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The reloc_howto_type is a structure which contains all the information that libbfd needs to know to tie up a back end's data.

struct symbol_cache_entry;             /* Forward declaration.  */

struct reloc_howto_struct
  /*  The type field has mainly a documentary use - the back end can
      do what it wants with it, though normally the back end's
      external idea of what a reloc number is stored
      in this field.  For example, a PC relative word relocation
      in a coff environment has the type 023 - because that's
      what the outside world calls a R_PCRWORD reloc.  */
  unsigned int type;

  /*  The value the final relocation is shifted right by.  This drops
      unwanted data from the relocation.  */
  unsigned int rightshift;

  /*  The size of the item to be relocated.  This is *not* a
      power-of-two measure.  To get the number of bytes operated
      on by a type of relocation, use bfd_get_reloc_size.  */
  int size;

  /*  The number of bits in the item to be relocated.  This is used
      when doing overflow checking.  */
  unsigned int bitsize;

  /*  Notes that the relocation is relative to the location in the
      data section of the addend.  The relocation function will
      subtract from the relocation value the address of the location
      being relocated.  */
  boolean pc_relative;

  /*  The bit position of the reloc value in the destination.
      The relocated value is left shifted by this amount.  */
  unsigned int bitpos;

  /* What type of overflow error should be checked for when
     relocating.  */
  enum complain_overflow complain_on_overflow;

  /* If this field is non null, then the supplied function is
     called rather than the normal function.  This allows really
     strange relocation methods to be accomodated (e.g., i960 callj
     instructions).  */
  bfd_reloc_status_type (*special_function)
    PARAMS ((bfd *, arelent *, struct symbol_cache_entry *, PTR, asection *,
             bfd *, char **));

  /* The textual name of the relocation type.  */
  char *name;

  /* Some formats record a relocation addend in the section contents
     rather than with the relocation.  For ELF formats this is the
     distinction between USE_REL and USE_RELA (though the code checks
     for USE_REL == 1/0).  The value of this field is TRUE if the
     addend is recorded with the section contents; when performing a
     partial link (ld -r) the section contents (the data) will be
     modified.  The value of this field is FALSE if addends are
     recorded with the relocation (in arelent.addend); when performing
     a partial link the relocation will be modified.
     All relocations for all ELF USE_RELA targets should set this field
     to FALSE (values of TRUE should be looked on with suspicion).
     However, the converse is not true: not all relocations of all ELF
     USE_REL targets set this field to TRUE.  Why this is so is peculiar
     to each particular target.  For relocs that aren't used in partial
     links (e.g. GOT stuff) it doesn't matter what this is set to.  */
  boolean partial_inplace;

  /* The src_mask selects which parts of the read in data
     are to be used in the relocation sum.  E.g., if this was an 8 bit
     byte of data which we read and relocated, this would be
     0x000000ff.  When we have relocs which have an addend, such as
     sun4 extended relocs, the value in the offset part of a
     relocating field is garbage so we never use it.  In this case
     the mask would be 0x00000000.  */
  bfd_vma src_mask;

  /* The dst_mask selects which parts of the instruction are replaced
     into the instruction.  In most cases src_mask == dst_mask,
     except in the above special case, where dst_mask would be
     0x000000ff, and src_mask would be 0x00000000.  */
  bfd_vma dst_mask;

  /* When some formats create PC relative instructions, they leave
     the value of the pc of the place being relocated in the offset
     slot of the instruction, so that a PC relative relocation can
     be made just by adding in an ordinary offset (e.g., sun3 a.out).
     Some formats leave the displacement part of an instruction
     empty (e.g., m88k bcs); this flag signals the fact.  */
  boolean pcrel_offset;

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