1 /* bfdlink.h -- header file for BFD link routines
2 Copyright 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2002, 2003
3 Free Software Foundation, Inc.
4 Written by Steve Chamberlain and Ian Lance Taylor, Cygnus Support.
6 This file is part of BFD, the Binary File Descriptor library.
8 This program is free software; you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 2 of the License, or
11 (at your option) any later version.
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with this program; if not, write to the Free Software
20 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
25 /* Which symbols to strip during a link. */
28 strip_none
, /* Don't strip any symbols. */
29 strip_debugger
, /* Strip debugging symbols. */
30 strip_some
, /* keep_hash is the list of symbols to keep. */
31 strip_all
/* Strip all symbols. */
34 /* Which local symbols to discard during a link. This is irrelevant
35 if strip_all is used. */
38 discard_sec_merge
, /* Discard local temporary symbols in SEC_MERGE
40 discard_none
, /* Don't discard any locals. */
41 discard_l
, /* Discard local temporary symbols. */
42 discard_all
/* Discard all locals. */
45 /* Describes the type of hash table entry structure being used.
46 Different hash table structure have different fields and so
47 support different linking features. */
48 enum bfd_link_hash_table_type
50 bfd_link_generic_hash_table
,
51 bfd_link_elf_hash_table
54 /* These are the possible types of an entry in the BFD link hash
57 enum bfd_link_hash_type
59 bfd_link_hash_new
, /* Symbol is new. */
60 bfd_link_hash_undefined
, /* Symbol seen before, but undefined. */
61 bfd_link_hash_undefweak
, /* Symbol is weak and undefined. */
62 bfd_link_hash_defined
, /* Symbol is defined. */
63 bfd_link_hash_defweak
, /* Symbol is weak and defined. */
64 bfd_link_hash_common
, /* Symbol is common. */
65 bfd_link_hash_indirect
, /* Symbol is an indirect link. */
66 bfd_link_hash_warning
/* Like indirect, but warn if referenced. */
69 enum bfd_link_common_skip_ar_aymbols
71 bfd_link_common_skip_none
,
72 bfd_link_common_skip_text
,
73 bfd_link_common_skip_data
,
74 bfd_link_common_skip_all
77 /* The linking routines use a hash table which uses this structure for
80 struct bfd_link_hash_entry
82 /* Base hash table entry structure. */
83 struct bfd_hash_entry root
;
84 /* Type of this entry. */
85 enum bfd_link_hash_type type
;
87 /* Undefined and common symbols are kept in a linked list through
88 this field. This field is not in the union because that would
89 force us to remove entries from the list when we changed their
90 type, which would force the list to be doubly linked, which would
91 waste more memory. When an undefined or common symbol is
92 created, it should be added to this list, the head of which is in
93 the link hash table itself. As symbols are defined, they need
94 not be removed from the list; anything which reads the list must
95 doublecheck the symbol type.
97 Weak symbols are not kept on this list.
99 Defined and defweak symbols use this field as a reference marker.
100 If the field is not NULL, or this structure is the tail of the
101 undefined symbol list, the symbol has been referenced. If the
102 symbol is undefined and becomes defined, this field will
103 automatically be non-NULL since the symbol will have been on the
104 undefined symbol list. */
105 struct bfd_link_hash_entry
*next
;
106 /* A union of information depending upon the type. */
109 /* Nothing is kept for bfd_hash_new. */
110 /* bfd_link_hash_undefined, bfd_link_hash_undefweak. */
113 bfd
*abfd
; /* BFD symbol was found in. */
115 /* bfd_link_hash_defined, bfd_link_hash_defweak. */
118 bfd_vma value
; /* Symbol value. */
119 asection
*section
; /* Symbol section. */
121 /* bfd_link_hash_indirect, bfd_link_hash_warning. */
124 struct bfd_link_hash_entry
*link
; /* Real symbol. */
125 const char *warning
; /* Warning (bfd_link_hash_warning only). */
127 /* bfd_link_hash_common. */
130 /* The linker needs to know three things about common
131 symbols: the size, the alignment, and the section in
132 which the symbol should be placed. We store the size
133 here, and we allocate a small structure to hold the
134 section and the alignment. The alignment is stored as a
135 power of two. We don't store all the information
136 directly because we don't want to increase the size of
137 the union; this structure is a major space user in the
139 bfd_size_type size
; /* Common symbol size. */
140 struct bfd_link_hash_common_entry
142 unsigned int alignment_power
; /* Alignment. */
143 asection
*section
; /* Symbol section. */
149 /* This is the link hash table. It is a derived class of
152 struct bfd_link_hash_table
154 /* The hash table itself. */
155 struct bfd_hash_table table
;
156 /* The back end which created this hash table. This indicates the
157 type of the entries in the hash table, which is sometimes
158 important information when linking object files of different
160 const bfd_target
*creator
;
161 /* A linked list of undefined and common symbols, linked through the
162 next field in the bfd_link_hash_entry structure. */
163 struct bfd_link_hash_entry
*undefs
;
164 /* Entries are added to the tail of the undefs list. */
165 struct bfd_link_hash_entry
*undefs_tail
;
166 /* The type of the link hash table. */
167 enum bfd_link_hash_table_type type
;
170 /* Look up an entry in a link hash table. If FOLLOW is TRUE, this
171 follows bfd_link_hash_indirect and bfd_link_hash_warning links to
173 extern struct bfd_link_hash_entry
*bfd_link_hash_lookup
174 (struct bfd_link_hash_table
*, const char *, bfd_boolean create
,
175 bfd_boolean copy
, bfd_boolean follow
);
177 /* Look up an entry in the main linker hash table if the symbol might
178 be wrapped. This should only be used for references to an
179 undefined symbol, not for definitions of a symbol. */
181 extern struct bfd_link_hash_entry
*bfd_wrapped_link_hash_lookup
182 (bfd
*, struct bfd_link_info
*, const char *, bfd_boolean
,
183 bfd_boolean
, bfd_boolean
);
185 /* Traverse a link hash table. */
186 extern void bfd_link_hash_traverse
187 (struct bfd_link_hash_table
*,
188 bfd_boolean (*) (struct bfd_link_hash_entry
*, void *),
191 /* Add an entry to the undefs list. */
192 extern void bfd_link_add_undef
193 (struct bfd_link_hash_table
*, struct bfd_link_hash_entry
*);
197 struct bfd_sym_chain
*next
;
201 /* How to handle unresolved symbols.
202 There are four possibilities which are enumerated below: */
205 /* This is the initial value when then link_info structure is created.
206 It allows the various stages of the linker to determine whether they
207 allowed to set the value. */
214 /* This structure holds all the information needed to communicate
215 between BFD and the linker when doing a link. */
219 /* TRUE if BFD should generate a relocatable object file. */
220 unsigned int relocatable
: 1;
222 /* TRUE if BFD should generate relocation information in the final
224 unsigned int emitrelocations
: 1;
226 /* TRUE if BFD should generate a "task linked" object file,
227 similar to relocatable but also with globals converted to
229 unsigned int task_link
: 1;
231 /* TRUE if BFD should generate a shared object. */
232 unsigned int shared
: 1;
234 /* TRUE if BFD should pre-bind symbols in a shared object. */
235 unsigned int symbolic
: 1;
237 /* TRUE if BFD should export all symbols in the dynamic symbol table
238 of an executable, rather than only those used. */
239 unsigned int export_dynamic
: 1;
241 /* TRUE if shared objects should be linked directly, not shared. */
242 unsigned int static_link
: 1;
244 /* TRUE if the output file should be in a traditional format. This
245 is equivalent to the setting of the BFD_TRADITIONAL_FORMAT flag
246 on the output file, but may be checked when reading the input
248 unsigned int traditional_format
: 1;
250 /* TRUE if we want to produced optimized output files. This might
251 need much more time and therefore must be explicitly selected. */
252 unsigned int optimize
: 1;
254 /* TRUE if ok to have multiple definition. */
255 unsigned int allow_multiple_definition
: 1;
257 /* TRUE if ok to have version with no definition. */
258 unsigned int allow_undefined_version
: 1;
260 /* TRUE if symbols should be retained in memory, FALSE if they
261 should be freed and reread. */
262 unsigned int keep_memory
: 1;
264 /* TRUE if every symbol should be reported back via the notice
266 unsigned int notice_all
: 1;
268 /* TRUE if executable should not contain copy relocs.
269 Setting this true may result in a non-sharable text segment. */
270 unsigned int nocopyreloc
: 1;
272 /* TRUE if the new ELF dynamic tags are enabled. */
273 unsigned int new_dtags
: 1;
275 /* TRUE if non-PLT relocs should be merged into one reloc section
276 and sorted so that relocs against the same symbol come together. */
277 unsigned int combreloc
: 1;
279 /* TRUE if .eh_frame_hdr section and PT_GNU_EH_FRAME ELF segment
280 should be created. */
281 unsigned int eh_frame_hdr
: 1;
283 /* TRUE if global symbols in discarded sections should be stripped. */
284 unsigned int strip_discarded
: 1;
286 /* TRUE if relaxation is being finalized. */
287 unsigned int relax_finalizing
: 1;
289 /* TRUE if generating a position independent executable. */
292 /* TRUE if generating an executable, position independent or not. */
293 unsigned int executable
: 1;
295 /* TRUE if PT_GNU_STACK segment should be created with PF_R|PF_W|PF_X
297 unsigned int execstack
: 1;
299 /* TRUE if PT_GNU_STACK segment should be created with PF_R|PF_W
301 unsigned int noexecstack
: 1;
303 /* What to do with unresolved symbols in an object file.
304 When producing static binaries the default is GENERATE_ERROR.
305 When producing dynamic binaries the default is IGNORE. The
306 assumption with dynamic binaries is that the reference will be
307 resolved at load/execution time. */
308 enum report_method unresolved_syms_in_objects
;
310 /* What to do with unresolved symbols in a shared library.
311 The same defaults apply. */
312 enum report_method unresolved_syms_in_shared_libs
;
314 /* Which symbols to strip. */
315 enum bfd_link_strip strip
;
317 /* Which local symbols to discard. */
318 enum bfd_link_discard discard
;
320 /* Criteria for skipping symbols when detemining
321 whether to include an object from an archive. */
322 enum bfd_link_common_skip_ar_aymbols common_skip_ar_aymbols
;
324 /* Function callbacks. */
325 const struct bfd_link_callbacks
*callbacks
;
327 /* Hash table handled by BFD. */
328 struct bfd_link_hash_table
*hash
;
330 /* Hash table of symbols to keep. This is NULL unless strip is
332 struct bfd_hash_table
*keep_hash
;
334 /* Hash table of symbols to report back via the notice callback. If
335 this is NULL, and notice_all is FALSE, then no symbols are
337 struct bfd_hash_table
*notice_hash
;
339 /* Hash table of symbols which are being wrapped (the --wrap linker
340 option). If this is NULL, no symbols are being wrapped. */
341 struct bfd_hash_table
*wrap_hash
;
343 /* The list of input BFD's involved in the link. These are chained
344 together via the link_next field. */
347 /* If a symbol should be created for each input BFD, this is section
348 where those symbols should be placed. It must be a section in
349 the output BFD. It may be NULL, in which case no such symbols
350 will be created. This is to support CREATE_OBJECT_SYMBOLS in the
351 linker command language. */
352 asection
*create_object_symbols_section
;
354 /* List of global symbol names that are starting points for marking
355 sections against garbage collection. */
356 struct bfd_sym_chain
*gc_sym_list
;
358 /* If a base output file is wanted, then this points to it */
361 /* The function to call when the executable or shared object is
363 const char *init_function
;
365 /* The function to call when the executable or shared object is
367 const char *fini_function
;
369 /* If non-zero, specifies that branches which are problematic for the
370 MPC860 C0 (or earlier) should be checked for and modified. It gives the
371 number of bytes that should be checked at the end of each text page. */
374 /* Non-zero if auto-import thunks for DATA items in pei386 DLLs
375 should be generated/linked against. Set to 1 if this feature
376 is explicitly requested by the user, -1 if enabled by default. */
377 int pei386_auto_import
;
379 /* Non-zero if runtime relocs for DATA items with non-zero addends
380 in pei386 DLLs should be generated. Set to 1 if this feature
381 is explicitly requested by the user, -1 if enabled by default. */
382 int pei386_runtime_pseudo_reloc
;
384 /* How many spare .dynamic DT_NULL entries should be added? */
385 unsigned int spare_dynamic_tags
;
387 /* May be used to set DT_FLAGS for ELF. */
390 /* May be used to set DT_FLAGS_1 for ELF. */
394 /* This structures holds a set of callback functions. These are
395 called by the BFD linker routines. The first argument to each
396 callback function is the bfd_link_info structure being used. Each
397 function returns a boolean value. If the function returns FALSE,
398 then the BFD function which called it will return with a failure
401 struct bfd_link_callbacks
403 /* A function which is called when an object is added from an
404 archive. ABFD is the archive element being added. NAME is the
405 name of the symbol which caused the archive element to be pulled
407 bfd_boolean (*add_archive_element
)
408 (struct bfd_link_info
*, bfd
*abfd
, const char *name
);
409 /* A function which is called when a symbol is found with multiple
410 definitions. NAME is the symbol which is defined multiple times.
411 OBFD is the old BFD, OSEC is the old section, OVAL is the old
412 value, NBFD is the new BFD, NSEC is the new section, and NVAL is
413 the new value. OBFD may be NULL. OSEC and NSEC may be
414 bfd_com_section or bfd_ind_section. */
415 bfd_boolean (*multiple_definition
)
416 (struct bfd_link_info
*, const char *name
,
417 bfd
*obfd
, asection
*osec
, bfd_vma oval
,
418 bfd
*nbfd
, asection
*nsec
, bfd_vma nval
);
419 /* A function which is called when a common symbol is defined
420 multiple times. NAME is the symbol appearing multiple times.
421 OBFD is the BFD of the existing symbol; it may be NULL if this is
422 not known. OTYPE is the type of the existing symbol, which may
423 be bfd_link_hash_defined, bfd_link_hash_defweak,
424 bfd_link_hash_common, or bfd_link_hash_indirect. If OTYPE is
425 bfd_link_hash_common, OSIZE is the size of the existing symbol.
426 NBFD is the BFD of the new symbol. NTYPE is the type of the new
427 symbol, one of bfd_link_hash_defined, bfd_link_hash_common, or
428 bfd_link_hash_indirect. If NTYPE is bfd_link_hash_common, NSIZE
429 is the size of the new symbol. */
430 bfd_boolean (*multiple_common
)
431 (struct bfd_link_info
*, const char *name
,
432 bfd
*obfd
, enum bfd_link_hash_type otype
, bfd_vma osize
,
433 bfd
*nbfd
, enum bfd_link_hash_type ntype
, bfd_vma nsize
);
434 /* A function which is called to add a symbol to a set. ENTRY is
435 the link hash table entry for the set itself (e.g.,
436 __CTOR_LIST__). RELOC is the relocation to use for an entry in
437 the set when generating a relocatable file, and is also used to
438 get the size of the entry when generating an executable file.
439 ABFD, SEC and VALUE identify the value to add to the set. */
440 bfd_boolean (*add_to_set
)
441 (struct bfd_link_info
*, struct bfd_link_hash_entry
*entry
,
442 bfd_reloc_code_real_type reloc
, bfd
*abfd
, asection
*sec
, bfd_vma value
);
443 /* A function which is called when the name of a g++ constructor or
444 destructor is found. This is only called by some object file
445 formats. CONSTRUCTOR is TRUE for a constructor, FALSE for a
446 destructor. This will use BFD_RELOC_CTOR when generating a
447 relocatable file. NAME is the name of the symbol found. ABFD,
448 SECTION and VALUE are the value of the symbol. */
449 bfd_boolean (*constructor
)
450 (struct bfd_link_info
*, bfd_boolean constructor
, const char *name
,
451 bfd
*abfd
, asection
*sec
, bfd_vma value
);
452 /* A function which is called to issue a linker warning. For
453 example, this is called when there is a reference to a warning
454 symbol. WARNING is the warning to be issued. SYMBOL is the name
455 of the symbol which triggered the warning; it may be NULL if
456 there is none. ABFD, SECTION and ADDRESS identify the location
457 which trigerred the warning; either ABFD or SECTION or both may
458 be NULL if the location is not known. */
459 bfd_boolean (*warning
)
460 (struct bfd_link_info
*, const char *warning
, const char *symbol
,
461 bfd
*abfd
, asection
*section
, bfd_vma address
);
462 /* A function which is called when a relocation is attempted against
463 an undefined symbol. NAME is the symbol which is undefined.
464 ABFD, SECTION and ADDRESS identify the location from which the
465 reference is made. FATAL indicates whether an undefined symbol is
466 a fatal error or not. In some cases SECTION may be NULL. */
467 bfd_boolean (*undefined_symbol
)
468 (struct bfd_link_info
*, const char *name
, bfd
*abfd
,
469 asection
*section
, bfd_vma address
, bfd_boolean fatal
);
470 /* A function which is called when a reloc overflow occurs. NAME is
471 the name of the symbol or section the reloc is against,
472 RELOC_NAME is the name of the relocation, and ADDEND is any
473 addend that is used. ABFD, SECTION and ADDRESS identify the
474 location at which the overflow occurs; if this is the result of a
475 bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
476 ABFD will be NULL. */
477 bfd_boolean (*reloc_overflow
)
478 (struct bfd_link_info
*, const char *name
, const char *reloc_name
,
479 bfd_vma addend
, bfd
*abfd
, asection
*section
, bfd_vma address
);
480 /* A function which is called when a dangerous reloc is performed.
481 The canonical example is an a29k IHCONST reloc which does not
482 follow an IHIHALF reloc. MESSAGE is an appropriate message.
483 ABFD, SECTION and ADDRESS identify the location at which the
484 problem occurred; if this is the result of a
485 bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
486 ABFD will be NULL. */
487 bfd_boolean (*reloc_dangerous
)
488 (struct bfd_link_info
*, const char *message
,
489 bfd
*abfd
, asection
*section
, bfd_vma address
);
490 /* A function which is called when a reloc is found to be attached
491 to a symbol which is not being written out. NAME is the name of
492 the symbol. ABFD, SECTION and ADDRESS identify the location of
493 the reloc; if this is the result of a
494 bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
495 ABFD will be NULL. */
496 bfd_boolean (*unattached_reloc
)
497 (struct bfd_link_info
*, const char *name
,
498 bfd
*abfd
, asection
*section
, bfd_vma address
);
499 /* A function which is called when a symbol in notice_hash is
500 defined or referenced. NAME is the symbol. ABFD, SECTION and
501 ADDRESS are the value of the symbol. If SECTION is
502 bfd_und_section, this is a reference. */
503 bfd_boolean (*notice
)
504 (struct bfd_link_info
*, const char *name
,
505 bfd
*abfd
, asection
*section
, bfd_vma address
);
506 /* A function which is called for reporting a linker error. ID is the
507 error identifier. The remaining input is the same as einfo () in
509 bfd_boolean (*error_handler
)
510 (int id
, const char *fmt
, ...);
512 /* Identifiers of linker error messages used by error_handler. */
513 #define LD_DEFINITION_IN_DISCARDED_SECTION 1
516 /* The linker builds link_order structures which tell the code how to
517 include input data in the output file. */
519 /* These are the types of link_order structures. */
521 enum bfd_link_order_type
523 bfd_undefined_link_order
, /* Undefined. */
524 bfd_indirect_link_order
, /* Built from a section. */
525 bfd_data_link_order
, /* Set to explicit data. */
526 bfd_section_reloc_link_order
, /* Relocate against a section. */
527 bfd_symbol_reloc_link_order
/* Relocate against a symbol. */
530 /* This is the link_order structure itself. These form a chain
531 attached to the section whose contents they are describing. */
533 struct bfd_link_order
535 /* Next link_order in chain. */
536 struct bfd_link_order
*next
;
537 /* Type of link_order. */
538 enum bfd_link_order_type type
;
539 /* Offset within output section. */
541 /* Size within output section. */
543 /* Type specific information. */
548 /* Section to include. If this is used, then
549 section->output_section must be the section the
550 link_order is attached to, section->output_offset must
551 equal the link_order offset field, and section->_raw_size
552 must equal the link_order size field. Maybe these
553 restrictions should be relaxed someday. */
558 /* Size of contents, or zero when contents size == size
559 within output section.
560 A non-zero value allows filling of the output section
561 with an arbitrary repeated pattern. */
563 /* Data to put into file. */
568 /* Description of reloc to generate. Used for
569 bfd_section_reloc_link_order and
570 bfd_symbol_reloc_link_order. */
571 struct bfd_link_order_reloc
*p
;
576 /* A linker order of type bfd_section_reloc_link_order or
577 bfd_symbol_reloc_link_order means to create a reloc against a
578 section or symbol, respectively. This is used to implement -Ur to
579 generate relocs for the constructor tables. The
580 bfd_link_order_reloc structure describes the reloc that BFD should
581 create. It is similar to a arelent, but I didn't use arelent
582 because the linker does not know anything about most symbols, and
583 any asymbol structure it creates will be partially meaningless.
584 This information could logically be in the bfd_link_order struct,
585 but I didn't want to waste the space since these types of relocs
586 are relatively rare. */
588 struct bfd_link_order_reloc
591 bfd_reloc_code_real_type reloc
;
595 /* For type bfd_section_reloc_link_order, this is the section
596 the reloc should be against. This must be a section in the
597 output BFD, not any of the input BFDs. */
599 /* For type bfd_symbol_reloc_link_order, this is the name of the
600 symbol the reloc should be against. */
604 /* Addend to use. The object file should contain zero. The BFD
605 backend is responsible for filling in the contents of the object
606 file correctly. For some object file formats (e.g., COFF) the
607 addend must be stored into in the object file, and for some
608 (e.g., SPARC a.out) it is kept in the reloc. */
612 /* Allocate a new link_order for a section. */
613 extern struct bfd_link_order
*bfd_new_link_order (bfd
*, asection
*);
615 /* These structures are used to describe version information for the
616 ELF linker. These structures could be manipulated entirely inside
617 BFD, but it would be a pain. Instead, the regular linker sets up
618 these structures, and then passes them into BFD. */
620 /* Glob pattern for a version. */
622 struct bfd_elf_version_expr
624 /* Next glob pattern for this version. */
625 struct bfd_elf_version_expr
*next
;
628 /* NULL for a glob pattern, otherwise a straight symbol. */
630 /* Defined by ".symver". */
631 unsigned int symver
: 1;
632 /* Defined by version script. */
633 unsigned int script
: 1;
635 #define BFD_ELF_VERSION_C_TYPE 1
636 #define BFD_ELF_VERSION_CXX_TYPE 2
637 #define BFD_ELF_VERSION_JAVA_TYPE 4
638 unsigned int mask
: 3;
641 struct bfd_elf_version_expr_head
643 /* List of all patterns, both wildcards and non-wildcards. */
644 struct bfd_elf_version_expr
*list
;
645 /* Hash table for non-wildcards. */
647 /* Remaining patterns. */
648 struct bfd_elf_version_expr
*remaining
;
649 /* What kind of pattern types are present in list (bitmask). */
653 /* Version dependencies. */
655 struct bfd_elf_version_deps
657 /* Next dependency for this version. */
658 struct bfd_elf_version_deps
*next
;
659 /* The version which this version depends upon. */
660 struct bfd_elf_version_tree
*version_needed
;
663 /* A node in the version tree. */
665 struct bfd_elf_version_tree
668 struct bfd_elf_version_tree
*next
;
669 /* Name of this version. */
671 /* Version number. */
673 /* Regular expressions for global symbols in this version. */
674 struct bfd_elf_version_expr_head globals
;
675 /* Regular expressions for local symbols in this version. */
676 struct bfd_elf_version_expr_head locals
;
677 /* List of versions which this version depends upon. */
678 struct bfd_elf_version_deps
*deps
;
679 /* Index of the version name. This is used within BFD. */
680 unsigned int name_indx
;
681 /* Whether this version tree was used. This is used within BFD. */
684 struct bfd_elf_version_expr
*(*match
)
685 (struct bfd_elf_version_expr_head
*head
,
686 struct bfd_elf_version_expr
*prev
, const char *sym
);