path: root/bfd/reloc.c

/* BFD support for handling relocation entries.
   Copyright (C) 1990-1991 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/*
SECTION
	Relocations

DESCRIPTION
	BFD maintains relocations in much the same was as it maintains
	symbols; they are left alone until required, then read in
	en-mass and traslated into an internal form. There is a common
	routine <<bfd_perform_relocation>> which acts upon the
	canonical form to to the actual fixup.

	Note that relocations are maintained on a per section basis,
	whilst symbols are maintained on a per BFD basis.

	All a back end has to do to fit the BFD interface is to create
	as many <<struct reloc_cache_entry>> as there are relocations
	in a particuar section, and fill in the right bits:

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

*/
#include "bfd.h"
#include "sysdep.h"
#include "libbfd.h"
/*doc*
@node typedef arelent, howto manager, Relocations, Relocations

SUBSECTION
	typedef arelent

*/

/*
FUNCTION
	bfd_perform_relocation

DESCRIPTION
	The relocation routine returns as a status an enumerated type:

.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,

	Unused 

.  bfd_reloc_notsupported,

	Unsupported relocation size requested. 

.  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.

.  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                 

.  rawdata_offset address;

	addend for relocation value        

.  bfd_vma addend;    

	if sym is null this is the section 

.  struct sec *section;

	Pointer to how to perform the required relocation

.  CONST struct reloc_howto_struct *howto;
.} arelent;


*/

/*
DESCRIPTION

	o sym_ptr_ptr
	The symbol table pointer points to a pointer to the symbol
	associated with the relocation request. This would naturally
	be 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. @item 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:

EXAMPLE

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

DESCRIPTION
	Could be compiled into:

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

DESCRIPTION

	This could create a reloc pointing to foo, but leave the
	offset in the data (something like)

EXAMPLE
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
DESCRIPTION

	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:

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

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

EXAMPLE
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

DESCRIPTION
	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.

	On 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 odd sized lumps. The designers of
	the a.out format chose not to use the data within the section
	for storing part of the offset; all the offset is kept within
	the reloc. Any thing in the data should be ignored. 
EXAMPLE
        save %sp,-112,%sp
        sethi %hi(_foo+0x12345678),%g2
        ldsb [%g2+%lo(_foo+0x12345678)],%i0
        ret
        restore

DESCRIPTION
	Both relocs contains a pointer to foo, and the offsets would
	contain junk.

EXAMPLE

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

DESCRIPTION

	o section  
	The section field is only used when the symbol pointer field
	is null. It supplies the section into which the data should be
	relocated. The field's main use comes from assemblers which do
	most of the symbol fixups themselves; an assembler may take an
	internal reference to a label, but since it knows where the
	label is, it can turn the relocation request from a symbol
	lookup into a section relative relocation - the relocation
	emitted has no symbol, just a section to relocate against. I'm
	not sure what it means when both a symbol pointer an a section
	pointer are present. Some formats use this sort of mechanism
	to describe PIC relocations, but BFD can't to that sort of
	thing yet. @item howto The howto field can be imagined as a
	relocation instruction. It is a pointer to a struct which
	contains information on what to do with all 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 
	<<reloc_howto_type>>

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

.typedef CONST struct reloc_howto_struct 
.{ 
	The type field has mainly a documetary use - the back end can
	to what it wants with it, though the normally the back end's
	external idea of what a reloc number would be would be stored
	in this field. For example, the a PC relative word relocation
	in a coff environment would have 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 - 0, is one byte, 1 is 2
	bytes, 3 is four bytes.

.  unsigned int size;

	Now obsolete

.  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;

	Now obsolete

.  unsigned int bitpos;

	Now obsolete

.  boolean absolute;

	Causes the relocation routine to return an error if overflow
	is detected when relocating.

.  boolean 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 (eg, i960 callj
	instructions).

.  bfd_reloc_status_type (*special_function)();

	The textual name of the relocation type.

.  char *name;

	When performing a partial link, some formats must modify the
	relocations rather than the data - this flag signals this.

.  boolean partial_inplace;

	The src_mask is used to select what parts of the read in data
	are to be used in the relocation sum. Eg, if this was an 8 bit
	bit 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_word src_mask;

	The dst_mask is what 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_word 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 (eg sun3 a.out).
	Some formats leave the displacement part of an instruction
	empty (eg m88k bcs), this flag signals the fact.
.  boolean pcrel_offset;
.} reloc_howto_type;

*/

/*
FUNCTION
	HOWTO
DESCRIPTION
	The HOWTO define is horrible and will go away.


.#define HOWTO(C, R,S,B, P, BI, ABS, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
.  {(unsigned)C,R,S,B, P, BI, ABS,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,false,false,FUNCTION, NAME,false,0,0,IN)
.
DESCRIPTION
	Helper routine to turn a symbol into a relocation value.

.#define HOWTO_PREPARE(relocation, symbol) 	\
.  {						\
.  if (symbol != (asymbol *)NULL) {		\
.    if (symbol->flags & BSF_FORT_COMM) {	\
.      relocation = 0;				\
.    }						\
.    else {					\
.      relocation = symbol->value;		\
.    }						\
.  }						\
.  if (symbol->section != (asection *)NULL) {	\
.    relocation += symbol->section->output_section->vma +	\
.      symbol->section->output_offset;		\
.  }						\
.}			

*/

/*
TYPEDEF
	reloc_chain

DESCRIPTION

	How relocs are tied together

.typedef unsigned char bfd_byte;
.
.typedef struct relent_chain {
.  arelent relent;
.  struct   relent_chain *next;
.} arelent_chain;

*/



/*
FUNCTION 
	bfd_perform_relocation

DESCRIPTION
	If an 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 (eg 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.

SYNOPSIS
	bfd_reloc_status_type
                bfd_perform_relocation
                        (bfd * abfd,
                        arelent *reloc_entry,
                        PTR data,
                        asection *input_section,
                        bfd *output_bfd);
*/


bfd_reloc_status_type
DEFUN(bfd_perform_relocation,(abfd,
                              reloc_entry,
                              data,
                              input_section,
                              output_bfd),
      bfd *abfd AND
      arelent *reloc_entry AND
      PTR data AND
      asection *input_section AND
      bfd *output_bfd)
{
  bfd_vma relocation;
  bfd_reloc_status_type flag = bfd_reloc_ok;
  bfd_vma addr = reloc_entry->address ;
  bfd_vma output_base = 0;
  reloc_howto_type *howto = reloc_entry->howto;
  asection *reloc_target_output_section;
  asection *reloc_target_input_section;
  asymbol *symbol;

  if (reloc_entry->sym_ptr_ptr) {
    symbol = *( reloc_entry->sym_ptr_ptr);
    if ((symbol->flags & BSF_UNDEFINED) && output_bfd == (bfd *)NULL) {
      flag = bfd_reloc_undefined;
    }
  }
  else {
    symbol = (asymbol*)NULL;
  }

  if (howto->special_function){
    bfd_reloc_status_type cont;
    cont = howto->special_function(abfd,
                                   reloc_entry,
                                   symbol,
                                   data,
                                   input_section);
    if (cont != bfd_reloc_continue) return cont;
  }

  /* 
    Work out which section the relocation is targetted at and the
    initial relocation command value.
    */


  if (symbol != (asymbol *)NULL){
    if (symbol->flags & BSF_FORT_COMM) {
      relocation = 0;
    }
    else {
      relocation = symbol->value;
    }
    if (symbol->section != (asection *)NULL)
        {
          reloc_target_input_section = symbol->section;
        }
    else {
      reloc_target_input_section = (asection *)NULL;
    }
  }
  else if (reloc_entry->section != (asection *)NULL)
      {
        relocation = 0;
        reloc_target_input_section = reloc_entry->section;
      }
  else {
    relocation = 0;
    reloc_target_input_section = (asection *)NULL;
  }


  if (reloc_target_input_section != (asection *)NULL) {

    reloc_target_output_section =
      reloc_target_input_section->output_section;

    if (output_bfd && howto->partial_inplace==false) {
      output_base = 0;
    }
    else {
      output_base = reloc_target_output_section->vma;

    }

    relocation += output_base +   reloc_target_input_section->output_offset;
  }

  relocation += reloc_entry->addend ;


  if(reloc_entry->address > (bfd_vma)(input_section->size)) 
      {
        return bfd_reloc_outofrange;
      }
          

  if (howto->pc_relative == true)
      {
        /*
          Anything which started out as pc relative should end up that
	  way too. 
	  
	  There are two ways we can see a pcrel instruction. Sometimes
	  the pcrel displacement has been partially calculated, it
	  includes the distance from the start of the section to the
	  instruction in it (eg sun3), and sometimes the field is
	  totally blank - eg m88kbcs.
	  */

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

        if (howto->pcrel_offset == true) {
          relocation -= reloc_entry->address;
        }

      }

  if (output_bfd!= (bfd *)NULL) {
    if ( howto->partial_inplace == false)  {
      /*
        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->section = reloc_target_input_section;
      if (reloc_target_input_section != (asection *)NULL) {
        /* If we know the output section we can forget the symbol */
        reloc_entry->sym_ptr_ptr = (asymbol**)NULL;
      }
      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
	     */

	  if (symbol != (asymbol *)NULL && reloc_target_input_section != (asection *)NULL) 
	      {
		reloc_entry->section = reloc_target_input_section;
		reloc_entry->sym_ptr_ptr  = (asymbol **)NULL;
	      }

        }
  }

  reloc_entry->addend = 0;


  /* 
    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)
    */
  relocation >>= howto->rightshift;

  /* Shift everything up to where it's going to be used */
   
  relocation <<= 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>
     */

#define DOIT(x) \
  x = ( (x & ~howto->dst_mask) | (((x & howto->src_mask) +  relocation) & howto->dst_mask))

    switch (howto->size)
        {
        case 0:
            {
              char x = bfd_get_8(abfd, (char *)data + addr);
              DOIT(x);
              bfd_put_8(abfd,x, (unsigned char *) data + addr);
            }
          break;

        case 1:
            { 
              short x = bfd_get_16(abfd, (bfd_byte *)data + addr);
              DOIT(x);
              bfd_put_16(abfd, x,   (unsigned char *)data + addr);
            }
          break;
        case 2:
            {
              long  x = bfd_get_32(abfd, (bfd_byte *) data + addr);
              DOIT(x);
              bfd_put_32(abfd,x,    (bfd_byte *)data + addr);
            }      
          break;
        case 3:

          /* Do nothing */
          break;
        default:
          return bfd_reloc_other;
        }

  return flag;
}



/*
@node howto manager,  , typedef arelent, Relocations
SECTION
	The howto manager 

DESCRIPTION
	When an application wants to create a relocation, but doesn't
	know what the target machine might call it, it can find out by
	using this bit of code.

*/

/*
TYPEDEF
	bfd_reloc_code_type

DESCRIPTION
	The insides of a reloc code

.typedef enum bfd_reloc_code_real {

	16 bits wide, simple reloc 

.  BFD_RELOC_16,	

	8 bits wide, but used to form an address like 0xffnn

.  BFD_RELOC_8_FFnn,

	8 bits wide, simple

.  BFD_RELOC_8,

	8 bits wide, pc relative

.  BFD_RELOC_8_PCREL,

	The type of reloc used to build a contructor table - at the
	moment probably a 32 bit wide abs address, but the cpu can
	choose.

.  BFD_RELOC_CTOR

. } bfd_reloc_code_real_type;



*/



/*
SECTION
	bfd_reloc_type_lookup

DESCRIPTION
	This routine returns a pointer to a howto struct which when
	invoked, will perform the supplied relocation on data from the
	architecture noted.

SYNOPSIS
	CONST struct reloc_howto_struct *
	bfd_reloc_type_lookup
	(CONST bfd_arch_info_type *arch, bfd_reloc_code_type code);
*/


CONST struct reloc_howto_struct *
DEFUN(bfd_reloc_type_lookup,(arch, code),
	CONST bfd_arch_info_type *arch  AND
	bfd_reloc_code_type code)
{
  return arch->reloc_type_lookup(arch, code);
}

static reloc_howto_type bfd_howto_32 =
 HOWTO(0, 00,2,32,false,0,false,true,0,"VRT32", false,0xffffffff,0xffffffff,true);


/*
INTERNAL FUNCTION
	bfd_default_reloc_type_lookup

DESCRIPTION
	Provides a default relocation lookuperer for any architectue 

SYNOPSIS
	CONST struct reloc_howto_struct *bfd_default_reloc_type_lookup
	(CONST struct bfd_arch_info *,
         bfd_reloc_code_type  code);

*/
CONST struct reloc_howto_struct *
DEFUN(bfd_default_reloc_type_lookup,(arch,  code),
     CONST struct bfd_arch_info *arch AND
      bfd_reloc_code_type  code)
{
    switch (code) 
    {
       case BFD_RELOC_CTOR:
	/* The type of reloc used in a ctor, which will be as wide as the
	   address - so either a 64, 32, or 16 bitter.. */
	switch (arch->bits_per_address) {
	   case 64:
	    BFD_FAIL();
	   case 32:
	    return &bfd_howto_32;
	   case 16:
	    BFD_FAIL();
	   default:
	    BFD_FAIL();
	}
       default:
	BFD_FAIL();
    }
return (struct reloc_howto_struct *)NULL;
}