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/* BFD support for handling relocation entries.

   Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,

   2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011

   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 3 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., 51 Franklin Street - Fifth Floor, Boston,

   MA 02110-1301, 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 "sysdep.h"

#include "bfd.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 bfd_symbol **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

        <<canonicalize_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 value overflows when considered as a signed

.     number one bit larger than the field.  ie. A bitfield of N bits

.     is allowed to represent -2**n to 2**n-1.  *}

.  complain_overflow_bitfield,

.

.  {* Complain if the value overflows when considered as a 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 bfd_symbol;             {* 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;

.

.  {*  The relocation is relative to the field being relocated.  *}

.  bfd_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 accommodated (e.g., i960 callj

.     instructions).  *}

.  bfd_reloc_status_type (*special_function)

.    (bfd *, arelent *, struct bfd_symbol *, void *, 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.  *}

.  bfd_boolean partial_inplace;

.

.  {* src_mask selects the part of the instruction (or data) to be used

.     in the relocation sum.  If the target relocations don't have an

.     addend in the reloc, eg. ELF USE_REL, src_mask will normally equal

.     dst_mask to extract the addend from the section contents.  If

.     relocations do have an addend in the reloc, eg. ELF USE_RELA, this

.     field should be zero.  Non-zero values for ELF USE_RELA targets are

.     bogus as in those cases the value in the dst_mask part of the

.     section contents should be treated as garbage.  *}

.  bfd_vma src_mask;

.

.  {* dst_mask selects which parts of the instruction (or data) are

.     replaced with a relocated value.  *}

.  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.  *}

.  bfd_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 != 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 (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 ();

    }

}

/*

TYPEDEF

        arelent_chain

DESCRIPTION

        How relocs are tied together in an <<asection>>:

.typedef struct relent_chain

.{

.  arelent relent;

.  struct relent_chain *next;

.}

.arelent_chain;

.

*/

/* N_ONES produces N one bits, without overflowing machine arithmetic.  */

#define N_ONES(n) (((((bfd_vma) 1 << ((n) - 1)) - 1) << 1) | 1)

/*

FUNCTION

        bfd_check_overflow

SYNOPSIS

        bfd_reloc_status_type bfd_check_overflow

          (enum complain_overflow how,

           unsigned int bitsize,

           unsigned int rightshift,

           unsigned int addrsize,

           bfd_vma relocation);

DESCRIPTION

        Perform overflow checking on @var{relocation} which has

        @var{bitsize} significant bits and will be shifted right by

        @var{rightshift} bits, on a machine with addresses containing

        @var{addrsize} significant bits.  The result is either of

        @code{bfd_reloc_ok} or @code{bfd_reloc_overflow}.

*/

bfd_reloc_status_type

bfd_check_overflow (enum complain_overflow how,

                    unsigned int bitsize,

                    unsigned int rightshift,

                    unsigned int addrsize,

                    bfd_vma relocation)

{

  bfd_vma fieldmask, addrmask, signmask, ss, a;

  bfd_reloc_status_type flag = bfd_reloc_ok;

  /* Note: BITSIZE should always be <= ADDRSIZE, but in case it's not,

     we'll be permissive: extra bits in the field mask will

     automatically extend the address mask for purposes of the

     overflow check.  */

  fieldmask = N_ONES (bitsize);

  signmask = ~fieldmask;

  addrmask = N_ONES (addrsize) | (fieldmask << rightshift);

  a = (relocation & addrmask) >> rightshift;;

  switch (how)

    {

    case complain_overflow_dont:

      break;

    case complain_overflow_signed:

      /* If any sign bits are set, all sign bits must be set.  That

         is, A must be a valid negative address after shifting.  */

      signmask = ~ (fieldmask >> 1);

      /* Fall thru */

    case complain_overflow_bitfield:

      /* Bitfields are sometimes signed, sometimes unsigned.  We

         explicitly allow an address wrap too, which means a bitfield

         of n bits is allowed to store -2**n to 2**n-1.  Thus overflow

         if the value has some, but not all, bits set outside the

         field.  */

      ss = a & signmask;

      if (ss != 0 && ss != ((addrmask >> rightshift) & signmask))

        flag = bfd_reloc_overflow;

      break;

    case complain_overflow_unsigned:

      /* We have an overflow if the address does not fit in the field.  */

      if ((a & signmask) != 0)

        flag = bfd_reloc_overflow;

      break;

    default:

      abort ();

    }

  return flag;

}

/*

FUNCTION

        bfd_perform_relocation

SYNOPSIS

        bfd_reloc_status_type bfd_perform_relocation

          (bfd *abfd,

           arelent *reloc_entry,

           void *data,

           asection *input_section,

           bfd *output_bfd,

           char **error_message);

DESCRIPTION

        If @var{output_bfd} is supplied to this function, the

        generated image will be relocatable; the relocations are

        copied to the output file after they have been changed to

        reflect the new state of the world. There are two ways of

        reflecting the results of partial linkage in an output file:

        by modifying the output data in place, and by modifying the

        relocation record.  Some native formats (e.g., basic a.out and

        basic coff) have no way of specifying an addend in the

        relocation type, so the addend has to go in the output data.

        This is no big deal since in these formats the output data

        slot will always be big enough for the addend. Complex reloc

        types with addends were invented to solve just this problem.

        The @var{error_message} argument is set to an error message if

        this return @code{bfd_reloc_dangerous}.

*/

bfd_reloc_status_type

bfd_perform_relocation (bfd *abfd,

                        arelent *reloc_entry,

                        void *data,

                        asection *input_section,

                        bfd *output_bfd,

                        char **error_message)

{

  bfd_vma relocation;

  bfd_reloc_status_type flag = bfd_reloc_ok;

  bfd_size_type octets = reloc_entry->address * bfd_octets_per_byte (abfd);

  bfd_vma output_base = 0;

  reloc_howto_type *howto = reloc_entry->howto;

  asection *reloc_target_output_section;

  asymbol *symbol;

  symbol = *(reloc_entry->sym_ptr_ptr);

  if (bfd_is_abs_section (symbol->section)

      && output_bfd != NULL)

    {

      reloc_entry->address += input_section->output_offset;

      return bfd_reloc_ok;

    }

  /* If we are not producing relocatable output, return an error if

     the symbol is not defined.  An undefined weak symbol is

     considered to have a value of zero (SVR4 ABI, p. 4-27).  */

  if (bfd_is_und_section (symbol->section)

      && (symbol->flags & BSF_WEAK) == 0

      && output_bfd == NULL)

    flag = bfd_reloc_undefined;

  /* If there is a function supplied to handle this relocation type,

     call it.  It'll return `bfd_reloc_continue' if further processing

     can be done.  */

  if (howto->special_function)

    {

      bfd_reloc_status_type cont;

      cont = howto->special_function (abfd, reloc_entry, symbol, data,

                                      input_section, output_bfd,

                                      error_message);

      if (cont != bfd_reloc_continue)

        return cont;

    }

  /* Is the address of the relocation really within the section?  */

  if (reloc_entry->address > bfd_get_section_limit (abfd, input_section))

    return bfd_reloc_outofrange;

  /* Work out which section the relocation is targeted at and the

     initial relocation command value.  */

  /* Get symbol value.  (Common symbols are special.)  */

  if (bfd_is_com_section (symbol->section))

    relocation = 0;

  else

    relocation = symbol->value;

  reloc_target_output_section = symbol->section->output_section;

  /* Convert input-section-relative symbol value to absolute.  */

  if ((output_bfd && ! howto->partial_inplace)

      || reloc_target_output_section == NULL)

    output_base = 0;

  else

    output_base = reloc_target_output_section->vma;

  relocation += output_base + symbol->section->output_offset;

  /* Add in supplied addend.  */

  relocation += reloc_entry->addend;

  /* Here the variable relocation holds the final address of the

     symbol we are relocating against, plus any addend.  */

  if (howto->pc_relative)

    {

      /* This is a PC relative relocation.  We want to set RELOCATION

         to the distance between the address of the symbol and the

         location.  RELOCATION is already the address of the symbol.

         We start by subtracting the address of the section containing

         the location.

         If pcrel_offset is set, we must further subtract the position

         of the location within the section.  Some targets arrange for

         the addend to be the negative of the position of the location

         within the section; for example, i386-aout does this.  For

         i386-aout, pcrel_offset is FALSE.  Some other targets do not

         include the position of the location; for example, m88kbcs,

         or ELF.  For those targets, pcrel_offset is TRUE.

         If we are producing relocatable output, then we must ensure

         that this reloc will be correctly computed when the final

         relocation is done.  If pcrel_offset is FALSE we want to wind

         up with the negative of the location within the section,

         which means we must adjust the existing addend by the change

         in the location within the section.  If pcrel_offset is TRUE

         we do not want to adjust the existing addend at all.

         FIXME: This seems logical to me, but for the case of

         producing relocatable output it is not what the code

         actually does.  I don't want to change it, because it seems

         far too likely that something will break.  */

      relocation -=

        input_section->output_section->vma + input_section->output_offset;

      if (howto->pcrel_offset)

        relocation -= reloc_entry->address;

    }

  if (output_bfd != NULL)

    {

      if (! howto->partial_inplace)

        {

          /* This is a partial relocation, and we want to apply the relocation

             to the reloc entry rather than the raw data. Modify the reloc

             inplace to reflect what we now know.  */

          reloc_entry->addend = relocation;

          reloc_entry->address += input_section->output_offset;

          return flag;

        }

      else

        {

          /* This is a partial relocation, but inplace, so modify the

             reloc record a bit.

             If we've relocated with a symbol with a section, change

             into a ref to the section belonging to the symbol.  */

          reloc_entry->address += input_section->output_offset;

          /* WTF?? */

          if (abfd->xvec->flavour == bfd_target_coff_flavour

              && strcmp (abfd->xvec->name, "coff-Intel-little") != 0

              && strcmp (abfd->xvec->name, "coff-Intel-big") != 0)

            {

              /* For m68k-coff, the addend was being subtracted twice during

                 relocation with -r.  Removing the line below this comment

                 fixes that problem; see PR 2953.

However, Ian wrote the following, regarding removing the line below,

which explains why it is still enabled:  --djm

If you put a patch like that into BFD you need to check all the COFF

linkers.  I am fairly certain that patch will break coff-i386 (e.g.,

SCO); see coff_i386_reloc in coff-i386.c where I worked around the

problem in a different way.  There may very well be a reason that the

code works as it does.

Hmmm.  The first obvious point is that bfd_perform_relocation should

not have any tests that depend upon the flavour.  It's seem like

entirely the wrong place for such a thing.  The second obvious point

is that the current code ignores the reloc addend when producing

relocatable output for COFF.  That's peculiar.  In fact, I really

have no idea what the point of the line you want to remove is.

A typical COFF reloc subtracts the old value of the symbol and adds in

the new value to the location in the object file (if it's a pc

relative reloc it adds the difference between the symbol value and the

location).  When relocating we need to preserve that property.

BFD handles this by setting the addend to the negative of the old

value of the symbol.  Unfortunately it handles common symbols in a

non-standard way (it doesn't subtract the old value) but that's a

different story (we can't change it without losing backward

compatibility with old object files) (coff-i386 does subtract the old

value, to be compatible with existing coff-i386 targets, like SCO).

So everything works fine when not producing relocatable output.  When

we are producing relocatable output, logically we should do exactly

what we do when not producing relocatable output.  Therefore, your

patch is correct.  In fact, it should probably always just set

reloc_entry->addend to 0 for all cases, since it is, in fact, going to

add the value into the object file.  This won't hurt the COFF code,

which doesn't use the addend; I'm not sure what it will do to other

formats (the thing to check for would be whether any formats both use

the addend and set partial_inplace).

When I wanted to make coff-i386 produce relocatable output, I ran

into the problem that you are running into: I wanted to remove that

line.  Rather than risk it, I made the coff-i386 relocs use a special

function; it's coff_i386_reloc in coff-i386.c.  The function

specifically adds the addend field into the object file, knowing that

bfd_perform_relocation is not going to.  If you remove that line, then

coff-i386.c will wind up adding the addend field in twice.  It's

trivial to fix; it just needs to be done.

The problem with removing the line is just that it may break some

working code.  With BFD it's hard to be sure of anything.  The right

way to deal with this is simply to build and test at least all the

supported COFF targets.  It should be straightforward if time and disk

space consuming.  For each target:

    1) build the linker

    2) generate some executable, and link it using -r (I would

       probably use paranoia.o and link against newlib/libc.a, which

       for all the supported targets would be available in

       /usr/cygnus/progressive/H-host/target/lib/libc.a).

    3) make the change to reloc.c

    4) rebuild the linker

    5) repeat step 2

    6) if the resulting object files are the same, you have at least

       made it no worse

    7) if they are different you have to figure out which version is

       right

*/

              relocation -= reloc_entry->addend;

              reloc_entry->addend = 0;

            }

          else

            {

              reloc_entry->addend = relocation;

            }

        }

    }

  else

    {

      reloc_entry->addend = 0;

    }

  /* FIXME: This overflow checking is incomplete, because the value

     might have overflowed before we get here.  For a correct check we

     need to compute the value in a size larger than bitsize, but we

     can't reasonably do that for a reloc the same size as a host

     machine word.

     FIXME: We should also do overflow checking on the result after

     adding in the value contained in the object file.  */

  if (howto->complain_on_overflow != complain_overflow_dont

      && flag == bfd_reloc_ok)

    flag = bfd_check_overflow (howto->complain_on_overflow,

                               howto->bitsize,

                               howto->rightshift,

                               bfd_arch_bits_per_address (abfd),

                               relocation);

  /* Either we are relocating all the way, or we don't want to apply

     the relocation to the reloc entry (probably because there isn't

     any room in the output format to describe addends to relocs).  */

  /* The cast to bfd_vma avoids a bug in the Alpha OSF/1 C compiler

     (OSF version 1.3, compiler version 3.11).  It miscompiles the

     following program:

     struct str

     {

       unsigned int i0;

     } s = { 0 };

     int

     main ()

     {

       unsigned long x;

       x = 0x100000000;

       x <<= (unsigned long) s.i0;

       if (x == 0)

         printf ("failed\n");

       else

         printf ("succeeded (%lx)\n", x);

     }

     */

  relocation >>= (bfd_vma) howto->rightshift;

  /* Shift everything up to where it's going to be used.  */

  relocation <<= (bfd_vma) howto->bitpos;

  /* Wait for the day when all have the mask in them.  */

  /* What we do:

     i instruction to be left alone

     o offset within instruction

     r relocation offset to apply

     S src mask

     D dst mask

     N ~dst mask

     A part 1

     B part 2

     R result

     Do this:

     ((  i i i i i o o o o o  from bfd_get<size>

     and           S S S S S) to get the size offset we want

     +   r r r r r r r r r r) to get the final value to place

     and           D D D D D  to chop to right size

     -----------------------

     =             A A A A A

     And this:

     (   i i i i i o o o o o  from bfd_get<size>

     and N N N N N          ) get instruction

     -----------------------

     =   B B B B B

     And then:

     (   B B B B B

     or            A A A A A)