reloc.c

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/* BFD support for handling relocation entries.
   Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
   2000, 2001
   Free Software Foundation, Inc.
   Written by Cygnus Support.

This file is part of BFD, the Binary File Descriptor library.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/*
SECTION
	Relocations

	BFD maintains relocations in much the same way it maintains
	symbols: they are left alone until required, then read in
	en-masse and translated into an internal form.  A common
	routine <<bfd_perform_relocation>> acts upon the
	canonical form to do the fixup.

	Relocations are maintained on a per section basis,
	while symbols are maintained on a per BFD basis.

	All that a back end has to do to fit the BFD interface is to create
	a <<struct reloc_cache_entry>> for each relocation
	in a particular section, and fill in the right bits of the structures.

@menu
@* typedef arelent::
@* howto manager::
@end menu

*/

/* DO compile in the reloc_code name table from libbfd.h.  */
#define _BFD_MAKE_TABLE_bfd_reloc_code_real

#include "bfd.h"
#include "sysdep.h"
#include "bfdlink.h"
#include "libbfd.h"
/*
DOCDD
INODE
	typedef arelent, howto manager, Relocations, Relocations

SUBSECTION
	typedef arelent

	This is the structure of a relocation entry:

CODE_FRAGMENT
.
.typedef enum bfd_reloc_status
.{
.       {* No errors detected *}
.  bfd_reloc_ok,
.
.       {* The relocation was performed, but there was an overflow. *}
.  bfd_reloc_overflow,
.
.       {* The address to relocate was not within the section supplied. *}
.  bfd_reloc_outofrange,
.
.       {* Used by special functions *}
.  bfd_reloc_continue,
.
.       {* Unsupported relocation size requested. *}
.  bfd_reloc_notsupported,
.
.       {* Unused *}
.  bfd_reloc_other,
.
.       {* The symbol to relocate against was undefined. *}
.  bfd_reloc_undefined,
.
.       {* The relocation was performed, but may not be ok - presently
.          generated only when linking i960 coff files with i960 b.out
.          symbols.  If this type is returned, the error_message argument
.          to bfd_perform_relocation will be set.  *}
.  bfd_reloc_dangerous
. }
. bfd_reloc_status_type;
.
.
.typedef struct reloc_cache_entry
.{
.       {* A pointer into the canonical table of pointers  *}
.  struct symbol_cache_entry **sym_ptr_ptr;
.
.       {* offset in section *}
.  bfd_size_type address;
.
.       {* addend for relocation value *}
.  bfd_vma addend;
.
.       {* Pointer to how to perform the required relocation *}
.  reloc_howto_type *howto;
.
.} arelent;

*/

/*
DESCRIPTION

        Here is a description of each of the fields within an <<arelent>>:

        o <<sym_ptr_ptr>>

        The symbol table pointer points to a pointer to the symbol
        associated with the relocation request.  It is
        the pointer into the table returned by the back end's
        <<get_symtab>> action. @xref{Symbols}. The symbol is referenced
        through a pointer to a pointer so that tools like the linker
        can fix up all the symbols of the same name by modifying only
        one pointer. The relocation routine looks in the symbol and
        uses the base of the section the symbol is attached to and the
        value of the symbol as the initial relocation offset. If the
        symbol pointer is zero, then the section provided is looked up.

        o <<address>>

        The <<address>> field gives the offset in bytes from the base of
        the section data which owns the relocation record to the first
        byte of relocatable information. The actual data relocated
        will be relative to this point; for example, a relocation
        type which modifies the bottom two bytes of a four byte word
        would not touch the first byte pointed to in a big endian
        world.

	o <<addend>>

	The <<addend>> is a value provided by the back end to be added (!)
	to the relocation offset. Its interpretation is dependent upon
	the howto. For example, on the 68k the code:

|        char foo[];
|        main()
|                {
|                return foo[0x12345678];
|                }

        Could be compiled into:

|        linkw fp,#-4
|        moveb @@#12345678,d0
|        extbl d0
|        unlk fp
|        rts

        This could create a reloc pointing to <<foo>>, but leave the
        offset in the data, something like:

|RELOCATION RECORDS FOR [.text]:
|offset   type      value
|00000006 32        _foo
|
|00000000 4e56 fffc          ; linkw fp,#-4
|00000004 1039 1234 5678     ; moveb @@#12345678,d0
|0000000a 49c0               ; extbl d0
|0000000c 4e5e               ; unlk fp
|0000000e 4e75               ; rts

        Using coff and an 88k, some instructions don't have enough
        space in them to represent the full address range, and
        pointers have to be loaded in two parts. So you'd get something like:

|        or.u     r13,r0,hi16(_foo+0x12345678)
|        ld.b     r2,r13,lo16(_foo+0x12345678)
|        jmp      r1

        This should create two relocs, both pointing to <<_foo>>, and with
        0x12340000 in their addend field. The data would consist of:

|RELOCATION RECORDS FOR [.text]:
|offset   type      value
|00000002 HVRT16    _foo+0x12340000
|00000006 LVRT16    _foo+0x12340000
|
|00000000 5da05678           ; or.u r13,r0,0x5678
|00000004 1c4d5678           ; ld.b r2,r13,0x5678
|00000008 f400c001           ; jmp r1

        The relocation routine digs out the value from the data, adds
        it to the addend to get the original offset, and then adds the
        value of <<_foo>>. Note that all 32 bits have to be kept around
        somewhere, to cope with carry from bit 15 to bit 16.

        One further example is the sparc and the a.out format. The
        sparc has a similar problem to the 88k, in that some
        instructions don't have room for an entire offset, but on the
        sparc the parts are created in odd sized lumps. The designers of
        the a.out format chose to not use the data within the section
        for storing part of the offset; all the offset is kept within
        the reloc. Anything in the data should be ignored.

|        save %sp,-112,%sp
|        sethi %hi(_foo+0x12345678),%g2
|        ldsb [%g2+%lo(_foo+0x12345678)],%i0
|        ret
|        restore

        Both relocs contain a pointer to <<foo>>, and the offsets
        contain junk.

|RELOCATION RECORDS FOR [.text]:
|offset   type      value
|00000004 HI22      _foo+0x12345678
|00000008 LO10      _foo+0x12345678
|
|00000000 9de3bf90     ; save %sp,-112,%sp
|00000004 05000000     ; sethi %hi(_foo+0),%g2
|00000008 f048a000     ; ldsb [%g2+%lo(_foo+0)],%i0
|0000000c 81c7e008     ; ret
|00000010 81e80000     ; restore

        o <<howto>>

        The <<howto>> field can be imagined as a
        relocation instruction. It is a pointer to a structure which
        contains information on what to do with all of the other
        information in the reloc record and data section. A back end
        would normally have a relocation instruction set and turn
        relocations into pointers to the correct structure on input -
        but it would be possible to create each howto field on demand.

*/

/*
SUBSUBSECTION
	<<enum complain_overflow>>

	Indicates what sort of overflow checking should be done when
	performing a relocation.

CODE_FRAGMENT
.
.enum complain_overflow
.{
.	{* Do not complain on overflow. *}
.  complain_overflow_dont,
.
.	{* Complain if the bitfield overflows, whether it is considered
.	   as signed or unsigned. *}
.  complain_overflow_bitfield,
.
.	{* Complain if the value overflows when considered as signed
.	   number. *}
.  complain_overflow_signed,
.
.	{* Complain if the value overflows when considered as an
.	   unsigned number. *}
.  complain_overflow_unsigned
.};

*/

/*
SUBSUBSECTION
        <<reloc_howto_type>>

        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.

CODE_FRAGMENT
.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 *abfd,
.					     arelent *reloc_entry,
.                                            struct symbol_cache_entry *symbol,
.                                            PTR data,
.                                            asection *input_section,
.                                            bfd *output_bfd,
.                                            char **error_message));
.
.       {* 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;
.
.};

*/

/*
FUNCTION
	The HOWTO Macro

DESCRIPTION
	The HOWTO define is horrible and will go away.

.#define HOWTO(C, R,S,B, P, BI, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
.  {(unsigned)C,R,S,B, P, BI, O,SF,NAME,INPLACE,MASKSRC,MASKDST,PC}

DESCRIPTION
	And will be replaced with the totally magic way. But for the
	moment, we are compatible, so do it this way.

.#define NEWHOWTO( FUNCTION, NAME,SIZE,REL,IN) HOWTO(0,0,SIZE,0,REL,0,complain_overflow_dont,FUNCTION, NAME,false,0,0,IN)
.

DESCRIPTION
	This is used to fill in an empty howto entry in an array.

.#define EMPTY_HOWTO(C) \
.  HOWTO((C),0,0,0,false,0,complain_overflow_dont,NULL,NULL,false,0,0,false)
.

DESCRIPTION
	Helper routine to turn a symbol into a relocation value.

.#define HOWTO_PREPARE(relocation, symbol)      \
.  {                                            \
.  if (symbol != (asymbol *)NULL) {             \
.    if (bfd_is_com_section (symbol->section)) { \
.      relocation = 0;                          \
.    }                                          \
.    else {                                     \
.      relocation = symbol->value;              \
.    }                                          \
.  }                                            \
.}

*/

/*
FUNCTION
	bfd_get_reloc_size

SYNOPSIS
	unsigned int bfd_get_reloc_size (reloc_howto_type *);

DESCRIPTION
	For a reloc_howto_type that operates on a fixed number of bytes,
	this returns the number of bytes operated on.
 */

unsigned int
bfd_get_reloc_size (howto)
     reloc_howto_type *howto;
{
  switch (howto->size)
    {
    case 0: return 1;
    case 1: return 2;
    case 2: return 4;
    case 3: return 0;
    case 4: return 8;
    case 8: return 16;
    case -2: return 4;
    default: abort ();
    }
}