/* BFD support for handling relocation entries.

   Copyright (C) 1990-2023 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"

#include "bfdver.h"

/*

DOCDD

INODE

  typedef arelent, howto manager, Relocations, Relocations

SUBSECTION

  typedef arelent

  This is the structure of a relocation entry:

EXTERNAL

.typedef enum bfd_reloc_status

.{

.  {* No errors detected.  Note - the value 2 is used so that it

.     will not be mistaken for the boolean TRUE or FALSE values.  *}

.  bfd_reloc_ok = 2,

.

.  {* 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,

.

.  {* Target specific meaning.  *}

.  bfd_reloc_other,

.

.  {* The symbol to relocate against was undefined.  *}

.  bfd_reloc_undefined,

.

.  {* The relocation was performed, but may not be ok.  If this type is

.     returned, the error_message argument to bfd_perform_relocation

.     will be set.  *}

.  bfd_reloc_dangerous

. }

. bfd_reloc_status_type;

.

.typedef const struct reloc_howto_struct reloc_howto_type;

.

CODE_FRAGMENT

.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;

.

.};

.

*/

/*

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 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 idea of

.     an external reloc number is stored in this field.  *}

.  unsigned int type;

.

.  {* The size of the item to be relocated in bytes.  *}

.  unsigned int size:4;

.

.  {* The number of bits in the field to be relocated.  This is used

.     when doing overflow checking.  *}

.  unsigned int bitsize:7;

.

.  {* The value the final relocation is shifted right by.  This drops

.     unwanted data from the relocation.  *}

.  unsigned int rightshift:6;

.

.  {* The bit position of the reloc value in the destination.

.     The relocated value is left shifted by this amount.  *}

.  unsigned int bitpos:6;

.

.  {* What type of overflow error should be checked for when

.     relocating.  *}

.  ENUM_BITFIELD (complain_overflow) complain_on_overflow:2;

.

.  {* The relocation value should be negated before applying.  *}

.  unsigned int negate:1;

.

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

.  unsigned int pc_relative:1;

.

.  {* 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.  *}

.  unsigned int partial_inplace:1;

.

.  {* 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., ELF); this flag signals the fact.  *}

.  unsigned int pcrel_offset:1;

.

.  {* Whether bfd_install_relocation should just install the addend,

.     or should follow the practice of some older object formats and

.     install a value including the symbol.  *}

.  unsigned int install_addend:1;

.

.  {* 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 normally be zero.  Non-zero values for ELF USE_RELA

.     targets should be viewed with suspicion as normally the value in

.     the dst_mask part of the section contents should be ignored.  *}

.  bfd_vma src_mask;

.

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

.     replaced with a relocated value.  *}

.  bfd_vma dst_mask;

.

.  {* 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.  *}

.  bfd_reloc_status_type (*special_function)

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

.     bfd *, char **);

.

.  {* The textual name of the relocation type.  *}

.  const char *name;

.};

.

*/

/*

FUNCTION

  The HOWTO Macro

DESCRIPTION

  The HOWTO macro fills in a reloc_howto_type (a typedef for

  const struct reloc_howto_struct).

.#define HOWTO_INSTALL_ADDEND 0

.#define HOWTO_RSIZE(sz) ((sz) < 0 ? -(sz) : (sz))

.#define HOWTO(type, right, size, bits, pcrel, left, ovf, func, name, \

.              inplace, src_mask, dst_mask, pcrel_off)      \

.  { (unsigned) type, HOWTO_RSIZE (size), bits, right, left, ovf, \

.    size < 0, pcrel, inplace, pcrel_off, HOWTO_INSTALL_ADDEND,   \

.    src_mask, dst_mask, func, name }

DESCRIPTION

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

.#define EMPTY_HOWTO(C) \

.  HOWTO ((C), 0, 1, 0, false, 0, complain_overflow_dont, NULL, \

.   NULL, false, 0, 0, false)

.

.static inline unsigned int

.bfd_get_reloc_size (reloc_howto_type *howto)

.{

.  return howto->size;

.}

.

*/

/*

DEFINITION

  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 undefined behaviour for N

   between zero and the number of bits in a bfd_vma.  */

#define N_ONES(n) ((n) == 0 ? 0 : ((bfd_vma) 1 << ((n) - 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;

  if (bitsize == 0)

    return flag;

  /* 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_reloc_offset_in_range

SYNOPSIS

  bool bfd_reloc_offset_in_range

    (reloc_howto_type *howto,

     bfd *abfd,

     asection *section,

     bfd_size_type offset);

DESCRIPTION

  Returns TRUE if the reloc described by @var{HOWTO} can be

  applied at @var{OFFSET} octets in @var{SECTION}.

*/

/* HOWTO describes a relocation, at offset OCTET.  Return whether the

   relocation field is within SECTION of ABFD.  */

bool

bfd_reloc_offset_in_range (reloc_howto_type *howto,

         bfd *abfd,

         asection *section,

         bfd_size_type octet)

{

  bfd_size_type octet_end = bfd_get_section_limit_octets (abfd, section);

  bfd_size_type reloc_size = bfd_get_reloc_size (howto);

  /* The reloc field must be contained entirely within the section.

     Allow zero length fields (marker relocs or NONE relocs where no

     relocation will be performed) at the end of the section.  */

  return octet <= octet_end && reloc_size <= octet_end - octet;

}

/* Read and return the section contents at DATA converted to a host

   integer (bfd_vma).  The number of bytes read is given by the HOWTO.  */

static bfd_vma

read_reloc (bfd *abfd, bfd_byte *data, reloc_howto_type *howto)

{

  switch (bfd_get_reloc_size (howto))

    {

    case 0:

      break;

    case 1:

      return bfd_get_8 (abfd, data);

    case 2:

      return bfd_get_16 (abfd, data);

    case 3:

      return bfd_get_24 (abfd, data);

    case 4:

      return bfd_get_32 (abfd, data);

#ifdef BFD64

    case 8:

      return bfd_get_64 (abfd, data);

#endif

    default:

      abort ();

    }

  return 0;

}

/* Convert VAL to target format and write to DATA.  The number of

   bytes written is given by the HOWTO.  */

static void

write_reloc (bfd *abfd, bfd_vma val, bfd_byte *data, reloc_howto_type *howto)

{

  switch (bfd_get_reloc_size (howto))

    {

    case 0:

      break;

    case 1:

      bfd_put_8 (abfd, val, data);

      break;

    case 2:

      bfd_put_16 (abfd, val, data);

      break;

    case 3:

      bfd_put_24 (abfd, val, data);

      break;

    case 4:

      bfd_put_32 (abfd, val, data);

      break;

#ifdef BFD64

    case 8:

      bfd_put_64 (abfd, val, data);

      break;

#endif

    default:

      abort ();

    }

}

/* Apply RELOCATION value to target bytes at DATA, according to

   HOWTO.  */

static void

apply_reloc (bfd *abfd, bfd_byte *data, reloc_howto_type *howto,

       bfd_vma relocation)

{

  bfd_vma val = read_reloc (abfd, data, howto);

  if (howto->negate)

    relocation = -relocation;

  val = ((val & ~howto->dst_mask)

   | (((val & howto->src_mask) + relocation) & howto->dst_mask));

  write_reloc (abfd, val, data, howto);

}

/*

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;

  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 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 && howto->special_function)

    {

      bfd_reloc_status_type cont;

      /* Note - we do not call bfd_reloc_offset_in_range here as the

   reloc_entry->address field might actually be valid for the

   backend concerned.  It is up to the special_function itself

   to call bfd_reloc_offset_in_range if needed.  */

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

              input_section, output_bfd,

              error_message);

      if (cont != bfd_reloc_continue)

  return cont;

    }

  if (bfd_is_abs_section (symbol->section)

      && output_bfd != NULL)

    {

      reloc_entry->address += input_section->output_offset;

      return bfd_reloc_ok;

    }

  /* PR 17512: file: 0f67f69d.  */

  if (howto == NULL)

    return bfd_reloc_undefined;

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

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

  if (!bfd_reloc_offset_in_range (howto, abfd, input_section, octets))

    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;

  output_base += symbol->section->output_offset;

  /* If symbol addresses are in octets, convert to bytes.  */

  if (bfd_get_flavour (abfd) == bfd_target_elf_flavour

      && (symbol->section->flags & SEC_ELF_OCTETS))

    output_base *= bfd_octets_per_byte (abfd, input_section);

  relocation += output_base;

  /* 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, 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)

      {

        /* 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;

      }

  }

    }

  /* 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)

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

     =   R R R R R R R R R R  put into bfd_put<size>

     */

  data = (bfd_byte *) data + octets;

  apply_reloc (abfd, data, howto, relocation);

  return flag;

}

/*

FUNCTION

  bfd_install_relocation

SYNOPSIS

  bfd_reloc_status_type bfd_install_relocation

    (bfd *abfd,

     arelent *reloc_entry,

     void *data, bfd_vma data_start,

     asection *input_section,

     char **error_message);

DESCRIPTION

  This looks remarkably like <<bfd_perform_relocation>>, except it

  does not expect that the section contents have been filled in.

  I.e., it's suitable for use when creating, rather than applying

  a relocation.

  For now, this function should be considered reserved for the

  assembler.

*/

bfd_reloc_status_type

bfd_install_relocation (bfd *abfd,

      arelent *reloc_entry,

      void *data_start,

      bfd_vma data_start_offset,

      asection *input_section,

      char **error_message)

{

  bfd_vma relocation;

  bfd_reloc_status_type flag = bfd_reloc_ok;

  bfd_size_type octets;

  bfd_vma output_base = 0;

  reloc_howto_type *howto = reloc_entry->howto;

  asection *reloc_target_output_section;

  asymbol *symbol;

  bfd_byte *data;

  symbol = *(reloc_entry->sym_ptr_ptr);

  /* 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 && howto->special_function)

    {

      bfd_reloc_status_type cont;

      /* Note - we do not call bfd_reloc_offset_in_range here as the

   reloc_entry->address field might actually be valid for the

   backend concerned.  It is up to the special_function itself

   to call bfd_reloc_offset_in_range if needed.  */

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

              /* XXX - Non-portable! */

              ((bfd_byte *) data_start

               - data_start_offset),

              input_section, abfd, error_message);

      if (cont != bfd_reloc_continue)

  return cont;

    }

  if (howto->install_addend)

    relocation = reloc_entry->addend;

  else

    {

      if (bfd_is_abs_section (symbol->section))

  return bfd_reloc_ok;

      /* 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;