include/bfdlink.h

   1 /* bfdlink.h -- header file for BFD link routines
   2    Copyright 1993 Free Software Foundation, Inc.
   3    Written by Steve Chamberlain and Ian Lance Taylor, Cygnus Support.
   4
   5 This file is part of BFD, the Binary File Descriptor library.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 #ifndef BFDLINK_H
  22 #define BFDLINK_H
  23
  24 /* Which symbols to strip during a link.  */
  25 enum bfd_link_strip
  26 {
  27   strip_none,           /* Don't strip any symbols.  */
  28   strip_debugger,       /* Strip debugging symbols.  */
  29   strip_some,           /* keep_hash is the list of symbols to keep.  */
  30   strip_all             /* Strip all symbols.  */
  31 };
  32
  33 /* Which local symbols to discard during a link.  This is irrelevant
  34    if strip_all is used.  */
  35 enum bfd_link_discard
  36 {
  37   discard_none,         /* Don't discard any locals.  */
  38   discard_l,            /* Discard locals with a certain prefix.  */
  39   discard_all           /* Discard all locals.  */
  40 };
  41 \f
  42 /* These are the possible types of an entry in the BFD link hash
  43    table.  */
  44
  45 enum bfd_link_hash_type
  46 {
  47   bfd_link_hash_new,            /* Symbol is new.  */
  48   bfd_link_hash_undefined,      /* Symbol seen before, but undefined.  */
  49   bfd_link_hash_undefweak,      /* Symbol is weak and undefined.  */
  50   bfd_link_hash_defined,        /* Symbol is defined.  */
  51   bfd_link_hash_defweak,        /* Symbol is weak and defined.  */
  52   bfd_link_hash_common,         /* Symbol is common.  */
  53   bfd_link_hash_indirect,       /* Symbol is an indirect link.  */
  54   bfd_link_hash_warning         /* Like indirect, but warn if referenced.  */
  55 };
  56
  57 /* The linking routines use a hash table which uses this structure for
  58    its elements.  */
  59
  60 struct bfd_link_hash_entry
  61 {
  62   /* Base hash table entry structure.  */
  63   struct bfd_hash_entry root;
  64   /* Type of this entry.  */
  65   enum bfd_link_hash_type type;
  66
  67   /* Undefined and common symbols are kept in a linked list through
  68      this field.  This field is not in the union because that would
  69      force us to remove entries from the list when we changed their
  70      type, which would force the list to be doubly linked, which would
  71      waste more memory.  When an undefined or common symbol is
  72      created, it should be added to this list, the head of which is in
  73      the link hash table itself.  As symbols are defined, they need
  74      not be removed from the list; anything which reads the list must
  75      doublecheck the symbol type.
  76
  77      Weak symbols are not kept on this list.
  78
  79      Defined and defweak symbols use this field as a reference marker.
  80      If the field is not NULL, or this structure is the tail of the
  81      undefined symbol list, the symbol has been referenced.  If the
  82      symbol is undefined and becomes defined, this field will
  83      automatically be non-NULL since the symbol will have been on the
  84      undefined symbol list.  */
  85   struct bfd_link_hash_entry *next;
  86   /* A union of information depending upon the type.  */
  87   union
  88     {
  89       /* Nothing is kept for bfd_hash_new.  */
  90       /* bfd_link_hash_undefined, bfd_link_hash_undefweak.  */
  91       struct
  92         {
  93           bfd *abfd;            /* BFD symbol was found in.  */
  94         } undef;
  95       /* bfd_link_hash_defined, bfd_link_hash_defweak.  */
  96       struct
  97         {
  98           bfd_vma value;        /* Symbol value.  */
  99           asection *section;    /* Symbol section.  */
 100         } def;
 101       /* bfd_link_hash_indirect, bfd_link_hash_warning.  */
 102       struct
 103         {
 104           struct bfd_link_hash_entry *link;     /* Real symbol.  */
 105           const char *warning;  /* Warning (bfd_link_hash_warning only).  */
 106         } i;
 107       /* bfd_link_hash_common.  */
 108       struct
 109         {
 110           /* The linker needs to know three things about common
 111              symbols: the size, the alignment, and the section in
 112              which the symbol should be placed.  On the assumption
 113              that a single common symbol will not take up incredible
 114              amounts of memory, we pack the size and the alignment
 115              into the space of a single integer.  The alignment is
 116              stored as a power of two.  */
 117           unsigned int alignment_power : 6;     /* Alignment.  */
 118           unsigned int size : 26;               /* Common symbol size.  */
 119           asection *section;                    /* Symbol section.  */
 120         } c;
 121     } u;
 122 };
 123
 124 /* This is the link hash table.  It is a derived class of
 125    bfd_hash_table.  */
 126
 127 struct bfd_link_hash_table
 128 {
 129   /* The hash table itself.  */
 130   struct bfd_hash_table table;
 131   /* The back end which created this hash table.  This indicates the
 132      type of the entries in the hash table, which is sometimes
 133      important information when linking object files of different
 134      types together.  */
 135   const bfd_target *creator;
 136   /* A linked list of undefined and common symbols, linked through the
 137      next field in the bfd_link_hash_entry structure.  */
 138   struct bfd_link_hash_entry *undefs;
 139   /* Entries are added to the tail of the undefs list.  */
 140   struct bfd_link_hash_entry *undefs_tail;
 141 };
 142
 143 /* Look up an entry in a link hash table.  If FOLLOW is true, this
 144    follows bfd_link_hash_indirect and bfd_link_hash_warning links to
 145    the real symbol.  */
 146 extern struct bfd_link_hash_entry *bfd_link_hash_lookup
 147   PARAMS ((struct bfd_link_hash_table *, const char *, boolean create,
 148            boolean copy, boolean follow));
 149
 150 /* Traverse a link hash table.  */
 151 extern void bfd_link_hash_traverse
 152   PARAMS ((struct bfd_link_hash_table *,
 153            boolean (*) (struct bfd_link_hash_entry *, PTR),
 154            PTR));
 155
 156 /* Add an entry to the undefs list.  */
 157 extern void bfd_link_add_undef
 158   PARAMS ((struct bfd_link_hash_table *, struct bfd_link_hash_entry *));
 159 \f
 160 /* This structure holds all the information needed to communicate
 161    between BFD and the linker when doing a link.  */
 162
 163 struct bfd_link_info
 164 {
 165   /* Function callbacks.  */
 166   const struct bfd_link_callbacks *callbacks;
 167   /* true if BFD should generate a relocateable object file.  */
 168   boolean relocateable;
 169   /* true if BFD should generate a shared object.  */
 170   boolean shared;
 171   /* Which symbols to strip.  */
 172   enum bfd_link_strip strip;
 173   /* Which local symbols to discard.  */
 174   enum bfd_link_discard discard;
 175   /* The local symbol prefix to discard if using discard_l.  */
 176   unsigned int lprefix_len;
 177   const char *lprefix;
 178   /* true if symbols should be retained in memory, false if they
 179      should be freed and reread.  */
 180   boolean keep_memory;
 181   /* The list of input BFD's involved in the link.  These are chained
 182      together via the link_next field.  */
 183   bfd *input_bfds;
 184   /* If a symbol should be created for each input BFD, this is section
 185      where those symbols should be placed.  It must be a section in
 186      the output BFD.  It may be NULL, in which case no such symbols
 187      will be created.  This is to support CREATE_OBJECT_SYMBOLS in the
 188      linker command language.  */
 189   asection *create_object_symbols_section;
 190   /* Hash table handled by BFD.  */
 191   struct bfd_link_hash_table *hash;
 192   /* Hash table of symbols to keep.  This is NULL unless strip is
 193      strip_some.  */
 194   struct bfd_hash_table *keep_hash;
 195   /* Hash table of symbols to report back via notice_callback.  If
 196      this is NULL no symbols are reported back.  */
 197   struct bfd_hash_table *notice_hash;
 198 };
 199
 200 /* This structures holds a set of callback functions.  These are
 201    called by the BFD linker routines.  The first argument to each
 202    callback function is the bfd_link_info structure being used.  Each
 203    function returns a boolean value.  If the function returns false,
 204    then the BFD function which called it will return with a failure
 205    indication.  */
 206
 207 struct bfd_link_callbacks
 208 {
 209   /* A function which is called when an object is added from an
 210      archive.  ABFD is the archive element being added.  NAME is the
 211      name of the symbol which caused the archive element to be pulled
 212      in.  */
 213   boolean (*add_archive_element) PARAMS ((struct bfd_link_info *,
 214                                           bfd *abfd,
 215                                           const char *name));
 216   /* A function which is called when a symbol is found with multiple
 217      definitions.  NAME is the symbol which is defined multiple times.
 218      OBFD is the old BFD, OSEC is the old section, OVAL is the old
 219      value, NBFD is the new BFD, NSEC is the new section, and NVAL is
 220      the new value.  OBFD may be NULL.  OSEC and NSEC may be
 221      bfd_com_section or bfd_ind_section.  */
 222   boolean (*multiple_definition) PARAMS ((struct bfd_link_info *,
 223                                           const char *name,
 224                                           bfd *obfd,
 225                                           asection *osec,
 226                                           bfd_vma oval,
 227                                           bfd *nbfd,
 228                                           asection *nsec,
 229                                           bfd_vma nval));
 230   /* A function which is called when a common symbol is defined
 231      multiple times.  NAME is the symbol appearing multiple times.
 232      OBFD is the BFD of the existing symbol; it may be NULL if this is
 233      not known.  OTYPE is the type of the existing symbol, which may
 234      be bfd_link_hash_defined, bfd_link_hash_defweak,
 235      bfd_link_hash_common, or bfd_link_hash_indirect.  If OTYPE is
 236      bfd_link_hash_common, OSIZE is the size of the existing symbol.
 237      NBFD is the BFD of the new symbol.  NTYPE is the type of the new
 238      symbol, one of bfd_link_hash_defined, bfd_link_hash_common, or
 239      bfd_link_hash_indirect.  If NTYPE is bfd_link_hash_common, NSIZE
 240      is the size of the new symbol.  */
 241   boolean (*multiple_common) PARAMS ((struct bfd_link_info *,
 242                                       const char *name,
 243                                       bfd *obfd,
 244                                       enum bfd_link_hash_type otype,
 245                                       bfd_vma osize,
 246                                       bfd *nbfd,
 247                                       enum bfd_link_hash_type ntype,
 248                                       bfd_vma nsize));
 249   /* A function which is called to add a symbol to a set.  ENTRY is
 250      the link hash table entry for the set itself (e.g.,
 251      __CTOR_LIST__).  RELOC is the relocation to use for an entry in
 252      the set when generating a relocateable file, and is also used to
 253      get the size of the entry when generating an executable file.
 254      ABFD, SEC and VALUE identify the value to add to the set.  */
 255   boolean (*add_to_set) PARAMS ((struct bfd_link_info *,
 256                                  struct bfd_link_hash_entry *entry,
 257                                  bfd_reloc_code_real_type reloc,
 258                                  bfd *abfd, asection *sec, bfd_vma value));
 259   /* A function which is called when the name of a g++ constructor or
 260      destructor is found.  This is only called by some object file
 261      formats.  CONSTRUCTOR is true for a constructor, false for a
 262      destructor.  This will use BFD_RELOC_CTOR when generating a
 263      relocateable file.  NAME is the name of the symbol found.  ABFD,
 264      SECTION and VALUE are the value of the symbol.  */
 265   boolean (*constructor) PARAMS ((struct bfd_link_info *,
 266                                   boolean constructor,
 267                                   const char *name, bfd *abfd, asection *sec,
 268                                   bfd_vma value));
 269   /* A function which is called when there is a reference to a warning
 270      symbol.  WARNING is the warning to be issued.  */
 271   boolean (*warning) PARAMS ((struct bfd_link_info *,
 272                               const char *warning));
 273   /* A function which is called when a relocation is attempted against
 274      an undefined symbol.  NAME is the symbol which is undefined.
 275      ABFD, SECTION and ADDRESS identify the location from which the
 276      reference is made.  In some cases SECTION may be NULL.  */
 277   boolean (*undefined_symbol) PARAMS ((struct bfd_link_info *,
 278                                        const char *name, bfd *abfd,
 279                                        asection *section, bfd_vma address));
 280   /* A function which is called when a reloc overflow occurs.  NAME is
 281      the name of the symbol or section the reloc is against,
 282      RELOC_NAME is the name of the relocation, and ADDEND is any
 283      addend that is used.  ABFD, SECTION and ADDRESS identify the
 284      location at which the overflow occurs; if this is the result of a
 285      bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
 286      ABFD will be NULL.  */
 287   boolean (*reloc_overflow) PARAMS ((struct bfd_link_info *,
 288                                      const char *name,
 289                                      const char *reloc_name, bfd_vma addend,
 290                                      bfd *abfd, asection *section,
 291                                      bfd_vma address));
 292   /* A function which is called when a dangerous reloc is performed.
 293      The canonical example is an a29k IHCONST reloc which does not
 294      follow an IHIHALF reloc.  MESSAGE is an appropriate message.
 295      ABFD, SECTION and ADDRESS identify the location at which the
 296      problem occurred; if this is the result of a
 297      bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
 298      ABFD will be NULL.  */
 299   boolean (*reloc_dangerous) PARAMS ((struct bfd_link_info *,
 300                                       const char *message,
 301                                       bfd *abfd, asection *section,
 302                                       bfd_vma address));
 303   /* A function which is called when a reloc is found to be attached
 304      to a symbol which is not being written out.  NAME is the name of
 305      the symbol.  ABFD, SECTION and ADDRESS identify the location of
 306      the reloc; if this is the result of a
 307      bfd_section_reloc_link_order or bfd_symbol_reloc_link_order, then
 308      ABFD will be NULL.  */
 309   boolean (*unattached_reloc) PARAMS ((struct bfd_link_info *,
 310                                        const char *name,
 311                                        bfd *abfd, asection *section,
 312                                        bfd_vma address));
 313   /* A function which is called when a symbol in notice_hash is
 314      defined or referenced.  NAME is the symbol.  ABFD, SECTION and
 315      ADDRESS are the value of the symbol.  If SECTION is
 316      bfd_und_section, this is a reference.  */
 317   boolean (*notice) PARAMS ((struct bfd_link_info *, const char *name,
 318                              bfd *abfd, asection *section, bfd_vma address));
 319 };
 320 \f
 321 /* The linker builds link_order structures which tell the code how to
 322    include input data in the output file.  */
 323
 324 /* These are the types of link_order structures.  */
 325
 326 enum bfd_link_order_type
 327 {
 328   bfd_undefined_link_order,     /* Undefined.  */
 329   bfd_indirect_link_order,      /* Built from a section.  */
 330   bfd_fill_link_order,          /* Fill with a 16 bit constant.  */
 331   bfd_data_link_order,          /* Set to explicit data.  */
 332   bfd_section_reloc_link_order, /* Relocate against a section.  */
 333   bfd_symbol_reloc_link_order   /* Relocate against a symbol.  */
 334 };
 335
 336 /* This is the link_order structure itself.  These form a chain
 337    attached to the section whose contents they are describing.  */
 338
 339 struct bfd_link_order
 340 {
 341   /* Next link_order in chain.  */
 342   struct bfd_link_order *next;
 343   /* Type of link_order.  */
 344   enum bfd_link_order_type type;
 345   /* Offset within output section.  */
 346   bfd_vma offset;
 347   /* Size within output section.  */
 348   bfd_size_type size;
 349   /* Type specific information.  */
 350   union
 351     {
 352       struct
 353         {
 354           /* Section to include.  If this is used, then
 355              section->output_section must be the section the
 356              link_order is attached to, section->output_offset must
 357              equal the link_order offset field, and section->_raw_size
 358              must equal the link_order size field.  Maybe these
 359              restrictions should be relaxed someday.  */
 360           asection *section;
 361         } indirect;
 362       struct
 363         {
 364           /* Value to fill with.  */
 365           unsigned int value;
 366         } fill;
 367       struct
 368         {
 369           /* Data to put into file.  The size field gives the number
 370              of bytes which this field points to.  */
 371           bfd_byte *contents;
 372         } data;
 373       struct
 374         {
 375           /* Description of reloc to generate.  Used for
 376              bfd_section_reloc_link_order and
 377              bfd_symbol_reloc_link_order.  */
 378           struct bfd_link_order_reloc *p;
 379         } reloc;
 380     } u;
 381 };
 382
 383 /* A linker order of type bfd_section_reloc_link_order or
 384    bfd_symbol_reloc_link_order means to create a reloc against a
 385    section or symbol, respectively.  This is used to implement -Ur to
 386    generate relocs for the constructor tables.  The
 387    bfd_link_order_reloc structure describes the reloc that BFD should
 388    create.  It is similar to a arelent, but I didn't use arelent
 389    because the linker does not know anything about most symbols, and
 390    any asymbol structure it creates will be partially meaningless.
 391    This information could logically be in the bfd_link_order struct,
 392    but I didn't want to waste the space since these types of relocs
 393    are relatively rare.  */
 394
 395 struct bfd_link_order_reloc
 396 {
 397   /* Reloc type.  */
 398   bfd_reloc_code_real_type reloc;
 399
 400   union
 401     {
 402       /* For type bfd_section_reloc_link_order, this is the section
 403          the reloc should be against.  This must be a section in the
 404          output BFD, not any of the input BFDs.  */
 405       asection *section;
 406       /* For type bfd_symbol_reloc_link_order, this is the name of the
 407          symbol the reloc should be against.  */
 408       const char *name;
 409     } u;
 410
 411   /* Addend to use.  The object file should contain zero.  The BFD
 412      backend is responsible for filling in the contents of the object
 413      file correctly.  For some object file formats (e.g., COFF) the
 414      addend must be stored into in the object file, and for some
 415      (e.g., SPARC a.out) it is kept in the reloc.  */
 416   bfd_vma addend;
 417 };
 418
 419 /* Allocate a new link_order for a section.  */
 420 extern struct bfd_link_order *bfd_new_link_order PARAMS ((bfd *, asection *));
 421
 422 #endif