1 /* bfdlink.h -- header file for BFD link routines
2 Copyright 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2002, 2003,
3 2004 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
;
85 /* Type of this entry. */
86 enum bfd_link_hash_type type
;
88 /* Undefined and common symbols are kept in a linked list through
89 this field. This field is not in the union because that would
90 force us to remove entries from the list when we changed their
91 type, which would force the list to be doubly linked, which would
92 waste more memory. When an undefined or common symbol is
93 created, it should be added to this list, the head of which is in
94 the link hash table itself. As symbols are defined, they need
95 not be removed from the list; anything which reads the list must
96 doublecheck the symbol type.
98 Weak symbols are not kept on this list.
100 Defined and defweak symbols use this field as a reference marker.
101 If the field is not NULL, or this structure is the tail of the
102 undefined symbol list, the symbol has been referenced. If the
103 symbol is undefined and becomes defined, this field will
104 automatically be non-NULL since the symbol will have been on the
105 undefined symbol list. */
106 struct bfd_link_hash_entry
*und_next
;
108 /* A union of information depending upon the type. */
111 /* Nothing is kept for bfd_hash_new. */
112 /* bfd_link_hash_undefined, bfd_link_hash_undefweak. */
115 bfd
*abfd
; /* BFD symbol was found in. */
117 /* bfd_link_hash_defined, bfd_link_hash_defweak. */
120 bfd_vma value
; /* Symbol value. */
121 asection
*section
; /* Symbol section. */
123 /* bfd_link_hash_indirect, bfd_link_hash_warning. */
126 struct bfd_link_hash_entry
*link
; /* Real symbol. */
127 const char *warning
; /* Warning (bfd_link_hash_warning only). */
129 /* bfd_link_hash_common. */
132 /* The linker needs to know three things about common
133 symbols: the size, the alignment, and the section in
134 which the symbol should be placed. We store the size
135 here, and we allocate a small structure to hold the
136 section and the alignment. The alignment is stored as a
137 power of two. We don't store all the information
138 directly because we don't want to increase the size of
139 the union; this structure is a major space user in the
141 bfd_size_type size
; /* Common symbol size. */
142 struct bfd_link_hash_common_entry
144 unsigned int alignment_power
; /* Alignment. */
145 asection
*section
; /* Symbol section. */
151 /* This is the link hash table. It is a derived class of
154 struct bfd_link_hash_table
156 /* The hash table itself. */
157 struct bfd_hash_table table
;
158 /* The back end which created this hash table. This indicates the
159 type of the entries in the hash table, which is sometimes
160 important information when linking object files of different
162 const bfd_target
*creator
;
163 /* A linked list of undefined and common symbols, linked through the
164 next field in the bfd_link_hash_entry structure. */
165 struct bfd_link_hash_entry
*undefs
;
166 /* Entries are added to the tail of the undefs list. */
167 struct bfd_link_hash_entry
*undefs_tail
;
168 /* The type of the link hash table. */
169 enum bfd_link_hash_table_type type
;
172 /* Look up an entry in a link hash table. If FOLLOW is TRUE, this
173 follows bfd_link_hash_indirect and bfd_link_hash_warning links to
175 extern struct bfd_link_hash_entry
*bfd_link_hash_lookup
176 (struct bfd_link_hash_table
*, const char *, bfd_boolean create
,
177 bfd_boolean copy
, bfd_boolean follow
);
179 /* Look up an entry in the main linker hash table if the symbol might
180 be wrapped. This should only be used for references to an
181 undefined symbol, not for definitions of a symbol. */
183 extern struct bfd_link_hash_entry
*bfd_wrapped_link_hash_lookup
184 (bfd
*, struct bfd_link_info
*, const char *, bfd_boolean
,
185 bfd_boolean
, bfd_boolean
);
187 /* Traverse a link hash table. */
188 extern void bfd_link_hash_traverse
189 (struct bfd_link_hash_table
*,
190 bfd_boolean (*) (struct bfd_link_hash_entry
*, void *),
193 /* Add an entry to the undefs list. */
194 extern void bfd_link_add_undef
195 (struct bfd_link_hash_table
*, struct bfd_link_hash_entry
*);
199 struct bfd_sym_chain
*next
;
203 /* How to handle unresolved symbols.
204 There are four possibilities which are enumerated below: */
207 /* This is the initial value when then link_info structure is created.
208 It allows the various stages of the linker to determine whether they
209 allowed to set the value. */
216 /* This structure holds all the information needed to communicate
217 between BFD and the linker when doing a link. */
221 /* TRUE if BFD should generate a relocatable object file. */
222 unsigned int relocatable
: 1;
224 /* TRUE if BFD should generate relocation information in the final
226 unsigned int emitrelocations
: 1;
228 /* TRUE if BFD should generate a "task linked" object file,
229 similar to relocatable but also with globals converted to
231 unsigned int task_link
: 1;
233 /* TRUE if BFD should generate a shared object. */
234 unsigned int shared
: 1;
236 /* TRUE if BFD should pre-bind symbols in a shared object. */
237 unsigned int symbolic
: 1;
239 /* TRUE if BFD should export all symbols in the dynamic symbol table
240 of an executable, rather than only those used. */
241 unsigned int export_dynamic
: 1;
243 /* TRUE if shared objects should be linked directly, not shared. */
244 unsigned int static_link
: 1;
246 /* TRUE if the output file should be in a traditional format. This
247 is equivalent to the setting of the BFD_TRADITIONAL_FORMAT flag
248 on the output file, but may be checked when reading the input
250 unsigned int traditional_format
: 1;
252 /* TRUE if we want to produced optimized output files. This might
253 need much more time and therefore must be explicitly selected. */
254 unsigned int optimize
: 1;
256 /* TRUE if ok to have multiple definition. */
257 unsigned int allow_multiple_definition
: 1;
259 /* TRUE if ok to have version with no definition. */
260 unsigned int allow_undefined_version
: 1;
262 /* TRUE if symbols should be retained in memory, FALSE if they
263 should be freed and reread. */
264 unsigned int keep_memory
: 1;
266 /* TRUE if every symbol should be reported back via the notice
268 unsigned int notice_all
: 1;
270 /* TRUE if executable should not contain copy relocs.
271 Setting this true may result in a non-sharable text segment. */
272 unsigned int nocopyreloc
: 1;
274 /* TRUE if the new ELF dynamic tags are enabled. */
275 unsigned int new_dtags
: 1;
277 /* TRUE if non-PLT relocs should be merged into one reloc section
278 and sorted so that relocs against the same symbol come together. */
279 unsigned int combreloc
: 1;
281 /* TRUE if .eh_frame_hdr section and PT_GNU_EH_FRAME ELF segment
282 should be created. */
283 unsigned int eh_frame_hdr
: 1;
285 /* TRUE if global symbols in discarded sections should be stripped. */
286 unsigned int strip_discarded
: 1;
288 /* TRUE if the final relax pass is needed. */
289 unsigned int need_relax_finalize
: 1;
291 /* TRUE if generating a position independent executable. */
294 /* TRUE if generating an executable, position independent or not. */
295 unsigned int executable
: 1;
297 /* TRUE if PT_GNU_STACK segment should be created with PF_R|PF_W|PF_X
299 unsigned int execstack
: 1;
301 /* TRUE if PT_GNU_STACK segment should be created with PF_R|PF_W
303 unsigned int noexecstack
: 1;
305 /* What to do with unresolved symbols in an object file.
306 When producing executables the default is GENERATE_ERROR.
307 When producing shared libraries the default is IGNORE. The
308 assumption with shared libraries is that the reference will be
309 resolved at load/execution time. */
310 enum report_method unresolved_syms_in_objects
;
312 /* What to do with unresolved symbols in a shared library.
313 The same defaults apply. */
314 enum report_method unresolved_syms_in_shared_libs
;
316 /* Which symbols to strip. */
317 enum bfd_link_strip strip
;
319 /* Which local symbols to discard. */
320 enum bfd_link_discard discard
;
322 /* Criteria for skipping symbols when detemining
323 whether to include an object from an archive. */
324 enum bfd_link_common_skip_ar_aymbols common_skip_ar_aymbols
;
326 /* Char that may appear as the first char of a symbol, but should be
327 skipped (like symbol_leading_char) when looking up symbols in
328 wrap_hash. Used by PowerPC Linux for 'dot' symbols. */
331 /* Function callbacks. */
332 const struct bfd_link_callbacks
*callbacks
;
334 /* Hash table handled by BFD. */
335 struct bfd_link_hash_table
*hash
;
337 /* Hash table of symbols to keep. This is NULL unless strip is
339 struct bfd_hash_table
*keep_hash
;
341 /* Hash table of symbols to report back via the notice callback. If
342 this is NULL, and notice_all is FALSE, then no symbols are
344 struct bfd_hash_table
*notice_hash
;
346 /* Hash table of symbols which are being wrapped (the --wrap linker
347 option). If this is NULL, no symbols are being wrapped. */
348 struct bfd_hash_table
*wrap_hash
;
350 /* The list of input BFD's involved in the link. These are chained
351 together via the link_next field. */
354 /* If a symbol should be created for each input BFD, this is section
355 where those symbols should be placed. It must be a section in
356 the output BFD. It may be NULL, in which case no such symbols
357 will be created. This is to support CREATE_OBJECT_SYMBOLS in the
358 linker command language. */
359 asection
*create_object_symbols_section
;
361 /* List of global symbol names that are starting points for marking
362 sections against garbage collection. */
363 struct bfd_sym_chain
*gc_sym_list
;
365 /* If a base output file is wanted, then this points to it */
368 /* The function to call when the executable or shared object is
370 const char *init_function
;
372 /* The function to call when the executable or shared object is
374 const char *fini_function
;
376 /* Non-zero if auto-import thunks for DATA items in pei386 DLLs
377 should be generated/linked against. Set to 1 if this feature
378 is explicitly requested by the user, -1 if enabled by default. */
379 int pei386_auto_import
;
381 /* Non-zero if runtime relocs for DATA items with non-zero addends
382 in pei386 DLLs should be generated. Set to 1 if this feature
383 is explicitly requested by the user, -1 if enabled by default. */
384 int pei386_runtime_pseudo_reloc
;
386 /* How many spare .dynamic DT_NULL entries should be added? */
387 unsigned int spare_dynamic_tags
;
389 /* May be used to set DT_FLAGS for ELF. */
392 /* May be used to set DT_FLAGS_1 for ELF. */
396 /* This structures holds a set of callback functions. These are
397 called by the BFD linker routines. The first argument to each
398 callback function is the bfd_link_info structure being used. Each
399 function returns a boolean value. If the function returns FALSE,
400 then the BFD function which called it will return with a failure
403 struct bfd_link_callbacks
405 /* A function which is called when an object is added from an
406 archive. ABFD is the archive element being added. NAME is the
407 name of the symbol which caused the archive element to be pulled
409 bfd_boolean (*add_archive_element
)
410 (struct bfd_link_info
*, bfd
*abfd
, const char *name
);
411 /* A function which is called when a symbol is found with multiple
412 definitions. NAME is the symbol which is defined multiple times.
413 OBFD is the old BFD, OSEC is the old section, OVAL is the old
414 value, NBFD is the new BFD, NSEC is the new section, and NVAL is
415 the new value. OBFD may be NULL. OSEC and NSEC may be
416 bfd_com_section or bfd_ind_section. */
417 bfd_boolean (*multiple_definition
)
418 (struct bfd_link_info
*, const char *name
,
419 bfd
*obfd
, asection
*osec
, bfd_vma oval
,
420 bfd
*nbfd
, asection
*nsec
, bfd_vma nval
);
421 /* A function which is called when a common symbol is defined
422 multiple times. NAME is the symbol appearing multiple times.
423 OBFD is the BFD of the existing symbol; it may be NULL if this is
424 not known. OTYPE is the type of the existing symbol, which may
425 be bfd_link_hash_defined, bfd_link_hash_defweak,
426 bfd_link_hash_common, or bfd_link_hash_indirect. If OTYPE is
427 bfd_link_hash_common, OSIZE is the size of the existing symbol.
428 NBFD is the BFD of the new symbol. NTYPE is the type of the new
429 symbol, one of bfd_link_hash_defined, bfd_link_hash_common, or
430 bfd_link_hash_indirect. If NTYPE is bfd_link_hash_common, NSIZE
431 is the size of the new symbol. */
432 bfd_boolean (*multiple_common
)
433 (struct bfd_link_info
*, const char *name
,
434 bfd
*obfd
, enum bfd_link_hash_type otype
, bfd_vma osize
,
435 bfd
*nbfd
, enum bfd_link_hash_type ntype
, bfd_vma nsize
);
436 /* A function which is called to add a symbol to a set. ENTRY is
437 the link hash table entry for the set itself (e.g.,
438 __CTOR_LIST__). RELOC is the relocation to use for an entry in
439 the set when generating a relocatable file, and is also used to
440 get the size of the entry when generating an executable file.
441 ABFD, SEC and VALUE identify the value to add to the set. */
442 bfd_boolean (*add_to_set
)
443 (struct bfd_link_info
*, struct bfd_link_hash_entry
*entry
,
444 bfd_reloc_code_real_type reloc
, bfd
*abfd
, asection
*sec
, bfd_vma value
);
445 /* A function which is called when the name of a g++ constructor or
446 destructor is found. This is only called by some object file
447 formats. CONSTRUCTOR is TRUE for a constructor, FALSE for a
448 destructor. This will use BFD_RELOC_CTOR when generating a
449 relocatable file. NAME is the name of the symbol found. ABFD,
450 SECTION and VALUE are the value of the symbol. */
451 bfd_boolean (*constructor
)
452 (struct bfd_link_info
*, bfd_boolean constructor
, const char *name
,
453 bfd
*abfd
, asection
*sec
, bfd_vma value
);
454 /* A function which is called to issue a linker warning. For
455 example, this is called when there is a reference to a warning
456 symbol. WARNING is the warning to be issued. SYMBOL is the name
457 of the symbol which triggered the warning; it may be NULL if
458 there is none. ABFD, SECTION and ADDRESS identify the location
459 which trigerred the warning; either ABFD or SECTION or both may
460 be NULL if the location is not known. */
461 bfd_boolean (*warning
)
462 (struct bfd_link_info
*, const char *warning
, const char *symbol
,
463 bfd
*abfd
, asection
*section
, bfd_vma address
);
464 /* A function which is called when a relocation is attempted against
465 an undefined symbol. NAME is the symbol which is undefined.
466 ABFD, SECTION and ADDRESS identify the location from which the
467 reference is made. FATAL indicates whether an undefined symbol is
468 a fatal error or not. In some cases SECTION may be NULL. */
469 bfd_boolean (*undefined_symbol
)
470 (struct bfd_link_info
*, const char *name
, bfd
*abfd
,
471 asection
*section
, bfd_vma address
, bfd_boolean fatal
);
472 /* A function which is called when a reloc overflow occurs. NAME is
473 the name of the symbol or section the reloc is against,
474 RELOC_NAME is the name of the relocation, and ADDEND is any
475 addend that is used. ABFD, SECTION and ADDRESS identify the
476 location at which the overflow occurs; if this is the result of a
477 bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
478 ABFD will be NULL. */
479 bfd_boolean (*reloc_overflow
)
480 (struct bfd_link_info
*, const char *name
, const char *reloc_name
,
481 bfd_vma addend
, bfd
*abfd
, asection
*section
, bfd_vma address
);
482 /* A function which is called when a dangerous reloc is performed.
483 The canonical example is an a29k IHCONST reloc which does not
484 follow an IHIHALF reloc. MESSAGE is an appropriate message.
485 ABFD, SECTION and ADDRESS identify the location at which the
486 problem occurred; if this is the result of a
487 bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
488 ABFD will be NULL. */
489 bfd_boolean (*reloc_dangerous
)
490 (struct bfd_link_info
*, const char *message
,
491 bfd
*abfd
, asection
*section
, bfd_vma address
);
492 /* A function which is called when a reloc is found to be attached
493 to a symbol which is not being written out. NAME is the name of
494 the symbol. ABFD, SECTION and ADDRESS identify the location of
495 the reloc; if this is the result of a
496 bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
497 ABFD will be NULL. */
498 bfd_boolean (*unattached_reloc
)
499 (struct bfd_link_info
*, const char *name
,
500 bfd
*abfd
, asection
*section
, bfd_vma address
);
501 /* A function which is called when a symbol in notice_hash is
502 defined or referenced. NAME is the symbol. ABFD, SECTION and
503 ADDRESS are the value of the symbol. If SECTION is
504 bfd_und_section, this is a reference. */
505 bfd_boolean (*notice
)
506 (struct bfd_link_info
*, const char *name
,
507 bfd
*abfd
, asection
*section
, bfd_vma address
);
508 /* A function which is called for reporting a linker error. ID is the
509 error identifier. The remaining input is the same as einfo () in
511 bfd_boolean (*error_handler
)
512 (int id
, const char *fmt
, ...);
514 /* Identifiers of linker error messages used by error_handler. */
515 #define LD_DEFINITION_IN_DISCARDED_SECTION 1
518 /* The linker builds link_order structures which tell the code how to
519 include input data in the output file. */
521 /* These are the types of link_order structures. */
523 enum bfd_link_order_type
525 bfd_undefined_link_order
, /* Undefined. */
526 bfd_indirect_link_order
, /* Built from a section. */
527 bfd_data_link_order
, /* Set to explicit data. */
528 bfd_section_reloc_link_order
, /* Relocate against a section. */
529 bfd_symbol_reloc_link_order
/* Relocate against a symbol. */
532 /* This is the link_order structure itself. These form a chain
533 attached to the section whose contents they are describing. */
535 struct bfd_link_order
537 /* Next link_order in chain. */
538 struct bfd_link_order
*next
;
539 /* Type of link_order. */
540 enum bfd_link_order_type type
;
541 /* Offset within output section. */
543 /* Size within output section. */
545 /* Type specific information. */
550 /* Section to include. If this is used, then
551 section->output_section must be the section the
552 link_order is attached to, section->output_offset must
553 equal the link_order offset field, and section->_raw_size
554 must equal the link_order size field. Maybe these
555 restrictions should be relaxed someday. */
560 /* Size of contents, or zero when contents size == size
561 within output section.
562 A non-zero value allows filling of the output section
563 with an arbitrary repeated pattern. */
565 /* Data to put into file. */
570 /* Description of reloc to generate. Used for
571 bfd_section_reloc_link_order and
572 bfd_symbol_reloc_link_order. */
573 struct bfd_link_order_reloc
*p
;
578 /* A linker order of type bfd_section_reloc_link_order or
579 bfd_symbol_reloc_link_order means to create a reloc against a
580 section or symbol, respectively. This is used to implement -Ur to
581 generate relocs for the constructor tables. The
582 bfd_link_order_reloc structure describes the reloc that BFD should
583 create. It is similar to a arelent, but I didn't use arelent
584 because the linker does not know anything about most symbols, and
585 any asymbol structure it creates will be partially meaningless.
586 This information could logically be in the bfd_link_order struct,
587 but I didn't want to waste the space since these types of relocs
588 are relatively rare. */
590 struct bfd_link_order_reloc
593 bfd_reloc_code_real_type reloc
;
597 /* For type bfd_section_reloc_link_order, this is the section
598 the reloc should be against. This must be a section in the
599 output BFD, not any of the input BFDs. */
601 /* For type bfd_symbol_reloc_link_order, this is the name of the
602 symbol the reloc should be against. */
606 /* Addend to use. The object file should contain zero. The BFD
607 backend is responsible for filling in the contents of the object
608 file correctly. For some object file formats (e.g., COFF) the
609 addend must be stored into in the object file, and for some
610 (e.g., SPARC a.out) it is kept in the reloc. */
614 /* Allocate a new link_order for a section. */
615 extern struct bfd_link_order
*bfd_new_link_order (bfd
*, asection
*);
617 /* These structures are used to describe version information for the
618 ELF linker. These structures could be manipulated entirely inside
619 BFD, but it would be a pain. Instead, the regular linker sets up
620 these structures, and then passes them into BFD. */
622 /* Glob pattern for a version. */
624 struct bfd_elf_version_expr
626 /* Next glob pattern for this version. */
627 struct bfd_elf_version_expr
*next
;
630 /* NULL for a glob pattern, otherwise a straight symbol. */
632 /* Defined by ".symver". */
633 unsigned int symver
: 1;
634 /* Defined by version script. */
635 unsigned int script
: 1;
637 #define BFD_ELF_VERSION_C_TYPE 1
638 #define BFD_ELF_VERSION_CXX_TYPE 2
639 #define BFD_ELF_VERSION_JAVA_TYPE 4
640 unsigned int mask
: 3;
643 struct bfd_elf_version_expr_head
645 /* List of all patterns, both wildcards and non-wildcards. */
646 struct bfd_elf_version_expr
*list
;
647 /* Hash table for non-wildcards. */
649 /* Remaining patterns. */
650 struct bfd_elf_version_expr
*remaining
;
651 /* What kind of pattern types are present in list (bitmask). */
655 /* Version dependencies. */
657 struct bfd_elf_version_deps
659 /* Next dependency for this version. */
660 struct bfd_elf_version_deps
*next
;
661 /* The version which this version depends upon. */
662 struct bfd_elf_version_tree
*version_needed
;
665 /* A node in the version tree. */
667 struct bfd_elf_version_tree
670 struct bfd_elf_version_tree
*next
;
671 /* Name of this version. */
673 /* Version number. */
675 /* Regular expressions for global symbols in this version. */
676 struct bfd_elf_version_expr_head globals
;
677 /* Regular expressions for local symbols in this version. */
678 struct bfd_elf_version_expr_head locals
;
679 /* List of versions which this version depends upon. */
680 struct bfd_elf_version_deps
*deps
;
681 /* Index of the version name. This is used within BFD. */
682 unsigned int name_indx
;
683 /* Whether this version tree was used. This is used within BFD. */
686 struct bfd_elf_version_expr
*(*match
)
687 (struct bfd_elf_version_expr_head
*head
,
688 struct bfd_elf_version_expr
*prev
, const char *sym
);