where bytes may be deleted. */
511  bfd_vma addr;
512
513  /* Number of bytes to be deleted.  */
514  int size;
515@};
516
517/* Note: the following are provided as inline functions rather than macros
518   because not all callers use the return value.  A macro implementation
519   would use a comma expression, eg: "((ptr)->foo = val, TRUE)" and some
520   compilers will complain about comma expressions that have no effect.  */
521static inline bfd_boolean
522bfd_set_section_userdata (bfd * abfd ATTRIBUTE_UNUSED, asection * ptr,
523                          void * val)
524@{
525  ptr->userdata = val;
526  return TRUE;
527@}
528
529static inline bfd_boolean
530bfd_set_section_vma (bfd * abfd ATTRIBUTE_UNUSED, asection * ptr, bfd_vma val)
531@{
532  ptr->vma = ptr->lma = val;
533  ptr->user_set_vma = TRUE;
534  return TRUE;
535@}
536
537static inline bfd_boolean
538bfd_set_section_alignment (bfd * abfd ATTRIBUTE_UNUSED, asection * ptr,
539                           unsigned int val)
540@{
541  ptr->alignment_power = val;
542  return TRUE;
543@}
544
545/* These sections are global, and are managed by BFD.  The application
546   and target back end are not permitted to change the values in
547   these sections.  */
548extern asection _bfd_std_section[4];
549
550#define BFD_ABS_SECTION_NAME "*ABS*"
551#define BFD_UND_SECTION_NAME "*UND*"
552#define BFD_COM_SECTION_NAME "*COM*"
553#define BFD_IND_SECTION_NAME "*IND*"
554
555/* Pointer to the common section.  */
556#define bfd_com_section_ptr (&_bfd_std_section[0])
557/* Pointer to the undefined section.  */
558#define bfd_und_section_ptr (&_bfd_std_section[1])
559/* Pointer to the absolute section.  */
560#define bfd_abs_section_ptr (&_bfd_std_section[2])
561/* Pointer to the indirect section.  */
562#define bfd_ind_section_ptr (&_bfd_std_section[3])
563
564#define bfd_is_und_section(sec) ((sec) == bfd_und_section_ptr)
565#define bfd_is_abs_section(sec) ((sec) == bfd_abs_section_ptr)
566#define bfd_is_ind_section(sec) ((sec) == bfd_ind_section_ptr)
567
568#define bfd_is_const_section(SEC)              \
569 (   ((SEC) == bfd_abs_section_ptr)            \
570  || ((SEC) == bfd_und_section_ptr)            \
571  || ((SEC) == bfd_com_section_ptr)            \
572  || ((SEC) == bfd_ind_section_ptr))
573
574/* Macros to handle insertion and deletion of a bfd's sections.  These
575   only handle the list pointers, ie. do not adjust section_count,
576   target_index etc.  */
577#define bfd_section_list_remove(ABFD, S) \
578  do                                                   \
579    @{                                                  \
580      asection *_s = S;                                \
581      asection *_next = _s->next;                      \
582      asection *_prev = _s->prev;                      \
583      if (_prev)                                       \
584        _prev->next = _next;                           \
585      else                                             \
586        (ABFD)->sections = _next;                      \
587      if (_next)                                       \
588        _next->prev = _prev;                           \
589      else                                             \
590        (ABFD)->section_last = _prev;                  \
591    @}                                                  \
592  while (0)
593#define bfd_section_list_append(ABFD, S) \
594  do                                                   \
595    @{                                                  \
596      asection *_s = S;                                \
597      bfd *_abfd = ABFD;                               \
598      _s->next = NULL;                                 \
599      if (_abfd->section_last)                         \
600        @{                                              \
601          _s->prev = _abfd->section_last;              \
602          _abfd->section_last->next = _s;              \
603        @}                                              \
604      else                                             \
605        @{                                              \
606          _s->prev = NULL;                             \
607          _abfd->sections = _s;                        \
608        @}                                              \
609      _abfd->section_last = _s;                        \
610    @}                                                  \
611  while (0)
612#define bfd_section_list_prepend(ABFD, S) \
613  do                                                   \
614    @{                                                  \
615      asection *_s = S;                                \
616      bfd *_abfd = ABFD;                               \
617      _s->prev = NULL;                                 \
618      if (_abfd->sections)                             \
619        @{                                              \
620          _s->next = _abfd->sections;                  \
621          _abfd->sections->prev = _s;                  \
622        @}                                              \
623      else                                             \
624        @{                                              \
625          _s->next = NULL;                             \
626          _abfd->section_last = _s;                    \
627        @}                                              \
628      _abfd->sections = _s;                            \
629    @}                                                  \
630  while (0)
631#define bfd_section_list_insert_after(ABFD, A, S) \
632  do                                                   \
633    @{                                                  \
634      asection *_a = A;                                \
635      asection *_s = S;                                \
636      asection *_next = _a->next;                      \
637      _s->next = _next;                                \
638      _s->prev = _a;                                   \
639      _a->next = _s;                                   \
640      if (_next)                                       \
641        _next->prev = _s;                              \
642      else                                             \
643        (ABFD)->section_last = _s;                     \
644    @}                                                  \
645  while (0)
646#define bfd_section_list_insert_before(ABFD, B, S) \
647  do                                                   \
648    @{                                                  \
649      asection *_b = B;                                \
650      asection *_s = S;                                \
651      asection *_prev = _b->prev;                      \
652      _s->prev = _prev;                                \
653      _s->next = _b;                                   \
654      _b->prev = _s;                                   \
655      if (_prev)                                       \
656        _prev->next = _s;                              \
657      else                                             \
658        (ABFD)->sections = _s;                         \
659    @}                                                  \
660  while (0)
661#define bfd_section_removed_from_list(ABFD, S) \
662  ((S)->next == NULL ? (ABFD)->section_last != (S) : (S)->next->prev != (S))
663
664#define BFD_FAKE_SECTION(SEC, SYM, NAME, IDX, FLAGS)                   \
665  /* name, id,  index, next, prev, flags, user_set_vma,            */  \
666  @{  NAME, IDX, 0,     NULL, NULL, FLAGS, 0,                           \
667                                                                       \
668  /* linker_mark, linker_has_input, gc_mark, decompress_status,    */  \
669     0,           0,                1,       0,                        \
670                                                                       \
671  /* segment_mark, sec_info_type, use_rela_p,                      */  \
672     0,            0,             0,                                   \
673                                                                       \
674  /* sec_flg0, sec_flg1, sec_flg2, sec_flg3, sec_flg4, sec_flg5,   */  \
675     0,        0,        0,        0,        0,        0,              \
676                                                                       \
677  /* vma, lma, size, rawsize, compressed_size, relax, relax_count, */  \
678     0,   0,   0,    0,       0,               0,     0,               \
679                                                                       \
680  /* output_offset, output_section, alignment_power,               */  \
681     0,             &SEC,           0,                                 \
682                                                                       \
683  /* relocation, orelocation, reloc_count, filepos, rel_filepos,   */  \
684     NULL,       NULL,        0,           0,       0,                 \
685                                                                       \
686  /* line_filepos, userdata, contents, lineno, lineno_count,       */  \
687     0,            NULL,     NULL,     NULL,   0,                      \
688                                                                       \
689  /* entsize, kept_section, moving_line_filepos,                    */ \
690     0,       NULL,          0,                                        \
691                                                                       \
692  /* target_index, used_by_bfd, constructor_chain, owner,          */  \
693     0,            NULL,        NULL,              NULL,               \
694                                                                       \
695  /* symbol,                    symbol_ptr_ptr,                    */  \
696     (struct bfd_symbol *) SYM, &SEC.symbol,                           \
697                                                                       \
698  /* map_head, map_tail                                            */  \
699     @{ NULL @}, @{ NULL @}                                                \
700    @}
701
702/* We use a macro to initialize the static asymbol structures because
703   traditional C does not permit us to initialize a union member while
704   gcc warns if we don't initialize it.
705   the_bfd, name, value, attr, section [, udata]  */
706#ifdef __STDC__
707#define GLOBAL_SYM_INIT(NAME, SECTION) \
708  @{ 0, NAME, 0, BSF_SECTION_SYM, SECTION, @{ 0 @}@}
709#else
710#define GLOBAL_SYM_INIT(NAME, SECTION) \
711  @{ 0, NAME, 0, BSF_SECTION_SYM, SECTION @}
712#endif
713
714@end example
715
716@node section prototypes,  , typedef asection, Sections
717@subsection Section prototypes
718These are the functions exported by the section handling part of BFD.
719
720@findex bfd_section_list_clear
721@subsubsection @code{bfd_section_list_clear}
722@strong{Synopsis}
723@example
724void bfd_section_list_clear (bfd *);
725@end example
726@strong{Description}@*
727Clears the section list, and also resets the section count and
728hash table entries.
729
730@findex bfd_get_section_by_name
731@subsubsection @code{bfd_get_section_by_name}
732@strong{Synopsis}
733@example
734asection *bfd_get_section_by_name (bfd *abfd, const char *name);
735@end example
736@strong{Description}@*
737Return the most recently created section attached to @var{abfd}
738named @var{name}.  Return NULL if no such section exists.
739
740@findex bfd_get_next_section_by_name
741@subsubsection @code{bfd_get_next_section_by_name}
742@strong{Synopsis}
743@example
744asection *bfd_get_next_section_by_name (bfd *ibfd, asection *sec);
745@end example
746@strong{Description}@*
747Given @var{sec} is a section returned by @code{bfd_get_section_by_name},
748return the next most recently created section attached to the same
749BFD with the same name, or if no such section exists in the same BFD and
750IBFD is non-NULL, the next section with the same name in any input
751BFD following IBFD.  Return NULL on finding no section.
752
753@findex bfd_get_linker_section
754@subsubsection @code{bfd_get_linker_section}
755@strong{Synopsis}
756@example
757asection *bfd_get_linker_section (bfd *abfd, const char *name);
758@end example
759@strong{Description}@*
760Return the linker created section attached to @var{abfd}
761named @var{name}.  Return NULL if no such section exists.
762
763@findex bfd_get_section_by_name_if
764@subsubsection @code{bfd_get_section_by_name_if}
765@strong{Synopsis}
766@example
767asection *bfd_get_section_by_name_if
768   (bfd *abfd,
769    const char *name,
770    bfd_boolean (*func) (bfd *abfd, asection *sect, void *obj),
771    void *obj);
772@end example
773@strong{Description}@*
774Call the provided function @var{func} for each section
775attached to the BFD @var{abfd} whose name matches @var{name},
776passing @var{obj} as an argument. The function will be called
777as if by
778
779@example
780       func (abfd, the_section, obj);
781@end example
782
783It returns the first section for which @var{func} returns true,
784otherwise @code{NULL}.
785
786@findex bfd_get_unique_section_name
787@subsubsection @code{bfd_get_unique_section_name}
788@strong{Synopsis}
789@example
790char *bfd_get_unique_section_name
791   (bfd *abfd, const char *templat, int *count);
792@end example
793@strong{Description}@*
794Invent a section name that is unique in @var{abfd} by tacking
795a dot and a digit suffix onto the original @var{templat}.  If
796@var{count} is non-NULL, then it specifies the first number
797tried as a suffix to generate a unique name.  The value
798pointed to by @var{count} will be incremented in this case.
799
800@findex bfd_make_section_old_way
801@subsubsection @code{bfd_make_section_old_way}
802@strong{Synopsis}
803@example
804asection *bfd_make_section_old_way (bfd *abfd, const char *name);
805@end example
806@strong{Description}@*
807Create a new empty section called @var{name}
808and attach it to the end of the chain of sections for the
809BFD @var{abfd}. An attempt to create a section with a name which
810is already in use returns its pointer without changing the
811section chain.
812
813It has the funny name since this is the way it used to be
814before it was rewritten....
815
816Possible errors are:
817@itemize @bullet
818
819@item
820@code{bfd_error_invalid_operation} -
821If output has already started for this BFD.
822@item
823@code{bfd_error_no_memory} -
824If memory allocation fails.
825@end itemize
826
827@findex bfd_make_section_anyway_with_flags
828@subsubsection @code{bfd_make_section_anyway_with_flags}
829@strong{Synopsis}
830@example
831asection *bfd_make_section_anyway_with_flags
832   (bfd *abfd, const char *name, flagword flags);
833@end example
834@strong{Description}@*
835Create a new empty section called @var{name} and attach it to the end of
836the chain of sections for @var{abfd}.  Create a new section even if there
837is already a section with that name.  Also set the attributes of the
838new section to the value @var{flags}.
839
840Return @code{NULL} and set @code{bfd_error} on error; possible errors are:
841@itemize @bullet
842
843@item
844@code{bfd_error_invalid_operation} - If output has already started for @var{abfd}.
845@item
846@code{bfd_error_no_memory} - If memory allocation fails.
847@end itemize
848
849@findex bfd_make_section_anyway
850@subsubsection @code{bfd_make_section_anyway}
851@strong{Synopsis}
852@example
853asection *bfd_make_section_anyway (bfd *abfd, const char *name);
854@end example
855@strong{Description}@*
856Create a new empty section called @var{name} and attach it to the end of
857the chain of sections for @var{abfd}.  Create a new section even if there
858is already a section with that name.
859
860Return @code{NULL} and set @code{bfd_error} on error; possible errors are:
861@itemize @bullet
862
863@item
864@code{bfd_error_invalid_operation} - If output has already started for @var{abfd}.
865@item
866@code{bfd_error_no_memory} - If memory allocation fails.
867@end itemize
868
869@findex bfd_make_section_with_flags
870@subsubsection @code{bfd_make_section_with_flags}
871@strong{Synopsis}
872@example
873asection *bfd_make_section_with_flags
874   (bfd *, const char *name, flagword flags);
875@end example
876@strong{Description}@*
877Like @code{bfd_make_section_anyway}, but return @code{NULL} (without calling
878bfd_set_error ()) without changing the section chain if there is already a
879section named @var{name}.  Also set the attributes of the new section to
880the value @var{flags}.  If there is an error, return @code{NULL} and set
881@code{bfd_error}.
882
883@findex bfd_make_section
884@subsubsection @code{bfd_make_section}
885@strong{Synopsis}
886@example
887asection *bfd_make_section (bfd *, const char *name);
888@end example
889@strong{Description}@*
890Like @code{bfd_make_section_anyway}, but return @code{NULL} (without calling
891bfd_set_error ()) without changing the section chain if there is already a
892section named @var{name}.  If there is an error, return @code{NULL} and set
893@code{bfd_error}.
894
895@findex bfd_get_next_section_id
896@subsubsection @code{bfd_get_next_section_id}
897@strong{Synopsis}
898@example
899int bfd_get_next_section_id (void);
900@end example
901@strong{Description}@*
902Returns the id that the next section created will have.
903
904@findex bfd_set_section_flags
905@subsubsection @code{bfd_set_section_flags}
906@strong{Synopsis}
907@example
908bfd_boolean bfd_set_section_flags
909   (bfd *abfd, asection *sec, flagword flags);
910@end example
911@strong{Description}@*
912Set the attributes of the section @var{sec} in the BFD
913@var{abfd} to the value @var{flags}. Return @code{TRUE} on success,
914@code{FALSE} on error. Possible error returns are:
915
916@itemize @bullet
917
918@item
919@code{bfd_error_invalid_operation} -
920The section cannot have one or more of the attributes
921requested. For example, a .bss section in @code{a.out} may not
922have the @code{SEC_HAS_CONTENTS} field set.
923@end itemize
924
925@findex bfd_rename_section
926@subsubsection @code{bfd_rename_section}
927@strong{Synopsis}
928@example
929void bfd_rename_section
930   (bfd *abfd, asection *sec, const char *newname);
931@end example
932@strong{Description}@*
933Rename section @var{sec} in @var{abfd} to @var{newname}.
934
935@findex bfd_map_over_sections
936@subsubsection @code{bfd_map_over_sections}
937@strong{Synopsis}
938@example
939void bfd_map_over_sections
940   (bfd *abfd,
941    void (*func) (bfd *abfd, asection *sect, void *obj),
942    void *obj);
943@end example
944@strong{Description}@*
945Call the provided function @var{func} for each section
946attached to the BFD @var{abfd}, passing @var{obj} as an
947argument. The function will be called as if by
948
949@example
950       func (abfd, the_section, obj);
951@end example
952
953This is the preferred method for iterating over sections; an
954alternative would be to use a loop:
955
956@example
957          asection *p;
958          for (p = abfd->sections; p != NULL; p = p->next)
959             func (abfd, p, ...)
960@end example
961
962@findex bfd_sections_find_if
963@subsubsection @code{bfd_sections_find_if}
964@strong{Synopsis}
965@example
966asection *bfd_sections_find_if
967   (bfd *abfd,
968    bfd_boolean (*operation) (bfd *abfd, asection *sect, void *obj),
969    void *obj);
970@end example
971@strong{Description}@*
972Call the provided function @var{operation} for each section
973attached to the BFD @var{abfd}, passing @var{obj} as an
974argument. The function will be called as if by
975
976@example
977       operation (abfd, the_section, obj);
978@end example
979
980It returns the first section for which @var{operation} returns true.
981
982@findex bfd_set_section_size
983@subsubsection @code{bfd_set_section_size}
984@strong{Synopsis}
985@example
986bfd_boolean bfd_set_section_size
987   (bfd *abfd, asection *sec, bfd_size_type val);
988@end example
989@strong{Description}@*
990Set @var{sec} to the size @var{val}. If the operation is
991ok, then @code{TRUE} is returned, else @code{FALSE}.
992
993Possible error returns:
994@itemize @bullet
995
996@item
997@code{bfd_error_invalid_operation} -
998Writing has started to the BFD, so setting the size is invalid.
999@end itemize
1000
1001@findex bfd_set_section_contents
1002@subsubsection @code{bfd_set_section_contents}
1003@strong{Synopsis}
1004@example
1005bfd_boolean bfd_set_section_contents
1006   (bfd *abfd, asection *section, const void *data,
1007    file_ptr offset, bfd_size_type count);
1008@end example
1009@strong{Description}@*
1010Sets the contents of the section @var{section} in BFD
1011@var{abfd} to the data starting in memory at @var{data}. The
1012data is written to the output section starting at offset
1013@var{offset} for @var{count} octets.
1014
1015Normally @code{TRUE} is returned, else @code{FALSE}. Possible error
1016returns are:
1017@itemize @bullet
1018
1019@item
1020@code{bfd_error_no_contents} -
1021The output section does not have the @code{SEC_HAS_CONTENTS}
1022attribute, so nothing can be written to it.
1023@item
1024and some more too
1025@end itemize
1026This routine is front end to the back end function
1027@code{_bfd_set_section_contents}.
1028
1029@findex bfd_get_section_contents
1030@subsubsection @code{bfd_get_section_contents}
1031@strong{Synopsis}
1032@example
1033bfd_boolean bfd_get_section_contents
1034   (bfd *abfd, asection *section, void *location, file_ptr offset,
1035    bfd_size_type count);
1036@end example
1037@strong{Description}@*
1038Read data from @var{section} in BFD @var{abfd}
1039into memory starting at @var{location}. The data is read at an
1040offset of @var{offset} from the start of the input section,
1041and is read for @var{count} bytes.
1042
1043If the contents of a constructor with the @code{SEC_CONSTRUCTOR}
1044flag set are requested or if the section does not have the
1045@code{SEC_HAS_CONTENTS} flag set, then the @var{location} is filled
1046with zeroes. If no errors occur, @code{TRUE} is returned, else
1047@code{FALSE}.
1048
1049@findex bfd_malloc_and_get_section
1050@subsubsection @code{bfd_malloc_and_get_section}
1051@strong{Synopsis}
1052@example
1053bfd_boolean bfd_malloc_and_get_section
1054   (bfd *abfd, asection *section, bfd_byte **buf);
1055@end example
1056@strong{Description}@*
1057Read all data from @var{section} in BFD @var{abfd}
1058into a buffer, *@var{buf}, malloc'd by this function.
1059
1060@findex bfd_copy_private_section_data
1061@subsubsection @code{bfd_copy_private_section_data}
1062@strong{Synopsis}
1063@example
1064bfd_boolean bfd_copy_private_section_data
1065   (bfd *ibfd, asection *isec, bfd *obfd, asection *osec);
1066@end example
1067@strong{Description}@*
1068Copy private section information from @var{isec} in the BFD
1069@var{ibfd} to the section @var{osec} in the BFD @var{obfd}.
1070Return @code{TRUE} on success, @code{FALSE} on error.  Possible error
1071returns are:
1072
1073@itemize @bullet
1074
1075@item
1076@code{bfd_error_no_memory} -
1077Not enough memory exists to create private data for @var{osec}.
1078@end itemize
1079@example
1080#define bfd_copy_private_section_data(ibfd, isection, obfd, osection) \
1081       BFD_SEND (obfd, _bfd_copy_private_section_data, \
1082                 (ibfd, isection, obfd, osection))
1083@end example
1084
1085@findex bfd_generic_is_group_section
1086@subsubsection @code{bfd_generic_is_group_section}
1087@strong{Synopsis}
1088@example
1089bfd_boolean bfd_generic_is_group_section (bfd *, const asection *sec);
1090@end example
1091@strong{Description}@*
1092Returns TRUE if @var{sec} is a member of a group.
1093
1094@findex bfd_generic_discard_group
1095@subsubsection @code{bfd_generic_discard_group}
1096@strong{Synopsis}
1097@example
1098bfd_boolean bfd_generic_discard_group (bfd *abfd, asection *group);
1099@end example
1100@strong{Description}@*
1101Remove all members of @var{group} from the output.
1102
1103